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NBS SPECIAL PUBLICATION 411

U.S. DEPARTMENT OF COMMERCE / National Bureau of Standards
NATIONAL BUREAU OF STANDARDS

The National Bureau of Standards' was established by an act of Congress March 3, 1901. The Bureau's overall goal is to strengthen and advance the Nation's science and technology

and facilitate their effective application for public benefit. To this end, the Bureau conducts

research and provides: (I) a basis for the Nation's physical measurement system, (2) scientific and technological services for industry and government, (3) a technical basis for equity in trade, and (4) technical services to promote public safety. The Bureau consists of the Institute for Basic Standards, the Institute for Materials Research, the Institute for Applied Technology,

the Institute for Computer Sciences and Technology, and the Office for Information Programs.

THE INSTITUTE FOR BASIC STANDARDS provides the central basis within the United

States of a complete and consistent system of physical measurement; coordinates that system

with measurement systems of other nations; and furnishes essential services leading to accurate and uniform physical measurements throughout the Nation's scientific community, industry, and commerce. The Institute consists of a Center for Radiation Research, an Office of Measurement Services and the following divisions: Applied Mathematics — Electricity — Mechanics — Heat — Optical Physics — Nuclear

Sciences ° — Applied Radiation " — Quantum Electronics ^ — Electromagnetics " — Time

and Frequency ' — Laboratory Astrophysics " — Cryogenics ^ THE INSTITUTE FOR MATERIALS RESEARCH conducts materials research leading to improved methods of measurement, standards, and data on the properties of well-characterized materials needed by industry, commerce, educational institutions, and Government; provides

advisory and research services to other Government agencies; and develops, produces, and

distributes standard reference materials. The Institute consists of the Office of Standard Reference Materials and the following divisions: Analytical Chemistry — Polymers — Metallurgy — Inorganic Materials — Reactor

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THE INSTITUTE FOR COMPUTER SCIENCES AND TECHNOLOGY conducts research and provides technical services designed to aid Government agencies in improving cost effec- tiveness in the conduct of their programs through the selection, acquisition, and effective

utilization of automatic data processing equipment; and serves as the principal focus within

the executive branch for the development of Federal standards for automatic data processing

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divisions: Computer Services — Systems and Software — Computer Systems Engineering — Information Technology.

THE OFFICE FOR INFORMATION PROGRAMS promotes optimum dissemination and

accessibility of scientific information generated within NBS and other agencies of the Federal Government; promotes the development of the National Standard Reference Data System and

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Maryland, unless otherwise noted; mailing address
2 1975 Fire Safety Research

Proceedings of a Symposium

Held at the National Bureau of Standards

Gaithersburg, Md., August 22, 1973

Mary Jo Butler and James A. Slater, Editors

Programmatic Center for Fire Research

Institute for Applied Technology

National Bureau of Standards C^^/t i ^0 -m j X^\^0 CLyir >^ • ^'

Washington, D.C. 20234

Sponsored by

National Bureau of Standards

U.S. DEPARTMENT OF COMMERCE, Frederick B. Dent, Secreiary

U*$i NATIONAL BUREAU OF STANDARDS, Richard W. Roberts, Director

Issued November 1 974
Library of Congress Cataloging in Publication Data

Main entry under title:

Fire Safety Research.

(National Bureau of Standards Special Publication 411) Supt. of Docs. No.: C13.10:411

1. Fire-Testing—Congresses. 2. Fire prevention—Research

Congresses. I. Butler, Mary Jo, ed. II. Slater, James A., ed.

III. United States. National Bureau of Standards. IV. Series: United States. National Bureau of Standards. Special Publication 411. QC100.U57 No. 411 [TH10921 389'.08s [628.9'22] 74-23736

National Bureau of Standards Special Publication 411

Nat. Bur. Stand. (U.S.), Spec. Publ. 411,251pages (Nov. 1974) CODEN: XNBSAV

U.S. GOVERNMENT PRINTING OFFICE

WASHINGTON: 1974 For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402 (Order by SD Catalog No. C13.10:411). Price $3.10
ABSTRACT

A Symposium on Fire Safety Research was held at the National

Bureau of Standards (NBS) , on August 22, 1973. The Symposium's

participants were NBS staff as well as outside contributors affiliated with the NBS fire program including representatives from

private industries, universities, government agencies, and the

National Fire Protection Association. The papers covered topics

in hazard analysis, standards development, flame chemistry, fire

modeling, fire detection, physiological effects of fire, fire

services, effect of fire on building materials, and field investigation methods for firefighters. Specifically included were papers

dealing with the development of the Children's Sleepwear Flammability Standards and mandatory sampling plans, mechanisms of flame

retardants, flame spread and radiant panel test methods, contribution of interior finish materials to fire growth, a field study

of non fire-resistive multiple dwelling fires, the Research Applied

to National Needs (RANN) Program of NSF, and other related topics.

Key words: Apparel fires; carbon monoxide; concrete beams; field

investigation; FIFI; fire; fire buildup; fire detection; fire engines;

fire growth; fire research; fire retardants; fire safety research;

firefighter training; flame inhibition; flame spread; flames; flammable fabrics standards; hazard analysis; injury severity; interior

finishes; mandatory standards; modeling; multiple dwelling fires;

oxygen; physiological effects of fire; polymeric materials; radiant

panel; RANN; red oak; smoke; standards; test methods; textile testing;

thermal decomposition; toxic effects of fire.

Contents

Page

WELCOME V

Richard W. Roberts, National Bureau of Standards

INTRODUCTION . vi

F. Karl Willenbrock, National Bureau of Standards

A COMPARISON BETWEEN POTENTIAL HAZARD REDUCTION FROM FABRIC

FLAMMABILITY STANDARDS, IGNITION SOURCE IMPROVEMENT AND PUBLIC

EDUCATION 1 Benjamin Buchbinder and Allan Vickers, National Bureau of

Standards

DEVELOPMENT OF THE STANDARDS FOR THE FLAMMABILITY OF CHILDREN'S

SLEEPWEAR 5 Emil Braun, James H. Winger and James A. Slater, National

Bureau of Standards

SAMPLING PLANS IN MANDATORY STANDARDS 16

Paul Gottfried, Consumer Product Safety Commission

HUMAN ACTIVITY PATTERNS AND INJURY SEVERITY IN FIRE INCIDENTS

INVOLVING APPAREL 20

Laura Baker Buchbinder, The Cotton Foundation

CHEMICAL ASPECTS OF FLAME INHIBITION 30

John W. Hastie, National Bureau of Standards

MECHANISM OF FLAME RETARDANT ACTION IN TEXTILES 37

Robert H. Barker, Clemson University

ADDITIONAL STUDIES OF THE TRANSFER OF FLAME RETARDANT EFFECTS

WITH CELLULOSIC FABRICS 50

Bernard Miller, Textile Research Institute

AN EVALUATION OF FLAME SPREAD TEST METHODS FOR FLOOR COVERING

MATERIALS 59

James Quintiere and Clayton Huggett, National Bureau of Standards

MATHEMATICAL MODELING OF RADIANT PANEL TEST METHODS . 90

J. A. Rockett, National Bureau of Standards

FLAME SPREAD OVER A POROUS SURFACE UNDER AN EXTERNAL RADIATION FIELD 97

Takashi Kashiwagi, National Bureau of Standards

PHYSIOLOGICAL AND TOXICOLOGICAL EFFECTS OF THE PRODUCTS OF THERMAL

DECOMPOSITION FROM POLYMERIC MATERIALS 105

M. M. Birky, National Bureau of Standards

I. N. Einhorn, M. L. Grunnett, S. C. Packham, J. H. Petajan and

J. D. Seader, University of Utah

CONTRIBUTION OF INTERIOR FINISH MATERIALS TO FIRE GROWTH IN A ROOM 125

J. B. Fang and D. Gross, National Bureau of Standards

FIRE BUILD-UP IN REDUCED SIZE ENCLOSURES 139

W. J. Parker and B. T. Lee, National Bureau of Standards

AN ANALYTIC MODEL FOR CALCULATING THE FIRE RESISTANCE OF SIMPLY

SUPPORTED PRESTRESSED AND REINFORCED CONCRETE BEAMS 154

Lionel A. Issen, National Bureau of Standards

V
SMOKE AND CARBON MONOXIDE GENERATION FROM BURNING SELECTED PLASTICS

AND RED OAK 165

Thomas Y. King, Armstrong Cork Company

A FIELD STUDY OF NON FIRE-RESISTIVE MULTIPLE DWELLING FIRES .... 178

Francis L. Brannigan, Montgomery College

THE CURRENT STATUS OF FIRE DETECTION 195

George Sinnott, National Bureau of Standards

SEQUENCING THE PURCHASE AND RETIREMENT OF FIRE ENGINES 201

Patsy B. Saunders and Richard Ku, National Bureau of Standards

FIFI — FIRE INFORMATION FIELD INVESTIGATION 215

F. James Kauffman and Martin E. Grimes, National Fire

Protection Association

NATIONAL SCIENCE FOUNDATION RANN PROGRAM 230

Ralph H. Long, Jr., National Science Foundation

APPENDIX - CONTRIBUTING AUTHOR INDEX ' 239

vi
WELCOME

Richard W. Roberts, Director

National Bureau of Standards, Washington, D.C.

Fire might be characterized as one of man's most important discoveries;

it is also one of our most useful tools. We use it to heat our homes and our

offices, to generate electricity, to power most forms of transportation, even though the bicycle is starting to make inroads, and we use it most in industrial

processes. I think it is a fair statement to say that life as we know it today

could not exist without fire; but along with all of these beneficial aspects

of fire come some very serious side effects.

In 1971, 12,000 Americans were killed by fire and over 100,000 were desperately injured by fire-related accidents. Fire takes a tremendous economic

toll in the United States. In fact, it is estimated that $2.8 billion worth

ot property damage occurred in 1971. Now to put these statistics in perhaps

a little more concrete terms, this means that by tomorrow morning, there will

be 1,500 families without a home because they suffered a fire.

The Bureau has been involved in fire research for a long period of time

and I think has made many significant contributions. I think the program today

will reveal many of these and perhaps point new directions for future activities.

vii
INTRODUCTION

F. Karl Willenbrock, Director

Institute for Applied Technology

National Bureau of Standards, Washington, D.C.

The problem of destructive fire continues to plague our nation. Each year,

at least 12,000 people are killed, many more seriously injured or crippled for

life, and billions of dollars in property lost. The need for fire protection

has become a public demand. We, at the National Bureau of Standards (NBS)

,

believe that technology can provide the public with a more fire-safe environment, one that is more fail-safe to human carelessness.

For sixty years, NBS has conducted a building fire program which has provided the technical base for many fire safety codes and standards. In the past

several years, however, NBS has acquired more responsibility for reducing fire

losses. The Fire Research and Safety Act of 196 8 greatly broadened the NBS

authority. Under this legislation, NBS developed a more extensive fire program

including technical support of the fire services. As a result of the 1967

amendment of the Flammable Fabrics Act, NBS, in 1968, established a flammable

fabrics program and assisted in the development of a number of mandatory flammability standards such as carpets and rugs, children's sleepwear and mattresses.

Although the responsibility for the development of standards under the Flammable

Fabrics Act was reassigned to the Consumer Product Safety Commission by the

Consumer Product Safety Act of 1972, this Act specifically directs the Commission

to use NBS for research in fabric flammability and for technical assistance in

developing product flammability standards. We are, therefore, working closely

with the Commission in carrying out these responsibilities.

Our several fire activities are unified to assure integration of building

fire safety, fire services, product flammability test development, fire research,

and analysis of fire accident data. We have organized these activities into

programs based on the chain of events which lead to fire losses, namely, exposure

of ignitable material to an ignition source; ignition of the material; and spread

of fire. To minimize fire losses, we must interrupt this chain of events.

Therefore, our fire programs, which are aimed at breaking the fire chain at each

juncture, consist of three major elements: fire prevention , fire control , and

fire suppression ; with foundation activities in research and hazard analysis . The foundation activities for these programs are based on understanding real

world fire problems through analysis of fire accidents (hazard analysis activity)

and through research on the physical characteristics of fire, to learn why and

how fire hazards exist. These activities provide a sound basis for outputs to

activities such as building fire codes, fabric flammability standards, and performance criteria for fire equipment.

Fire Prevention ; Fire prevention is a prime area in which a major impact in

saving human lives and property is possible. We have projects directed towards:

encouraging the fire services to assist home owners in voluntary inspections;

exploring new designs for common ignition sources, such as kitchen ranges,

matches, and lighters; and providing the technical basis to the Consumer Product

Safety Commission for mandatory national standards on the flammability of

clothing and interior furnishings.

Fire Control : Fire control can be accomplished through reduction of fire loads

in buildings, through early detection and suppression of fire, and through minimization of smoke and fire movement in burning buildings. NBS has received

funding to conduct a nation-wide survey of fire loads in office buildings from

which a representative picture of fire loads will be developed. Once the nature

of these fire loads has been more accurately determined, we will be better able

to design buildings that resist the spread of fire. In automatic fire control,

NBS is emphasizing smoke detectors. We have analyzed many cominercial smoke

detectors and recommended design changes which some manufacturers have already

viii
incorporated, producing more effective fire detectors. We are also developing

recommended performance criteria for residential detectors, and exploring new

approaches to early detection of fire, as well as measuring unique fire signatures to reduce false alarms. The use of sprinklers in life safety applications

for residences is being explored as a further extension of the automatic detection and control concept. In addition, we are developing design criteria and

flammability tests for building materials and systems leading to viable building

standards for fire-safe buildings. Under development are building design

standards for smoke control based on the results of full scale tests on several

multi-story buildings, fire safety standards for day care centers, and a new

flammability test for carpets aimed at more fire-safe corridor exits.

Fire Suppression : Our fire suppression activities are in direct support of the

fire services. We have tested the effectiveness of clothing and equipment for

firefighters and discovered some inadequacies in protective coats, helmets, and

ladders which may help reduce the dangers associated with firefighting which is one of the most dangerous of the professions. To help correct these inadequacies, we are developing performance specifications to aid firemen in selecting

safe and effective equipment. We are also developing guides to enable optimum

use and placement of firefighting resources, to balance specific local needs.

We are also conducting a project to develop analytical tools with which a local

fire chief can analyze the injuries his firefighters suffer. Based on this

analysis, the Chief can decide how to modify his firefighting tactics, training,

or equipment so as to reduce injuries.

Research ; Research can provide valuable new solutions to old problems. The

NBS approach is to work on those fire problems in which new knowledge in

science and technology can make a contribution to saving lives and property.

Our investigation of the chemistry and physics of combustion processes could

lead to improved fire retardant materials or improved fire extinguishers.

The exploration of the dynamics of fires could lead to improved fire detectors

and fire-safe building design.

Hazard Analysis : Accurate accident data are needed on which to base our priorities and to monitor our progress. This information must be detailed enough

so that its analysis can clearly indicate the cause of fires. We have, therefore, contracted for the design of a national fire loss data system which will

collect data from various state and local sources to provide a true picture of

the nature and causes of fire loss. As a model, the NBS Flammable Fabrics

Accident Case and Testing System (FFACTS) , which includes detailed data about

thousands of fires involving fabrics, has guided priorities in the development

of fabric flammability standards. What is the future of the fire programs at

NBS? The report of the National Commission on Fire Prevention and Ccjntrol,

"America Burning," has resulted in the introduction of several legislative

proposals in Congress for an expanded fire program. Recent hearings before

the Subcommittee on Science, Research and Development of the House Committee on

Science and Astronautics indicate that the Department of Commerce and NBS will

be called upon to play a larger role in future fire safety programs. A new

fire research laboratory is now under construction at the NBS Gaithersburg site.

When completed, this laboratory will provide a modern facility for conducting

large scale fire experiments. NBS is preparing for an expanded role in reducing

the nation's fire losses.

The papers that follow appear in the order in which they were presented

at the Symposium. May I take this opportunity to express my appreciation to

the authors of these papers and other participants who contributed toward

making the Symposium a success, to Dr. Radford Byerly who was instrumental in

the direction and initiation of the Fire Safety Research Symposium, to

Dr. Clayton Huggett who graciously accepted to host the Symposium, to Mrs. Sara

Torrence and Mrs. Mary Jo Butler for their help with the coordination of the

Symposium, and to Mr. James Slater and Mrs. Mary Jo Butler for editing and

managing the production of the Proceedings. Special thanks is due to Mrs. Carol

Thompson and Mrs. Evelyn Granger for their editorial and production skills.

ix

NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 411, Fire Safety Research,

Proceedings of a Symposium Held at NBS , Gaithersburg , Md . , August 22, 1973,

(Issued November 1974)

A COMPARISON BETWEEN POTENTIAL HAZARD REDUCTION FROM

FABRIC FLAMMABILITY STANDARDS , IGNITION SOURCE

IMPROVEMENT AND PUBLIC EDUCATION

Benjamin Buchbinder and Allan Vickers

National Bureau of Standards, Washington, D.C.

Mandatory standards have been and are being promulgated for

flammable fabric item types (e.g., children's sleepwear, mattresses,

upholstered furniture) to reduce the fire hazard inherent in the use of common ignition sources (e.g., matches, cigarettes, kitchen

ranges) . Trade-offs should be made between potential hazard reduction from fabric item standards and from design changes or improved

quality control in ignition source fabrication. Public education

is a third approach to the reduction of certain hazards.

Key words: Cigarettes; education; fabric; fire; f lammability

;

hazard; ignition source; kitchen ranges; matches; mattresses;

sleepwear; standards; upholstered furniture.

The hazard represented by fabric fire accidents may be studied from many

points of view. In this paper we will look at the kinds of considerations involved in addressing the reduction of the fabric fire hazard by means of three

approaches: fabric f lammability standards, improved safety in ignition sources

and effective public education.

First, our source of data, the Flammable Fabrics Accident Case and Testing

System, which we call FFACTS, provides the data for fabric fire studies at the

National Bureau of Standards' (NBS) Fire Technology Division. FFACTS is a com- puterized data base now containing 2,660 cases, rich in detail, with over 130

data elements for each case. These data are derived from detailed case history

investigations of fabric fire accidents, performed largely by Consumer Product

Safety Commission contractors and Food and Drug Administration field investigators, augmented by laboratory analysis, at NBS, of fabric samples submitted

with the reports. The detailed data in FFACTS permit the identification of

patterns of accident parameters which define different accident types. These

parameters encompass both fire characteristics and human involvement.

In this paper, four FFACTS data elements have been used, namely fabric item

first to ignite, ignition source, age of victim and sex of victim, to examine the

kinds of considerations inherent in choosing a course of action for hazard re- duction . Other Fire Technology Division studies encompass additional FFACTS data

elements including victim's activity prior to ignition and reaction after

ignition, injury and economic loss and test data from fabric sample laboratory

analysis. The purposes of these studies range from the development of hazard

related test methods for flammability standards to an investigation of the

causal relationship of human activities to injury severity.

In order to discuss the pros and cons of the three approaches to hazard

reduction, let us first define several hazards in terms of our four data elements. For purposes of this discussion, a hazard is defined as a combination

of ignition source, human involvement and flammable material with a high probability of injury.

Table 1, based on the data base level of 1,964 cases, shows the number of cases in FFACTS for which sleepwear, shirts and blouses and upholstered furniture were the first fabric item types to ignite. (This "f irst-to-ignite" criterion is useful in determining the most important item involved in a fire

accident, when more than one fabric item is involved.) The incidence of sleep- wear cases was primarily among females, the shirt/blouse category incidence was

1
Table 1. Incidence of FFACTS^ Cases For Selected Item Types

(First-to-Ignite) , By Sex of Victim

Item Type Number of Cases

Male Female Total

Upholstered Furniture . .

79 253 332

. 193 49 242

52 57 126*^ ^Based on a data base of 1,964 cases.

'-'Total includes 17 cases with sex of victim unknown

or not applicable.

primarily male; and both sexes were involved almost equally in upholstered furniture cases. Table 2 shows the number of cases in FFACTS for which matches,

cigarettes, cigars and pipes, kitchen ranges, and open fires we.re the ignition

sources. Matches and cigarettes involved both sexes, kitchen ranges involved

more females, and open fires involved more males. Neither the item type/sex

classification of incidents such as in table 1 nor the ignition source/sex

classification of table 2 is sufficient for our hazard definitions. ^

Table 2. Incidence of FFACTS^ Cases For Selected Ignition

Sources By Sex of Victim, Where Item First to Ignite Is Known

Ignition Source Niimber of Cases

Male Female Total

145 124 269

Cigarettes, Cigars & Pipes. 123 117 240

78 204 282

99 40 139

^Based on a data base of 1,964 cases.

The categories of table 3 further define hazards by a cross tabulation

of n\imbers of cases by item type and ignition source. Sex is used to modify

the item type classification only where the involvement of that item is primarily for one sex. Age is introduced in the first two item type classes,

to more specifically define particular problem areas. For our purposes today,

the data in table 3 are adequate to provide examples of hazards. We will re- turn to these data to discuss seven different hazards and the potential effectiveness of item type flammability standards, ignition source safety improvement and public education in addressing them. First, let us define generalized

criteria for assessing the potential effectiveness of each remedial approach,

in terms of a series of questions. These questions fall into three categories — state-of-the-art, public acceptance and protection of some at the expense

of others — and these questions will be addressed relative to each of our three approaches in turn.

First, for fabric item flammability standards:

Does state-of-the-art technology permit the development of flame retardant

material, and does potential industry capacity exist for production of sufficient material?

Will the properties and the cost of the new product meet public acceptance?

(If not, will public rejection in favor of homemade items or substitutes counter

the intent of the standard?)

Does the standard protect one group at the expense of others?

2
Table 3. Incidence of FFACTS Cases By Item Type

First to Ignite and Ignition Source

Item Type Ignition Source

Match Cigarette^ Range Open Fire Other Total

Female Sleepwear (21+) t*. . . 25 - 54 4 46 129

Children's Sleepwear (0-12)'^ 46 - 60 12 47 165

Dresses (Female)'^ 22 - 30 7 34 93

Shirts (Male)t> 46 - 36 32 79 193

Pants (Male)*^ 15 - 5 29 33 82

Upholstered Furniture. ... 5 94 - - 27 126

Mattresses and Pads 10 38 1 - 16 65

Others 100 108 96 55 171 530

Total 269 240 282 139 453 1,383

^Includes cigars and pipes.

'^This item type primarily involved a specific age group or sex. Only the

indicated data have been included to more specifically identify the particular

hazard.

Improvements in ignition source safety may be made in production quality

control to reduce the incidence of defective products, and in product re-design

to reduce the hazard inherent in its normal use (or misuse) . In terms of the

three categories above, we ask relative to ignition source safety improvement:

Does state-of-the-art technology permit enough improvement to be made to

significantly reduce the hazard, and will the changes impair the primary

function of the product or inadvertently introduce new safety hazards?

Can the changes be made within the constraints of cost and public acceptance?

Will the changes protect one group at the expense of others?

Public education does not require increased industrial capacity or tradeoffs between safety and product performance. However, we ask:

Is the state-of-the-art in educational programs adequate both to reach

the intended audiences and to significantly influence behavior?

Is education cost effective?

Returning to table 3 , let us examine in turn the hazards represented by

adult female sleepwear, male shirts and pants, female dresses, upholstered

furniture, mattresses, kitchen ranges, and cigarettes. They were chosen to

illustrate the potential effectiveness of the three approaches to hazard reduction, rather than necessarily to reflect the greatest hazards.

First, consider hazards potentially addressable by item type standards.

The hazards related to upholstered furniture and mattresses are suggested for

this category, for the following reasons:

1. State-of-the-art technology permits the development of the required

materials

.

2. Although a single ignition source category, cigarettes, cigars and

pipes, is involved in 75 percent of upholstered furniture cases and

59 percent of mattress ignitions, it is not likely that improved

safety in these ignition sources can easily be obtained.

3
3. Looking at the cigarette coliamn of table 3 we see that 94 plus 38, or 132 cigarette ignitions, 55 percent of the total of 240 cases,

involved the two item types, upholstered furniture and mattresses.

This indicates that these two item type standards would also address

55 percent of a major ignition source hazard.

Second, let us consider hazards addressable by improved safety in ignition sources. There are two categories of item types in table 3 which present hazards not directly addressable by item type standards. Adult female

sleepwear is the first item type. Non-flammable material is not at present

available in sufficient quantity to produce flame resistant sleepwear for all

adult women. The hazard is most severe for elderly women, but unlike the situation with regard to children's sleepwear, there is no size difference to permit a distinction to be made between elderly female sleepwear and other adult

female sleepwear. Even if sufficient fabric were available for an overall female sleepwear standard, a large portion of the population would be unnecessarily s\ibjected to the higher cost and changed product characteristics of flame

resistant sleepwear. The second item type not directly addressable by an item

type standard is dresses, for similar reasons. It appears that the improvement of safety in kitchen ranges offers good potential for the reduction of

kitchen range accidents in general (20 percent of all f irst-to-ignite cases involve ranges) , and for the reduction of the adult female sleepwear and dress

hazards as well. Table 3 shows that 54 adult female sleepwear cases (42 percent of the total) and 30 dress cases" (32 percent of the total for dresses)

involve ranges

.

Finally, consider hazards partially addressable by public education. The

hazard represented by male shirt and pants ignitions is at present not com- pletely addressable by either item type standards or improved ignition source

safety, for the following reasons:

1. Of the 193 cases in which male shirts were first to ignite 135 (70

percent) involved males age 16 and older. This indicates that the

shirt fire hazard is largely an adult problem, and at present sufficient flame resistant shirt fabric is not available.

2. Even if technological considerations permitted a standard to be promulgated, a large portion of the hazard would not be addressed. This

is because the fabric fire hazard to adult males is strongly related

to flammable liquid involvement. Forty- four percent of male shirt and

pants ignitions involved flammable liquids. Even a flame retardant

fabric will support combustion if it is soaked in gasoline.

3. There are many ignition sources involved with shirt and pants ignitions; therefore, improved ignition source safety would require effort

in many areas. For these reasons, public education should be explored, perhaps in concert

with the other two approaches, to fully address the male shirt and pants hazard

The examples given above are intended to illustrate the complexity of the

fabric flammability problem. The item type standards now in force and in

various stages of development address obvious hazards. The voluntary actions

of the kitchen range and book match industries, which are currently considering

ways to make their products safer, address another segment of the problem.

Public education is a third approach which should be explored, because the

magnitude and complexity of flammable fabric hazards make it necessary to use all available approaches to reduce these hazards.
NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 411, Fire Safety Research,

Proceedings of a Symposium Held at NBS , Gaithersburg , Md . , August 22, 1973,

(Issued November 1974)

DEVELOPMENT OF THE STANDARDS FOR THE FLAMMABILITY

OF CHILDREN'S SLEEPWEAR

Emil Braun, James H. Winger and James A. Slater

National Bureau of Standards, Washington, D.C.

The general methodology used in the development of a mandatory

flammability Standard is presented. An illustrative summary is

given of the hazard analysis of the accident data and the subsequent test development and laboratory investigations conducted in

the development of the children's sleepwear flammability standards

(DOC FF-3-71 and DOC PFF-5-73) . Some of the problems encountered

in the development of a mandatory standard and the resolution of

those problems are discussed.

Key words: Children; flammable fabrics; sleepwear; standards development; statistics.

1 . INTRODUCTION

In 1967, Congress issued amendments to the 1953 Flammable Fabrics Act [1]

that directed the Secretary of Commerce^ to issue mandatory standards for limiting the flammability of fabrics , wearing apparel , and interior furnishings

in those areas where "unreasonable risk" has been shown to exist. The act further stipulated that all standards must be reasonable, appropriate, and technologically practicable. In an effort to insure that standards comply with

these criteria, they must logically be developed from a careful study of accident data and laboratory experiments. The end product of this study is a mandatory flammability standard that removes "unreasonable risk" from the market

place

.

Flammability standards are a synthesis of three distinct elements. First,

there is the basic test method that must, as far as possible, relate small

scale performance to real world performance. Then there is the acceptance

criterion that sets the level of performance desired; and, finally, a sampling

plan that insures that an allowable level of statistical risk to the consumer

is not exceeded. In this paper we will concern ourselves only with the development of the first two points - the test method and the superimposed acceptance criterion.

The Proposed Children's Sleepwear Standard [2] for ages 6-12 years old,

and the manner in which it differs from the Children's Sleepwear Standard [3]

for ages 0-5 years old will provide illustrative examples of the evolutionary

history of a test method and the acceptance criterion that form the foundation

upon which a mandatory flammability standard is built. These standards will

also serve to illustrate the direct relationship between the analysis of accident statistics and the finding of need for a standard, its scope, and the appropriateness of the test method employed.

2. TEST METHOD

A flammability test method is effectively determined by specifying four

interrelated parameters: the variable to be measured, the source of ignition,

the specimen configuration, and the preparation of the specimen prior to testing. Each item must be carefully defined so that the end result is a test that

is repeatable and reproducible, as determined by an interlaboratory evaluation,

and that reflects real life performance as far as is consistent with the re- quirements of a practical test method.

^The Consumer Product Safety Act of 1972 has since transferred the standards

setting responsibilities to the Consumer Product Safety Commission effective

May 14, 1973.

5
I

I

2.1. Variable to Be Measured

There are several different variables that can be used to describe the

relative degree of the f laitimability of a fabric. One could measure the time

to ignition, the burn rate, or both simultaneously - as is done in CS-191-53

(Flammability Standard For General Wearing Apparel) . The tendency of a fabric

to self-extinguish before it is consumed could also be measured or the rate of

heat transfer to a known substrate. Procedures have already been developed to measure any one of these variables. The question that first must be answered

is which procedure is appropriate for children's sleepwear?

Accident data^ [4] , tables 1 and 2, indicate that children between 0 and 12

years old are more prone to flammable sleepwear injuries than any other age

group. Table 1 is a percentage breakdown of all sleepwear cases in the National Bureau of Standards' Flammable Fabrics Accident Case and Testing System

(FFACTS) [5] . Table 2 is a normalization of table 1 based on the actual percentage of the population [6] represented by each age group. Table 2 shows tha

as a subtotal of the entire U.S. population, children 0 to 5 years old and 6 to 12 years old are found in the data base far in excess of what would be ex- pected from population figures - 2.7 and 1.7 times, respectively. From this

information along with data from other sources [4] , it was concluded that children under age 13 are exposed to sleepwear fires more frequently than other

segments of the population or are less capable of correctly initiating a protective reaction at the first sign of danger.

Table 1 . Age and Sex Distribution of Persons Involved in All

FFACTS First-to-Ignite Uncontaminated Sleepwear Incidents

Age Female Male Total

(%) (%) (%)

0-5 16 11 27

6-12 19 5 24

13-20 3 1 5^

21-45 12 1 13

46-65 13 2 15

66+ 13 3 16

Total 76 24^ 100

^Independently rounded.

Table 2. Ratios of Persons Involved in FFACTS Sleepwear Incidents^

to Corresponding U.S. Population Totals By Age Group

Age Female Male Total

0-5 3.2 2.2 2.7

6-12 2.7 0.7 1.7

13-20 0.4 0.1 0.3

21-45 0.8 0.1 0,4

46-65 1.3 0.2 0.8

66 + 2.2 0.8 1.6

^For incidents in which a fabric item involved

was the first item ignited and was not con- taminated by flcunmable liquids.

^Accident statistics are based on a FFACTS data file containing 1,964 cases.

i
In addition, full scale mannequin studies of fabrics similar to those

found in FFACTS, have shown that massive involvement of a child's garment occurs very rapidly - on the order of 20-30 seconds after ignition. This, of

course, should have a direct bearing on the appropriateness of a test method

and its ability to protect against the hazards for which the test is supposedly

designed.

The measured variable in a test must be one that provides maximum protection in order to significantly reduce deaths and injuries. The requirement of

maximum protection immediately eliminates burn rate and rate of heat transfer

to the body as possible alternatives for test methods. Both of these variables

implicitly assume that, given a finite amount of time, the victim can rapidly

extinguish or remove a burning garment. Research has also removed ignition

time as a viable alternative. It has been shown that ignition of a fabric usually occurs before the wearer experiences thermal pain [7]

It follows from the concept of maximum protection that the use of a test

that measures a fabric's ability to self-extinguish is the only appropriate

selection. This insures that thermal injury is minimized and that it is independent of the reactions of an individual on encountering a source of ignition.

2.2. Source of Ignition

A review of available test procedures indicates that there exist several

test methods for flame retardant fabrics. They all rate a fabric's ability to

self-extinguish by measuring afterflame and/or char length. Afterflame refers

to the time of flaming on the fabric after the burner has been removed, while

char length refers to the extent of the damage that has occurred on the fabric,

as measured by a tear test.

Since all existing tests (table 3) employ a Bunsen or Tirrell type of

burner as the heat source with a variety of gases for the fuel, one could

easily select a similar heat source without providing any rational motivation.

However, this would violate the requirement that the test relate to real life

performance. Therefore, it becomes necessary to investigate accident data in

order to justify the use of an open flame.

Table 3 . Partial List of Requirements of

Vertical Flammability Tests

Test Method Sample Size Conditioning Ignition Time

ASTM

D 626-55T

2" X 12-1/2" 16 hrs @ 70°F

65% RH

12 sec

AATCC

34-1966

2-3/4" X 10" 8 hrs @ 70°F

65% RH

12 sec

Fed. Spec.

CCC-T-191B

Method 5903

2-3/4" X 12" 4 hrs (a 70°F

65% RH

12 sec

NFPA

701

Small Scale

2-3/4" X 10" 1 to 1-1/2 hrs.

@ 140-145°F

12 sec

Underwriters Laboratory

214-1969

2-3/4" X 10" 1 to 1-1/2 hrs.

@ 140-145°F

12 sec

7
For example, table 4, which is extracted from FFACTS [4], is a listing of

the major sources of ignition that children 6-12 years old have encountered

while wearing sleepwear. Almost 50 percent of the incidents reported involved

electric or gas kitchen ranges. This is followed by matches and heaters, with

approximately 17 percent and 16 percent, respectively. Tabulation of the heat

sources - open flame, glowing surface, etc. - is shown in table 5. The mode o heat transfer most frequently experienced in real life situations should be

simulated in some manner in a test method. Since approximately 65 percent of

the reported cases were the result of an exposure to an open flame, the selection of a Bunsen type of burner is justifiable. This is in contrast to the case of mattresses [8] where the typical mode of heat transfer is a smoldering

ignition (e.g. a cigarette). The selection of a cigarette as the ignition

source for the children's sleepwear standards is as inappropriate as the selec

tion of an open flame ignition is for mattresses.

Table 4. Sources of Ignition For First-to-Ignite Uncontaminated

Sleepwear Worn By Children Ages 6-12^

Ignition

Source

Paj amas Nightgowns Robes All

Male Female Male Female Male Female Sleepwear

Kitchen Range 5 22 9 1 1 38

Match/Lighter 4 1 6 2 13

Heater/Furnace 2 1 9 12

Open Fire 1 1 1 5

1^ 9 Candle/Lantern 1 2 1 1 5 Total 13 27 1 30 2 4 77

^Source : FFACTS

.

Table 5. Mode of Heat Transfer For First-to-Ignite Uncontaminated

Sleepwear Worn By Children Ages 6-12^

Heat Transfer

Mechanism

Pajamas Nightgowns Robes All

Male Female Male Female Male Female Sleepwear

Open Flame 6 16 1 20 2 4 49

Glowing Surface 4 10 5 19

Spark 1 1 1 3 Radiant Heat 1 1 2 Unknown 1 3 4 Total 13 27 1 30 2 4 77

^Source: FFACTS.

In both DOC FF-3-71 and the Proposed Flammability Standard for Children's

Sleepwear 7-14, methane was selected as the standard fuel for the test burner

on the basis that it is the gas closest to that presently used in homes.

The ignition source is not completely defined until the duration of flame

application has been specified. As can be seen in table 3, the traditional

duration of flame impingement is 12 seconds. During a preliminary investigation of the effects of flame impingement time on char length, it was found

that longer impingement time did not necessarily produce correspondingly longe

char lengths. McCarter [9] has shown that for some marginally treated cottons

longer char lengths were produced at relatively short exposure times as com- pared to tests conducted at longer exposure times. Figure 1 shows the effect

of flame impingement over a range of exposure times on a marginally treated

cotton fabric and a well treated cotton fabric. The well treated fabric ex8
a

0) p

(0uo

<+-) pc

0)

(d • u co G +J O -Po

0)

u e

-p eo p -p C +J

0) o E X!

0)CnC -a

•rH OJ g (C H Q)

4-1 +J OP H O

(U (0

M-l

C

IH -H

<U (71

(U (0e

Eh T!C • (d u o 3 -p

fa I 9
hibits char lengths that become progressively longer with increasing flame

impingement time until an upper limit is reached. However, the char length of

the marginal fabric is shorter for 12 than for 3 second exposures. This behavior is accounted for by postulating the occurrence of oxygen partitioning between the fabric and the burner flame. That is to say, the flame from the

test burner decreases the concentration of oxygen in the fabric's combustion

zone. If the concentration of oxygen falls below a minimum value required for

self-sustained burning, the fabric self -extinguishes

.

Consequently, the use of a double exposure time was prescribed in the Proposed Standard For the Flammability of Children's Sleepwear 0-6X [10] - a 3 second application of the burner flame followed by a 12 second impingement of

the burner flame. However, subsequent testing revealed that of all fabrics

tested only thermoplastic fabrics would pass a 3 second impingement and fail

a 12 second impingement of the burner flame. It was observed that the failure

of the thermoplastic fabric at 12 seconds was not accompanied by any flaming.

It was also noted that the resultant char length for a thermoplastic fabric was a function of fabric weight and flame exposure time. Figure 2 shows the

test results of a series of nylon fabrics exposed to a 3 second flame and a 3 plus 12 second flame, as described in the proposed standard. The effect of

the increased time was to simply shift the line upwards. Based to a large ex- tent on a subjective appraisal of the relatively low hazard associated with a melting but not flaming thermoplastic, the 12 second exposure was deleted from

the final standard for children's sleepwear sizes 0-6X.

12 -

a>o

cX

I-z

LlI <

X

o

NYLON FABRICS

VERTICAL CHAR LENGTH

3 + 12 Seconds

,3 Seconds

0 6 8 10 12 FABRIC WEIGHT, mg/cm^

14 16

Figure 2. The effect of impingement time on vertical char length

for nylon fabrics.

10
2.3. Specimen Configuration

Flammability tests have been developed that measure some property that can

be related to a material's "inherent" hazard. These tests are conducted with

the specimen held at various angles and with specimens of various sizes, depending upon the test specification.

The angle has been varied from the horizontal (0°), as in the Department

of Transportation test (MVSS No. 302) , to the vertical (90°) with other often

used angles of 30°, 45° and 60°. Test specimen size has also been varied from

a small two-inch circle used in some ignition tests to a 6 inch x 16 inch specimen used in a new vertical test under consideration by ASTM (semi-restraint

test)

.

Because of a desire to provide maximum protection to children of ages 0-5

,

the most vulnerable age group, the decision was made to use a vertical orientation with ignition at the lower edge of the specimen.

The effect of specimen width on average char length was studied for a

2 inch and a 4 inch specimen width. Figure 3 shows a least squares fit of the

data from tests conducted in the equipment described in DOC FF-3-71. If specimen width did not affect char length results (an ideal situation where experimental and material variability were zero) , the fitted line would have a slope

of 1. The actual regression line shown has a slope of 1.051. Introducing test

and material error, one can see that specimen width does not affect char length

(at a 95% level of significance) . The specimen length was also investigated in

the same manner and also indicated no significant effect on test results.

Based on these results the exposed specimen size was established to be 2 inches

by 10 inches.

TWO INCH WIDTH AVG. CHAR LENGTH, inches

Figure 3. A comparison of char lengths obtained at two

specimen widths.

11
1

2.4. Specimen Preparation

As can be seen in table 3 the conditioning specifications for vertical ;! test methods have generally required that the specimen be placed in an atmo- , sphere set at 65% RH and 70°F, the standard textile testing conditions. This, i however, does not correspond to realistic end use conditions. It is, of j course, impossible as well as unnecessary to duplicate the test under all possible conditions. If one is attempting to provide the maximum attainable pro- , tection, which is the case with children's sleepwear, then one need only deter-i

mine the most hazardous conditions and measure the flammability of fabrics

that are exposed to a heat source under these conditions.

A second factor not previously considered, but forced upon us by the above

results, concerns test reproducibility (i.e. agreement between laboratories).

Figure 4 [11] shows that, if testing were done in different laboratories under

different hximidity conditions, the agreement between laboratories would be poor, for some fabrics. This phenomenon could present both technical problems, in

the form of disagreement between seller and purchaser, and possible legal problems, in the form of enforceability.

The latter requirement, reproducibility, precludes the use of a range of

conditions within which testing can be done. It forces the selection of a given humidity condition under which the test shall be performed. The former

requirement, maximum protection, imposes the need for the selection of the most

hazardous conditions. This leads one to the selection of "bone dry" specimens

(oven dried at 105 °C and cooled in a desiccator) as a reasonable conditioning

requirement.

EFFECT OF HUMI DITY ON CHAR LENGTH

COTTON

10

8

in

a>u

cI

O

2

6

Io 4 PROBAN 5.2 oz/yd* WOVEN

PROBAN 4.2 oz/yd'

/yd* WOVEN

I* WOVEN

0

40 60

RELATIVE HUMIDITY- %

80 0 20

Figure 4. several

The effect of humidity on char length for

treated cotton fabrics.

12
3. ACCEPTANCE CRITERION

As mentioned earlier, the acceptance criterion sets the level of performance that is desired within the context of the test method. Irrespective of

the measured variable, the level of performance chosen must meet the test of

technological practicability. This means that industry must be capable of producing flame retardant goods and that these goods be acceptable to the constimer

In the case of children's sleepwear, this requires knowledge of the performance in the vertical flammability test of available flame retardant treatments and/or in making flame retardant fabrics that are suitable for use in

this segment of the textile industry. During the early stages of the development of DOC FF-3-71 the availability of materials with satisfactory vertical

flammability performance was limited to specialty end uses, predominantly for

the military. However, sufficient research and development had been completed

to make possible the marketing of a small quantity of flame retardant cellulosic children's sleepwear. Based on the performance of these pre-market and

market materials in the vertical test, a char length criterion was developed.

Figure 5 shows the results of tests performed on readily available fabrics that exhibited self-extinguishing properties. The histogram indicates

that, of the materials tested, an aveirage char length greater than 7 inches

tended to result in complete specimen burns (specimen length is 10 inches)

,

while the mean of all the average char lengths less than 7 inches was approximately 3.5 inches. Therefore, the selection of 7 inches as the char length

criterion appears reasonable and technologically practicable.

30

28

26 —

24

hi<

t-U

o

:

UJ

22

FREQUENCY DISTRIBUTION

OF VERTICAL CHAR LENGTH

I i ffl 4 6

CHAR LENGTH, inches

10

Figure 5. A histogram showing the distribution of average char length

for a group of fabrics tested in the vertical test.

13
A criterion (referred to as "residual flame time") was developed for molten material that continued to burn on the floor of the test cabinet, limiting

burn times of such material to 10 seconds. This was incorporated in the

standard for children of ages 0-5 years (sizes 0-6X) , because it was noted

that flaming material falling from a garment represented two additional risk

factors. The potential existed for the falling material to cause relatively

deep localized burns and increased the likelihood of secondary ignition of

other materials thereby increasing the extent of injury. However, there is

a difference between hazard and an unreasonable risk. These flaming drips can be considered an unreasonable risk to children that are relatively immobile

(i.e. sizes 0-6X covered by DOG FF-3-71) , but are less of a risk to older more mobile children (i.e. sizes 7-14).

The proposed acceptance criteria for children's sleepwear sizes 7-14,

therefore, differ from the criteria found in DOC FF-3-71. For children's

sleepwear sizes 7-14 (PFF-5-73) , the residual flame time criterion is deleted.

In DOC FF-3-71, the most critical criterion is that the average char length

shall not exceed 7 inches for a set of 5 replicate specimens. Secondary criteria are that no single specimen have a char length of 10 inches (specimen

size: 3.5" X 10") and that no single specimen exceed the 10 second limit on residual flame time. The latter two criteria are secondary only in that a failure of average char length results in a unit rejection under the accompanying sampling plan. The same is not true of the single specimen criterion,

which allows for sample retesting before unit rejection occurs.

4. CONCLUSIONS

A description of the methodology used in developing the children's sleep- wear standards clearly establishes the need for a synthesis between accident

data and laboratory experimentation. The basic approach taken has application

in areas other than f lammability . Any consumer oriented product safety standard must consider the best available end use and accident data and, at the same time, represent state-of-the-art technology with regard to repeatability

and reproducibility.

The continued surveillance of accidents should, in several years, indicate

the success or failure of this approach.

5 . REFERENCES

[1] The Flammable Fabrics Act, 81 Stat. 568, 15 U.S.C. 1191, as amended and

revised Dec. 14, 1967.

[2] Children's Sleepwear Sizes 7 Through 14, Notice of Proposed Flammability

Standard, DOC PFF-5-73, Federal Register, 38, no. 47 (Mar. 12, 1973),

6700-6710.

[3] The Standard For the Flammability of Children's Sleepwear, DOC FF-3-71,

Federal Register, 37, no. 141 (July 21, 1972), 14624-14632 (Revised).

[4] Slater, J. A., Fire Incidents Involving Sleepwear Worn By Children Ages

6-12, Nat. Bur. Stand. (U.S.), Tech. Note 810 (Dec. 1973).

[5] The Flammable Fabrics Program 1970, Nat. Bur. Stand. (U.S.), Tech. Note

596 (Sept. 1971) , 28.

[6] U. S. Bureau of the Census, 196 0 Census of Population, United States,

General Population Characteristics, Advance Report, PC(V2)-1 (Feb. 1971).

[7] Heskestad, G. , Kalelkar, A. S., and Kung, H. C, A Study of Pre-ignition

Heat Transfer Through a Fabric-Skin System Subjected to a Heat Source - Annual Report, (Factory Mutual Research Corporation), Dec. 1971.

14
[8] Mattresses, Notice of Finding that a Flammability Standard May Be Needed,

Federal Register, 35, no. 112 (June 10, 1970), 8944-8945.

[9] McCarter, R. J. , The Cause of Anomalous Behavior in the Vertical Flammability Test, Textile Chemist and Colorist, 4, no. 4 (Apr. 1972).

[10] Proposed Standard For the Flammability of Children's Sleepwear, DOC

PFF-3-70, Federal Register, 35, no. 223 (Nov. 17, 1970), 17670-17673.

[11] The Flammable Fabrics Program 1971, Nat, Bur. Stand. (U.S.), Tech. Note

749 (Dec. 1972) , 62.

15
NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 411, Fire Safety Research,

Proceedings of a Symposium Held at NBS , Gaithersburg , Md . , August 22, 1973,

(Issued November 1974)

SAMPLING PLANS IN MANDATORY STANDARDS

Paul Gottfried^

Consumer Product Safety Commission, Washington, D.C.

The Children's Sleepwear Standard for sizes 0-6X provides an example of the necessary interplay between sampling theory, industry

capabilities and consumer safety assurance. The sampling plan imposes requirements for the fabric, for garment design and for garment production. These requirements address the differences between

hazards due to design and those due to production errors. The re- quirements also interact to provide improved assurance of safety by

limiting the potential for severe injury.

Key words: Flammable fabrics; product safety; sampling; standards.

1. THE NEED FOR SAMPLING

The Flammable Fabrics Act and other product safety legislation administered by the Consumer Product Safety Commission do not in themselves require

product testing; they require only that products comply with applicable standards developed under such legislative authority.

In the past, standards have been enforced on the basis of compliance testing done by a regulatory agency. A failure discovered by the agency would

result in an action against the manufacturer or his product, causing him to cease production of that particular product and withdraw that product from the

market. Under such procedures, it is commonly found that failures are not detected until large quantities of the product are in the hands of retailers and

and consuming public. Demands for "one hundred percent compliance" in this

"post-mortem mode" can protect the consumer only after the fact and can cause severe hardship to manufactuers as well.

A more satisfactory way of protecting the consumer and limiting the risk

to be accepted by the honest manufacturer is to require testing prior to marketing. When defective products are prevented from reaching the market, the consumer is protected more effectively and the risks and costs of product re- call are decreased. At the same time, the amount of testing that can be done

is increased because industry resources as well as Commission resources can be

put to use. When testing is destructive in nature, as it generally must be in the flam

mability context, it obviously is necessary to resort to sampling. Even in

other situations, sampling may be the preferred approach because one hundred

percent inspection can be prohibitively expensive. Furthermore, one hundred

percent inspection is generally found to be much less than one hundred percent

effective; effectiveness on the order of 70 to 80 percent is observed commonly.

Finally, any regulatory agency is inherently limited to sampling; it could not

obtain all of each product even if that were permitted by its resources.

2. EFFECTIVENESS OF SAMPLING

Few, if any, manufacturing processes are capable of turning out a consistently perfect product, just as few, if any, test procedures yield results of

absolute accuracy and reproducibility. Sampling has similar limitations, and

these arise from theory as well as from reality. Every sampling plan carries

^The author was a consultant to the Consumer Product Safety Commission at the

time this paper was presented. The opinions expressed are those of the author

and do not necessarily reflect the views of the Commission.
with it a finite probability of accepting a "bad" lot of products and of re- jecting a "good" lot of products. Increasing the sample size can reduce these

probabilities, but with diminishing returns at essentially linear increases in

cost.

In quality control, the conventional buyer-seller relationship has led to

the development of several concepts closely related to the problems of "error"

in acceptance and rejection. Among these concepts are: Concentration on the "consumer risk" or "lot tolerance percent defective" — the probability of erroneous acceptance and the corresponding

fraction defective — when isolated lots are sampled.

The desirability of reduction of both risks, at the expense of increased sample size, for large lots in view of the disproportionately

increased severity of the consequences of error.

• The notion of the "average outgoing quality limit" or AOQL arising

from the effects of 100% inspection following lot rejection.

These conventional concepts have virtually no applicability in the context

of product safety and destructive testing. The notion of AOQL is obviously inapplicable when one hundred percent inspection is impossible. From the consumer standpoint, lot size is irrelevant because no individual consumer acquires

more than a very small fraction of any lot. Downgrading of lot tolerance percent defective concepts arises from less obvious considerations and hence com- mands more of our attention.

The costliness of destructive testing discourages the use of large samples

and this in turn makes it difficult to limit comsumer risk in the usual ways.

Fortunately, the physical phenomena that lead to destructive testing also lead

to strong economic incentives on the manufacturer: in general, it is at best

very difficult to rework a rejected lot and alternate markets are virtually

nonexistent. The consequence is that the manufacturer must achieve a very high

probability or frequency of lot acceptance in order to survive as a producer.

We estimate — we think conservatively -- that at least a 95% acceptance probability must be maintained routinely; that is, no manufacturer is expected to

survive if more than one of every twenty lots is rejected. This means that or- dinarily only the behavior of the sampling plan at low levels of "defectiveness

is of major concern; of course; we will still want to limit the chances that an occasional defective lot will slip through, but this is not as compelling a con sideration as it is in conventional situations.

3. CHOOSING A TARGET

Having established that the manufacturer will need to control his process

so as to achieve at least 95% acceptance probability leaves open the question

of what level of quality -- what process average — should correspond to this

target value. Here, we enter an area demanding many tradeoffs — which often

must be made with incomplete information, largely because the response of an industry to the challenges posed by a mandatory standard is not entirely predictable . There is a better than even chance that any standard, especially when flam

mability is involved, will drastically reduce available choices among materials

and designs. This implies reduced consumer freedom-of -choice and increased

costs that ultimately impact on the consumer. When a product is a necessity, as is generally the case for basic wearing

apparel, a further major consideration is the need to assure adequate availability of the product. (Nudism is a sure cure for garment flammability problems,

but might introduce some health problems of its own.) Large cost increases or

17
availability reductions for other textile-related products whose purchase is more discretionary, such as a replacement mattress, may have effects that are counterproductive from the standpoint of consumer safety. The delayed replacement of existing hazardous products in the interests of introducing a nearly

perfect product rather than a merely superior one can mean avoidable casualties

in the interim.

A prospective standard, including those aspects of stringency that arise

from its sampling plan, therefore must be scrutinized carefully from the standpoint of its total impact on the public and the industry.

4. AN EXAMPLE: CHILDREN'S SLEEPWEAR STANDARD (SIZES 0-6X)

The standard for the flammability of children's sleepwear (sizes 0-6X)

,

which went into full effect recently, provides illustrations of a number of the

points in this discussion. It also provides an example of the way in which a multi-tiered approach can reduce the burden of consumer product safety improvement.

In many products, it is possible and appropriate to distinguish between

hazards associated with the design characteristics of the product and those

that can arise due to production errors. These distinctions lead to two sets

of tests, each conducted on a different sampling basis. Design characteristics

are evaluated appropriately by relatively stringent tests conducted on prototype (preproduction or early production) items; under some circ\imstances , it

may be desirable to require that these tests be repeated at relatively long

intervals. The presence of production errors, on the other hand, requires detection by the use of representative samples from production quantities. To

the extent permitted by procurement practices, processes and industry structure, such samples should be drawn from internally homogeneous lots of production items. To reduce potential confusion with definitions of "lot" that may

be traditional to an industry, standards now refer to these homogeneous production quantities as "production units", whose maximum size is limited by the

standard

.

Children's sleepwear is unusual in that a major component — the fabric — is itself amenable to control by a standard. This standard therefore involves a sequence of fabric production testing — garment prototype testing —

garment production testing. (Fabric prototype testing was judged to have no special value or validity, as the dominant problems are of the production error

type .

)

In normal sampling, the production test employs ten fabric specimens.

Each of two samples contains three specimens taken in one direction and two in

the other, as the flammability characteristics may differ along warp and fill.

The average char length over each five-specimen sample must not exceed seven

inches; any violation of this requirement leads to rejection, so excessive

average char length is treated as a "critical" defect. Any individual specimen

fails if it chars its entire ten-inch length or if flaming of any fragments or molten material persists for more than ten seconds. If any single specimen

fails, an additional sample of five specimens (all aligned in the direction

experiencing the failure) must pass without further failure. If more than one specimen fails, the production unit is rejected.

It is worth noting that even a fabric production unit that is substandard — i.e., has a specimen fraction defective above the target value — and is

passed as a result of statistical phenomena is certain to be vastly superior

to fabrics in common use prior to issuance of the standard. Some of the latter

fabrics consistently would burn entirely and, if tested, would certainly be rejected. Any "defective" fabric passed under the sampling plan could be defective only in the sense that it had locally variable characteristics such as might result from uneven application of flame retardants; such a fabric would

18
not be subject to general and extensive burning. Sampling-plan rejects have

f laminability characteristics superior to 90 percent of the fabric in general

use two years ago.

Fabrics that can pass more stringent sampling plans exist, but not in

quantities adequate to meet sleepwear requirements. The target level here was

set to admit the required variety of fabrics, with consideration being given

to the capacity growth that could be anticipated in the period between the

standard's promulgation and its date of full effectiveness.

It is known that the flammability characteristics of a fabric can be com- promised by the thread material and construction used in garment seams and by

the presence of trim materials. These problems can arise directly from flammability of the added materials or the mechanical or synergistic effects. The

garment prototype test addresses these problems by requiring testing of specimens involving major seams and trim items of non-trivial dimensions. The number

of specimens required is larger, but there also is an allowance for a larger

number of failures (except in the case of the seven-inch average char length

limit) . It is unusual to allow these failures in a prototype test, but this

approach is necessary here because the garments must be made from production

fabric that may be imperfect and the garment cannot be required to be better

than the fabric.

Finally, production garments are tested using three samples of five speci- mens each and the same specimen pass- fail criteria. The specimens are obtained

from the seamed areas involving the longest seam in the garment. As many as three of the fifteen specimens are permitted to fail before rejection occurs;

the absolute character of the average-char-length requirement remains intact.

The failure allowance again reflects the accumulation of effects and the availability of materials. Note, however, that most of the garment consists of the

plain fabric that was previously required to pass the most stringent. of the

tests. Protection against the most serious of the garment flammability hazards — the large-area burn — thus is still provided; in fact, it is enhanced to

the extent that the seam tests constitute further validation of fabric characteristics .

The result of this three-tier sampling approach is a dramatic improvement

in sleepwear flammability with a minor cost increment due to the testing burden

per se. Increasing availability of suitable fabrics permits an impending extension of standards coverage to sleepwear in the 7-14 size range. Although details of approach will differ according to circumstances, the children's sleep- wear standard can serve as a model for future mandatory standards in several

areas of consumer product safety.

19
NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 411, Fire Safety Research,

Proceedings of a Symposium Held at NBS , Gai thersburg , Md . , August 22, 1973,

(Issued November 1974)

HUMAN ACTIVITY PATTERNS AND INJURY SEVERITY

IN FIRE INCIDENTS INVOLVING APPAREL

Laura Baker Buchbinder^

The Cotton Foundation, Memphis, Tennessee

Activities immediately preceding an apparel fire are identified,

classified and related to the age/sex groups involved. The level of

severity of burn injuries resulting from apparel fire accidents is

discussed and is related to the type of activity causing the accident. The relationships defined in the study indicate the importance of the human behavioral aspects of a fire accident and aid in

defining types of remedial action likely to be effective in reducing human loss due to fabric fires.

Key words: Accident patterns; apparel; apparel fires; burn injury;

FFACTS; fire; flammable fabrics; flammable liquids; garment fires;

garment parameters; injury severity; victim's activity; victim's

reactions.

1 . INTRODUCTION

It has already been noted that burn accidents result from the interaction of a number of environmental, human and physical factors. The activity

of the victim, the ignition source, the involvement of flammable materials,

including flammable liquids, and the reaction of the victim to an accidental

fire are all variables which may determine whether the victim suffers little or no burn injury or severe burns over much of his body.

In order to gain a complete understanding of the total burn problem and

to place the various factors leading to a burn injury in proper perspective,

it is necessary to understand the interrelationships of all of the factors in a fire accident. Therefore, the purpose of this study is to identify patterns in

these variables, activity, reaction, and garment parameters, and relate them to

each other and to the severity of the injury incurred. This paper will deal

primarily with two of the accident variables--activity of the victim and the

level of injury severity.

2. STUDY DESCRIPTION

Eleven hundred twenty-six (1,126) cases from the National Bureau of

Standards' FFACTS data base^ met the criteria for this study which were:

1. Apparel was involved

2. Total area of body burned was given

3. Information on the activity or the reaction of the victim was given.

Because of the extremely detailed information required, it was necessary to

go back to the original case histories, gather the appropriate information on activities, reactions and garment involvement, and classify and code the

information. The major classifications are shown in table 1. They fall

into 3 groups: those dealing with activities, those dealing with the reaction of the victim and those dealing with the garment involved.

^The author is currently a research associate at the National Bureau of

Standards, Washington, D.C. where the work reported here was performed

^At the time of this study, the FFACTS data base contained 1,964 cases.

20
Table 1. Major Information Classifications For Activity of Victim

CLASSIFICATION EXAMPLES

General Accident

Type

Involvement of flammable liquids,

gases, high voltage electricity

flammable

General Activity

Type

Using fire, playing with an ignition source,

using flammable liquids

Additional Information

on Activity

Body action, ignition source

Occupational

Relationship and Location

Work, non-work, play

Contributing

Circumstances

Physically disabled, intoxicated, senile

3. RESULTS

3.1. Accident Patterns

Accidents in the study were divided into four major categories which

attempt to define the general type of accident by the physical mechanisms

involved in it. Table 2 shows the number of accidents in each category.

Fifty-seven percent of the cases in the study involved no flammable liquids,

gases, or explosives; 35 percent did involve flammable liquids; and 7 percent

involved gas or explosives. There were only 12 cases which involved high

voltage electricity.

The first group is the one most affected by fabric flammability standards. The effectiveness of fabric flammability standards in preventing injury in the last three types of accidents is much less likely since flammable

liquids will burn regardless of the fabric and the primary hazard from explosions

is usually directed at exposed skin areas. The secondary level of classification specifies the general type of

activity the victim was engaged in before the accident. As can be seen in

table 2, the most frequent activities for all types of accidents were:

1. Using fire

2. Starting a fire

3. Playing with an ignition source

4. Using flammable liquids.

The kinds of activities the victims were engaged in varied with the general

accident type. For example, in accidents not involving flammable liquids

or gases, "using fire" and "playing with an ignition source" were the two most

frequent activities. When flammable liquids were involved, "using flammable liquids" was the largest group, accounting for one-third of the cases. Fifty-three percent of the accidents involving flammable gases or explosives

happened as the victim was starting a fire —most of these as he lighted a match in a gas-filled room or attempted to light a malfunctioning furnace or

gas water heater. Table 3 shows the number of accidents for males and females

in six age groups. When compared with the distribution of these age groups in

the general population, the 0-5, 6-10 and over 65 age groups are overrepresented, and the other groups somewhat under-represented. There were an equal number of males and females in the 0-10 age group, but males outnumbered

females in the groups from 11-65. Only in the over 65 group did women outnumber males.

21
Table 2. Number of Males and Females Involved By- Accident Type and Activity. Type

Accident Type

Activity Type

No Flammable

Liquids

Involved

Flammable

Liquids

Involved

Gas or Explosives

Involved

High Voltage

Electricity

Involved

All

Types

M F M F M F M F M F Total

Starting a fire . . . 31 39 27 16 zy lb 87 70 157

Using fire or similar

ignition source . . . 71 166 45 11 3 2 119 179 298

Using flammable or volatile liquids. . . 108 19 3 - - 111 19 130

Using special

ignition sources^ . . 9 1 9 18 1 19 Extinguishing a

7 5 15 12 22 17 39 Escaping a fire . . . 5 1 6 1 - - 11 2 13 Standing, sitting or moving near an igni27 53 16 5 - 7 50 58 108

Standing near an

1 - 19 1 21 6 1 42 7 49 Playing or climbing

near an ignition

17 37 1 1 2 21 37 58 Playing with an ignition source . • . 64 77 6 - J — 73 77 150

Playing with a flam9 2 - - 9 2 11

Playing with ignition source and flammable

49 6 49 6 55

Miscellaneous . . . • 1 1 1 1 2

14 15 3 2 1 2 20 17 37

Total ^ 246 395 314 75 61 23 12 633 493 1,126

^Ignition sources such as • aiding torches, soldering irons, bunsen burners, etc.

22
Table 3. Age/Sex Distributions For FFACTS Apparel

Cases and For the United States as a Whole

i t: -L *w ell L. "D O Y* Q "f" Age Niimber of Cases of All of U.S.

M F Total Cases Population^

0-5 . 86 91 177 15.7 10. 3 6-10. 76 75 151 13.4 10.0

11-15. , 86 39 125 11.1 10.2

16-20. . 57 13 70 6.2 9.1

21-65. . . 274 185 459 40.7 50.8

Over 65 50 90 140 12. 4 9.6

Unknown . 4 0 5 0.4

Total . 633 493 1,126 99.9^ 100.0

^Derived from 19 70 U.S. Bureau of the Census population

statistics

'Total does not equal 100.0 due to rounding.

Fire accident patterns seem to be strongly related to the sex of the

victim. While 55 percent of the victims in the cases studied were male, 81

percent of the accidents involving flammable liquids had male victims. Males

were the victims in 73 percent of the accidents involving flammable gases, and

all 12 of the victims were males in accidents involving high voltage electricity.

Females, on the other hand, accounted for 62 percent of the accidents involving

none of the above intermediary materials.

Results shown in table 4 indicate that diversification of hazardous

activities between the sexes begins at an early age. In the 0-5 group,

playing with matches was the major activity leading to clothing ignition

for both males and females, but in subsequent age groups, accident patterns

reflect the traditionally different activity patterns of the two sexes. Flammable liquid involvement was the dominant pattern in "pre-ignition"

activities for males 6-65, with almost 70 percent of the accidents to males

between the ages of 11 and 20 involving flammable liquids. Females, however,

incurred more of a hazard from direct contact with an ignition source in

activities involving ranges, space heaters and other open fires. Males

over 65 seemed prone to accidents resulting from lighting or smoking cigarettes and elderly females were especially susceptible to garment ignition

as they were using kitchen ranges.

3.2. Injury Severity

Having discussed patterns in activities preceding a burn accident,

let's turn our attention to the injury resulting from these accidents. The

severity of a burn injury is dependent upon several factors:

1. The area of the burn—that is, the percent of the total area of the

body burned

2. The thickness of the burn—that is, whether it is superficial involving only the upper layers of skin or whether it is a full

thickness or 3rd degree burn involving all layers of skin

3. The location of the burn, with such areas as the face, hands and

neck posing more of a problem than other areas of the body.

23
Table 4. Major Activities Leading to Burn Injuries,

By Age/Sex Group, Showing Flammable Liquid Involvement

(Upper case denotes flammable liquid involvement)

Age

Group

(yrs)

Males Females

Major Activities Percent of

for Group Group Involved

Major Activities Percent of

for Group Group Involved

0-5

Playing with ignition

source 55 Playing or climbing

near an ignition

source 15

Playing with ignition

source 52 Playing or climbing

near an ignition

source 24

6-10

PLAYING WITH AN

IGNITION SOURCE

AND FLAMMABLE LIQUID 30 Playing with ignition

source 17

Using fire 32

Playing with ignition

source 32

11-20^

UoXNG rLAMMABLE

VOLATILE LIQUIDS 22 PLAYING WITH IGNITION

SOURCE AND FLAMMABLE

LIQUID 13 Using fire 9

Using fire 46

Standing, sitting or moving near ignition

source 18

21-65^

USING FLAMMABLE VOLATILE LIQUIDS 23 USING FIRE 13 Using fire (no

flammable liquid) 11

Using fire 35

Starting a fire 13 Standing, sitting or moving near an ignition

source 11

Over

65

Starting a fire 20 Using fire 18 Standing, sitting or moving near an ignition

source 12

Using fire 53 Starting a fire 16

^A total of 69 percent of the accidents for males in the 11-20 age group involved

flammable liquids.

A total of 53 percent of the accidents for males in the 21-65 age group involved

flammable liquids.

24
Development of a severity or morbidity index encompassing the above factors

is in progress. However, until a better index is developed, percent of total area of body burned will be used to indicate the severity of the injury.

Figure 1 shows the distributions of total area of burn and area of full

thickness burn for the 1,126 cases in the study. It can be seen that the two

distributions have similar shapes. Thirty-nine percent of the cases suffered

a total area of burn of 10 percent or less and 60 percent of the cases had a burn of 20 percent or less. Forty- three percent of the 868 cases in which the area of full thickness burn was given suffered no full thickness injury.

3.2.1. Accident Type and Severity of Burn

It would seem that the severity of the burn is related to the type of

accident causing the injury. Figure 2 shows the area of the body burned for

each of the three major types of apparel fires. The greatest difference

seems to occur between the distribution of total area of burn for accidents

involving no flammable liquids, gas, etc., and the distribution of total

area of burn for accidents involving flammable liquids. This difference in

the distributions is statistically significant. ^ The difference in injury

severity between accidents involving flammable liquids and those not involving flammable liquids becomes highly significant when the effect of age--

that is, the very young and the very old —is removed by considering only the

adult (21-65) age group. It can be seen in figure 3 that accidents involving

flammable liquids have a lower percentage of minor injuries, more moderately

serious injuries and a smaller percentage of very serious injuries.

Presence of a flammable liquid presumably affects the course of the fire

during the first seconds after ignition. Unlike most apparel fires not involving flammable liquids, ignition may occur at several points simultaneously—wherever the flaming liquid comes in contact with the garment. In addition to this, a flammable liquid fire gives off a great amount of heat and is

very difficult to extinguish until the flammable liquid has burned off. Any

of these factors would tend to make injury in the critical first few seconds

of the fire more serious than if a flammable liquid were not involved.

50| 1 1 1 1 1 1 \ \ 1 1

0 l-IO 11-20 21-30 31-40 41-50 51-60 61-70 71-80 81-90 91-100 PERCENT OF BODY BURNED

Figure 1. Frequency distribution of the percent of total area of body

burned and of the area of full thickness burn.

'All references to statistical significance refer to chi-square contingency

tests

25
60

50

NO FLAMMABLE LIQUIDS, GAS OR EXPLOSIVES INVOLVED FLAMMABLE LIQUIDS INVOLVED -

GAS OR EXPLOSIVES INVOLVED

l-IO 11-20 21-30 31-40 41-50 51-60 61-70 71-80 81-90 91-100 PERCENT OF TOTAL AREA OF BODY BURNED

Figure 2. Frequency distribution of the percent of total area of

body burned for three types of burn accidents.

T- NO FLAMMABLE LIQUIDS, GAS OR EXPLOSIVES INVOLVED

l-IO 11-20 21-30 31-40 41-50 51-60 61-100 * PERCENT OF TOTAL AREA OF BODY BURNED

Figure 3. Percent total area of body burned in accidents with and

without flammable liquid? for age group 21-65.

The apparent rise in the right tails of the distributions is due to combination of the highest four deciles of the distributions. These four deciles

are combined because there is little practical significance, in terms of

probability of survival, between total area of burn values in the range

60%-100%

.

26
3.2.2. Age and Injury Severity

The severity of burn seemed to be somewhat related to the age and sex group involved. Females had a higher percentage of burns covering over 50%

of the body than males. However, the most striking difference in injury

severity patterns is seen in figure 4 where the area of the body burned is

considered in relation to various age groups. While the 0-10, 11-20 and 21-65

age groups have very similar injury curves, the over 65 group has a significantly lower percentage of relatively minor burns and a larger percentage of

burns covering 50% or more of the body. The significance of the difference in

injury severity patterns for the over 65 group versus all other age groups has

been established at the 99% level. This predominance of more severe burns in

the over 65 age group may be due in part to the decreased "defensive capability"

of elderly people. Preliminary results of this study indicate that the ability

of the victim to effectively react to garment ignition is very important in

determining the severity pf the resultant burn injury. The defensive capability of the victim was estimated based on the following criteria:

1. Was the victim immediately aware of ignition?

2. Did the victim have normal adult reaction capability or were his

reactions impaired by age, illness, or physical or mental handicaps?

3. Did the victim have help immediately available to help extinguish

the fire?

The total area of body burned for the 70 cases in the study in which the

defensive capability was judged to be very good was compared with the total

area of body burned in the 56 cases at the other extreme with poor defensive

capability. The results, shown in figure 5, indicate that victims with bad

defensive capability had fewer minor injuries and a much higher percentage of

severe injuries than the other group, indicating that the level of burn severity is in part a function of the defensive capability of the victim. Elderly

people often have limited defensive capability since they often live alone

and are usually not as physically and mentally fit as other groups in the

population. Therefore the relationship between defensive capability and injury severity may partially explain the increased severity of burns to people

over 65.

4. CONCLUSIONS AND RECO'^'IMENDATIONS

At this point in the study, patterns in activities leading to fire accidents are evident. As might be expected, these activity patterns are related

to the age and sex of the victims involved. It has also been shown that the

severity of injuries resulting from burn accidents varies greatly, with the

majority of the accidents in this study resulting in less than 20% total area

of the body burned. Injury severity also seems to be related to such variables as accident type and the age, sex and defensive capability of the victim. Therefore, it would seem advisable to consider not only numbers of accidents but also the relative severity of the accident and to look at all factors

contributing to a burn accident before determining the most effective remedial

action.

This study and others'* have indicated some problem areas such as young

children playing with ignition sources; males from 6-65 improperly using

flammable liquids; females of all ages, but especially the elderly, igniting

their clothing while working near kitchen ranges; and adults of both sexes,

especially those over 65, igniting their clothing as they light or smoke

cigarettes. There are a number of ways to accomplish a reduction in fire

For example: Slater, J. A,, Buchbinder, B. and Tovey, H. , Matches and

Lighters in Flammable Fabric Incidents: The Magnitude of the Problem, Nat.

Bur. Stand. (U.S.), Tech. Note 750 (Dec. 1972).

27
I-IO 11-20 21-30 31-40 41-50 51-60 61-100*

PERCENT OF TOTAL AREA OF BODY BURNED

Figure 4, Frequency distributions of percent of total area of

body burned for four age groups.

Figure 5. Comparison of the frequency distributions of percent of

total area of body burned between cases with "good" and "poor"

defensive capabilityThe apparent rise in the right tails of the distributions is due to combination of the highest four deciles of the distributions. These four deciles

are combined because there is little practical significance, in terms of

probability of survival, between total area of burn values in the range

60%-100%.

28
accidents in these groups, including fabric flammability standards, redesign

of ignition sources and public education. However, it is important to re- member that fabric flammability standards alone won't solve the problem.

For example, the apparel fire accident problem for males of ages 6-65 is

closely tied to the use and misuse of flammable liquids. Since this is

largely a behavioral problem and is difficult to approach from a technological basis, it would seem that a broadly based educational program may be

the most effective means of preventing this type of accident.

Further investigation is needed to effectively determine the hazard

involved in various types of fire accidents and to consider the cost-benefit

aspects of the various means of protecting people from fire injury. In addition, more detailed information is necessary for the development and implementation of effective educational programs. In relation to these needs,

further analysis is in progress to define activity, reaction and garment parameter patterns in greater detail and to determine the relationship of these

factors to each other and to the severity of the resultant burn injury.
NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 411, Fire Safety Research,

Proceedings of a Symposium Held at NBS , Gaithersburg , Md . , August 22, 197 3,

(Issued November 1974)

CHEMICAL ASPECTS OF FLAME INHIBITION

John W. Hastie

National Bureau of Standards, Washington, D.C.

The role played by inorganic chemical additives in fire

retardancy and flame inhibition is considered. Particular

attention is given to the molecular level aspects of commercially important systems containing compounds of antimony and

halogens

.

Key words: Fire retardants; flames: inhibition^

For purposes of discussion, consider a fire where the fuel is supplied

by pyrolysis of a polymeric substrate, such as a nylon or polyester carpet.

The gases in the immediate vicinity of the carpet will usually consist of a fuel-rich mixture of pyrolysed and vaporized hydrocarbons together with en- trained air. At a somewhat greater distance from the decomposing substrate,

this fuel-air mixture may support combustion in the form of a flame.

Now, it is well known that one can extinguish such a fire, either by

adding chemicals to the polymer substrate or externally throwing chemicals at

the fire such as with an extinguisher containing halocarbons or alkali metal

carbonates. The present discussion is concerned with the mode of inhibition

that occurs when chemicals are added to the substrate. What we have to find

out is how these chemicals are released from a pyrolysing substrate and then

how the released molecular species interact with the flame reactions. The

important reactions in flames are radical reactions and one can chemically

affect the flame propagating radicals which are mainly hydrogen atoms, hydroxyl

radicals and oxygen atoms. By reducing the steady state radical concentration, we can inhibit the flame and even extinguish it. So that is the problem that we are addressing ourselves to. I should mention that the main chemicals that

are currently being used by industry are compounds of antimony, phosphorus and

chlorides or bromides. We have been studying the mechanisms by which com- pounds containing these elements inhibit fires, but in this paper I am just

going to discuss the antimony system.

There are two modes by which such chemicals can affect fires. They can alter the course of decomposition of the polymer such that a less flammable

mixture is produced, or they can release chemicals to the vapor phase which

actually poison the flame, and it is this latter mode of action which I am going to emphasize.

The antimony oxide halogen system is usually comprised of a mixture of

antimony oxide solid and an organic halogen compound such as polyvinylchloride

or some chlorinated paraffin. This mixture is added to the substrate that we want to fire retard. It has widespread use in industry; however, the mechanism

by which it operates as a fire retardant is not very well understood. We have,

therefore, chosen this as a model system for extensive study.

At the molecular level, without going into technical details, we are able

to monitor the pyrolysis chemistry by using a mass spectrometer as a detector

for the different vapor species. Our principal observations from this kind of

research are that the hydrogen chloride which is released from the decomposing

organic chloride additive interacts with the antimony oxide solid over a temperature interval of about 250-500°C, which is an interval characteristic for

A more extensive discussion of the subject matter dealt with here may be found

in the following reference: Hastie, J. W. , Molecular Basis of Flame Inhibition,

J. Res. Nat. Bur. Stand. (U.S.), 77A (Phys. and Chem. )

, No. 6, 733-754 (Nov.-

Dec. 1973).

30
the pyrolysis of many commercial polymers. The main products of this interaction have been found to be gaseous antimony trichloride and water vapor.

Also, during the course of this interaction we find that solid oxychlorides

are formed. These oxychlorides really control the rate at which the antimony

trichloride is released to the vapor phase. This is demonstrated in figure 1. The curves A, B and C give a measure of the rate of release of antimony trichloride to the gas phase at different temperatures. We have started out with

an antimony oxychloride solid and gone through a heating sequence with a very

small rate so that we could attempt to approach an equilibrium condition. The

important thing about this observation, i.e., figure 1, is that the antimony

trichloride is released in the form of three bursts, rather than being released

all at once. If the trichloride was released just at one temperature, like

250°, we would rapidly lose all of the additive that had been introduced into

the polymer, and the chances of the system being an effective fire retardant

would be reduced because the extinguishant is only being released over a very

narrow temperature interval which may not correspond with the temperature at

which the polymer is decomposing. The rule of thumb here is that we want the

vapor active ingredient to be released at about the same time as the polymer

is producing flammable fuel, and in many cases that is up in the temperature

interval of about 300 to 400°C.

To summarize the results of an extensive study on this system — the

release of antimony trichloride is controlled by the formation of solid oxychloride phases which are listed in table 1. This is fairly peculiar to the

antimony oxide system. One would not expect to find a similar behavior in

many other oxide-halogen fire retardant systems that one could conceive of.

Ql EJ I

I LL L_

200 300 400 500

TEMPERATURE °C

(rate**' 0.27min.)

Figure 1. Pressure variation of the vapor species SbCl^ (curves A, B and C)

and Sb^Og (curve D) as a function of temperature and time using solid

SbOCl as a source and a heating rate of about 0.2°C min""^.

31
i

I Table 1. Antimony Oxide - Halogen Substrate Reactions ! For Typical Substrate of [R • HCl + Sb^O-, + Fabric]^ ' _ .

j

[R • HCl]

HCl + [Sb202]

A 5[SbOCl]

B 4[2SbOCl • Sh^O^]

C 3[SbOCl • Sb202]

D 2[Sb20^]

f'Square brackets denote solids.

"Could also be [2SbOCl • 3Sb,0,]

.

Now, let me address the problem of how this antimony halide vapor actually

affects the flame. In studying the chemistry of these additives in flames,

there are two approaches that we can use, either a macroscopic level of observation -- which would involve measuring such things as flame speed, temperature,

combustion limits and initial and final composition — or we can look at the

microscopic level which involves looking at all the molecular species present

in the flame, and for this we would use optical and mass spectroscopic techniques. The important thing here is that if we can characterize the microscopic

character of these flames and also the additives in the flames, then by use of

kinetics and thermodynamics we can actually calculate these macroscopic properties. If this calculation agrees with the results of macroscopic measurements, then our model for inhibition which has been developed by the microscopic

route is most likely a correct one. This is the approach that we are working

towards.

Table 2 gives a rating of chemicals as flame inhibitors. The large numbers mean that only a small amount of inhibitor is required to reduce the velocity

of a particular laboratory flame. Note that antimony trichloride has a rating

of about 26, relative to say, a value of only 0.8 for carbon dioxide. Thus,

there are many chemicals that are much more effective than chemicals which are currently being used as extinguishants and, in particular, some of the heavy

metal systems are extremely effective. It is conceivable that such systems may

be used in future retardant forraulations . By looking at the molecular level

processes of these chemicals in flames, one can eventually understand why an individual chemical has the particular effectiveness that it does on flame

speed

.

Now, in order to get at the molecular basis, we need to develop a system

for analyzing flames at one atmosphere and to be able to extract very active

species, such as radicals, from these flames. An apparatus developed for this

purpose is shown schematically in figure 2; basically, it is a molecular beam mass spectrometer. The sampling of flames is carried out through a small pin

hole in the tip of a conical probe into a vacuum system. The gas then freezes

into a molecular beam-form and passes into the mass spectrometer where it is mass analyzed.

The position of the burner, and hence the flame, can be varied relative

to the sampling probe. The mass spectrometer then tells us what the distribution of molecular species is in a laboratory flame. Typical results are given in figure 3. The zero is the burner tip and the luminous reaction zone

for this flame is at the 9 mm distance position. From this, we see that one

'\'250°C

R + HCl

[SbOCl]

[2SbOCl • Sb202] + SbCl3

5 [SbOCl • Sb203]'^ + SbCl3

4 [Sb203] + SbCl^

4 6

Temperature

Increasing

'^.550°C

32
can monitor the decomposition of the fuel, the depletion of oxygen and the

appearance of combustion products. More importantly, using molecular beam

sampling, we can look at the distribution of radical species which are con- trolling the speed of these flames as shown in figure 4. The most important

species in fuel—rich hydrocarbon flames are the hydrogen atom, hydroxyl radical

and the methyl radical. Note that the hydrogen atom appears well upstream of

the flame. It is diffusing back upstream and most of the pre-flame chemistry

is probably the chemistry of this hydrogen atom.

Table 2. Relative Effectiveness, ^ , of Selected Flame Inhibitors

Inhibitor Flame Type

n - hexane/air H2 - air

C02 0. 86

C12 1.8 -0.26

Si(CH3)4 3.9

CCI4 4.2

Br^ 8.4

SiCl^ 10. 5 3.5

(CH3)3P04 23.0

SbCl3 26. 0

TiCl^ 30. 0 10.0

SnCl^ 31.0 12. 9

POCI3 31. 0 7.2

PCI3 39.0 4.5

PBr3 39.0

Cr02Cl2 =244.

Fe (CO)

356. 0 19. 0

390. 0

33
PHASE SENSITIVE DETECTOR

1 I I Figure 2. Schematic of mass spectrometric system for sampling 1 Atm flames.

A representative gas sample passes through a cone system (c) into an evacuated chamber (region II) ; the beam then passes through an adjustable

orifice into region III, which contains a wheel (w) for mechanical modulation of the beam, an ion source (g) for partial conversion of the

molecular species into positive ions, and a mass filter and ion detection

system (p)

.

34
0 4 8 'tl2 16 DISTANCE (mm)

Figure 4. Concentration profiles

for the main radical species in

a fuel-rich CH^ - ©2 flame.

20

We find that addition of antimony tribromide to such a flame gives composition profiles of the type indicated by figure 5. The hydrogen bromide and

methyl bromide intermediates are only stable in the pre-flame region. The

temperatures in this region and the rate constants for reactions of these bromides with hydrogen atoms are known, and it is generally agreed that at least

some inhibition occurs in this pre-flame region. However, we also believe that

there is a strong inhibition effect at the reaction zone where the radicals all

have their maximum concentration. In this antimony case, we believe that it

is the antimony monoxide species which is affecting the radicals by interacting

with hydrogen atoms and catalyzing a recombination of hydrogen atoms to molecular hydrogen. This lowers the flame speed and causes inhibition.

Let me sum up this discussion by indicating a reasonable approach to this

problem of chemically controlling flames as summarized by table 3. The primary

problem that we have been dealing with up to now is to identify the flame species.

Once these are established, then we have to worry about the kinetics of the

reactions of these species in flames. Unfortunately, very little of this data

is available and we will need to obtain some of it using the mass spectrometric

flame sampling system; Once the flame kinetics are known, one can apply well

developed flame theory and test a molecular model. When the model has been

established, one can then look at basic data to see what other kinds of species

would be good flame inhibitors. For instance, we think that species such as antimony oxide, phosphorus monoxide and tin monoxide are good flame inhibitors

at the present time. Once we know what the various optimum flame retarding

species should be — such as antimony trihalide, the molecular precursor to

antimony monoxide. We then have to be concerned with the solid state chemistry

such as the interaction of antimony oxide and the organic halogens to generate

these molecular precursors. Finally, there is the problem of how to incorporate

these additives into real polymers. Clearly, there are many chemical problems

to be solved before a definitive understanding of chemical fire retardance can

result.

35
1900

Figure 5. Concentration profiles

for species resulting from SbBr

addition to a 1 Atiti fuel-rich

CH. - 0_ flame.

Table 3. Flame Inhibition And Extinction - Systems Approach

Programs Classification

(a) identify flame species spectroscopy

(b) determine flame kinetics basic data

(c) test kinetic models theory

- flame equations

(d) determine optimum

flame species for

inhibition

basic data

(e) design stable molecular

precursors to inhibitor

species

thermodynamics

kinetics

basic data

(f

)

determine solid sources of

such molecular precursors

thermochemistry

basic data

(g) define chemistry of

incorporation of additives

to polymer substrates

thermochemistry

solid state

- structural studies

36
NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 411, Fire Safety Research,

Proceedings of a Symposium Held at NBS , Gaithersburg , Md . , August 22, 1973,

(Issued November 1974)

MECHANISM OF FLAME RETARDANT ACTION IN TEXTILES

Robert H. Barker

Clemson University, Clemson, South Carolina

Flame retardants may exert their effect on textile materials

by either modifying the pyrolysis reactions of the polymer substrates so that smaller quantities of flammable gases are produced

or by interfering with the oxidation reactions in the flame. The

modes of action for several common types of retardants on cellulose,

nylon, and polyester have been determined by use of thermal analysis,

pyrolysis-gas chromatography, oxygen index, and calorimetric techniques . Key words: Calorimetry; cellulose; flames; flammable gases; nylon;

oxidation reactions; oxygen index; phosphorus; polyester; polymer

substrates; pyrolysis-gas chromatography; textiles; thermal analysis.

1. INTRODUCTION

For combustible textile materials the most serious hazard is usually that

associated with their propensity toward flaming combustion. It is therefore

the flaming reaction which is most commonly the focus of inhibitory action.

This flaming process is basically cyclic in nature. In the initial stages of

the process heat is supplied to the non-volatile polymer substrate to initiate

an endothermic degradation reaction which for most polymer systems is thought

to be predominantly pyrolytic in nature. There seems to be little evidence of

significant oxidative processes occurring in the condensed phase except in the case of afterglow. The products of this polymer pyrolysis migrate to the surface of the fabric and are released into the atmosphere immediately above the

fabric. As they diffuse away from the surface of the fabric, they begin to

mix with the oxygen of the air so that combustion can take place. The combustion

is, of course, an exothermic process, and the heat thus liberated can be returned

in part to the fabric surface. This heat causes further pyrolysis of the polymer, assuring a continuous supply of fuel for further flame propagation.

Because of the cyclic nature of this process, it is usually amenable to

attack at any of several points. Effective flame retardants may, therefore,

act either in the condensed phase, or in the vapor phase above the decomposing

polymer. Retardants which act in the gas phase exert their effect by functioning

as either inert diluents or as free radical inhibitors which slow the oxidation

processes and decrease the heat returned to the fabric surface. Those retardants

which act in the condensed phase may operate by several mechanisms. They may

inhibit the polymer pyrolysis so that it does not break down to produce the

small volatile molecules necessary for flame propagation. More commonly , however, they act to alter rather than inhibit this pyrolysis reaction. The

alteration is such that the mode of pyrolysis is changed and lesser quantities

of flammable gas are produced. Finally, they may also exert their effect in

a physical rather than a chemical manner. In this case they act as a shield

to prevent the transfer of heat from the flame back to the fabric surface.

This reduces the rate of polymer pyrolysis and fuel production is decreased.

In order to evaluate a particular flame retardant system, it becomes

necessary to determine the mechanism of action of the various flame retardants

on the fabric. This usually requires a knowledge of whether the flame retardant

is gas phase or condensed phase active. Once this is known an investigation

may be begun to determine the actual chemical mechanism involved in the retardation process.

37
2. DETERMINATION OF THE SITE OF FLAME RETARDANT ACTIVITY

A wide variety of phosphorus-containing flame retardants are known to be

effective on cellulosic substrates. Of these, phosphoric acid is one of the

simplest and most effective. For many years, it has been postulated that this

material acts completely in the condensed phase to alter the fuel producing

reaction. That this is actually the case has been shown in a recent study. [1]

Thermal analysis of cotton fabrics treated with various amounts of phosphoric

acid are shown in figure 1. The DTA curves show that the endothermic pyrolysis

T T T T T T

<

K

liJ a.z

UJ

I--I<

u

u.o

CELLULOSE/H3P04

5.2% P

^ *

CELLULOSE /H3PO4

3.8% P

CELLULOSE /HJ»0^

2.3% P * ^

CELLU LOSE /HSPO4

1.8 %P

CELLULOSE/ H3PO4

l.l%P

CELLULOSE

ISO 200 250 300 350 400

REFERENCE TEMPERATURE (*C)

Figure 1. Thermal analysis of cotton

fabrics treated with various amounts

of phosphoric acid.

reaction of the cellulose occurs at progressively lower temperatures as increasing amounts of phosphoric acid are present. In fac't, the endothermic

decomposition reaction becomes two endotherms in the presence of phosphoric

acid. These endotherms correspond to catalyzed decomposition and catalyzed

phosphorylation of the cellulose. This is possible in the case of cellulose

because of its ability to undergo decomposition by at least two competing

pathways, as shown in figure 2. The decomposition to carbon dioxide water

proceeds only very slowly in the absence of catalysts. In the presence of a catalyst such as phosphoric acid, however, this reaction becomes the predominant one at the expense of the fuel producing reaction.

38
H2O + CO2 + Char

<250»

SLOW

CELLULOSE

>250» CH2—

FAST I ^Flammable Gases

Figure 2. Decomposition of cellulose by two competing pathways.

This reduction in fuel supply is reflected in the behavior of these

samples in the oxygen index tester. Fenimore and Martin have suggested that

the oxygen index tester constitutes a good probe into flame retardant mechanisms

when more than one oxidation medium is used. [2] If a flame retardant exhibits

similar efficiencies in two or more oxidizing agents, it is generally considered

that the flame retardant does not interact with the oxidant itself, but acts

only to alter the amount of fuel supplied to the flame. That this is the case with phosphoric acid treated cellulose can be easily seen from figure 3. Measurements using oxygen and nitrous oxide as oxidants exhibit very similar

dependency upon the concentration of retardants present as shown by the parallel

lines. These results together with the DTA results show quite conclusively that

essentially all of the phosphoric acid activity is confined to the condensed

phase. However, it is necessary to use both techniques in order to reach this

conclusion.

This approach has been used quite successfully in several cases. For

example, a number of transition metal salts are known to be good flame retardants for cellulosic fabrics, but their mechanism of action is almost completely

unknown at present. [3] The oxygen index data shown in figures 4 and 5 show

that the molybdates and vanadates are particularly efficient even when compared

with phosphoric acid. [4] This is surprising since most sodium salts of phosphorus acids are quite ineffective as flame retardants.

Differential thermal analyses shown in figure 6 and thermogravimetric

analyses, figures 7 and 8, indicate considerable condensed phase activity with

both the sodium and ammonium salts. [4] Both series seem to be capable of

catalyzing the cellulose decomposition and increasing the amount of residue

remaining at the end of pyrolysis. In the case of sodium salts such as sodium

molybdate, this seems to be the most important activity of the retardants.

Their effect is almost completely in the condensed phase as indicated by the

oxygen index results shown in figure 9. The ammonium molybdate, however, seems capable of additional reactivity in the vapor phase (fig 10); however, the

relative importance of these two modes of action cannot be determined. It

should also be pointed out that there is no particular reason to assume that

the condensed phase activity of the ammoniiam molybdate is the same as that of

the sodium molybdate

39
01

25.0

23.0

21.0

19.0

17.0

15.0

AMMONIUM SALTS

1 1 1

AMMONIUM META-VANAOATE A AMMONIUM TUNGSTATE • AMMONIUM MOLYBDATE _ o PHOSPHORIC ACID

10 1.5 2.0 2.5 % METAL

Figure 4. Cotton fabrics treated

with ammoniuin salts.

-1 1 1

CELLUL0SE/Na2W04-2H20

CELLULOSE/( NH4)6M07024-4H20 0.85% Mo CELLULOSE/ NoVO^ZHgO

200 300 REFERENCE TEMPERATURE CO

Figure 6. Differential thermal

analysis thermograms for

cotton cellulose treated with

sodium and ammonium salts.
10

200

T

(2-3)0.85% Mo

(4-3)l.04%V

-X-K-X-K- (7-3) 1.28% W

—X—X

"

300 400

TEMPERATURE PC)

500 1.0 1.5 % METAL

Figure 7. Thermogravimetric analysis

thermograms for cotton cellulose

treated with ammonium salts.

Figure 9. Cotton fabric treated

with sodium molybdate.

T

(I-3)0.86%W

(3-4) 0.99% V

x-X-x-X (6-3) 0.91% Mo

200 300 400

TEMPERATURE PC)

500

Figure 8. Thermogravimetric analysis

thermograms for cotton cellulose

treated with sodium salts.

01

26.0

25.0

24.0

23.0

22.0

21.0

20.0

19.0

18.0

17.0

16.0

15.0

AMMONIUM MOLYBDATE

1 /1 1 1 i

/

/ /

/ / / /

' //

- //

A 01 '// NOI Y

1 1 1

1 .5 1.0 1.5 2.0 2.5 % METAL

Figure 10. Cotton fabric treated

with ammonium molybdate.

NOI

49.0

48.0

47.0

46.0

45.0

44.0

43.0

42.0

41.0

40.0

39.0

38.0

41
This technique has been

retardants on cellulosic subs

strates. Triphenylphosphine

polyester. [5] The results,

considerable vapor phase acti

and thermogravimetric analysi

polymer when the phosphine ox able to assume that there is

phosphine oxide on polyester

extremely useful in studying many types of flame

trates. It is, however, not limited to such suboxide has been studied as a flame retardant for

as shown in figure 11, indicate that there is

vity in this system. Differential thermal analysi

s show no differences in the decomposition of the

ide is present (fig. 12) . It is therefore reasonno condensed phase activity exerted by triphenylTriphenylphosphine oxide has also been investigated as a flame retardant

for nylon-6. [6] The oxygen index results shown in figure 13 indicate that

the triphenylphosphine oxide acts in the vapor phase in this system also.

Similar studies of samples containing varying amounts of triphenylphosphine,

triphenylphosphite and triphenylphosphate are shown in figures 14-16. In all cases the dependence of the flame retardant efficiency on the chemical nature

of the oxidant indicates considerable vapor phase activity. As with the polyesters, thermal analysis of the treated nylons shows no significant alteration

in the decomposition pattern when the flame retardants are present. On this

basis it can be concluded that these types of thermally stable phosphorus com- pounds act almost completely in the vapor phase. This is, of course, of con- siderable importance in these systems since it indicates that they will produce

no alteration in the melt-drip characteristics of the thermoplastics. It also

has significance in terms of smoke and carbon monoxide evolution since all of

these vapor phase flame retardants act to inhibit oxidation and should, therefo:

increase the amount of incomplete combustion products present in the off-gases

from the burning fabrics.

I] Fi

NOI

58.0

57.5

57.0

56.5

56.0

55.5 55.0 E 54.5 t-X

<s 54.0

UJ

53.5

.1 .2 .3 .4 Vo PHOSPHORUS

Figure 11. Plot of oxygen index

and nitrous oxide index versus phosphorus content in the PET/

TPPO System.

PET PET WITH 4.0 MOLE a TPPO

50 100 150 200 250 300 350 400 450 TEMPERATURE CO

500

Figure 12. TGA thermograms of

PET and PET with 4.0 mole

percent TPPO.

42
- 43.0

- 42.0

J4 1.0

.50 1.00 1.50 2.00 2.50 3.00 % PHOSPORUS

Figure 14. Plot of Oxygen Index (01)

and Nitrous Oxide Index (NOI) versus percent phosphorus for triphenylphosphine.

01

23.0 -

22.0 -

21.0 -

20.0 -

19.0

- 42.0

4 1.0 2.00 4.00 6.00 6.00 10.00 12.00 V. PHOSPHORUS

Figure 13. Plot of Oxygen Index (01)

and Nitrous Oxide Index (NOI) versus percent phosphorus for triphenylphosphine oxide.

01

23.0 -

22.0 -

2 1.0 -

20.0 -

19.0

NOI

- 45.0

41.0

.50 1.00 1.50 2.00 ZJ50 3.00 % PHOSPHORUS

Figure 15. Plot of Oxygen Index (01)

and Nitrous Oxide Index (NOI) versus percent phosphorus for triphenylphosphite

Figure 16. Plot of Oxygen Index (01)

and Nitrous Oxide Index (NOI) versus percent phosphortis for triphenylphosphate

01

23.0

22.0 -

2 1.0

20.0

19.0

n r

"1 1 r

01 o

NOI

D

J L

NOI

45.0

- 44.0

- 43.0

- 42.0

41.0

.50 1.00 1.50 2.00 2.50 3.00 % PHOSPHORUS

43
1 similarly, and perhaps more surprisingly, a commercial chlorine containing!

organic flame retardant in combination with antimony oxide in a polypropylene ' matrix shows little indication of vapor phase activity in the oxygen index ' tester (fig. 17) . Although it is usually assumed that halogen compounds act } primarily as vapor phase inhibitors, this is not the first case in which only

condensed phase activity has been observed for organochlorine compounds.

j Fenimore and Martin observed such behavior in the case of chlorinated polyethylene s. [2] 1 Even in the case of organobromine compounds where activity is almost always}

found in the vapor phase the possibilities for condensed phase activity cannot

be ignored. This is particularly important since such condensed phase activity 1 is not always desirable. A good example of this phenomenon can be found in

nylon-6 samples treated with organobromine compounds. [7] Differential thermal , analysis (fig. 18) and thermogravimetric analysis (fig. 19) of a nylon-6 sample ' containing hexabromobiphenyl shows that the bromine-containing flame retardant

induces marked changes in the pyrolysis reaction of the nylon. Using only thesej

data, and the results of the oxygen index tester, it is possible to conclude

that both condensed phase and vapor phase activity are important in the flame

retardation process. It is not possible, however, to determine the relative

importance of the two processes. This is particularly significant in this

system since further investigation shows that the vapor phase process is the

only one responsible for inhibition of the flaming reaction. [7] That activity

which occurs in the condensed phase turns out to have a deleterious effect on

the combustibility properties of the. nylon. This can be seen quite clearly by

gas chromatographic analysis of the pyrolysis products when the reaction is

carried out in the presence of the hexabromobiphenyl (fig. 20) . Under these

conditions the only observed pyrolysis products are the e-caprolactam and the

cyclic dimers and trimers normally found in the pyrolyzate from untreated nylon.

The only other peak in the chromatagram is the carbon tetrachloride used as a solvent for the pyrolyzate mixture. On this basis it is possible to conclude

that the hexabromobiphenyl acts in the condensed phase to catalyze the decomposition without altering the nature of the reaction. Thus the effect of the

hexabromobiphenyl is to increase the amount of gaseous fuel produced by the

pyrolyzing nylon. This, of course, makes the flame more difficult to inhibit

and results in a much lower efficiency than would be expected for these types

of compounds.

3. DETERMINATION OF HEAT EVOLUTION DURING BURNING

Although oxygen index testing and thermal analysis are frequently sufficient to gain considerable insight into fire retardance mechanisms , there are many cases similar to that of the hexabromobiphenyl in nylon-6 where additional

techniques must be used to provide enough information to allow even tentative

elucidation of the fire retardant mechanism. In many such cases calorimetry

provides the most useful mechanistic probe available since the net effect of a flame retardant is almost always reflected in a reduction in the heat produced

by the burning fabric. For this reason, considerable effort has been expended

both at Clemson University and at the National Bureau of Standards to develop

calorimetric techniques for the measurement of such heat evolution. One of

the simplest of these is based on static oxygen bomb calorimetry and involves

only one major limitation. [8]

When a fabric burns in open air, the evolved heat can usually not be

measured directly without the aid of a specially designed isoperibol calorimeter

[9] ; but under certain circumstances it can be calculated from more easily

measurable quantities such as the standard specific heat of combustion of the

polymer and the standard specific heat of combustion of the char resulting

from burning the polymer in the open air. [8] This calculated value, designated

as A, corresponds quite closely to the actual heat liberation in the case of

light-weight cellulosic fabrics where essentially all of the flammable gases

44
100 90 80 70 60 50 40 30

Vo POLYPROPYLENE

T

1 1

1 r

H 1 1 1 1 1 1 1 ^ 100 200 300 400 500 TEMPERATURE CO

Figure 19. Plot of the thermogravimetric analysis (TGA) curve

of Nylon 6 compared to the TGA

curve of Nylon 6 treated with

Hexabromobiphenyl . Samples were

decomposed at a heating rate of

6°C per minute.

Figure 17. Polypropylene containing

animony oxide and organo chlorine

flame retardant.

/ /

DTA curve of Nylon 6 J DTA curve of Nylon 6 * treated with Hexabromobiphenyl

1 -!- 1 -!-

1

I \ / H 1- 1 1 1 1 100 200 300 TEMPERATURECC)

500

Figure 18. Plot of the differential

thermal analysis (DTA) curve of

Nylon 6 compared to the DTA curve

of Nylon 6 treated with Hexabromobiphenyl .

60 120 180 240 300

RETENTION TIME. SECONDS

Figure 20. Gas chromatograph of

Nylon 6 treated with hexabromobiphenyl programmed at 15°/

minute from 90°C to 250°C.

45
are burned to produce carbon dioxide and water. This is shown diagramatically

in figure 21. This value is closely related to the total f lammability of the

system and is, therefore, of considerable importance. Its significance, however

lies primarily in the fact that it can be further interpreted to produce information relating to the exact molar efficiency of a particular flame retardant

system. The heat value, A, can be related to the amount of cellulose undergoing

decomposition to produce flammable gases by the relationship shown in figure 22.

As indicated, A equals the sum of Y, the weight fraction of cellulose converted

to flammable gases, multiplied by the heat of combustion of the cellulose, and

X the weight fraction of reagent on the sample, multiplied by the heat of com- bustion of the reagent. The fraction of cellulose converted to flammable gases

can then be easily calculated as Y/(l-X). The dependence of Y/{l-X) as a function of the concentration of the flame retardant on the fabric provides a measure of the efficiency of the flame retardant system. Using this methodology

it has been possible to study the relationship between the structure of the

phospnorus-containing group and its efficiency in imparting flame retardant

characteristics to cotton fabric. These results were the subject of several

recent reports. [10,11]

POLYMER

(AH(. ) polymer

HEAT

O2' PRESSURE. HEAT

^^^PRY^ POLYMER

+ + HETEROATOMS

PRESSURE

HEAT

^^^C^CHAR

AIR

(^•^C ^ GASES

(AH?) = A+R(AH°), C ' POLYMER """^''^ "C 'CHAR

A= (AHpRy) POLYMER "( AMT. OF FLAM M ABLE GAS) (AH^ )gASES

= (AH° )poLYMER " R^^Hc )chAR

Figure 21. Thermochemistry of polymer combustion.

46
-Char + COg + H2O

\p2

X • Reagent + (l-x) Polymer , ^ Total Combustion Products \^ FLAMMABLE GASES'

X = WEIGHT FRACTION OF TREATING REAGENT

R = WEIGHT FRACTION OF POLYMER CONVERTED TO CHAR

Y= WEIGHT FRACTION OF POLYMER CONVERTED TO FLAMMABLE GASES Figure 22. Thermo-decomposition pathways.

In the investigation of simple phosphorus flame retardants for cellulose

the results shown in figure 23 were obtained. [8] Compounds such as phosphoric

acid, diammonium phosphate, and the THPOH-ammonia polymer were all found to have

essentially the same efficiency characteristics. This indicates that the

limiting factor in determining the efficiency of these types of flame retardants

is not their chemical structure but rather is their ability to break down to

form phosphorus oxides. These phosphorus oxides are the common intermediate

in the reaction of the retardants with the cellulose substrate. The ultimate

efficiency of such non-thermally stable systems is, therefore, given by the

effectiveness of the interaction between cellulose and the phosphorus oxides.

The only possibility for their efficiency to be enhanced vrould be for them to

be converted into some degradation product other than phosphorus oxides by a preceding reaction with an additional reagent applied to the cellulose. This

has been found to constitute the basis for the phosphorus-nitrogen synergistic

effects observed by many workers. [11]

The situation becomes considerably more complex when the flame retardants

are thermally stable up to the point of polymer degradation. In such systems

the nature of the phosphorus-containing functional group is important in determining the flame retardant efficiency of the system. Figures 24 and 25 show

that for the phenyl derivatives, the efficiency of the flame retardant system

increases as the number of oxygen bonded to the phosphorus increases. [10] An

exception to this behavior is observed with triphenylphosphate which probably

represents a special case because of its volatility. This would indicate that

for thermally stable flame retardant additives the efficiency of the system can

be limited by the chemical nature of the phosphorus compound. These results,

when viewed in the context of other experiments involving product analysis and

model compound studies [12,13] allow the elucidation of the complete chemical

mechanism for the interaction of phosphorus flame retardants with cellulose.

The efficiency of such reagents appears to be related to the electron density

at the phosphorus atom. As the electron deficiency increases, the molecule

becomes more electrophilic and more acidic. This leads to enhanced interaction

in phosphorylation reactions and increases its efficiency in catalyzing the

degradation of the cellulose. Both of these reactions inhibit the formation

of flammable volatiles from the cellulose and promote formation of char and

incombustible volatiles.

Although such correlations are fairly straightforward in most cases, the

calorimetric technique is also capable of discerning unusual and unexpected

effects. For example, it has recently been found that for structures of Type I the flame retardant efficiency of the phosphorus compound depends strongly upon

the chemical nature of the moiety attached to the other end of the carbon chain

[11] (fig. 26) Q

(CH3O)— P— —CH2R

I R - CN

C(0)0CH3

C (0)NH2

C (0)NHCH„OH

47
I

'

I—I—I—I I I n

'—I—'—I

'

I ' I

a HjPO, O (NH4)2HP04 THPOH-NH3 • (CeHsOjj PO

I I I I

I I

I I 0 3.0 4.0 5.0

_1 1 I , I I I 20 30 40 50 60

Figure 23. Estimated tar formation

for treated cotton.

Figure 24. Flammable gas production

from cotton treated with trivalent

phosphorus compounds.

0.5 1.0 2.0 3.0 4.0 5.0 6.0

LOG 7o P

Figure 26. Flammable gas production

from cotton treated with aliphatic

phosphonates

.

0.5 1.0 2.0 3.0 4.0 5.0 iD

LOG % P

'igure 25. Flammable gas production

from cotton treated with pentavalent

compounds

.

1.0 2.0 3.0 4.0 5.0

LOG % P 48
The reasons for these unusual structural effects are not obvious from the

calorimetric data alone; but these results have been interpreted in terms of

an interaction between the phosphorus and nitrogen-containing groups within the same molecule. This happens prior to interaction with the cellulose so that

the species which reacts with the cellulose is most probably a phosphoramide

rather than a phosphonate.

4. CONCLUSIONS

It has been shown that considerable insight into the mechanism of flame

retardant action on textiles can be obtained by a combination of oxygen index

testing using two or more oxidants, thermal analysis, and static oxygen bomb

calorimetry. The first two methods, when used together, allow a determination

of the site of activity of the flame retardants. The calorimetry gives a more detailed picture of the type of interaction involved and allows, in many cases,

a quantitative estimation of the efficiency of this interaction.

5. REFERENCES

[1] Hendrix, J. E., Bostic, J. E., Jr., Olson, E. S. and Barker, R. H.,

J. Appl. Poly. Sci., Vol. 14, 1701 (1970).

[2] Fenimore , C. P. and Martin, F. J., Proceedings of the 4th Materials

Research Symposium, National Bureau of Standards, 1970.

[3] Wu, H. S., M.S. Thesis, Clemson University, 1970.

[4] Archie, W. A., Gill, J. T. and Barker, R. H., Abstracts of Papers

Presented, 163rd National Am. Chem. Soc . Meeting, Boston, Mass.,

April, 1972, CARB-22.

[5] Bostic, J. E. , Jr., Ph.D. Dissertation, Clemson University, 1972.

[6] Barker, R. H. , Bostic, J. E. , Jr., Reardon, T. J. and Strong, R. A.,

Abstracts of Papers Presented, 16 4th National Am. Chem. Soc. Meeting,

New York, N.Y. , August, 1972, CELL-67.

[7] Reardon, T. J., M.S. Thesis, Clemson University, 1972.

[8] Yeh, K. and Barker, R. H. , Text. Res. J., Vol. 41, 932 (1971).

[9] Birky, M. and Yeh, K. , J, Appl. Poly. Sci., Vol. 17, 239 (1973).

[10] Batavia, B. A. and Barker, R. H., Abstracts of Papers Presented, 162nd

National Am. Chem, Soc. Meeting, Washington, D.C., Sept., 1971, CELL-47.

[11] Drews, M. J., Yeh, K. and Barker, R. H., Textilveredlung , Vol. 8, 180

(1973) .

[12] Hendrix, J. E. , Drake, G. , Jr. and Barker, R. H. , J. Appl. Poly. Sci.,

Vol. 16 , 41 (1972) .

[13] Hendrix, J. E., Drake, G. L. , Jr. and Barker, R. H. , J. Appl. Poly. Sci.,

Vol. 16, 257 (1972)

49
NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 411, Fire Safety Research,

Proceedings of a Symposium Held at NBS , Gai thersburg , Md . , August 22, 197 3,

(Issued November 1974)

ADDITIONAL STUDIES OF THE TRANSFER OF FLAME

RETARDANT EFFECTS WITH CELLULOSIC FABRICS

Bernard Miller

Textile Research Institute, Princeton, New Jersey

Burning rate measurements on double layers of the same fabric

when one layer has been treated with a flame retardant have indicated that certain effects of the retardant can be transferred to

the untreated layer. To learn more about the mode and chemistry

of this phenomenon, a study of non-flaming combustion of cellulosics

has been carried out on mixed systems using thermogravimetric analysis. By arranging to have untreated cotton physically separated

from the flame retardant material during heating it was possible

to determine that the transfer depends on a chemical process and is

most likely the effect of a volatile product generated during

heating. Data are presented also showing that rayon containing an alkoxy-phosphazene flame retardant does not transfer its flammability properties to untreated rayon.

Key words: Cellulosics; cotton; DAP; fabric f lammability ; flame

retardants; f lammability ; rayon; thermogravimetric analysis.

1. INTRODUCTION AND BACKGROUND

The customs of usage of textile materials make it highly probable that

many fabrics will be used, either deliberately or inadvertently, as components

of multilayer assemblies. When such structures have layers made up of different materials, it is necessary for us to know whether or not the flammability

behavior of the combinations would be predictable from knowledge of the behavior

of the individual fabrics involved. A large amount of experimental data is

needed to answer this question; much of it is still to be obtained. We have

been studying one aspect of the problem: the behavior of double layers of a single material when one of the layers has been treated with a flame retardant.

In a previous publication [1] it was shown that the effect of a flame retardant,

in terms of altering the burning rate, could be transferred to an adjacent

untreated fabric. This was found to be the case for cotton treated with diammonium phosphate (DAP), for nylon treated with thiourea, and for polyester

treated with tris (2 ,3-dibromopropyl) phosphate (T23P) . With cotton plus DAP,

transfer was most evident when the treated layer was placed underneath the

untreated cotton (during horizontal burning) . This has led to the conjecture

that the transfer effect is the result of the crossover of a volatile product

formed during the heating of the treated fabric (that is, physical contact

between the layers may not be a necessary condition for this phenomenon)

.

It was thought that useful information relevant to this and other points

might be obtained if potential transfer situations could be studied without

the occurrence of flaming combustion. Consequently, an experimental program

was devised to study the pyrolysis behavior of such systems with controlled

degrees of contact between components.

2. PYROLYSIS WEIGHT LOSS STUDIES

Weight loss studies on heating in air were carried out with the aid of a thermogravimetric analyzer (TGA) which used a platinum cup as a macro sample

holder (fig. 1) . This holder, considerably larger and deeper than the sample

holders of most commercial TGA units, allowed the stacking of materials one above the other. One material could be placed in the bottom of the cup below

a removable metal mesh screen which served to support a piece of fabric as the

upper component. It was thus possible to obtain weight loss data under programmed heating for a variety of stacked combinations.

50
Programmed

temperature

furnace

Platinum

crucible

To

recording

balance

Thermocouple

Metal

screen

Figure 1. TGA assembly for stacked sample systems,

51
2.1. TGA of Cotton and DAP-Cotton Fabric Systems

Figure 2 compares TGA thermograms for an untreated cotton fabric and the j same fabric treated with flame retardant. A considerable change in the pattern

of weight loss with increasing temperature is introduced by the addition of i 7.8% DAP; both the temperature at which the maximum rate of weight loss occurs

and the amount of weight loss are reduced. Figure 3 shows thermograms for two

systems containing equal weights of the untreated and the treated cotton, in ' one case intimately mixed, and in the other separated, with the treated fabric

underneath. Two weight loss peaks occur close together in the case of the inti- i mate mixture, the first one at a temperature slightly higher than the maximum ! rate of loss temperature for the treated fabric. For the separated system, the j

two peaks are discrete. In both instances, the second drop in weight occurs at I

a temperature lower than the peak rate of loss temperature for plain cotton. ^ This is an indication that the effect of DAP on the peak rate of loss temperature!

of cotton is in some measure transferred from treated to untreated layer even when the two are not in contact.

In table 1 are listed the amounts of residual char at 500 °C (taken from the

thermograms) for the four systems studied, and the directly measured final

weights of residue in the two-layer experiment after heating to 560 °C. It is seen that DAP, like most flame retardants for cellulose, increases char production. The results for the mixed systems substantiate that cotton is modified in

the presence of DAP-treated fabric even without contact. If there were no interaction, the total char weight at SOO^C for each of the mixed systems should be no more than (17.5 + l)/2 = 9.3%, whereas the percentages are 13.8% and 17.2%.

Further, since plain cotton leaves virtually no char after heating to 560 °C,

the weight of residue in the cotton layer after the two-layer experiment, if

there were no transfer, should be insignificant rather than the measured 5.0%.

A control experiment in which two separated layers of untreated cotton were heated produced a 1% residue, with no significant difference between the amounts

of solid remaining in each layer.

Table 1. Residual Char Weights After Heating In Air

System At 500°C After 560°C^

Cotton

7.8% DAP-Cotton

Cotton + 7.8% DAP-Cotton (1/1)

Cotton /T /n X 7.8% DAP-Cotton ^ Layers (1/1)

<1%

17.5%

13.8%

17.2%

Ash

5.0% (of original cotton)

12.6% (of original

treated cotton)

Final weights of each layer after heating to 560°C and cooling to room temperature

.

2.2. TGA of Cotton Fabric Pyrolyzed Over Solid DAP

A series of two-layer TGA experiments were run involving varying proportions of plain cotton fabric and solid DAP, with the latter in the bottom of the

crucible. By itself DAP salt begins to lose weight slowly at 150°C; at 500°C

under these heating conditions it has lost 29% of its original weight, a few

percent more than the theoretical value if the only loss were two molecules of

cimmonia. Allowing for this, the weight of cotton residue can be calculated

from the total weight loss of the system.

52
TSA TNERMOaRAMS

100-r

3M

TEMP. (°C)

Figure 3. Weight losses

on heating in air at

15°/min.: untreated

cotton and cotton

treated with 7.8%

diammonium phosphate,

in one case intimately

mixed and in the other

,

separated, with the

treated fabric underneath.

Figure 2. Weight losses

on heating in air at

15°/min. : untreated

cotton and cotton

treated with 7.8%

diammoni\am phosphate.

T6A THERMOGRAMS

101

80

^ 60"

i

i 40

20+

COTTON

....tvtr.... TREATED COTTON

iio 300 400

TEMP.rO

53
I

I

I

1 The thermograms of figures 4 and 5 and the weights of cotton residue at 1 500 °C listed in table 2 appear to confirm that properties conferred by DAP are I transferred from the solid to the fabric though the two are not in contact. I The peak rate of weight loss for 75 mg of cotton over 25 mg of DAP (fig. 4) \ occurs at a temperature lower than that for cotton alone, and there is more residue (4%) at 500°C than expected if there were no interaction. For 50 mg

each of cotton and DAP in the same arrangement, the peak rate of weight loss occurs at an even lower temperature and again there is appreciable cotton resi-j

due (5%) . Surprisingly, the trend toward lower peak decomposition temperature

is reversed when 25 mg of cotton is pyrolyzed over 75 mg of DAP, the maximum | rate of weight loss coming -at a higher temperature than for plain cotton I (fig. 5). The amount of cotton char is increased to 26%, however, which I presumably indicates a high degree of imposed flame retardancy. This last

effect is essentially duplicated when the same proportions of cotton and DAP I are intimately mixed and pyrolyzed (fig. 5) : the weight loss curve falls more i gradually than for the separated components, but the greatest loss is still at \ a higher temperature than for cotton; again, the amount of cotton char is I high — 35% of the original sample.

j

i Table 2. Weight Losses of Cotton Heated to 500 °C in Air Over DAP

Cotton Over Total Weight Cotton Weight Cotton

DAP Loss Loss^ Residue

(mg/mg) (mg) (mg) (%)

75/25 79 . 2 72.0 4.0

50/50 62 . 0 47.5 5.0

25/75 40.3 18.5 26.0

25 + 75 (mixed) 38 . 0 16.5 35.0

^Calculated by adjusting for a 29% loss in weight of DAP.

2.3. TGA of Cotton and Pyrovatex-CP -Cotton Fabric Systems

Although DAP is a convenient prototype of a phosphate flame retardant for

cellulose, it is not chemically bound to cotton before heating. It was of

interest to determine if transfer effects occur in a system involving a "permanent" retardant, chemically combined with the cotton. Pyrovatex-CP was con- sidered such a permanent retardant in view of its fastness to washing, and a sample of cotton treated with this phosphorus-containing additive to an unknown

but effective add-on level was run in the TGA apparatus. Its weight loss

behavior, shown in figure 6, is very similar to that of DAP-cotton (fig. 2).

Here the maximum weight loss occurs near 3 00°C and 24.7% of the sample remains

at 500 °C. In a two-layer experiment with 50 mg of cotton fabric above an equal

weight of this treated fabric (fig. 6) , just as in the parallel experiment with

DAP-cotton (fig. 3) , the weight loss peak for the untreated material drops to

a lower temperature than for cotton alone, and there remains an appreciable

cotton char residue at 500°C (8.8%).

2.4. Direct Test For Transfer of Phosphorus

A series of experiments was performed to determine whether phosphorus j could be detected as having transferred to untreated cotton under appropriate J conditions. Cotton sheeting was stretched over the top of a dish (2-1/2" deep) |i containing either DAP or cotton treated with DAP. The dish was placed on a hot

plate and heated for at least one hour at temperatures between 150 - 200°C.

54
T6A THERMOGRAMS

100

80--

? 80 -

3

g 40"

20--

TlMl OAF

....•¥fr.... 2Smc dap

50m| COTTON

....mr.... Semg DAP

Figure 4. Weight losses

on heating in air at

15°/min: Cotton/DAP

two-layer systems.

2^0 300

TEMP. (°C)

400

IOOt

w—i

Figure 5. Weight losses

on heating in air at

15°/min: Cotton/DAP

(1/3) . 21-

llni COTTON

....fvtr.... 79Mg DAP

300

TEMP. rC)

400

55
m THERMOGRAMS

SOiNi COTTON

200 300 411

TEMP. 1*^0

Figure 6. Weight losses on heating in air at

15°/min: Pyrovatex-CP treated cotton and

untreated cotton.

Part of the cotton sheeting was masked from below with aluminum foil and asbestos to supply a control for each transfer experiment. After heating, a qualitative test for phosphate was performed by digesting the fabrics with nitric

acid and ammonium molybdate. The formation of a yellow precipitate indicated

the presence of phosphate. [2] In all cases, a significant positive test for

phosphorus transfer was obtained.

3. BURNING RATE STUDIES WITH FLAME RETARDANT RAYON

In extending our studies on flame retardant transfer effects, one system

has been found to be anomalous in that burning rates for mixed double layers

do not reflect the presence of the flame retardant. This occurs with PFR

rayon, a commercial fiber produced by adding an alkoxy-phosphazene to viscose

spinning dope to accomplish the deposition of this additive in the regenerated

rayon filaments. [3] Burning rates for various double layer combinations are shown in table 3. It can be seen that, whereas a double layer of 13% PFR rayon

56
Table 3. Burning Rates For Rayon Double Layers

Propagation Mass Burning

System Top Layer Rate Rate

\^ \J 1 1 J_ ^ Vl \X ±. ^ 1 "Ro'htmTi Ti^^vPT ( in/rnin

)

foz/TTiin — in)

Horizontal

at

Rayon

Rayon

PFR (13%)

PFR (±J-8j

4.15

6.28

0.026

0.034

29.5% 0^ Rayon

Jrr K ^ Z D ^ ^ 4.51 0.026

45° Upward

at

Rayon

Rayon

PFR (13%)

PFR (13%)

13.7

23.3

0. 085

0.126

21.7% 0^ Rayon

PFR (25%)

14.5 0.084

Rayon

PFR (13%)

14.0 0,081

burns faster than a comparable sample of untreated rayon ^, a mixed system of

untreated rayon over 25% PFR rayon has the same burning rate as the untreated

material. Indeed, it seems that the burning rate of each mixed system is determined by the untreated rayon and not influenced by the amount of additive in

the treated layer. This is in sharp contrast to the results found with other

flame retardant cellulose materials. [1]

4. CONCLUSIONS^

The pyrolysis data obtained in this investigation reinforce the earlier

observation that the effect of a flame retardant can be transferred to an adjacent untreated layer of material. Also, it seems possible for this to occur without actual physical contact between the solid phases. Since certain effects

of flame retardants are not desirable (e.g., enhancement of the burning rate

of treated cellulosics) , it is necessary that we increase our knowledge about

how such mixed systems will behave. The absence of any transfer effect with

flame retardant rayon reiterates the oft-repeated warning that no generalization

can be made as yet as to the influence of chemical factors on flammability

behavior

The reader might be surprised to note that flame retardant treated rayon burns

faster than untreated rayon; however, this is not an unexpected result. Every

flame retardant for cellulose tested so far actually increases the flame propagation rate across the material. An example of this is given in the earlier

paper on the transfer effect [1] and a more extensive report on this phenomenon

is being prepared. The reputation of so-called flame retardants for cellulose

is based on their ability to enhance the self -extinguishability of the material,

as determined by char length or oxygen index tests (see table 4)

57
Table 4. Oxygen Index Values

For Rayon Double Layers

Top Layer

Bottom Layer

Oxygen

Index

Rayon

Rayon

0.189

Rayon

PFR (13%)

0.223

- Rayon

PFR (25%)

0.226

PFR (13%)

PFR (13%)

0.259

PFR (25%)

PFR (25%)

0.263

5 . REFERENCES

[1] Miller, B. and Turner, R, , Textile Res. J., Vol. 42 , 629 (1972).

[2] Feigl, F., Laboratory Manual of Spot Tests, 176-177, Academic Press

(1943) .

[3] Godfrey, L. E. A. and Schappel , J. W. , Ind, & Eng. Chem. , Products

Research and Development, Vol. 9, 426 (1970).

58
NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 411, Fire Safety Research,

Proceedings of a Symposium Held at NBS , Gaithersburg , Md., August 22, 1973,

(Issued November 1974)

AN EVALUATION OF FLAME SPREAD TEST METHODS FOR

FLOOR COVERING MATERIALS

James Quintiere and Clayton Huggett

National Bureau of Standards, Washington, D.C.

Flanimability properties of materials have traditionally

been measured by small scale laboratory tests. The relationships

between test results and performance in real fires have been

largely inferred by intuition or subjective judgement. Flame

spread test methods for floor covering materials are examined.

Through full-scale fire experiments and laboratory studies the

nature of the potential flame spread hazard of flooring materials

is presented. The factors promoting flame spread in each test

method are identified. Test method results are compared with

relevant full-scale fire experiments involving floor covering

materials in a corridor. An effort is made to relate test results,

where possible, to the potential flame spread hazard of floor

covering materials in building corridors and exitways.

Key words: Corridor fires; fire test methods; flame spread;

flaramability tests; floor covering f lammability ; floor coverings.

1. FIRE SPREAD OVER FLOOR COVERINGS IN BUILDINGS

In the last decade, concern has been expressed about the flammability

hazard of floor covering materials. This concern has probably been induced by

the widespread use of carpeting and by several fire incidents which have suggested that the floor covering was a significant factor in fire spread. Yuill

[1] described the state of this issue in 1970. Previous to this, except for

fire safety regulations for hospitals financed under the Hill-Burton Act (1965)

fire officials had not considered floor coverings to be a significant fire

hazard, although, several fires had indicated that carpeting could be significant in the early spread of a fire. Using a 5 lb wood crib as an ignition

source, Yuill demonstrated that two high-cut pile (shag) carpets would propagate a flame over a 5 ft wide x 15 ft long corridor. (One carpet had a flame

spread rating of 55 by ASTM E-84 [14], the other had a rating of 11001) With

the introduction of DOC FF-1-70 [2] , a mandatory nationwide flammability

standard for carpets incorporating the "Pill Test" , one may assume that no carpets easily ignited by "small" ignition sources entered commerce after April 15

1971. However, the flammability hazard associated with carpets which pass the

Pill Test and with other floor covering materials not subject to regulation

remains to be defined and dealt with.

1.1. Fire Incidents

In recent years several fires in nursing or retirement homes and hotels,

apparently aggravated by floor covering flame spread, have resulted in deaths

and extensive loss in property. Thus, one of the objectives of the evaluation

reported here has been an analysis of the reports of these and other fires

with the purpose of gaining some appreciation of the role played by the floor

covering material in the spread of fire.

Robertson [3] has reviewed the available statistics. The following is

taken from this report, where tables 1 and 2 of this paper are condensed

versions of tables developed by Robertson. He states

"...the data available are not voluminous. They comprise reports published in the NFPA Fire Journal and fire injury reports in the NBS

59
FFACTS^ file which specifically mention floor covering materials as influencing fire spread. A total of seven Fire Journal reports were studied while the 135 reports of carpet related fire accidents in the

NBS records were carefully reviewed. In most of the latter reports

it became clear that either the carpeting involved was excessively

flammable on the basis of DOC FF-1-70 (the Pill Test) or data were, lacking to clearly identify the carpeting as a significant contributor

to the fire. From study of these reports only seven cases have been

identified in which the floor covering material appears to have

actively participated in spread of the fire. These are summarized

in table 1. Table 2 summarizes information on some of the fires in

which fire spread was attributed to the influence of the floor

covering. It seems likely though that in most of these instances

the floor covering involved would have failed the ignition and

spread test currently applicable to carpeting under DOC FF-1-70. In

both tables the order of listing is in apparent decreasing relevance

to the problem in question."

Hence, only seven fire incidents, which indicate a major contribution to

fire spread by carpets that pass the Pill Test, have been identified from a data base of fabrics fires. In all cases a large ignition source was necessary

before the carpeting apparently became involved in fire spread. The first two

fire incidents in table 1 clearly illustrate the potential hazards of floor

covering fires in corridors. This type of fire blocks paths of escape, can

increase the spread of fire and smoke to adjoining compartments, and make

suppression and rescue operations difficult. Other incidents listed in table

1 demonstrate other factors relevant to the potential hazard of flooring fires.

The Palm Beach case clearly shows that the relative hazard of combustible wall

lining is far greater than that associated with combustible flooring. Indeed,

in this case, given an ignition exposure of a room fire, the fire chose to

spread along the upper wall carpeting, and no significant spread developed on

the floor carpeting. Also, draft conditions determined by wind and building

stack effects direct the flow of fire products within the building and thus

affect the spread of fire on combustible flooring. From case 3269 (table 1)

,

it is reasoned that the fire did not spread along the flooring into the north

corridor because the products of combustion were channeled into the elevator

shafts and the east corridor first. With insufficient heating of the north

corridor, the fire did not continue to propagate on the floor.

In addition to these cases, the data bank on fire incidents in the

United Kingdom provides a source of information on flooring fires. A study

of building fires by Chandler [4] in which the floor covering material was

first ignited yields table 3. Also, these data reveal that in 1962, 75 percent

of floor covering fires were due to space heaters, 86 percent did not spread

beyond the room of origin and that an increase in the number of non-wool carpets

resulted in an increase in the number of carpet fires.

More recent data from the United Kingdom by Fry [5] are displayed in

table 4. It is significant here that floors, stairs, and skirting board fires

are listed in addition to floor covering fires. Fry reports that although

building fires have increased in frequency since 1962, there has been a decrease

in fires started by open fires. It is apparent that floors and stairs, presiamably of wood construction, are involved in the initial spread of fires as frequently as floor coverings, such as carpets and tile.

This acronym, FFACTS, stands for "Flammable Fabrics Accident Case and

Testing System." The case numbers in this system involve uniform five

digit numbers. The zero prefix digits have not been included in this report.

60
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62
Table 3. Fires in Buildings in Which Carpets and Floor

Coverings Were Ignited, 1955-62, United Kingdom [4]

Percentage of

Year

Fire in Which

Were Ignited

Fires in Which

Were Ignited

Floor Covering

Incidents

Involving Carpets

Total Fires

in Buildings

1955 692 904 76.5 50,492

1956 624 844 73.9 51,464

1957 603 816 73.9 50,694

1958 648 860 75. 3 51,992

1959 708 908 78.0 61,328

1960 800 1,228 65.

62,460

1961 950 1, 344 70.7 69,588

1962 1,046 1,452 72.0 73,406

Table 4. Fires Involving Floors and Floor

Coverings From the United Kingdom [5]

Year Floor Coverings

Floors,

Skirting-Boards

Stairs

1961 1,344 1,828

1962^ 1,452 1,880

1963^ 1,454 1,878

1964 1,216 1,428

1965 1,225 1,621

1966 1,049 1,171

1967 1,034 1,141

1968 1,160 1,176

1969 1,282 1,172

1970 1,181 1,174

The years 1962 and 1963 had severe winters with an unusually high frequency of fires associated with

the use of heating equipment.

63
1.2, Full-Scale Fire Experiments m

To identify more precisely the hazard of floor covering materials, attenI

tion has been focused on full-scale fire experiments in which floor covering I materials (i.e., an assembly placed over a subfloor) have been examined in a { room — corridor environment. In particular, these experiments involve a largea

fire in a room connected to the corridor by an open doorway. The corridor is

lined with negligibly combustible materials along the walls and ceiling but

with a combustible flooring assembly. This simulates the least combustible

class of assemblies in which corridor fire spreads. Corridors lined with com- bustible wall and ceiling materials as well as floor covering represent a more

severe fire hazard. Several organizations have conducted room/corridor fire

experiments to investigate the hazard of combustible lining material in corridors. They include the National Research Council of Canada (NRC) , Illinois

Institute of Technology Research Institute (IITRI) , and the National Bureau

of Standards (NBS) . Although the room/corridor arrangement has been similar

in these experiments, a variety of ignition sources have been used, ventilation

conditions have varied, and overall construction materials have been different.

Moreover, recorded measurements have ranged from visual observations to extensive data from automatic record instrumentation. At a minimum, these experimental results serve to establish a spectrum of corridor building fires and serve to provide a definition of the hazards.

1.2.1. NBS Corridor Fires

The NBS corridor system is depicted in figure 1. A total of 18 experiments involving floor covering materials have been made. In 14 experiments the

principal corridor combustible lining has been the flooring assembly, of which,

11 involved sustained rapid flame propagation to the exhaust window ("flameover") ; and the remaining 3 experiments resulted in partial or no sustained

flame spread. A summary of results from these experiments is shown in table 5. Recent publications have described this program [6,7,8].

BURN ROOM

30 ft.

NBS CORRIDOR FACILITY

Figure 1. NBS corridor facility.

64
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66
Table 5B. Material Identification Code

Code Material

A-1 Acrylic carpet, woven level loop, 55 oz/yd^

A-2 Acrylic carpet, random shear, 69 oz/yd^

N-l/F Nylon carpet with integral foam back, 89 oz/yd^

N-3 Nylon carpet, level loop, 69 oz/yd^

NO Aromatic polyamide carpet

0-1-g Olefin carpet, level loop, bonded, 55 oz/yd^

R-4g Vinyl sheet, bonded, inorganic backing

RO Red oak flooring

RO-v Red oak flooring with spar varnish

U-1 Rubberized hair-jute underlayment

VT-g Vinyl asbestos tile, bonded

W-1 Wool carpet, woven level loop, 76 oz/yd^

A typical corridor fire test resulting in flameover is composed of 7 distinct stages of fire development. (1) The test commences with the ignition

of four 40 pound wood cribs in the burn room. In several minutes the crib fire

reaches a state of fairly steady burning. It appears that approximately half

of the air required to support crib combustion flows into the burn room through

the two floor level vents, while the remaining air supply enters from the

corridor. (2) Products of combustion flow from the room along the corridor

heating its walls and ceiling. Inlet air flows over the corridor floor which

is heated by radiative transfer from upper hot walls and ceiling and by hot

smoke products. (3) Once the crib fire builds-up, ignition occurs on a 2 1/2 ft

wide floor covering runner which extends from the corridor into the burn room. This ignition results from a high radiant heating exposure over this runner and

from flaming crib embers falling to the floor. Once ignition occurs at a location on the runner rapid flame spread follows over the entire runner in the burn

room. (4) This flooring fire then begins to emerge and spreads slowly into the

corridor. The flame fans out from the doorway advancing upwind against the

incoming air flow and is driven by radiant heating of the floor. (5) As this

fire advances it depletes the oxygen of the incoming air and preheats this air.

This results in a buoyant force which diverts some air flow from entering the

burn room. (6) It appears that the occurrence of flameover is preceded by a reduction in air supply from the corridor to the burn room such that the crib

fire becomes fuel rich. The crib fires continue to produce pyrolysis products

at the same rate but complete combustion is not possible within the burn room. Thus, a cloud of combustion products, probably including aerosols and soot, enter

the corridor flowing out over the floor fire which extends not more than about

5 ft down the corridor. This is followed by the onset of flameover or rapid

flame spread within the corridor. (7) Flameover occurs as. a wave of flames

and hot combustion products advance down the corridor producing a large increase

in corridor temperatures and heat flux. In the order of 1 minute the flames

emerge from the window completing the flameover process. More detailed data

will be presented to further illustrate these processes.

During steady burning rate of the wood cribs a maximum energy- release

rate of 8 0,000 Btu/min occurs. Some of this energy is lost to the burn room

and the rest enters the corridor. The convective energy flow values were calculated by Fung, et al [8] , based on two to three velocity and temperature

67
measurements in the doorway. These are plotted against the initiation time of

flameover, tp^, shown as open symbols in figure 2. (These flameover times do

not agree with values given by Fung, et al [8] since they termed flameover

the first indication of observed flooring fire in the corridor.) A straight i line drawn through these points indicates a nominal convective energy flow rate j to the corridor of 60,000 Btu/min and an average induction time of 220 .seconds ' before this rate of energy was released. The time preceding steady crib burning

generally occurs after 5% weight loss results (t^^) . If the flameover time

is adjusted for each test by subtracting t^^ from tp^, then the solid symbols

in figure 2 yield the same burning rate with the intercept through zero. These

results indicate the degree of reproducibility for the crib fire source, and

the extent to which energy input rate may be regarded as a step function of

time

.

When the floor covering runner ignites in the burn room it releases an amount of energy which can become significant with respect to the crib fire.

This sudden release of energy is indicated by an increase in the gas temperature near the corridor ceiling. Figure 3 shows this effect for a nylon carpet

(N-3/U) which had a large energy release rate as compared to a vinyl sheet

flooring (R-4) in which there was negligible energy release rate. This pair

of tests (348 and 346) tends to bracket the range of conditions which result

from exposure to the crib fire source in the burn room. They will be used to

illustrate other phenomena which result during the fire development in order

to contrast the range of resulting conditions.

During the relatively slow advancement of flooring flame along the corridor, radiant heat transfer to the floor tends . to promote continued flame spread

The radiation levels developed depend strongly on the primary crib fire source but are also influenced by the rate of energy release of the flooring material.

The exiting hot gases and ceiling temperatures along the corridor determine the

extent of radiant heat transfer. Figures 4 and 5 illustrate typical radiation

flux distributions along the corridor floor before flameover is initiated. In

test 34 6 the flux was essentially due to the crib energy release; while, in

test 348 the radiant flux (at 300 sec) includes the effect of energy release

(and most likely smoke) from the sudden ignition of the nylon runner in the

burn room. Before flameover the corridor temperature distribution between the floor

and ceiling was greatly stratified with hot products of combustion at the top

and cool air flow at the bottom. At the inception of flameover, temperatures

at all heights increased rapidly and significantly throughout the corridor

space. This is illustrated in figure 6. As pointed out earlier, air flow between the corridor and burn room appeared to become affected by the advancing floor fire. Eventually, this

reduction of air supply to the burn room affected the crib burning rate. In

fact, after flameover the crib burning rate always dropped. However, before

flameover significant changes occurred in air supply to affect the nature of

combustion in the burn room. Figure 7 illustrates this phenomenon by examining

the measured crib weight loss rate and the maximum (estimated) burning rate

which could occur within the burn room. This potential maximum rate was estimated from velocity and temperature measurements of the exhaust products at the

burn room doorway (an assumed air to fuel ratio of 4 was used) . No flameover

occurred in test 346 and no drop in air supply is seen in figure 7. In test

348 the flooring fire had spread into the corridor by 320 seconds, and near 440

seconds (the onset of flameover) , the figure suggests that most of the fuel

generated in the burn room probably burned within the corridor space. Thus,

the release of fuel-rich combustion products from the burn room to the corridor

can be a contributing factor in causing flameover in addition to radiant heating

of the floor covering.

68
Figure 2. NBS corridor flameover

time compared to total energy

input.

mo

a

sr. q:o

oa

a.

Z3V)>

o

IT

UJ

ENSEMBLE OF ENERGY SUPPLY TO CORRIDOR AT FLAMEOVER

Note: Energy only includes convective flow, radiotive Input is approximately 10% of convective component, and energy supply due to combustion within corridor is not included.

SLOPE~60,000

4 -

3 -

1"

SLOPE ~ 60,000 BTU

TEST

No. 'fo fo333 A A

335 V

340 0

341 <1 '4 342 o • 343 344 0 345 <> 348 -o- •- 349 A

200 400 600

TIME (SEC) 800 1000 1200

800 -

700-

600

500

400-

300

200-

Figure 3. Comparison of corridor

temperatures developed by two

floor-coverings in the NBS

experiments

200 400 600 800 1000 1200 TIME, sec.

69
NBS CORRIDOR TEST 346

INCIDENT RADIATION TO FLOOR

-0 Radiometer readings corrected for sapphire window (q) 420 sec. -- Radiometer readings corrected for sapphire window (cD 900 sec. Calculated values based on upper walls and ceiling temperatui'es.

12 16 20 28 30

DISTANCE, Y (ft) Figure 4. Incident radiant flux to floor in NBS Corridor Test 346

2.6 r

Q. Measured (uncorrected for sapphire window)

-Calculated based on temperature of upper walls and ceiling.

8 12 16 20 28 30

DISTANCE, Y (FT)

Figure 5. Incident radiant flux to floor in NBS Corridor Test 348

70
TEMPERATURE, "C Figure 6. Corridor temperature distributions in NBS Corridor Test 348.

•i 50

05m

cco

U-o

UJI—

<t

IX.

S 20

CO

CO 10

No.348, FLAMEOVER BEGAN AT 440 sec.

N«.346, NO FLAMEOVER

Max. Est.

Measured

200 400 600 800 1000 1200 TIME, sec.

Figure 7, A comparison of fuel burning rate with available burning rate

based on air flow.

71
In summary, flame spread in these experiments, and in similar systems,

depends on radiant heat transfer and the gas flow patterns as well as on the

flooring material properties. These factors can be related to independent

initial parameters of the system. Thus, flameover is a function of:

1. energy release rate of the ignition fire , (i.e., room occupancy type)

;

2. corridor geometry , principally height and width;

3. ventilation openings between compartments;

4. flooring flame spread response under external radiation ; and

5. material thermal properties in general.

1.2.2. IITRI Corridor Fires

The IITRI room/corridor experimental fire facility has been described

by Christian and Waterman [9] , Information regarding the use of this facility

to examine the flammability hazard of carpets in corridors has been furnished

by T. E. Waterman [10] and by W. M. Segall [11]. A new interpretation of their

results has been made from the available information. An overall comparison

between the IITRI corridor system and the NBS corridor system is shown in figure

8. The values listed on the figure are based on the effects of the ignition

fire only and do not include the effect on the flooring fire. It appears that

radiant heating near the doorway was greater in the IITRI corridor than the

NBS corridor. Also the air supply to the IITRI corridor system was greater

than that in the NBS system, and the higher oxygen concentration in the IITRI

exhaust flow implies more excess air than in the NBS system. The doorway and

window openings in the IITRI system are larger than the NBS system. Thus, it

appears that the heating conditions were greater in the IITRI corridor, and

ventilation effects — more availability of air flow — were greater in the

IITRI corridor than NBS. The differences in ventilation factors may be the reason for the differences in fire spread behavior of carpets between the IITRI

and NBS systems. In only one experiment did IITRI observe a flameover behavior

(for a carpet which had failed the Pill Test) . It is believed that these differences are due to overall dynamics of the room/corridor systems and not due

to the nature of the flooring material tested. The questions raised by these

results reflect the range of real-life building fire conditions and represent

our ignorance in understanding in a quantitative way all of the factors promoting flameover.

1.2.3. NRC Corridor Fires

J. H. McGuire [12] has described the NRC corridor fire experiments which

included some work with floor lining materials. This system had a corridor

63 ft long, 8 ft high and 6 ft wide with an adjoining burn room and with a variety of small and large inlet and exhaust vents. In one experiment a large room fire sustained flame spread over a cellulose triacetate carpet to a distance of 4 0 ft from the burn room. The other corridor lining materials were noncombustible and the carpet had a rating (Ig) of 435 by ASTM E-162 [16]

.

McGuire reached the conclusion from this study that flooring with an ASTM E-162

index of 220 and less made little contribution to the propagation of fire along

the large scale NRC corridor (compared with a rating of 130 or less for ceiling

linings, and 35 or less for wall linings).

72
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73
1.3. Summary of Statistics and Experiments

In reviewing the statistics and experiments, several factors emerge.

First, floor covering materials are potentially less hazardous than comparable

wall or ceiling materials with regard to fire spread. Second, based on the U.K.

data, carpets in general do not appear to be more hazardous than other flooring

materials. Third, extensive and possibly rapid flame spread over flooring

materials in corridors and exitways where little additional combustibles are present is the primary potential hazard to be dealt with. Fourth, most floor

covering materials require radiant heating from a large ignition source before

flame spread can develop. Fifth, the dynamics of radiative heating and fire

development depend on the nature of the building's interior design.

Given these factors, the question of a relevant test method for flooring

and its application to the establishment of standards can be addressed.

2. EVALUATION OF TEST METHODS

A variety of methods and varying performance criteria have been used by

many regulative agencies to regulate the potential fire hazard properties of

floor covering materials. Such non-uniformity of regulation of flooring

materials produces confusion and hampers industrial development to meet acceptable performance criteria. For this reason an investigation has been made of

the performance, characteristics, and applicability of test methods as they

relate to the flame spread hazard of flooring materials under conditions which

simulate real fires from a relatively large ignition source. The methods discussed in this study are ASTM E-84 , ASTM E-162 , UL-992 Chamber, "Model Corridor"

and the Flooring Radiant Panel. Although this is not a thorough study, some

of the more significant factors and indications can be reported.

Up to now most test methods have been used to determine the comparative

flammability of materials by an empirical scale of measure. If fire safety

is to become a science the factors determining potential fire hazard must be

known, as well as the necessary parameters to be measured by flammability

tests. Only then can the test results be related to the potential hazard in

a meaningful manner. Ultimately, several flammability properties for a material

would have to be combined with design parameters of the building in a relationship to express potential fire hazard.

The previous discussion given for flooring fires in buildings serves to

present a definition of the potential hazard of flooring fires and the factors

promoting such fires. If flameover is accepted as the hazard, then two mechanisms are apparent for its cause: gas-phase dynamics and radiant heating of

the flooring appear to be the cause of rapid flame spread. The gas-phase mechanism depends on the aero-dynamics of the fuel produced from the developing

fire and the available combustion air. This mechanism clearly depends on the

size of the ignition fire and the building interior design. In extreme instances flame propagation in corridors may depend only weakly on the flooring

material. On the other hand, burning of the flooring material does seem important to flameover stimulated by radiant heating which depends on the size of the

ignition fire and geometry of the building. Thus, it should be within the

scope of a test method to measure the flame spread behavior of a material under

radiant heating. Other factors would have to be assessed by an analysis of the

building geometry and potential fire load.

74
2.1. Description of Test Methods

2.1.1. ASTM E-84 Tunnel Test

The ASTM E-84 Tunnel Test was first described by Steiner [13] , and is

currently described in ASTM E-84-70 [14] . Basically the apparatus consists of

a horizontal duct (12 in high by 17 in wide) 25 feet long with a test specimen

mounted on the ceiling of the duct. Initially air is forced into the duct at

240 ft/min and an ignition fire of 5,000 Btu/min with about a 5 ft flame impingment is released. Upon ignition of the specimen the flame propagates downwind under the influence of forced convection. An observer records the flame

tip position advancing over the specimen. A more recent study on the reproducibility and repeatibility of this method as applied to floor coverings has

been published by Lee and Huggett [15] . Although this method also measures

smoke production and energy release, only the flame spread performance measure

will be considered here. The flame spread factor (FSC) is an empirical parameter which gives a relative measure of distance burned or average flame spread

velocity compared to the burning of red oak. In this test, carpet specimens

are bonded to asbestos board (or held in place with a wire screen if an underlayment is used)

2.1.2. ASTM E-162 Radiant Panel

The ASTM E-162 Radiant Panel test method [16] has been discussed elsewhere by Robertson, Gross, and Loftus [17], Gross and Loftus [18], and Lee,

Loftus and Gross [19] . It measures downward flame spread travel and energy

release rate under a varying radiant flux distribution of about 4 to 0.3 W/cm^

Flame spread is against the induced air flow generated by buoyancy and the

exhaust hood over the specimen. Its flammability index Ig combines a flame

spread rate factor Fg and maximum energy release rate Q as

Ig = Fg. Q (1)

The index Ig tends to correlate with the FSC of the E-84 tunnel.

2.1.3. UL 992 Chamber Test

The development of the Underwriters Laboratory Chamber Test emerged from

a growing concern over the flammability of carpets. It sought to determine a flooring flame spread behavior when tested in its normally installed orientation

(in contrast with the inverted position of the E-84 tunnel) . The test and some results have been described by Engermann [20] . An ignition burner flame (500

Btu/min) is applied to a sample mounted on the floor of a duct 8 ft long, 10 in

high and 22 in wide. Air is drawn through the system at an initial inlet velocity of 100 ft/min. A flame spread index is determined by a formula which uses

the distance burned or the time to burn the full length of the duct (8 ft)

Flame propagation is downwind directed by forced convection.

2.1.4. Model Corridor Test Method

This method is based on the physical system of the UL chamber test but

has used asbestos board for its construction rather than fire brick and forces

cool air into the test section as opposed to exhausting hot products by a fan

as in UL 992. Its design and operation has been described by W. Denyes and J. Raines [21] . Its characteristics and mode of performance measure has been discussed by W. Denyes and J. Quintiere [22] . The bimodal flame propagation displayed by UL 992 has been used to relate the measured test results to the

flameover hazard of building corridor fires. The Model Corridor gives this measure of performance by determining, by trial and error, the maximum gas

75
!

!

I

I burner energy flow rate to a specimen such that flameover does not occur in the

Model Corridor. Thus, critical energy rate is its performance measure. I

I

; t 2.1.5. Flooring Radiant Panel j i

The system is similar in concept to E-162 except that the sample under '

i test is horizontally "floor" mounted, and the radiant panel and specimen are enclosed in a vented chamber. A recent report by G. Hartzel [23] (continuing

the development of this concept as a NBS Research Associate from Armstrong Cork

i

Company) describes this system's performance and characteristics. The radiant I flux prescribed varies from about 1 to 0.1 W/cm^ over the sample length. Air | flow is induced into the chamber by the hot radiant panel and flame spread is

generally against the wind. The performance measure is expressed as the total

length of flame spread over the sample. This distance can be related to radiant

flux from the panel at the point of extinguishment.

i An alternative mode of operation for this apparatus has used a different | radiant flux distribution which ranged from 2.7 to 0.3 W/cm^ over the specimen.

At these conditions, distance burned or time to burn the sample length relative

to the burning of red oak is used to express a relative flame spread index. i

2.2. Comparison of Results with NBS Corridor '

No discussion of test method results would be complete without some com- parison to full-scale fire experiments. Since most of the flooring materials

examined in the NBS corridor experiments have been evaluated by the above test

methods a direct comparison can be made. The measure of performance in the I NBS corridor chosen for comparison is the time at the onset of flameover, tp^. i This time will be used, although its interpretation could be refined by con- \ sidering the nature of the flame spread results (fig. 9) and the nature of the !

ol I I I I 1 I 0 200 400 600 800 1000 1200 TIME (sec) Figure 9. Flame spread results in the NBS corridor experiments.

76
corridor energy input rate. For example, an adjusted time could be used as a performance criterion. This could be defined as tpQ minus the crib build-up

time, t5| (table 3). If crib fire development and flooring ignition were similar for each experiment, the reciprocal of flameover time would represent

an "average" flame spread rate during radiant heating of the floor. Hence, tp^

may tend to correlate with flame spread tests which measure flame spread velocity as the index of performance.

A comparison of test method results with flameover time is shown in table

6. The range of E-84 FSC values given for some materials represents variation

between different laboratories [15] . The FSC index has the significance of

flame spread velocity for values above 78. Correlation may be judged as fair

for E-84. The Ig index for E-162 yields a similarly fair correlation, yet the

flame spread factor Fg does not demonstrate any significant trend. The UL I factor yields poor results but it should be realized that these low numbers for

I only represent a distance burned in the test method. Hence, they would not

likely agree with tpQ. Moreover, the Model Corridor critical energy and Flooring

Panel distance burned would not necessarily yield any agreement with tp^. However, attempts at interpreting these two test methods in a manner more consistent

with flameover time has been done. A weighted flameover time in the Model Corridor based on the product of gas burner energy supply rate and time was compared

and yields a fair correlation. Also, an average velocity measured in the Flooring

Radiant Panel was compared with tp^ and yields fair results. Since the driving

forces and measure of performance generally differ between test method and fullscale corridor fires, successful correlation between the two need not be ex- pected. However, the relevance of each test can be judged on its phenomenological similarity with full-scale fires.

2.3. Characteristics of Each Test Method

The parameter being measured by a test method must be understood, and its

relationship to the controlling variables of the test must be known. Only then can the applicability and limitation of the test method be addressed.

2.3.1. Characterization of E-84

Recently an E-84 tunnel facility has been instrumented with thermocouples,

pitot tubes, and a heat flux sensor in order to determine a quantitative measure

of its character. Although these results have not been completely analyzed,

some of the findings can be presented. Beyond the burner flame, vertical gas

temperature distributions in the tunnel can vary from 400 to 150 °C with no burning specimen. The energy release rate from the burner should be about

5,000 Btu/min, yet the steady-state enthalpy flow rates, m c (T-T ), (based on

a p 00 a steady mass flow of air, m^ = 25.4 Ib^^/min) at 15 and 24 ft from the burner

are about 3,000 and 2,500 Btu/min respectively. This means that about 40 percent of the burner energy release is lost within the first 15 ft from the

burner. Part of this loss can be radiation from the flame and perhaps incomplete combustion due to quenching of the flame on the ceiling. Thus, a speci- men would receive a severe heating load near the burner in this test. Measurements on air inflow to the tunnel during a test have confirmed initial calculations which suggested the fall off of air flow as the temperature of gases

within the tunnel increases. This is firstly a thermal effect as a result of

maintaining constant pressure drop over the system during a test: and secondly.

77
>i

00 o ro CM 00 in 00 00 00 in Cp-h e • • • • • • • 1 • \ ro o CM CN CM CM CN

i-i 0 E

(U iH

O

a) > dJ c < >

(d ,—, c

rH

a .H

-P

g in o o in a" CM VD

O CO

4J in 1 CM « in S

•H 0 D J

C

—

H00 X

iH

(d

(1) fa a\ o [- o CO 1 00 CO ro in ^ VD o a Si in rH rH rH

•H

-H >1 • o o o O o o o

(fl tnO 3 o o o o o o o 0 P M h 4J 00 1 1 o ID 1 1 CM CN I 0 (D m «. Eh C -P in rH VD in in 00 0

CJ

lO (d >i • c

rH 0 CPO o O o O o o o o o o O o

•H

M Cl, E o o in in in in o in in o in ' in

t) P 0) \ ID r- CM r- ro rsj ro r- CM 0 rH C +> 3 » - a -P rH rH rH rH rH U CQ A| Al Al Al Al

<N

<J\

CTv i-H ID

O 1 rH 1 1 M

|J| 1 1-1 1 1 1 rH CM

O

D

(N

n o r- CM o CM CM rH 00

O

ID 01 1 in iH 1 rH VD VD r- r- 00 00 <y\ 1 rH rH rH Ha

Eh in in ro o H rH CM \o H 00 ID 00 1 o in CM >* r-j "a- < "3" rH rH rH ^a" rH rH

00 rH r- o 1 u a\ O a> r- ro o in CTl t- 00 H W 1 <N r~- in VD 1 ro o >D 1 1 1 in 1 (N rH rH 1 rH ro a oo o <N (N

Eh o o W (N CM

<cU tJ 0 U <D -O 0) C - - •H > o H -a M 0 Id (d U 0) U O (N O o in o o o 4-1 a) 0 e 0) O in ro •a- in u = U (0 10 ro ro CN ^ 3 a iH rH w m

CO ro

ca 0 z z

T3

4J 0) -P ,—.

4->

D x; 0) (U 4J Oi 4-1 in a 4-1 C 0) tt

(D

U 4J a) •rt P IH d)

H 3 U

(!) 4J 0)

n c CU la 0)a c 0) n)

a MH rH (d 0) 3 0 -H M u o< u IH 04 u u (U cn o rH (1) rH 0 M (fl M la Id IH (0 rH ^^ •H s: 01

0)

U o (fl

u > M la o o o o EH

—

w ^

fa > •» 'H

O ^ CJ •rl 0 > a D rH D C D D rH o X - 0) rH rH 0) - rH u fa 0 \ >i srH \ 0 > \ >1 0) tP tt V >1 >1 3

rH

H CM

U

H 0 ro rH 1 TJ rH 0 rH

U - e rH IH rH

MC rH 1 >1 1 U 1 O 1 >i O <D 1 o 1 u o o 1 Id 1 u •H 0< 1 tH 2 2 < < 2 2 « « < < 2 2 o o <: < > ^ « > ae

Id 03

78
it is due to the release of fuel gases from the specimen. It can be shown that

the average inlet air velocity at the tunnel slit orifice follows the relationship.

2AP/p^

Vawe = 1/ K +

(2)

where pj^ is the inlet air density,

Ap is the pressure drop between tunnel inlet and the manometer station,

is inlet air temperature,

T is average tunnel gas temperature

,

K is the entrance loss coefficient,

e and is the duct loss coefficient which includes the skin friction effect.

If the internal flow losses dominate the losses in the system then the

velocity at the inlet during a test is related to the initial inlet flow,

V, A , by approximately

a , 1 V

a,i

(3)

Thus, an increase in average gas temperature by a factor of 2, can lead to a

30 percent decrease in inlet air flow to the tunnel. Figure 10 illustrates

this behavior by changes in the mass flow rate of air at the tunnel inlet

orifice

30

= 20

10

E-84 AIR FLOW CHARACTERISTICS

SPECIMEN: NYLON CARPET WITH A PAD (N-3/U) CALIBRATION SETTING (240 FT/MIN. TEST SECTION)

I 1^

NOTE: AT 15 ft FROM THE BURNER THE AVERAGE

GAS TEMPERATURE IS ABOUT SSO'C AT 250 sec.

50 100 150 200 250 300 350 400

TIME, sec Figure 10. E-84 air flow characteristics,

79
Another aspect of air supply is its effect on the combustion process. Iti

has been estimated that, irrespective of the subsequent drop in air supply ' rates the initial air supply may not be sufficient to completely burn a 24 ft ' length of some materials. Although this estimate has not been substantiated

directly, low oxygen concentrations have been reported for the E-84 tunnel

which would then support this indication of oxygen deficiency. If this is

true then work done on the study of fuel-rich fire spread over the lining

material of ducts [24,25,26] would apply to fully-developed flame spread in

E-84. This question bears further examination.

The processes affecting flame spread in E-84 are complex and no theory

exists to explain flame behavior generally for this system. Some results for

flooring samples are shown in figure 11.

2.3.2. Characterization of E-162

This method can measure flame spread rate and energy release rate under a prescribed radiant flux distribution. Some typical flame spread results are shown in figure 12.

It would be helpful to have a theory which can predict this method's

results for classes of materials. A first attempt at this which was con- sidered by Rockett [27] examines

4qF 6.

TT (KpC)

(4)

where ^ "I K / ^

as an approximate empirical expression for flame spread velocity. The symbols

are defined as

q" is the heat flux from the flame,

q" is the heat flux from the panel

,

^Vap ignition temperature of the material,

T is the initial temperature,

CO h is a convective/radiative loss coefficient,

c is specific heat of the material,

6„ is the flame downstream heat transfer zone length,

r

P is density of the material,

a is the thermal diffusivity of the material,

K is thermal conductivity of the material,

and t is time.

In the least, this equation illustrates the processes affecting flame spread

in E-162.

80
1 1 r

0 4 8 12 16 20 24 28 32

TIME, min.

Figure 12, E-162 flame spread results.

81
2.3.3. Characteristics of the UL Chamber Test

One obvious fact from the results of Engermann [20] is that the system

acts in such a manner that there is either complete flame spread propagation

over the test section length or propagation of 1 to 2 ft beyond the ignition

flame. This characteristic has been observed by others in similar experimental facilities [22,24,25,28]. In addition, Engermann [20] reports that

initial inlet air velocities of less than or greater than 100 ft/min led to

reduced flame spread potential for a given material. Yet, air flow is not

maintained constant during a test, but allowed to vary according to the

burning characteristics developed and the characteristics of the exhaust fan.

2.3.4. Characteristics of the Model Corridor

The driving force for flame spread in the Model Corridor is radiation

heating of the flooring ahead of the flame front. This radiation results from

the energy supply of the burner and the combustion of the flooring material

which heats the ceiling and upper walls of the test section and which in turn

reradiate to the floor. An empirical correlation [22] of a series of experiments for the same materials at various energy levels and ceiling heights

displays clearly the critical propagation condition in dimensionless form in

figure 13. This dimensionless correlation suggests a method of determining

full-scale conditions by scaling the energy release rate of the ignition fire

(Eg) , the height of a corridor (H) and its width (W) . The effect of air flow

rate has also been examined and an optimum air velocity for propagation is

apparent. Its effect is not completely understood at this time.

2.3.5. Characterization of the Flooring Radiant Panel

Typical flame -spread results are shown in figure 14. This flame spread

behavior is described roughly by eq (3) . Since flame spread is very slow,

the transient heating term in eq (4) would approach a constant value dependent

on the radiative flux and surface heat transfer coefficient. Thus, the flame

spread appears quasi-steady. If the flame heat flux plus the local radiant

flux is insufficient to heat the specimen to its ignition temperature, eq (4)

has no solution; physically, flame spread will cease at a critical flux value.

A comparison of these results with those of Kashiwagi [29] shown in table 7 indicates support for this concept of critical irradiance for flame spread.

Actual flux values in the flooring panel can be greater than those established

initially since radiative interaction of the burning specimen with the panel

and enclosure has not been accounted for.

2.4. Applicability of Test Method Results to Flooring Hazard

2.4,1. E-84 Tunnel Test

Because of the lack of understanding of the factors promoting flame spread

in the tunnel, it is difficult to relate its results to the flameover hazard of

floor coverings. It is apparent that both radiation and convection serve to

preheat the specimen in the tunnel.

The National Building Code of Canada (1970) has recently been revised

(July 1972) such that a floor-mounted-specimen version of E-84 is now prescribed

for a measure of flame spread on floor surfaces. It requires a FSC of 25 in

exit ways and 300 for corridors (previous prescriptions for the standard E-84

test method were 25 and 200 respectively) . Tests have shown that general correlation exists for FSC values between floor and ceiling mounted materials except

for some shag and acrylic carpets. Although the correlation indicates a 5 0 percent increase in FSC-ceiling compared with FSC-floor ratings, the Canadian

82
10

Figure 13,

2-

MODEL CORRIDOR FLAME PROPAGATION FOR A4/U

EFFECT OF ENERGY RATE (Eg , BTU/min.)

AND GEOMETRY, (H,W, In.) AT CONSTANT AIR FLOW ( Va,= lOOft/mi.

)

4^= 4>\'"p2

WHERE

<^,= 0.292-

(Er/W) ^3

O NO SUSTAINED PROPAGATION • FLAMEOVER

( ) TIME ATFO.

O

O

O

O

(5.7)

(5.4)

(3.6)

(5.0)

(2.7)

o o

_L

OqO o

0 0.04 0.08 0.12 0.16

DIMENSIONLESS THERMAL PARAMETER <P Correlation of flame spread results in the model corridor.

100 —

eo

oQ.o01

80

60

40

20

FLOORING RADIANT PANEL

MAX. FLUX = 0.9 W/Cm^

FLAME SPREAD

A-z/u

16 20

TIME, min

Figure 14. Flooring radiant panel flame spread results under a maximum

radiant flux of 0.9 W/cm2.

83
Table 7. Comparison of Minimum Radiant Flux

to Support Flame Spread Under Several Flux Conditi

Sample

Tested

Uniform

Irradiation^

[29]

Radiant Flux At Extinguishment

Electric

'^nnrr-p f ? 9 1 600°C

w/ cm

Flooring Panel

Temperature [23]

670°C

W/cm^

550°C

W/cm^

490"C

W/cm2

W-1 >1. 2 1. 35 0. 61 0.60

N-4 '^1. 0- 0. 35 0.27 0.25

A-1 '^1. 0 0.46 0.50

RO '\'0. 8

! 0. 25

A4

'^'0. 7 0.60 0. 36 0.44 0. 38

A-4/U '^'0. 5 0. 48 0.25

A2

<0. 44 0. 38 0.28 0.31 0.29

A-2/U <0. 44 0. 35 0.20 0.16

A5<0. 44 < 0. 24 0.26 0.24 0.25

A-5/U <0. 44 < 0, 24 0. 20 0.16

A-l/U <0. 44 <0.24 <0.19 0.11

Three minute sample preheat followed by a three minute pilot flame

exposure.

building code has increased its FSC acceptance level for corridors in the floor

mounted version of E-84 by 50 percent over its earlier code. Thus, they apparently have weakened their flammability requirement for flooring materials in

building corridors.

2.4.2. E-162 Radiant Panel

Although the concept behind E-162 is potentially useful in achieving

quantitatively meaningful and useful information for fire safety design, it is

not used that way and is not directly suited for flooring evaluation. The sampl

orientation provides a well-defined flame front progressing upwind as occurs in

the early spread of flooring fires, but since it spreads do\^mward it is inappropriate for flooring materials. Such an orientation does not allow flooring

assemblies to be mounted as they may be installed, and more importantly, the

physical deterioration of the sample during burning will affect combustion significantly. The melt, drip, run effect of polymers which accelerates flame

spread is a case in point. Moreover, the radiant flux level prescribed seems to

be at least twice as high as those typical of corridor flooring fires with non- combustible walls and ceiling. These factors tend to preclude E-162 as a suitable method for measuring flooring flammability.

2.4.3. UL 992 Chamber Test

The sample mounting and the testing of the entire flooring assembly is a favorable attribute of UL 992 in relating to the real-life performance of

flooring materials. The index used to measure the potential hazard can provide a relative measure of potential flame spread, yet it is not suitable for

84
I any quantitative interpretation. The bimodal flame spread behavior of this

test leads to a non-continuous index classification scale for materials.

I These factors and others relating to reproducibility of results between facilities have been addressed by Huggett and Lee [30],

2.4.4. Model Corridor

The similarity of the flameover mode in the Model Corridor and the NBS

corridor fires, as well as the guidance of partial scaling relationships are good features of this method in its bearing on the real-life hazard. However,

the accuracy of such scaling relationships have still to be assessed. Moreover,

the energy release contributed by the material tested is an important factor

in determining flameover in the Model Corridor. Thus, this energy release

property is also inherently measured by the system. Table 8 demonstrates the

effect and magnitude of energy release from the tested material. The effect

Table 8. 2 ft x 1 ft Model Corridor - Estimation

of energy release rate of floor coverings and effect of

available floor covering on flameover energy requirement

Conditions: V = 100 fpm, H=ll in, W=24 in

CFT Material FO

Burner

Eg (Btu/min)

Maximum Energy Release Rate

Before Flame-out or Before

Flameover

Based on Exit

Gas Temp.

Based on Heat

Balance

129 A-4/U yes 500 1,200

194 A-4/U yes 600 1,500

141 N-3 no 1, 000 900

142 N-3 yes 1, 250 1,150

171 W-1 no 1,250 350

261 RO no 1,250 250

195 N-5 no 500 700

196 N-5/U yes 500 1,500-2,000

CFT Material

Minimum Burner

Input Rate to

Flameover

(Btu/min)

Time at

Flameover

(min : : sec)

173 A-3, 2 ft X 8 ft sample 750 4: :50

441 A-3, 7 1/2 in X 8 ft sample 1,500

443 A-3, 7 1/2 in x 18 in initial

section, 2 ft w x 75 in follows

1,000 4: :51

444 A-3, 2 ft X 8 ft sample with

3 in deflector plate at burner

750 4: :48

85
of air flow on flame propagation could also prove troublesome in such systems

if good design is not achieved. These latter factors detract from this system's!

ability to produce a complete design parameter for the material, and could i affect reproducibility between systems.

2.4.5. Flooring Radiant Panel

This test method offers the most promise of obtaining a meaningful design

parameter which relates to the haz ard and can be related to the building system with increasing predictive accuracy as more knowledge of building fires is

developed. As our understanding has developed on the potential hazard of flame

spread over flooring materials, it has become clear that radiation from an external source is a very important factor in this type of fire spread. In

particular, the application intended from this program has been the limitation

of fire spread through corridors and exitways. Hence, the determination of the

minimum radiant flux level necessary to sustain flame spread on flooring

materials is a parameter directly related to the hazard and potentially useful

in a fire safety design analysis in buildings. Hopefully, a flooring radiant

panel system can be designed and operated satisfactorily to measure, with a suitable degree of precision, this "property" referred to as the "critical

irradiance to support flame spread." In addition, a theoretical development

of flame spread under an external radiant source, as proposed by eg (3) , would

enhance the understanding of this test method, and support the "property" interpretation of "critical flame spread irradiance." Thus, some additional work

needs to be done to support the design and interpretation of this method.

A final consideration is the application of the performance measured by

such a flooring radiant panel test method. Initially, judgement might be

applied in setting performance acceptance levels for building corridors and

exitways in various building occupancies. Guidance from recent full-scale

experimental fires could be used to set performance levels. In addition, an empirical design approach could be used to determine acceptable performance

and guidance in extrapolation to full-scale data. For example, calculations

can be made based on energy release from a fire within a corridor spreading

products in two directions. The radiation flux levels to the floor can be

estimated for different fire energy release rates (E) and different corridor

heights (H) and widths (W) . Some results of this kind of analysis are shown

in figure 15. In this calculation it was assumed that all of the radiation

comes from the ceiling and upper walls which are heated to the temperature of

the fire plume intersecting the ceiling. A simple line fire plume theory was used and based on an analysis by Alpert [31] the gas temperature of the ceiling

jet does not greatly vary with corridor length. The corridor was assumed infinitely long and no accounting was made for direct flame radiation. The

result for floor radiant flux is

0.0348

m +

1

1 ^ 0.014 sk/ml^ Btu

f t^sec

where E is fire energy release rate in Btu/min

,

H is ceiling height in ft,

and W is corridor width in ft.

Thus, this equation could be used to calculate the potential radiative floor

flux in a building corridor. The "critical irradiance" measured by the flooring

radiant panel test could then be used as a means of evaluating the material for

the building corridor considered.

86
10.0

Figure 15. Estimated radiant flux to floors in building corridor fires.

3 . CONCLUSIONS

The f laininability of flooring materials has been examined through accident

analysis and full-scale fire experiments. These results indicate that (except

for carpets failing the Pill Test) a large ignition source is necessary to

initiate flame spread on flooring material. Radiant heating of the flooring

material due to a large ignition fire, along with building interior geometry,

can lead to rapid flame spread over the flooring. This is recognized as the

potential hazard of flooring materials in building corridors. Flame spread

through corridors would block escape routes and transmit the fire to other

areas of the building.

Available and proposed test methods for flame spread of flooring materials

have been examined. Based on this study and on the dynamics of corridor fires

a radiant panel test is recommended for flooring materials. Since this test

can measure the flame spread behavior of flooring material under a controlled

external radiant flux, it can yield data of quantitative value. Moreover, by

estimating potential radiant flux levels in particular building occupancy type,

a direct means of linking the test result to the application of the product

can be achieved.

87
4 . REFERENCES

[1] Yuill, C. H. , The Flammability of Floor Coverings, J. Fire & Flammability

,

Vol. 1, 64 (Jan. 1964)

.

[2] Carpet and Rug (Pill Test) Standard for the Surface Flammability of

Carpet and Rugs, DOC FF-1-70, Federal Register, 35, No. 74 (Apr. 16,

1970) , 6211.

[3] Robertson, A. F., Private Communications, National Bureau of Standards,

May 1973.

[4] Chandler, S. E., Fires Due to the Ignition of Carpets and Floor Coverings,

1955-62, Fire Res.' Note No. 62 3, Fire Res. Station, Borehamwood, Herts,

U.K.

[5] Fry, J. F., Private Communication -- Fires Involving Floors and Floor

Coverings FRO/80/018, Fire Res. Station, Borehamwood, Herts, U.K.,

April 10, 1973.

[6] Fung, F. C. W. , Suchomel, M. R. and Oglesby, P. L., The NBS Program on Corridor Fires, Fire Journal, 41 (May 19 73).

[7] Huggett, C, Carpet Flammability and the NBS Corridor Fire Program,

Standardization News, Vol. 1, No. 5 (May 1973).

[8] Fung, F. C. W. , Suchomel, M. R. and Oglesby, P. L., NBS Corridor Fire

Tests: Energy and Radiation Models, Nat. Bur. Stand. (U.S.), Tech.

Note 794 (Oct. 1973)

.

[9] Christian, W. J. and Waterman, T. E., Fire Behavior of Interior Finish

Materials, Fire Technology, 165 (Aug. 1970).

[10] Waterman, T. E., Private Communications, IIT Research Institute,

February 1973.

[11] Segall, W. M. , Private Communications, The Carpet and Rug Institute,

January 8, 1973.

[12] McGuire, J. H. , The Spread of Fires in Corridors, Fire Technology, Vol. 4,

No. 2 (May 1968) .

[13] Steiner, A. J., Method of Fire-Hazard Classification Building Materials,

ASTM Bulletin, 19-22, (Mar. 1943).

[14] Standard Method of Test for Surface Burning Characteristics of Building

Materials, ASTM E-84-70, American Society for Testing and Materials,

Philadelphia, Pennsylvania (1970)

.

[15] Lee, T. G. and Huggett, C, Interlaboratory Evaluation of the Tunnel Test

(ASTM E-84) Applied to Floor Covering, Nat. Bur. Stand. (U.S.), NBSIR

73-125 (Mar. 1973)

.

[16] Surface Flammability of Materials Using a Radiant Heat Source, ASTM

E-162-77, American Society for Testing and Materials, Philadelphia,

Pennsylvania (1968)

.

[17] Robertson, A. F., Gross, D. and Loftus , J., A Method for Measuring

Surface Flammability of Materials Using a Radiant Energy Source, Proceedings, Am. Soc. Testing and Materials, Vol. 56, 1956, 1437-1453.

[18] Gross, D., and Loftus, J. J., Flame Spread Properties of Building

Finish Materials, ASTM Bulletin, No. 230, 56-60 (May 1958).

88
[19] Lee, T. G., Loftus, J. J. and Gross, D., Effect of Moisture on Surface Flammability of Coated and Uncoated Cellulosic Materials,

ASTM Special Tech. Publication, No. 385, 112-123 (1965).

[20] Engermann, H. S., Floor Covering System -- A Test for Flame Propagation

Index, J. Fire and Flammability, Vol. 2, 11 (Jan. 1971).

[21] Denyes, W. and Raines, J., A Model Corridor for the Study of Flammability of Floor Coverings, Nat. Bur. Stand. (U.S.), NBSIR 73-200

(May 1973)

[22] Denyes, W. and Quintiere, J., Experimental and Analytical Studies of

Floor Covering Flammability with a Model Corridor, Nat. Bur. Stand.

(U.S.), NBSIR 73-799 (May 1973).

[23] Hartzel, L. G. , Development of a Radiant Panel Test for Flooring

Materials, Nat. Bur. Stand. (U.S.), NBSIR 74-495 (May 1974).

[24] Roberts, A. F. and Clough, G. , The Propagation of Fires in Passages

Lined with Flammable Materials, Combustion and Flame, Vol. 11 (1967).

[25] Roberts, A. F., Fires in the Timber Lining of Mine Roadways: A

Comparison and Data from Reduced-Scale and Large Scale Experiments,

Safety in Mines Research Establishment, Report 26 3, Sheffield, Eng.

1970.

[26] de Ris, Duct Fires, Combustion and Science Technology, Vol. 2, 239-

258 (1970) .

[27] Rockett, J., Mathematical Modeling of Radiant Panel Test Methods,

Fire Safety Research, Proceedings of the NBS in Action Series-IV Fire,

Nat. Bur. Stand. SP, Gaithersburg , Md., August 22, 1973 (to be

published)

[28] Rhodes, A. C. and Smith, P. B. , Experiments with Model Mine Fires, The

Use of Models in Fire Research, National Academy of Science, Berl, W. G.

,

Ed., Washington, D.C. (1961).

[29] Kashiwagi, T. , Private Communications, National Bureau of Standards,

1973.

[30] Huggett, C. and Lee, T. G. , Investigation of Carpet Flammability Test

Methods, Nat. Bur. Stand., NBS Report 10585 (Sept. 24, 1971).

[31] Alpert, R. L. , Fire Induced Turbulend Ceiling-Jet, Factory Mutual

Research Corp. , FMRC Ser. No. 19722-2 (May 1971)

89
NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 411, Fire Safety Research,

Proceedings of a Symposium Held at NBS , Gaithersburg , Md., August 22, 1973,

(Issued November 1974)

MATHEMATICAL MODELING OF RADIANT PANEL TEST METHODS

J. A. Rockett

National Bureau of Standards, Washington, D.C.

Standard flame spread tests characterize complex physical phe- nomena by a relatively simple experiment. Analytic modeling of the

standard test identifies the sample geometry and material properties

controlling the test outcome. Systematic variation of the model parameters verifies the analytic model for many broad classes of test

samples provided parameter values appropriate to each test are determined by independent measurements. In most cases the standard test

is not a satisfactofy way to quantify the important sample parameters.

The standard test is a suitable way to verify the applicability of

a particular model or set of analytic models for a particular sample.

If sample parameters are independently determined, the applicable

models may then be used for hazard determination.

Key words: Fire modeling; fire test methods; flame spread; test

method

.

1 . INTRODUCTION

There are several recognized fire test methods in which a sample is exposed

to a radiant energy flux and, after either self or piloted ignition, burns [1,2]

The standard measurement of material performance is either the extent or rate of

burning. Commonly, an index is computed from the measured quantities and is the

only test result usually reported. An analytic model of a test method can provide information on the material properties and sample characteristics controlling the test outcome. This information, much more than the contrived test fig- ure of merit, tells something about the burning characteristics to be expected

from materials in actual fire situations. The modeling process yields material

properties and sample characteristics important to the specific burning situations modeled and illuminates what the test does (and does not) measure. The

model also allows some inferences on the extent to which test results fully char

acterize the material and sample variables needed to predict performance in fire

situations

.

2. FLAME SPREAD AGAINST THE WIND

A decade ago Gross and Loftus presented a simple model for radiant panel

tests [3] . Their model suggested some similarity relations which were well

verified by their experiments. Recently, J. Quintiere has developed a more detailed model for flame spread under a situation similar to that found in

radiant panel tests. His model, derived for the case of propagation of flames

against the ambient wind, appears to represent quite well the principal features

of the test methods for sufficiently thin samples. This is appropriate because,

although there is no forced convection with most radiant panel test methods, a certain amount of natural convection is always present, and in some test con- figurations quite a bit. Usually, the experimental configuration is arranged

so that the flame propagates against such wind as is present.

Because of the importance of test modeling, Quintiere 's model has been

rederived in a somewhat more general way and extended to more general sample

configurations. The present model is for thermally thick and laminated fuel

beds. The model assumes there is a heat flux, Q, acting on the sample which

is composed of two parts: the heat flux, Qj^, supplied to the sample from the

radiant panel, which is normally a function of distance along the sample length,

and the reflexive heat flux, Q_, from the flame back to the sample surface.

r 90
Qp is a rapidly decreasing function of the distance ahead of the flame. The

Gross-Loftus model includes only Q-p^ and neglects loss of heat from the surface,

but is otherwise similar to the present model.

In developing the present model it was assumed [4,5] that:

1. Negligible heat is transferred from the burning zone or flame to the

unburned fuel ahead of the flame via the fuel bed.

2. For upwind flame propagation, heat transferred from the flame to the

fuel ahead of the flame is localized to a very short region ahead of

the flame

3. The sample ignites when its surface temperature reaches a fixed,

critical value. This is a surrogate for the more accurate but very

much more complex and analytically intractable ass\imptions needed to

describe the pyrolysis kinetics within the sample.

The new model which encompasses Quintiere's thin bed and Gross-Loftus '

models as special cases is obtained by solving the one-dimensional transient

heat conduction equation for a laminated fuel bed on a semi-infinite solid

backing with a given applied surface flux, Q, and loss of heat proportional to

surface temperature [6] . The one-dimensional solution may be used since heat

flow in the fuel bed in the direction of flame spread is ignored.

The solution of the differential heat conduction equation is straight forward through the method of Laplace transformation. Transformed expressions can

be readily written for single or multilayer fuel beds. The multilayer expressions are more complex and harder to invert. Unfortunately, test results are often sensitive to the backing behind the sample; consequently, such samples

are not well modeled by the single layer expressions. For these, a multilayer

model seems essential. The transformed expression evaluated at the sample

surface for a two layer fuel bed (on an inert, insulating backing) consisting

of an outer, exposed layer (1) of thickness d^^, a core layer (2) of thickness

d2 and an inert insulating backing is:

L(o,p) = Qg/p(Hg + k-j^q^^) (1)

where

L(o,p) = the transformed fuel surface temperature

p = the transformed time

kj^q^^ cosh (q^dj^) cosh (q2d2) + k2q2sinh (q^^d^^) sinh (q2d2) ^ k^q-j^sinh (q^^dj^) cosh (q2d2) + k2q2COSh (q^^d^) sinh (q2d2)

H = surface heat transfer coefficient

k-j^ = thermal conductivity of layer 1

k2 = thermal conductivity of layer 2

q^ =/lj^ = thermal diffusivity of layer 1

'^2 =J-E = thermal diffusivity of layer 2 la_ 2

91
At this writing a detailed study has only been undertaken for single layer fuel

beds on an insulating backing, k2 = 0 . For this case inspection of the transform shows

L(o,p) = Q/p[H + k^q-]_tanh (q^d-,^) ] (3)

This in turn has two limiting forms which may be readily inverted. For large

q-j^d-]^, or time relatively short compared to that required for the temperature

of the rear face to rise appreciably.

and, for small

L^(o,p) - Q/p(H + k-^q-^)

long times.

(4)

Lq(o,p) - Q/p[H k^d^q2]

(5)

Q/p[H + (pc d^

]

P 1 P] .

Here, p is the fuel density and c is the fuel specific heat.

An exact inversion of the more general expression has not been found. Calculations reported here were carried out using the approximate function whose

transform satisfied these two limiting conditions. This can be written as

I(t) = I^(t)exp(- Ht

PCpd + I^(t) [1 - exp(-^i:^) (6)

where I(t) is the temperature response of the fuel to a unit step change in heat

flux, and 1^ are the functions whose Laplace transforms are and , re- spectively, and d is the fuel thickness. The thin bed approximation, 1^ , valid

for short times, yields Quintiere's thin bed model. However, for small but

finite time this approximation breaks down. The short time during which the

flame heat, Qp , is felt is the limiting factor in this. For practical purposes

the thin bed model is valid only for films thinner than about 1/10 centimeter.

The model treats the two components of the incident heat flux slightly

differently. The heat flux due to the radiant panel is treated using the heat

transfer analysis stated above. The heat from the flame, however, is felt ahead

of the flame for so short a period of time prior to arrival of the flame that

only the limiting form for short times (large q^^d^) was used for computing the

flame induced part of the fuel surface temperature rise. A thickness effect

correction is included, however, since I, eq (6), does vary with thickness.

For very thin samples a velocity formula based on the thin bed model should be

used. The result of this and the further assumption that the flame velocity

is constant over the time interval in which a particular element of the fuel

surface feels the heat of the approaching flame, leads to the flame spreadvelocity expression:

V = pCpk J 2D

Qt

1 + CpkQi

Ok

K(t) h2(1 + H2d2 q2 (7)

where

Qp/ Qr/ p, c , H and d are as previously defined

(Qr + 6pQ^)I

92
R dx

= g^-^-^' I(t) being the approximate heat flow solution, eq (6)

V = rate of flame spread

= ignition temperature of the fuel

= distance ahead of the flame over which heat from the flame

is felt by the fuel

Q-p = incident heat flux at the flame leading edge due to the flame

^ oExperimental data from test samples have been used to evaluate the parameter groups in eq (7) . The reciprocal of the velocity expression (7) was numerically integrated with respect to distance to give time, t, as a function

of the flame location, x. [The basic data recorded in the ASTM E-162 and some other radiant panel tests is the time at which the flame passes fixed positions

thus, the integral could be compared directly with experimental data. The re- sult of the numerical integration for fixed values of the parameters in eq (7) was compared with experimental data and the parameters were adjusted to minimize the square error.

N

E = E [Yi - t(Xi)]2

i=l

where y^ is the experimental time of flame passage measured at x^, and t(x^)

is the computed time from the integration.

Measured radiant flux distributions Qd(x) were used and these measured

values were numerically differentiated with respect to distance to give Q-^.

Four of the parameters were adjusted:

Qpo' ^'^c ' ^/^P'^-p^ ^-p- '^^o other

parameters enter but were not varied in individual data fits. They were varied

for sets of data from a group of similar samples. One of these is the sample

thickness parameter, k/Hd, which is important for relatively thin or slow burning samples. This parameter enters eq (7) in several terms: (1) it changes I,

and, through the change in I , it changes D, and (2) it changes K which appears

in one of the terms under the square root. Thickness dependence in these two

terms has little effect on V for a range of thickness large enough to effectively change I from I,^ to Iq. However, in eq (7) , the last term on the right

under the square root contains the thickness parameter and it does have an important effect. A discussion of the origin of this term is beyond the scope

of this paper but it is associated with the heating of the sample by the flame.

This term becomes increasingly important as the decrease in sample thickness

allows the insulating effect of the backing to be felt such that less of the

flame's heat is lost to the interior of the sample. The second "fixed" parameter, a constant of integration, is the time delay between sample insertion

and ignition. This time is not usually recorded on the data sheet because the

actual moment of ignition is hard to observe. The computed ignition is strongly influenced by the assumed heat flux from the pilot ignition flame. It was

found that good data fits were obtained for E-162 tests with the pilot flame

strength about 1.35 times the peak radiant panel flux, Qj^- For these tests,

a variation of ±10% in the assumed pilot strength significantly changed the

qualitative shape of the time-distance curve between the origin and second

(6 inch) measuring point and changed the fit at the first measuring point (3

inch) slightly. There was little effect on the other parameters. Once a suitable pilot strength had been found it seemed to be satisfactory for all

tests with the same test apparatus configuration. Of the four "variable" para- meters , Qp and HT^ changed the shape of the time-distance curve, and H//pc k

93
and 6 changed its scale with H//pc k having the greater influence. For this

model the least squares fits are non-linear in the parameters. As expected in | such cases, convergence did not always result in a good fit; there are several

local minima for the error, E. The final fit was found by systematic variation!

of initial parameter guesses. Some results of this fitting are presented in i table 1. I

Table 1. Parameter Evaluation For Several Materials

Sample Designation H//pCpk k/Hd

NBS Std. Hardboard 1/4" 0.101 2 . 37 14.22 0 .127 0.5

NBS Std. Hardboard 1/4" (a) 0.098 2, 35 14.14 0 .129 0.5

Common Hardboard 1/8" 0.110 2 .20 14.65 0 .149 1.0

Common Hardboard 1/16" 0.153 2.04 13.75 0 .119 2.0

Common Hardboard 1/32" 0.177 2 .02 13.74 0 .123 4.0

Fiberboard J #9 [3] 0.160 2.09 9.09 0 .274 (b)

Exterior Plywood #30 [3] 0.107 2.13 9.19 0 .252 (b)

Perforated Tile #17 [3] 0.127 1.73 7.70 0 .541 (b)

^Repeat test, indicates degree of reproducibility.

^Fits insensitive to thickness parameter for range of values explored.

"Estimated" magnitudes of the quantities appearing in table 1 are given

below and are of interest in assessing these data. Estimates are based on typical values for hard wood [6] . Convective component of the heat loss coefficient, H, was derived using McAdams , Chapter VIII [7].

(2.77 x 10~3 W/cm2.°c for a surface temperature of 350°C

H =]

(4.33 X 10~3 w/cm2.°C for a surface temperature of 490°C

T^ = 350°C [8]

(0.970 W/cm2 at 350°C

HT^ =j

(2.122 W/cm^ at 490°C

a = 1.3 X 10"-^ cm^/s

k = 1.4 X 10"3 W/cm-°C

(0.0713 s"-"-/^ for H = 2.77 x 10-3 w/cm^

/^^Tk '0.1115 s-1/2 for H = 4.33 x lO'^ w/cm^

ir * Ji = 0.505 for d = 1 cm

Qf^ =4.0 W/cm2 [8]

6p = 0.1 cm [8]

There are several implications

somev7hat surprising. Comparing the

H//pCpk and 6p are reasonably close

Qp^, however, are about twice those

of the data in table 1 which, if true, are "fitted" values with estimates suggests that

to what one might expect. The values of

expected [8] , although there is little

94
published data to compare with these values. A recent paper by Hirano et al

[9] suggests a value of 20 to 22 W/cm^ for Qp^ for cellulosic material. Also,

the implied value of for hardboard is close to 490 °C, 100 °C above the value

experiments would suggest [8]

Gross and Loftus [3] found an experimental correlation over a range of

two orders of magnitude in thermal inertia, pc k. This suggests that the theoretical dependence on thermal inertia of eq (7) is correct. However, it is

not possible to evaluate the thermal inertia of a particular sample from ex- amination of E-162 test data: one can only obtain values for parameter groups

containing thermal inertia and other parameters. ^

3. FLAME SPREAD WITH THE WIND

Fire, starting low and spreading upward, burns into the unburned fuel preheated by the rising fire gases, and develops rapidly. On the other hand, fire

starting high on an object and burning down moves against the natural convection and travels slowly. Aside from the obvious difference in direction of

flame travel relative to the local natural draft, there are other basic differences in controlling physical processes. A hazard rating, based on a standard

test of flame spread against the wind, might supply information needed to predict spread with the wind, but only if the test included supplemental measurements in addition to surface flame spread. The ASTM E-162 standard test method

appears to recognize this by measurement of the total sample heat release rate

in addition to flame spread.

There are several standard tests in which the surface flame spread measure

ments are made with the wind. Pro'bably the most widely used test methods are

the "Steiner Tunnel," ASTM Standard E-84, the "45° Fabric Test," CS 191-53, and

the recently adopted vertical test, DOC FF3-71. If against-the-wind and withthe-wind tests each fully evaluated a sample material, it would be possible,

through mathematical modeling of both tests, to cross predict the fire performance of the material. If this could be accomplished, a considerable step would

have been made in predicting real fire growth in a building from standard test

data. At present, this is not possible. On the other hand, if it could be

shown that the result of one standard test did not allow prediction of that of

the other, we would know why the test failed to fully characterize the hazard

of the tested sample. Thus, it is worthwhile looking into the mathematical

model of flame propagation with the wind and comparing this with the upwind

propagation model.

A model for with-the-wind spread of a turbulent flame has been developed

recently. This model is a generalization of a model proposed by de Ris [10]

The de Ris model is a quasi-steady analysis of a thin fuel bed and the generalized model is a transient analysis of thicker fuel beds, de Ris assumes that a turbulent flame produces a layer of gas, at the (constant) flame temperature,

and that the heat transfer rate from this flame to the fuel is constant over

the entire length of the flame projected along the sample surface. The generalized de Ris analysis has been used with some success to model E-162 stack

heat data. However, the variability of measured stack heat for repeat tests

of nominally identical samples suggests further work on this aspect of the radi

ant panel tests is needed.

95
4 . CONCLUSIONS

The general theory presented here seems to satisfactorily represent the

flame spread behavior of samples tested in the E-162 apparatus. Numerical con- stants found from actual data fits are generally of the expected magnitude.

The effect of sample pyrolysis which does not appear in the present model is

found to be significant. This important burning characteristic does influence

the stack temperature measurement which is a part of the E-162 protocol but not

of some other proposed radiant panel tests. To the extent that these other

tests are essentially against-the-wind flame propagation tests and would presumably be well modeled by this same analysis, they will characterize the same groups of parameters found important here; and they will not include the effect , of sample pyrolysis rate. Some additional feature, such as stack heat, or other'

heat release rate measurement should be included to quantify this important

burning characteristic of materials.

5 . REFERENCES

[1] Robertson, A. F., Gross, D. and Loftus, J., A Method For Measuring Surface!

Flammability of Materials Using a Radiant Energy Source, Proceedings of

the American Society for Testing and Materials, Vol. 56, American Society ' for Testing and Materials, Philadelphia, Pa., 1956, 1437-1453.

[2] Anon., Fire Tests of Building Materials and Structures - Spread of Flame

Test for Materials, British Standards Institution, BS 476: Part 7 (1971).

[3] Gross, D. and Loftus, J,, Surface Flame Propagation in Cellulosic Materials

Exposed to Thermal Radiation, Journal of Research, Nat. Bur. Stand. (U.S.);

67C (Eng. and Instr.), No. 3, 251-258 (July-Sept. 1963).

[4] Simms, D. L., Ignition of Materials Exposed to Thermal Radiation, Combustion and Flame, Vol. 4, No. 3, 293-300 (Dec. 1960).

[5] de Ris, J. N. , Spread of a Laminar Diffusion Flame, Twelfth Symposium j (International) on Combustion, University of Poitiers, Poitiers, France,

July 14-20, 1968, 241-252 (The Combustion Institute, Pittsburgh, Pa.,

1969) .

[6] Carlslaw, H. S. and Jaeger, J. C. , Conduction of Heat in Solids, 2nd Ed.

(Clarendon Press, Oxford, 1959).

[7] McAdams, W. H., Heat Transmission (McGraw-Hill, New York, 1942).

[8] Parker, W. , Flame Spread Model For Cellulosic Materials, Journal of Fire

and Flammability, Vol. 3, 254-269 (July 1972). m

[9] Hirano, T., Noreikis, S. and Waterman, T. E., Measured Velocity and

Temperature Profiles of Flames Spreading Over A Thin Combustible Solid,

Interim Technical Report No. 2, House Sponsored Project J1139, IIT

Research Institute, Chicago, 111. (May 7, 1973).

[10] de Ris, J. N., Technical Proposal, Dynamics of Textile Fire: A Study

of its Mechanisms - Theory and Experiment, Factory Mutual Research Corporation, Ser. No. 205883, el-e5 (May 1971).

9.6
NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 411, Fire Safety Research,

Proceedings of a Symposium Held at NBS , Gaithersburg , Md., August 22, 1973,

(Issued November 1974)

FLAME SPREAD OVER A POROUS SURFACE UNDER AN EXTERNAL RADIATION FIELD

Takashi Kashiwagi

National Bureau of Standards, Washington, D.C.

Flame spread over carpet surfaces was studied under various

constant external radiant fluxes from 0.4 to 1.2 W/cm^ , Characteristics of ignition and flame spread including speed of spread

and net heat release rate were measured. The results indicate

that these values increase rapidly with increasing external radiant flux. It was also observed that there exists a minimum radiant

flux necessary to sustain steady flame spread for each carpet. The

underlayment of a carpet has a significant effect on. ignition and

flame spread speed for nylon carpets due to melting of fibers before

flameover. However, this effect is negligible for low pile density

acrylic carpets.

Key words: Carpet f lammability ; flame spread; ignition.

1. INTRODUCTION

It has been observed in full scale experiments that radiation from ceiling, walls and hot smoke and gas heats a carpet before flameover in a corridor

and this radiant preheating plays an essential role in flame spread over the

carpet surface [1]. Under this condition, it is sometimes reported that flame

will spread very rapidly over a carpet which passes the present carpet test

standard, the so-called "pill-test". The objective of this study was to observe the characteristics of flame spread over various types of carpets under

various radiant fluxes which simulate those measured in the full scale experiments. It was expected that we would learn about the behavior of flame spread

over a carpet surface and that we could use this information to design a better

test method for measuring carpet f lammability

2. EXPERIMENTAL APPARATUS

A schematic illustration of the apparatus is shown in figure 1. The radiant panel consists of twelve nichrome ribbons on a ceramic support. Its dimensions are 15 in x 33 in. This panel is electrically heated and its ribbon

temperature can be controlled at about 600°C. A test specimen (6 in x 21 in)

is held by a support and located on the cement asbestos board table. The distance between the panel and the test specimen surface can be varied by lowering

or raising the table. Distances of 16 inches, 20 inches, 24 inches, 28 inches,

and 32 inches were used in this study. Radiant flux distribution over a speci- men surface is fairly uniform (within 10%) except at the 16 inch distance (15%)

A shutter is used to allow a test specimen to be exposed suddenly to a constant

radiant flux after the panel reaches the equilibrium condition. One end of the

specimen is ignited by a pilot burner which is designed to produce a linear

diffusion flame. Preheating time of the specimen is controlled by the time at

which the pilot burner is turned on after the opening of the shutter. The

pilot burner is turned off after the specimen is ignited and sustains a flame.

This ignition time is significantly different for different specimens. After

the pilot burner is turned off, the flame spreads over the specimen surface.

The steady flame spread speed is attained within a few inches of the pilot

burner. Flame spread speed is observed by eye with a stop watch used to time

the passage of the flame front by scribed distance markers. A fine mesh screen

surrounds the test apparatus to prevent air motion in the room from affecting

flame spread.

97
A=ELECTRICALLY

HEATED RADIANT PANEL

SHUTTER

PILOT GAS BURNER

TEST SPECIMEN

SCREENING

Figure 1. Schematic illustration of experimental apparatus.

98
A description of the carpets used in this study is given in table 1. The

carpet specimens and underlayment were conditioned at 50% humidity and 23±2°C

temperature for at least 48 hours prior to use.

Table 1. Carpet Designation

vg/cm / Code Fiber Type Backing Pile Backing Pile Height (cm)

A-1 100% Acrylic Woven Level Loop Jute/Cotton 0.18 0.51 0.64

A

100% Acrylic Random Shear Polypropylene /Jute 0.087 0.46 0.16 - 0.80

A

100% Acrylic Random Shear Jute/Jute 0.16 0.51 0.32 - 0.96

A

100% Acrylic Plush Polypropylene/Jute 0.074 0. 52 0.91

N-4 Nylon (6 & 66) Shag Jute/Jute 0.086 0.51 0.99

N-5 BCF Nylon (66) Multi-level loop Jute/Jute 0.061 0.51 0.59

Pad Rubberized Hair

Jute 0. 18 1.18

3. RESULTS AND DISCUSSION

Ignition is the initiation process of fire and it is one of the important

parameters used to characterize the flammability of a material. In this study,

I ignitability was measured by observing the minimum duration time of the pilot

flame necessary for a carpet to sustain flame after the pilot burner is turned

off. The results are shown in figure 2. The data show that the minimum ignition time varies significantly from one material to another. The acrylic carpets A-2 and A-5 of low pile density require very short duration times. The

effect of a pad on the ignition time is negligible for these carpets. On the

j other hand, nylon carpets N-4 and N-5 require much longer ignition times and

I the effect of a pad is significant. Acrylic carpets A-1 and A-4 of heavy pile

1 density are intermediate in their behavior. It is observed that the fibers in

nylon carpets melt before they ignite. This melting process requires a longer

minimum pilot flame duration at high radiant fluxes compared with non-melting

carpets

The relation between speed of flame spread and incident radiant flux is

shown in figure 3. It is observed that there exists a minimum radiant flux for

a carpet to support flame spread without extinguishment, although this study

did not conduct experiments at a radiant flux low enough to extinguish carpets

A-5, N-4, and N-5. Since these carpets pass the pill test, they will not support a flame in the absence of an external energy flux. The trends described

in the above discussion, such as the significant effects of pile density and

composition on ignition, are not observed in the value of minimum radiant flux.

The effect of a pad on the minimum radiant flux is negligible for the low pile

density carpets A-2, and A-5, but significant for others. This is similar to

the trend observed in the ignition study discussed above. The value of the

minimum radiant flux necessary to support flame spread is one of the important

characteristics by which to judge the fire safety of a carpet.

Another important characteristic shown in figure 3 is that speed of flame

spread increases rapidly with increasing incident radiant flux for all carpets

tested. Speed of flame spread increases in the order of nylon carpets N-4 and

N-5, heavy pile density acrylic carpets A-1 and A-4, and low pile density

acrylic carpets A-2 and A-5. This is the same order as observed for minimum

ignition time. Therefore, in this range of radiant flux level and preheating

time, the flame spread mechanism is considered to be a successive ignition process. From these results it is found that the type of pile of a nylon carpet

has little effect on flame spread and ignition because the melting process

ahead of the flame destroys the pile structure. However, the pile structure

99
100
II

of acrylic carpets has a significant effect on ignition and flame spread. The

other experimental parameter is the duration of preheating. Except at the

highest radiant flux used in this study, 1.15 W/cm^, a preheating time longer

than three minutes does not increase speed of flame spread significantly. At a radiant flux of 1.15 W/cm^ , the longer preheating time produces smoking and

partial charring of the sample surface before it is ignited by the pilot burner.

After pilot ignition and a transient stage, very rapid flame spread is observed.

It spreads so fast that accurate measurement of its speed by eye is very difficult. The order of speed is a few centimeters per second. With a still higher

radiant flux, this speed would eventually reach the flame propagation speed for

the mixture of decomposed fuel vapor and surrounding air, which is about an order of magnitude larger. This rapid flame spread phenomenon is also observed

in the full scale experiments [1]

This phenomenon can spread fire and smoke throughout a building, causing

loss of life and extensive property damage. Therefore, the relation between

radiant flux and preheating time leading to this rapid flame spread is an important factor by which to judge the fire safety of a carpet. There are three

important parameters: ignitability , minimum energy flux to sustain constant

flame spread, and the domain of rapid flame spread controlled by radiant flux

and preheating time. The general trends of these parameters with incident

radiant flux and pilot burner duration time are shown in figure 4. It is considered here that the minimum radiant flux is an asymptotic value of external

INCIDENT RADIANT FLUX

Figure 4. Qualitative relations between ignition and incident

radiant flux and between flame spread velocity and incident

radiant flux under variable preheating time.

101
radiant flux for sustained flame propagation. The plotted curves are relative

ones and each carpet has its own characteristic curves. From the test standard

point ot view, ignitability and the domain of rapid flame spread should be

measured by a pilot ignition study (because the preheating times and the external radiant fluxes necessary to cause rapid flame spread are well correlated

with the pilot ignition delay time) and minimum radiant flux to sustain flame

spread should be measured by a flame spread test under a radiation flux field

which decreases in intensity along the sample surface.

Thus, we have discussed flame spread and ignition under an external energy

flux. However, in an actual fire, there is another important energy source which is heat release from the burning carpet. This energy will also contribute to the rate of flame spread. For this reason, the heat release rate from

a carpet over which the flame spreads with constant speed was measured. First,

the total heat release from the unburned carpet is measured by the oxygen-bomb

[2] method. Then, heat release from the char remaining after the flame spread

test is also measured with the same technique. The difference between these

values, adjusted to represent equal areas, is the net heat release which is

measured per unit surface area. The product of this net heat release and the

constant flame spread speed is the net heat release rate per unit width. The

results are shown in figure 5 for various radiant fluxes. The data indicate

that the net heat release rate increases rapidly with increasing incident radiant flux. It is interesting to note that net heat release rates of low pile

density carpets A-2 and A-5 are smaller than those of other carpets at low

radiant fluxes although flame spread speeds of A-2 and A-5 are faster than those

of other carpets. This means that flame spread over A-2 and A-5 involves only

a shallow zone near the surface. However, the other carpets burn more deeply.

This is confirmed by the measurement of weight loss of carpets after flame

spread tests. Net heat release rate decreases considerably when the carpets

are burned without a pad even for low pile density carpets A-2 and A-5. This

behavior is quite different from the negligible effect of a pad on ignition and

flame spread speed for A-2 and A-5. This is illustrated in figure 6, which

compares the flame shape with a pad and without a pad under the same radiant

flux. Without a pad, there is only a main flame. This means that the carpet

burns longer and over a larger area with these smaller flames. This behavior

is observed only at high radiant fluxes. At low radiant flux, the width of

flame increases slightly.

4 . SUMMARY

1. For carpets which pass the pill test there exists a minimum radiant flux

necessary to sustain flame spread over the carpet surface without extinguishment .

2. Speed of flame spread increases rapidly with increasing radiant flux and

approaches values of flame propagation speed characteristics of the gas

phase

.

3. The construction of the pile layer of acrylic carpets significantly affects

ignition, flame spread speed and net heat release rate. With nylon carpets

the effect is smaller due to melting of the pile ahead of the flame front,.

4. The effect of a pad on ignition and flame spread speed is significant for

carpets of heavy pile density, but small for acrylic carpets of light pile

density. However, the effect on heat release rate is significant for all

carpets tested.

102
0

*

1 1 1 1 1

1 r

1 0.4 0.6 0.8 1.0 1.2

INCIDENT RADIANT FLUX {W/cm2)

Figure 5. Relation between net heat release rate and incident radiant flux.

103
WITH PAD

WITHOUT PAD

Figure 6. The effect of pad on flame shape. Flame travels from right to

left (0.86 W/cm2)

.

5 . REFERENCES

[1] Fung, F. C. W. , Suehome1 , M. R. and Oglesby, P. L., Fire Journal, Vol. 67,

41 (1973) .

[2] Ambrosius, E. E. and Fellows, R. D., Mechanical Engineering LaboratoryPractice, 245-247 (Ronald Press, N.Y., 1957).

104
NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 411, Fire Safety Research,

Proceedings of a Symposium Held at NBS , Gaithersburg , Md . , August 22, 197 3,

(Issued November 1974)

PHYSIOLOGICAL AND TOXICOLOGICAL EFFECTS OF THE PRODUCTS

OF THERMAL DECOMPOSITION FROM POLYMERIC MATERIALS

M. M. Birkyl

National Bureau of Standards, Washington, D.C.

I. N. Einhorn, M. L. Grunnett, S. C. Packham, J. H. Petajan, J. D. Seader

University of Utah, Salt Lake City, Utah

A program that combines the capabilities of the College of

Medicine and the College of Engineering of The University of Utah

has been instituted to evaluate the physiological and toxicological effects of the products of thermal degradation and combustion

of cellulose, a polyvinyl chloride, a flexible polyurethane , and

wood (Douglas fir) . The products produced from these materials

are being identified and quantified with a gas chromatograph-mass

spectrometer-computer system. In addition, a National Bureau of

Standards smoke chamber has been modified with a weight loss transducer to correlate, on a continuous basis, the quantities of smoke

produced with sample weight loss. Extensive studies on the effects

of these degradation products on rats is in progress. The results

of exposure of the rats to carbon monoxide are reported. All of

the laboratory results are being correlated with full-scale fire

studies at the National Bureau of Standards.

Key words: Combustion; polymer; pyrolysis; smoke; specific optical

density; toxic gases; toxicity.

1. INTRODUCTION

The flammability research program at The University of Utah is sponsored

by the National Science Foundation's Research Applied to National Needs (RANN)

Program. The program is directed to the physiological and toxicological aspects

of humans during fire exposure and is divided into the following thirteen tasks:

Task Activity

1 Materials Selection and Characterization

2 Development of a Chamber for Smoke Studies

3 Animal Exposure Chamber

4 Measurement of Smoke

5 Analysis of Smoke

6 Effects of Fire Retardants on Smoke

7 Gross Physiological Effects of Smoke

8 The Influence of Volatile Degradation Products of

Combustion on the Survival Responses of the Rat

9 Toxicological Studies

10 Visual Aspects Dependent on Smoke Exposure

11 Neuropathological Studies Related to Fire Exposure

12 Large-scale Fire Tests (NBS)

13 Analysis of Fire Injury by Smoke

This paper was written during the 1973-1974 academic year while Dr. Birky was a visiting Professor at The University of Utah.

105
The program has been in existence approximately one year. The National Bureau

of Standards has been, and is presently, supporting the program in a regular

consulting mode and through interchange of a senior scientific staff member.

This paper is a review of the technical accomplishments of the various tasks

of the program at this date.

2. TECHNICAL ACCOMPLISHMENTS OF THE VARIOUS TASKS OF THE PROGRAM

2.1. Task 1 - Materials Selection and Characterization

Task 1 was completed early with the selection of cellulose, a PVC, a flexible urethane and Douglas fir as the four materials of interest. Douglas

fir was chosen because of its extensive use in the building industry and since

many building codes state simply that the use of new materials in buildings

should be no more hazardous than wood (from a fire hazard view point) . Wood

then becomes a reference in determining the relative hazard of the two plastic

materials chosen in the program. The effects of fire retardants on smoke and

toxic gas profile (Task 6) will not be covered at this time since it is to be

studied at a later date.

2.2. Task 2 - Development of a Chamber for Smoke Studies

and Task 4 - Measurement of Smoke

2.2.1. Physical Characteristics of Smoke

Smoke may be defined as the airborne products from smoldering or burning

materials. Thus, besides gas, smoke may contain various types of solid and

liquid particulate matter. The physical characteristics of smoke that are of

major interest are light transmission, airborne mass loss, particulate mass,

and particulate size, shape and phase state. A relatively large number of

variables may influence these dependent characteristics, such as polymer type,

exposed area, sample thickness, weight, density, orientation, fire retardant

additives, surface coatings, oxygen availability, and heat flux.

Light transmission has been considered from a theoretical point of view.

If the smoke is considered to consist only of small spherical particulate

matter, the light to be monochromatic, and the scattering to be single and

independent, then combining Rayleigh and Bouguer laws leads to the following

expression for the widely used specific optical density parameter D^:

p \ / \ exposed surface area of material

attenuated light intensity

source light intensity

optical path length

particulate index of refraction

radius of particulates

sample thickness

smoke chamber volume

fraction of mass loss that is particulates

wave length of light beam

density of sample

density of particulates.

where A =

F =

n =

r =

t = V =

r =

X =

106
This relation predicts that the specific optical density is directly proportional

to material density and thickness. Limited experimental data from the NBS [1]

and Hilado [2] tend to confirm this prediction provided that the light transmission is not attenuated to values less than about one percent. Figures 1, 2,

and 3 show that, as predicted by eq (1) , the maximum specific optical density

(maximum value of D^) is linearly dependent on sample thickness and density.

The above relationship suggests that the sample weight loss is an important parameter to correlate with the quantity of smoke produced from any given

material and may indeed be a means of predicting the potential smoke hazard of

a material. A new smoke index, referred to here as the mass-optical density,

may be obtained from a rearrangement of eq (1) to the relation

where m is the sample mass loss.

As a result of this theoretical development, the NBS smoke chamber has been

modified to include a sensitive weight loss transducer system so as to simultaneously record weight loss and light transmission on a continuous basis.

Details of the modification have been reported by Chien, Seader, and Birky [3],

Data using the modified smoke box in the non-flaming mode at 2,5 watts/cm^ for

a flexible polyurethane are shown in figure 4. In this case, after discounting

the time lag of the light transmission because of the finite time for the particulate to spread through the chamber, the initial airborne mass loss appears

to contribute less to the smoke particulate than the later mass loss. Correlation of mass loss with optical density is clearly indicated. The two curves

in figure 4 can be combined according to eq (2) , This type of data treatment

for the urethane and other materials is shown in figure 5 for comparative

purposes. In all cases, the data is for non-flaming using a radiant flux of

2.5 watts/cm^. Significant differences are noted among the materials with the

cellulosics occupying a central position. Significant differences in rate of

smoke production are also evident which need to be investigated.

Of particular importance in the use of the NBS chamber for the evaluation

of materials is the maximum value of Dg, referred to as Dj^. Values of Dj^ and mass loss for the materials shown in figure 5 are tabulated in table 1 along

with the maximum, specific optical density normalized to the mass lost. These

values are shown in column 5 of this table. Mass normalization of the maximum

specific optical density shows a dramatic difference in the smoke hazard as compared to the maximum specific optical density alone as shown by column 2 and

if materials of grossly different properties such as thickness, density, surface

porosity, etc. are to be intercompared, then mass loss must be taken into

account.

The standard non-flaming test utilizes a heat flux of 2.5 watts/cm^ which

is sufficient to prevent ignition of a-cellulose, as well as most other materials.

In order to study the effect of radiant heat flux on the specific optical density,

a new heat source was designed for higher temperatures. Results, using the new

heat source for 0,030-inch thick a-cellulose and 1/4-inch thick Douglas fir are shown in figures 6 and 7, respectively. Data are plotted for a heat flux range

of approximately 1.2 to 7.5 watts/cm^. In both cases, the maximum specific

optical density appears to go through a maximum just prior to ignition. In the

flaming region, Dj^ values are generally significantly reduced below those for

most of the non-flaming region. The effect of heat flux is particularly important if 2.5 watts/cm^ is on the part of the specific optical density curve that

is changing rapidly for any given material. When this is the case it will be

difficult to obtain reproducible results, especially during interlaboratory

evaluation of the smoke test method using that material. Thus, the effect of

heat flux appears to be sufficiently important to warrant more study.

(2)

107
1

1

1

1 1

' 1

o/

1% LIGHT TRANSMITT,INC£_

- if V

J

J/

/ x> ^ ^^^^^

1 ,

1 1 , 1

"1 \ 1 1 r

B\010J

J L

SAMPLE THICKNESS, inchm

6 8 10 12 FOAM DENSITY , poondl/ft'

Figure 1. Effect of thickness

on maximum specific optical

density for relatively thick

materials

.

Figure 3. Effect of material

density on maximum specific

optical density.

> 500

o 300 —

0.06 0 08 0 10 0.12 SAMPLE THICtaCSS. inches Figure 2. Effect of thickness

on maximum specific optical

density for relatively thin

materials

.

CO

TIME, minutes

Figure 4. Specific optical

density and sample weight

loss curves for polyurethane foam (TDI-type)

.

108
Figure 5, Mass-optical density

for several materials.

0 5 10 15 20

TIME, minutes

Figure 6. Effect of energy flux

on maximum corrected specific

optical density of a-cellulose

(SRM 1006)

0 2 4 6 S ENERGY FLLIX , watt8/cm^

Figure 7. Effect of energy flux

on maximum corrected specific

optical density of Douglas fir.

109
Table 1. Maximum Specific Optical Density

and Mass Loss For Several Materials

m (corrected)

Material Dm

m % mass m/A

(corrected) ( ^in) loss ( r^Tn ^ / rrm ^

\ ^^iii / y ill / DIT r\vj 1 Y^\7T ^V^l ^v* t ^ xy V xny xcxixDX xcic plasticized. . . . 350 2. 30 63.7 6,430

877 6 . 75 14.1 5,490

IX/X XJCloc=Ll XXcAXJJXc

polyurethane . . . 198 1, 78 97. 2 4,690

173 2.19 87.6 3,340

UlJU.v^Xcto J- XI. marine plywood . . 533 7. 73 47.0 2,910

620 9. 39 53. 7 2,790

436 8. 38 53.9 2,230

Polymethylmethacrylate . . . 724 20. 00 40.4 1,530

Polyvinylchloride. . 177 6.40 53.1 1,170

In the normal operation of the NBS smoke density chamber, ventilation is

prohibited in order to measure the maximum smoke density. In a. fire, however,

some ventilation may be present, and for this reason Gaskill [4] has used a modified NBS-type chamber to determine the effect of ventilation on a wide

variety of materials. His results show that most materials exhibit a significant

monotonic decrease in with ventilation rates in the non-flaming mode. For

flaming combustion the effect of ventilation is not as clear cut. The availability of oxygen in the smoke box measurements was shown by Gross et al [1]

to have a very significant effect on both the maximum specific optical density

and on the time required to achieve D . m

Results reported by Birky and Manka [5] from the full-scale corridor fires

involving floor covering materials show rather extensive oxygen depletion related

to limited ventilation rates. The effects of this oxygen depletion on the rate \ of smoke formation and maximum amounts of smoke produced, has not been studied

in any detail. All of this work suggests that another area of fruitful research ' for the elucidation of the potential smoke hazard involves studying the effect

of oxygen on the optical density in the smoke chamber.

2.3. Task 5 - Analysis of Smoke | 2.3.1. Chemical Characterization of Smoke

The chemical analysis of smoke is a very complex problem due to the large

number of possible products involved. Birky and Manka [5] collected the smoke

from an acrylic carpet fire and followed the methodology used by Hueper et al

[6] as shown in figure 8. The wet chemical separation was followed by gas

chromatographic separation of the neutral fraction which contains the aliphatic,

aromatic, and oxygenated fraction. The chromatographic separation and the

temperature programming used to obtain the separation is shown in figure 9. The individual peaks in the chromatogram have not been . identified

.

110
CRUDE SAMPLE

1

EXTRACT WITH ETHER, EXTRACT WITH WATER,

FILTER

WATER-ETHER

INSOLUBLES

ETHER LAYER 1 SOLUTION 1

ETHER LAYER 2

EXTRACT WITH HYDROCHLORIC ACID t

SOLUTION 2

EVAPORATE WATER

«

WATER SOLUBLES

EXTRACT WITH

SODIUM HYDROXIDE t

SOLUTION 4 T SATURATE WITH CARBON DIOXIDE, EXTRACT WITH ETHER

ETHER LAYER 5 SOLUTION 5

EVAPORATE

ETHER

ACIDIFY EXTRACT WITH ETHER

WEAK ACID GROUP

STRONG ACID GROUP

ETHER LAYER 4 IEVAPORATE

ETHER

NEUTRAL 1

GROUP

CHROMATOGRAPHY

ADD SODIUM HYDROXIDE EXTRACT WITH ETHER I

ETHER LAYER 3 I

EVAPORATE

ETHER

SOLUTION 3

1

AMPHOTERIC

COMPOUNDS

[DISCARD]

BASIC GROUP

ISOOCTANE

ELUATE BENZENE

ELUATE

CHLOROFORMMETHANOL

ELUATE

EVAPORATE 1

EVAPORATE 1 EVAPORATE • f

ALIPHATIC AROMATIC DXYGENATED

FRACTION FRACTION FRACTION

Figure 8. Schematic for separation of smoke into compound classes.

Ill
For the complex pyrolysis and combustion product analysis, a computer has ' been interfaced to a mass spectrometer-gas chromatograph for the qualitative \ and quantitative analysis. A computerized library of mass spectra is being ! developed for the combustion products of materials under study. The computer I search format used a search routine based on the given number of mass spectral ! peaks and their relative abundance. Details of this system and preliminary ' results have been reported by Einhorn and Seader [7] . The results of the chro-j matographic separation of the products of combustion of a flexible urethane ' foam and the computer reconstruct are shown in figures 10 and 11. The computer! identification of the eluted compounds from the chromatograph based on the

fragmentation pattern of the mass spectrometer is still in progress. i

2.4. Task 3 - Animal Exposure Chamber and

Task 8 - The Influence of Volatile Degradation Products of

Combustion on the Survival Responses of the Rat

The physiological and behavioral effects of carbon monoxide (CO) intoxi- ' cation are being studied. Figures 12 and 13 illustrate a rat in the CO exposud

chamber. Previous research has defined five levels of CO intoxication:

(1) Ataxia; (2) Loss of Survival Response; (3) Loss of Postural Tonus;

' (4) State of Anoxic Shock - Complete motor collapse and failure to respond to direct electrical stimulation while respiratory rate is reduced from 1/2 - 1/3 ' normal; (5) Death.

Animals recovering from Level 4 have been found to exhibit damage to the

Schwann cell, which produces and maintains the myelin sheath around the nerve

fiber. Demyelination of the sheath is associated with decreased nerve conducti( velocity. Conduction velocity of nerve impulses in the ventral caudal nerve

is presently being investigated during and following CO intoxication. An

example of pilot data of this work is shown in figure 14.

A behavioral conditioning chamber is shown in figure 15. The sling j restrainer allows movement of the limbs and leg flexion conditioning. A

flashing light, conditioned stimulus (CS) , is presented and a leg flexion with-'

in a 2-5 second CS-US (unconditioned stimulus) interval opens the electric ; shock (US) circuit allowing the subject to avoid shock so long as a flexed ' position is maintained. The percent of trials on which the response is made

during the CS-US interval provides one index of avoidance while the duration of'

the sustained flexed position is a measure of both avoidance and vigilance.

' Following conditioning training, the subjects are exposed to 1,100-1,500 ppm

' of CO (in air). Carboxyhemoglobin, avoidance, and response vigilance are moniI

tored during the development of intoxication. I

2.4.1. Effect of Carbon Monoxide on Skeletal Muscle '

The toxicity of carbon monoxide has been considered to be primarily a i function of its ability to combine with hemoglobin and displace oxygen. As a | consequence of the decreased oxygen-carrying capacity of the blood, tissue \ hypoxia and dysfunction results. Further studies have indicated that carbon

monoxide reacts with other heme compounds such as myoglobin and components of i the cytochrome system. Under conditions existing during states of hypoxia and j owing to the different shapes of the equilibrium curves, the affinity of carbon I monoxide for certain tissue pigments such as myoglobin may actually exceed its , affinity for hemoglobin. These findings suggest that a direct effect of carbon [ monoxide upon tissue function may be of theoretical as well as practical importance. In addition, the poorly understood late-onset sequelae of carbon monoxid

intoxication manifested primarily as disordered nervous system function may

result from more permanent carbon monoxide binding by intracellular components.

112
Figure 9. Gas chromatographic

separation of smoke

components

TEMPERATURE, 'C —r—'

1 .

1 . r- S 10 12 14 TIME, min.

Figure 11. Computer reconstructed

chromatograph combustion of

f lexible-urethane foam - 1180°C.

SCAN NUMBER

113
V 26.8) (TAIL TEMPERATURE- "O

(273^

(27 3)

0«-H—I—I—I—I—I—f—I—l-H—I—I—I H

1 3 5 7 9 11 13 15 17 19 21 2^ 25 24 4 MINUTES

TIME HOURS

Figure 12. Animal exposure chamber. Figure 14, Nerve conduction velocity

of ventral caudal nerve of rat aftei

60-minute exposure to 435 ppm carbon

monoxide

.

114
Based on these considerations, experiments have been conducted to determine

muscle fatique in vitro during exposure to three conditions: (1) hypoxia;

(2) carbon monoxide and hypoxia; (3) carbon monoxide and oxygen. Six gracilis

anterior muscles were studied for each condition. The presence of carbon monoxij ide in the medium was found to enhance the development of fatique (fig. 16) . At the end of the experimental period of hypoxia, tension had fallen to 24 percent

of control level, while in the presence of hypoxia and carbon monoxide, tension

fell to 7 percent of control level. During recovery, ten minutes after the

experimental period, muscles exposed to hypoxia alone had recovered to 88 percent

of control tension, while those exposed to hypoxia and carbon monoxide had

recovered to only 39 percent of control tension (all differences significant

at p <.01). In addition, tension did not ultimately recover to the level

achieved by the muscles recovering from hypoxia alone. A decrement in tension

I and more profound delay in recovery also occurred when the muscle was exposed

j to the 8 0 percent oxygen - 20 percent carbon monoxide mixture (fig. 17) . Tetanic

' stimulation resulted in complete loss of tension and prolongation of recovery

time when the muscle was exposed to hypoxia and carbon monoxide.

TIME(MINUTES) TIME (MINUTES)

Figure 16. Enhancement of muscle

fatigue by carbon monoxide.

Figure 17. Enhancement of muscle

fatigue by carbon monoxide-oxygen.
There is evidence for a direct effect of carbon monoxide upon twitch tension This effect is most likely mediated by the influence of the gas upon' intracellular oxygen transport, but other sites of action may also exist The' impaired recovery of tension in the presence of carbon monoxide suggests the displacement of oxygen from intracellular binding sites by carbon monoxide The duration of carbon monoxide binding and the ability of oxygen to displace carbon monoxide apparently determines the persistence of long-term effects and perhaps even the appearance of the sequelae of intoxication. The greater impairment of recovery when the muscle is exposed to both carbon monoxide and oxygen suggests a greater binding of carbon monoxide when the muscle continues to metabolize in the presence of carbon monoxide. Exposure of binding sites ' during active oxygen transport may facilitate carbon monoxide binding. Factors influencing tissue binding of carbon monoxide are being investigated.

2.5. Task 11 - Neuropathological Studies Related to Fire Exposure

Studies on rats indicate that as a result of CO intoxication, behavior

can become disorganized sufficiently to prevent an appropriate survival respons even though the animal is physically capable of responding. At low levels of ambient CO this implies that survival may be impossible for a period of time before intoxication to levels which immobilize the animal exist.

cardiac

Loss of motor response occurs before obvious impairment of respiratory or though

function from an impairment in peripheral nerve conduction. Sus e?en fully paralyzed, if rescued, survival is likely.

o,,,,/?"?:^^^"* occur

sequelae manifested as neurological deficits are most likely to following more profound intoxication. Level 4. At this level CO bind inn by tissue would seem to be an important factor ' ^^^^^i^g

The results of neuropathological studies on CO-exposed rats suaaest th^ concept Of Schwann cell or neuronal injury with a dying bick"europl^hy ra^he than a segmental demyelmating neuropathy. Figures 18-21 are electron microaTrlL''^"^°^"T''' carbon

°' °" --ts exposed to LeJel 4 dSrinc monoxide exposure.

^v^x uuj.xm

I

r.^v-^ Figure 18 shows a longitudinal section through a myelinated axon of the

?t shoSi T"""^ °f ^ ^^^^^ exposure to CO to the anoxia shock level. It shows a normal myelin sheath but a marked increase in neurofilaments and the

appearance of double walled structures.

^ncimenrs ana tne <

A cross section through the ventral caudal nerve of a rat, 30 days after exposure to CO to the anoxic shock level, can be seen in figur^ 19. Myell^atel

Sea?h °Lm;^v''fH"^"K°'''"r"^' "'^^ ^-"i-g - Reduplicated myelS^

shapes."

""^y^^^^^t^^ f^b^^s show increased microtubules and abnormal fiber J

^ A cross section through a myelinated axon and Schwann cell cytoplasm of the ventral caudal nerve of a rat, 30 days after exposure to CO to the anoxic shock

thlck;n^.' T increased neurofilaments and a rough

thickened myelin sheath. The most striking change is the marked dilation of the endoplasmic reticulum of the Schwann cell.

^^^^on or tne

3 ra/^^n""^ a rat,

^^^""^ ^ longitudinal section through the ventral caudal nerve of 30 days after exposure to CO to the anoxic shock level. It shows a toSirrS k"""" ""^l^ an outpouching of axoplasm containing vesicular structure toward the basement membrane of the Schwann cell at the node of Ranvier

116
Figure 18. Myelinated axon with

increased neurofilaments.

Figure 20. Schwann cell with

dilated endoplasmic reticulum.
2.6. Task 12 - Large-Scale Fire Tests

In order to obtain information on the behavior of floor coverings (mainly

carpeting) under conditions simulating a real building fire, full-scale experiments are being carried out in a corridor-experimental facility at the National

Bureau of Standards. The primary objective of the program is to determine the

nature of the hazard associated with carpeting and under-layment in a fire

situation, and the relationship or non-relationship of this hazard to current

test methods and small-scale laboratory measurements. One of the ultimate goal

is the development of a test method that takes into account the hazard associat

with combustion gases and smoke. The results of this program are also being

interfaced with the toxicological program at The University of Utah.

The experiments with fully developed fires are being conducted in the

facility described previously [8] . The corridor is instrumented at numerous

points for the measurement of temperature, heat flux, air flow, smoke density,

and gas sampling.

Two gas sampling techniques were used to assess the corridor atmosphere

during the tests: (1) continuous measurement of CO, and CO 2 concentrations

and (2) grab samples collected in pre-evacuated 2-liter flasks for laboratory

analyses. In addition, continuous measurements of HCl were made on a vinyl

sheet flooring material. A technique is also under development for continuous

measurements of hydrogen cyanide in fires involving polymeric materials that

contain nitrogen (nylon, acrylic, wool, and urethane)

.

Figures 22 and 23 show the continuous carbon monoxide, carbon dioxide and

oxygen data for a wool and a nylon floor covering material. These curves are quite typical of the rates of oxygen depletion and rates of increase of carbon

dioxide and carbon monoxide that occurred in most of the corridor fires, indicating a ventilation-controlled fire. In most of the experiments a "gas phase

flashover" occurred. In all of the experiments the carbon dioxide curves approximate mirror images of the oxygen concentration as one would expect and

the carbon monoxide appeared during extensive oxygen depletion.

The results of the continuous hydrogen chloride measurements in experiment

346 are shown in figure 24. The areas burned and charred, as determined by

temperature measurements and estimated by visual observations during the test, are overlaid on this graph. The correlation, although not exact, is fairly

good.

The grab samples were used for more extensive analysis of the corridor

atmosphere. Most of the analysis was performed with a dispersive infrared

spectrophotometer using a 1-meter cell. A gas chromatograph was used in some

of the later analysis. Analysis was made for CO, CO2/ CH^, C2H^, and C2H2

which were, by far, the predominant gases. Hydrogen cyanide also appeared in some of the sample analysis, and in these cases, the amount of HCN was estimated. The results of these measurements are shown in table 2.

2.6.1. Discussion of Corridor Results

An effort to assess the hazard due to oxygen depletion, carbon monoxide,

carbon dioxide, and high concentrations of smoke in the absence of special tox

gases such as HCN is shown in table 3. A word of caution is in order in inter

pretation of the table since large concentration gradients exist in the corrido

at any given time, with the highest concentrations of CO and CO2 and the lowes

O2 concentration being near the ceiling where the sampling tube was positioned

Consequently, the hazard of CO or O2 depletion in terms of survival times may

the worst cases. However, the relative hazard of CO vs. O2 depletion should be

valid. The picture is further complicated by extremely high concentrations of

118
Figure 22. Results of continuous

CO, » and measurement from

wool carpet.

OXYGEN CARBON DIOXIDE CARBON MONOXIDE

500 FLASH 1000 TIME, sec. 1500

24 TEST No. 343

GAS DATA • OXYGEN

O CARBON DIOXIDE A CARBON MONOXIDE

1000 1500

TIME, sec.

Figure 23. Results of continuous

CO, CO2 and measurement from

nylon carpet.

Figure 24. Results of continuous

HCl measurement.

TIME, sec

119
Table 2. Corridor Gas Sample Analysis

Est. Flash

rjxp • riatenax Time ( sec) % % Time

M.

ff Position* CH^ ^2^4 ^2^2 (ppm). ( sec

)

334 Acrylic Pad (A-1) 395 b 3 5 0.6 0.2 0.2 0

Z U a

3J cD n 7 u . z flU.J7. n

335 Oak Varnish 445 a 4 14 2 1 0.2 0 444

485 b 2 18 0.1 + + 0 590 a

o X 01X u . z flu . z9 u J z9 flu 600 b 2 10 0.1 + + 0 780 c 0. 5 6 <0.1 0 0 0 1,020

J J / rit- xyxXL* V" -!-^ 360 a

/I X^1 9 VJ . 0 nu . z9 flU 1 . X 49fl 4 z u 450 b 3 13 0.4 0.3 0.1 + 465 c 3 12 0.3 0.1 0.1 1,000

r cL 71 X 0 0 7 . J J50\^ t h

QO X J X1 fl . u flU fi

. D J fifin , u u u

t c 8 17 2.8 0. 6 0.3 2,000

O O 17 I3XcillJS. 615 a X \J \j flu

fi7 R Ku X u flu u 740 c _|_ n u u u

340 Acrylic Pad (A-2) 327 a 1 10 0 0 0 0 360 a X z X . u flU.J fl 4 X1 fififi

, u u u

o y u D u . t U U.J X1 flflfl

, u u u 345 C

/I XD U.J U

flU 1

. X J flu flu

341 Wool Pad (W-1) 454 a 0. 5 10 0 0 0 0 460

530 a o X Q

0 flu . R0 flU.J^ 4 flu flu

DDI. iJ X / u . 0 flU.J flU.JT J flu flu 568 C X D U.J flU.JT flU 1 . X z9 flu flu

342 Nylon Pad 285 a 2 15 0.2 0.3 0. 06 100 300

308 a J X D U.J nU . 7/

fl fl <=; U . U J z9flfl u u

J

"5 Z9 Z9 D

O X 0 u . 4 flu • z9 flU 1

• X X1 flfl u u 338 C

c0 X D X . 4 U . D flU.J^ D flU flU

343 Wool (W-1) 237 a 2 14 0.1 0.3 0. 05 + 297 a £. X D U . X flu . z9 flu . fl7 u / f) KFIN • X/n • hD

oJ X4 u • 0 flU • D flU , A4 u 327 c X 0 u • u . 0 u . 0 J flu flu

344 Nomex 360 a 1 12 0 0 0 0 740

457 a

1X 10 0

flu f)u n 470 b 1X 8 0 f) u n 490 C 0. 3 5 0 0 0 0

345 Wool (W-1) 308 a 0. 3 9 + + 0 0 490 a 4 14 0.6 0.3 0.2 1,000 N.D.

500 b 4 15 0.2 + 0.2 500

510 C 3 10 0.3 + + 1,000

* Position: a = 8 ft, b = 7 ft, c = 4 ft from floor.

Indicates trace amount.

tTimes are unknown.

N.D. - No Data

120
Table 2. Corridor Gas Sample Analysis (cont'd)

Est. Flash

Exp. Material Time (secl^ % % % % % HCN Time

# Position CO CO 2 C2H4 ^2^2 (ppm) (sec)

346 Vinyl Asbestos Sheet 497 a U.J 7 u u

f\u u None

765 b 0.3 8 0 0 0 0 805 c 0.2 5 0 0 0 0

347 Polypropylene 390 a 2 13 0.1 + + 50 840

900 a ±o X • D U . _) U . 1

1 Ann 1 , UUU

910 b 4 17 1.5 0.5 0.1 2,000

935 c 4 17 0.6 0.2 0. 06 2,500

348 Nylon Pad 450 a 5 15 1.5 0.6 0.6 + 440

570 a 4 18 0.8 0.3 0.4 2,000

585 b 4 18 0.4 0.3 0.1 3,000

605 c 3 14 0.2 0.2 0.1 500

349 Oak 635 a 8 18 2.8 0.9 0.7 0 630

755 a 2 12 0.4 + + 0 760 b 3 9 0.7 0.5 0.1 0 765 c 2 8 0.5 0.2 + 0 *Position: a = 8 ft, b = 7 ft, c = 4 ft from floor.

•"Indicates trace amount.

tTimes are unknown.

N.D. - No Data

Table 3. Comparison of 0~-Depletion , CO and Smoke Hazard

Time (min) of Time (min)

Experiment % O2 % CO2 O2/CO2 Appearance of 80%

No. of CO at Attenuation

(at time of 0.5% CO) .5% Level From Smoke

330 10.5 5 2.1 2.5 2 333 17. 5 6 2.9 6 3.6 - 4.1

334 13. 7 5.5 2.5 6 3.4

335 10.5 10.5 1 5.4 3 - 6 336 11 * 9.5 1.2 6.2 4.0 - 5.0

337 N.D. 5.5 N.D. 6 2.0 - 4.0

338 11 6.0 1.8 5.2 1.5 - 4.5

341 13 N.D. N.D. 6.5 4 343 9 12.5 .72 5.3 3.0 - 3.2

344 9 11 .81 4.2 2.8

345 10. 5 9.0 1.2 6.3 3 347 12.5 7.0 1.8 6.2 N .D. 348 18.5 7.0 2.6 4.0 N .D. 349 10.5+ 7.6 1.4 5. 0 N .D. Average 12.1 7.8 1.7 5.2 2.9 - 4.2

*N.D. - No Data.

"•"Taken from exhaust window.

121
smoke. The time required to reach 80 percent optical attenuation as measured

across the corridor was chosen as a level of untenable smoke from the point of

view of escape and inhalation. Based on data from Jin [9] for smoke of various

types, with 2 0 percent transmission one would be able to see an illuminated sign

at a distance of about 15 feet. However, studies using human subjects indicate

that the limitation on visibility is not due to light obscuration of exit signs,

but due to lachrymal effects of irritating products on the eyes. This limitation frequently occurred prior to serious obscuration [10] . An additional

consideration is inhalation toxicity that is not defined well enough to put into

quantitative terms.

With these conditions in mind, table 3 was constructed. The second and

third coliimns in this table give the percent of oxygen and carbon dioxide when

the carbon monoxide level reached the 0.50 percent level. In column 6 of the

table, the first number is the time (minutes) required after ignition for a 7-

foot meter to reach 8 0 percent optical attenuation and the second number is the

time for 80 percent attenuation for a 4-foot meter. The time required to give

80 percent visual attenuation is comparable to the time to produce a CO concen- tration of 0.50 percent. The time to collapse from (0.50 percent) CO can be

calculated from the relationship of Minchin [11]

t , , , . , = 4. 5% T % CO collapse (mm)

For the 0.50 percent level one gets about nine minutes. In all the experiments

except two, the O2 level (column 2) at the time for 0.50 percent CO is low enough

that muscular coordination for skilled movement (12-15 percent) is lost and

faulty judgment occurs at the 10 to 14 percent oxygen level [12] . The high

carbon dioxide levels further complicate the picture by increasing the respiratory rate. In addition, the hydrogen cyanide is also present in many of the

fires. Based only on the carbon monoxide concentrations, one has something

less than 10 minutes to leave the corridor, however, the smoke level by the

5-minute mark is quite severe and perhaps beyond the survival limit except very

close to the floor. This data would suggest that the smoke hazard is as serious

as the carbon monoxide and combining this with the Very rapid oxygen depletion

suggests a survival time less than either hazard alone would indicate.

The conclusions regarding oxygen depletion would tend to support the con- clusions of Kingman et al [13] . The hazard that exists in another room con- nected to the corridor may not be oxygen depletion, but CO, which is the con- clusion of Robinson et al [14] in rooms above the fire although the results

from the corridor do not suggest that one hazard is predominant.

Another hazard that contributes to the observed rapid flame spread rate

in the corridor experiments, that has not been considered, is the "gas phase

flash-over" phenomena. As indicated in table 2 there were significant concen- trations of methane, ethylene, and acetylene in the grab samples. The table

further indicates that the total hydrocarbon content of these samples was high

at the time when "flash-over" occurred.

The "flash-over" phenomena seen in the corridor experiments consists of

the build-up of a combustible gas mixture, and is not the same phenomena that

results when a material, such as furniture, bursts into flames when exposed to

a large radiant energy source in another area of a room. While it is true that

radiant energy contributed to the build-up of a combustible gas mixture, the

rapid flame spread down the corridor appears to be a gas phase phenomenon.

A further verification of this was obtained in experiments 348 and 349

using a combustible gas detector located at the exit window of the corridor.

In experiment 348 the detector showed a rapid rise at 450 seconds and in experiment 349 a rapid rise was recorded at 640 seconds, correlating well with observed

"flash-over" times of 440 and 630 seconds, respectively.

122
since the purpose of the full-scale floor covering fire experiments was to

determine the nature of the hazard and the relevance of present test methods,

the obvious question is: what insights and guidance can be obtained from these

experiments for developing a laboratory scale or model for testing purposes that

is realistic and assesses the hazard? If a laboratory measurement of the amount

of smoke produced from a floor covering material such as in the NBS smoke box

is to be realistic, then the dependence or independence of smoke quantities of

oxygen availability must be determined in the light of the extensive oxygen

depletion found in the corridor. Perhaps smoldering combustion and flaming

combustion conditions will actually be the boundary extremes that represent the

maximum and minimum smoke-producing conditions and it will not be necessary to

control the atmosphere in the smoke box. However, this can only be determined

by actual experimentation, as indicated earlier.

In relation to the toxicological hazard, it may also be necessary to

determine the relative toxicity of the type of products produced in an oxygen

limited atmosphere in addition to the increased CO production. One might raise

the question, is the production of HCN, HCl and other toxic products enhanced

in the limited oxygen atmosphere? And, is there a correlation between smoke

production and carbon monoxide?

The hazard associated with the rapid "gas phase flash-over" must also be

investigated. It may well be that the rapid flame spread reported in fires

involving floor covering materials is actually a gas phase phenomenon resulting

from the build-up of products related to the incomplete combustion process due

to the limited availability of oxygen as seen in the corridor experiments and

not just due to radiant energy.

3 . ACKNOWLEDGEMENTS

The authors would like to acknowledge the contributions of Mr. F. D. Hileman, Mrs. E. C. Hare, and Mr. B. D. Buchanan.

4. REFERENCES

[1] Gross, D., Loftus, J. J. and Robertson, A. F., Method for Measuring

Smoke from Burning Material: A Symposium on Fire Test Methods —

Restraint and Smoke 1966, American Society for Testing and Materials,

Philadelphia, Pa. (1967), 166-204.

[2] Hilado, C, Jr., The Effect of Chemical and Physical Factors on Smoke

Evolution from Polymers, J. Fire and Flammability , Vol. 1, 217-238

(July 1970)

[3] Chien, W. P., Seader, J. D.* and Birky, M. M. , Monitoring Weight Loss

in a NBS-Smoke Density Chamber, paper submitted for publication to

Fire Technology.

[4] Gaskill, J. R. , Smoke Development in Polymers During Pyrolysis or Combustion, J. Fire and Flammability, Vol. 1, 183-216 (July 1970)

[5] Birky, M. M. and Manka, M. J., The Use of Room and Corridor Tests in

Predicting Fire Parameters, paper presented at the 1973 Polymer Conference

Series, Fire Prevention and Control - A Major Societal Problem, June 4-9,

1973, The University of Utah, Salt Lake City, unpublished.

[6] Hueper, W. C, Kotin, P., Tabor, E. C. , Payne, W. W. , Falk, H. and

Sawicki, E., Arch. Pathology, Vol. 74, 89 (1962).

123
[7] Einhorn, I. N. and Seader, J. D. , Methods for the Identification of

Products of Combustion of Polymeric Materials — A Computerized Analytical

System, paper presented at the 1973 Polymer Conference Series, Flammability Characteristics of Materials, June 11-15, 1973, The University of

Utah, Salt Lake City, unpublished.

[8] Fung, F., Suchomel, M. and Oglesby, P., Fire Journal, Vol. 67, 41 (1973).

[9] Jin, T. , Visibility Through Fire Smoke, Report of Fire Research

Institute of Japan, Vol. 31, 33 (1971).

[10] Lopez, E. L. , Study of Smoke Emission From Burning Cabin Materials and

the Effect on Visibility in Wide-Bodied Jet Transports, Report No. DOC

FA 72 NA-655 (May 1973).

[11] Minchin, L. T. , Mild Carbon Monoxide Poisoning as an Industrial Hazard,

Ind. Chemist, Vol. 30, 381 (1954).

[12] Bulletin of Research No. 53, Underwriters' Laboratories, Inc., 49.

[13] Kingman, F. E, T. , Coleman, E. H. and Rasbash, D. J., J. of Applied

Chemistry, Vol. 3, 463-468 (1953).

[14] Robinson, M. M. , Wagner, P. E. and Fristrom, R. M. , The Accumulation

of Gases on an Upper Floor During Fire Buildup," APL/JHU (Apr. 1972).

124
NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 411, Fire Safety Research,

Proceedings of a Symposium Held at NBS , Gai thersburg , Md . , August 22, 1973,

(Issued November 1974)

CONTRIBUTION OF INTERIOR FINISH MATERIALS

TO FIRE GROWTH IN A ROOM^

J. B. Fang and D. Gross

National Bureau of Standards, Washington, D.C.

Characterization of the fire environment from the burning of

the combustible contents of wastebaskets , upholstered furniture

and interior finish materials is important for developing rational

tests and establishing design criteria for reduction of fire hazard

in buildings. Some experimental results on the burning characteristics of an upholstered chair, contents of waste receptacles and

wood crib arrays in a well-ventilated room are presented. A procedure has been developed for evaluating the contribution to fire

growth of wall and ceiling panels in a full-scale room corner with

a standardized wood crib duplicating the conditions produced by an incidental fire. Results of full-scale and laboratory tests with

selected interior finish materials on ease of ignition, surface

f lammability , flame penetration and smoke and heat generation

measurements are presented and compared.

Key words: Buildings; fire intensity; flame spread; flames; furnishings; heat release; interior linings; material ignitability

room fires; smoke; upholstery; waste receptacle; wood crib.

1. INTRODUCTION

Interior finish materials on walls, ceilings and floors represent large

exposed areas over which flame may spread, and rapid flame spread is one of the

most frequent contributing factors to residential fire fatalities. An obvious

method of reducing fire losses in buildings is to reduce the possibility of

ignition and spread of a fire. This can be achieved by limitations on the use

of materials with a high contribution to fire growth, confinement of the fire

to the room of its origin with the aid of fire resistant constructions, and

installation of fire detection and/or sprinkler systems for early warning and

control of developing fires. In recent years, the rapidly increasing use of new interior finish materials in building construction introduces building fire

safety problems since some of these newer materials can contribute to the rapid

spread of fire in its early states. Urgently needed is the evaluation of the

contributions made by these materials to the development of a compartment fire

and to establish more meaningful performance criteria of building materials and

constructions

Small-scale laboratory tests can provide a comparative measure of surface

f lammability , flame penetration, heat release and smoke producing properties

which are important from the standpoint of life hazard and property damage.

However, there is little substantiation that the test conditions prevailing in

most laboratory scale experiments simulate real fire environments.

The corner formed by the intersection of a ceiling and two adjacent walls

constitutes a critical configuration for the evaluation of the fire performance

of interior finish materials since fires within a corner represent a severe

fire exposure through an increase of heat and confinement of combustion products

In order to compare flame spread characteristics of various building materials,

corner wall fire tests have been developed to serve as an evaluation tool at

the Forest Products Laboratory [1], Factory Mutual, Underwriters' Laboratories

and other laboratories. Most recently, corner fire tests initiated by small

incidental fire exposure were used to demonstrate residential fire hazards [2]

^This work was supported in part by the U.S. Department of Housing and Urban

Development.

125
This paper presents the results of full-scale corner fire tests conducted

for evaluating the contribution to room fire growth of a variety of interior

finish materials typical of those used in residential dwellings, and a comparison

of these full-scale test results with those obtained by existing laboratory

test methods. Experimental study of the characterization of the environment

produced by typical incidental fires and the development of standardized wood

cribs to simulate various levels of incidential fires are also described.

2, EXPERIMENTAL DETAILS

2.1. Test Compartment

The experiments were conducted in a 2.9 x 3.2 x 2.4 m (9.5 x 10,5 x 7.9 ft)

high burn room with a door measuring 0.9 m (35 in) wide x 2 m (80 in) high in one of the smaller compartment walls. The door remained fully open during the course of the test. The test compartment was constructed of reinforced concrete

and the interior surfaces were lined with 16 mm (5/8 in) thick gypsiam wallboard

finished with a vermiculite gypsum plaster. The whole test compartment was situated within a larger building to permit a wind and draft-free condition.

2.2. Instrumentation

The temperatures of the plume gas along the flame axis above the upholstered

chair or wood crib,, of the surfaces of interior finish materials, and of the

product gas and air at selected locations inside the test compartment were measured by bare-beaded Chromel-Alumel thermocouples of 0.56 mm diameter wire

Commercial radiometers and heat flux meters mounted on the walls, ceiling and

floor were used to determine the rates of heat transfer from test fires to the

enclosure walls. Stainless steel pitot tubes fastened horizontally at the doorway of the burn room in conjunction with variable reluctance pressure transducers

were used to acquire information on horizontal air velocity profiles.

Continuous measurements of the weight loss rate of the burning furniture were made with a weighing device consisting of a platform mounted on four

supporting beams which carried electrical resistance strain gauges. The burning

rate of a standardized wood crib was measured directly by a 227 kg (500 lbs)

capacity strain gauge load cell supporting a weighing platform.

The concentration of the smoke generated by the test specimen was determined

by obscuration measurements using light beam and photocell set-ups. Smoke

measurements were made at three locations — one horizontal measurement at 1.5 m

(5 ft) height within the compartment, and two vertical measurements^ one at the

center of the room, and the other at the doorway.

Continuous measurements of carbon monoxide, carbon dioxide and oxygen con- centrations inside the room and at the upper edge of the doorway were conducted

using infrared analyzers.

For each experiment, 110 channels of the output signals from thermocouples,

radiometers, heat flux meters, load cell, pitot tubes, gas analyzers, and smoke

meters were directly recorded on a magnetic tape at 10 second intervals using

a high speed digital acquisition system.

2.3. Test Specimens

The chairs and sofas obtained from a local used furniture outlet were of

different weights and constructions, and had undergone various degrees of use

and wear. In addition to wooden frames, the upholstery fabrics utilized for

the test furniture included cotton, nylon and rayon. The cushion pads were

made of cotton batting, latex rubber and polyurethane foam.

126
The standardized wood cribs were developed to duplicate the fire environment produced by typical incidental fires. A large crib, measuring 560 x 560

X 550 mm (22 x 22 x 21-3/4 in) high and weighing approximately 33 kg (72 lbs),

constructed of cross piles of 34 pieces of nominal 51 x 102 x 560 mm (2 x 4 x 22

in) long hemlock sticks was used to simulate a moderate intensity furniture

fire. A smaller 360 x 360 x 300 mm (14 x 14 x 12 in) high crib weighing about

6.3 kg (14 lbs) constructed by stacking 28 pieces of nominal 51 x 51 x 360 mm

(2 X 2 X 14 in) long sticks was used to represent an incidental fire of shorter

duration and lower flame height. The large crib consisted of nine layers,

except two sticks for the bottom layer, each containing four sticks with a 6 3.5 mm (2.5 in) stick spacing. The small sized crib had six four-stick and two

two-stick layers, with successive layers laid cross-wise. The spacing between

the sticks, except for the bottom two layers, was 51 mm (2 in). The moisture

content of the wood cribs was found to be approximately 9 percent.

Seven types of interior lining materials and bare asbestos-cement board were selected to represent a wide range of flame spread and smoke levels. The

surface treatments and nominal thickness of these interior finish materials are summarized in table 1.

Table 1. Results of Small-Scale Tests on Ease of Ignition, Surface Flame Spread, Heat Release and Smoke Generation

Material

Ease of

Ignition

Flame Spread Heat Release Smoke

Index

Rate

(W/cm2)

Total

(J/cm2)

Dm

Name Thickness

(mm)

Ignition

Time

(sec)

ASTM E84

Tunnel

ASTM E162

Radiant

Panel Flamipg

Non- Flaming

Gypsum board

finished with

2 coats of

latex paint

12.7 00 24 8 7.4 540 33 51

Vinyl covered

Evpsum board

12.7 CO 33 23 5.9 580 54 85

Particle

board,

unfinished

15.9 153 153 118 20.6 13400 398 570

Douglas fir

plywood,

pref inished

6.4 105 103 135 15.8 4580 146 445

Lauan plywood, un- finished

4.4 95 167 141 16.5 2720 50 310

Melamine

finished

tempered

hardboard

4.0 151 226 117 52.4 6100 89 465

Acoustic

Tile (fiber

board base)

12.7 74 101 60 12.2 5840 113 261

127
3. TEST PROCEDURE

For each chair test, a methenamine "timed burning" tablet placed at the corner between the chair back and the seat cushion was used as the ignition

source.

In the corner fire tests, three 1.2 x 2.4 m (4x8 ft) full sized interior

finish test panels were used to cover a corner of the test compartment. Two

test panels were separately mounted on steel studs at a spacing of 89 mm (3.5

in) from the two adjacent walls in the room corner, and one test panel was attached to the ceiling on wood joists to form an "L" shape along the walls.

An air space of approximately 19 mm (3/4 in) was left between the panel and

enclosure ceiling. A standardized small wood crib was erected in the corner at

254 mm (10 in) measured above the floor and 51 mm (2 in) away from the walls.

For the wood crib and corner test the fire was initiated by application of

an open flame to ignite 8 0 ml of 95 percent ethyl alcohol in a steel pan placed

beneath the crib. All recording instruments were turned on simultaneously at

ignition of the alcohol. The height of visible crib flame, the ignition of the

test materials and the progress of flames up the walls and onto the ceiling were noted and recorded. Data for corner fire tests were usually collected for

an 8 minute period. For non-combustible materials slightly longer periods were

observed.

4. TEST RESULTS

The time history of the temperatures of product gases at 25 mm (1 in)

below the ceiling above the fires involving an upholstered chair, plasticized

milk cartons in a waste receptacle and two standardized wood cribs is shown in

figure 1. The ASTM E 119 standard temperature-time curve was also plotted in

the same figure for comparison. As shown in the figure, the gas temperatures

due to a waste receptacle fire, which was obtained by burning 2 . 8 kg (6.2 lbs)

of plasticized paper milk cartons in a 0.12 m^ (31 gallons) capacity steel

trash container, increased faster than either chair or crib fires as the result

of the high rate of heat release. The chair, waste receptacle and crib fires

had a relatively short period of peak temperature whereas the standard ASTM E

119 curve increased continuously.

Figure 2 shows a comparison plot of the level of heat flux incident on a vertical surface measured at a height of 730 mm above the floor in the vicinity

of test fires and a fully developed room fire. The latter curve has been

calculated from the ASTM E 119 standard temperature- time curve with the assumption that the fire filling a 2.4 m (8 ft) high room can be considered as a blackbody emitter of infinite width compared with the dimension of a receiver

located at a spacing of 610 mm (24 in) and 730 mm (29 in) above the floor

level. The waste receptacle fire had a relatively rapid start and shorter

duration in comparison to furniture and crib fires as indicated in the figure.

The typical furniture and crib fires had a relatively short period of peak heat

output whereas the heat flux level for a fully developed room fire increase

rapidly and continuously.

A plot of heat flux measured incident on a vertical plane 730 mm above the

floor at the peak fire condition against dimensionless Reparation distance on log-log coordinates is given in figure 3. The dimensionless separation distance

is equal to the distance between the axis of the fire source and the receiver

divided by the radius of the source. It can be seen that the rate of heat

output from the burning chairs varied widely and was dependent upon the type of

padding materials, design and construction of the furniture item involved. As

shown in the figure, the data from many different tests plot as straight lines o equal slope, and the resultant heat flux levels created by the developed wood

arrays lay within those produced by incidental (furniture) fires.

128
129
2 3 4

SEPARATION DISTANCE

RADIUS OF FIRE SOURCE

Figure 3. Relationship between incident heat flux at various

locations and dimensionless separation distance.

Typical curves showing the calculated rate of heat release as a function

of time for fires involving upholstered chairs, standardized wood cribs and

plasticized milk cartons in a waste receptacle are presented in figure 4. The

heat release rate was calculated from the rate of weight loss multiplied by the

calorific value of the combustible involved divided by the projected area of

the combustible item on the floor. When the total projected floor area of the

item involved is accounted for, the maximiom rate of heat output and the total

heat energy released per unit area by different types of fires was estimated to

be approximately 120 kW (6,830 Btu/min) and 2.7 x 10** J/cm^ (2, 370 Btu/ft^),

respectively, for the waste receptacle fire, 320 kW and 15 x lO'* J/cm^ for the

fire with the large crib, 130 kW and 6.1 x lO'* J/cm^ for the furniture fire of

moderate intensity. As shown in the figure, the wood arrays can be designed to

duplicate fire buildup conditions for particular furniture items since the heat

output pattern of standardized crib fires approximately match those of furniture fires. The levels of heat flux to the surroundings from both furniture

and crib fires can be expected to be on the same order as the rate of heat

transfer from a freely burning fire and was found to be directly proportional

to the heat release rate [3]

.

130
TEST NO. 60^

5, j

Chair

35 Waste Receptacle

TIME (minute)

Figure 4. Comparison of calculated rate of heat release for

furniture, wood crib and waste receptacle fires.

Summary data from full-scale corner tests on ease of ignition, surface

flame spread, flame penetration, room flashover, smoke generation and emerging

flames for various combinations of seven types of interior finishes as wall and

ceiling covering materials are presented in table 2. It can be noted that the

times taken for ignition of combustible wall materials varied from 2 minutes

for acoustic tile to approximately 3.5 minutes for vinyl covered gypsum board.

I Except for tests with painted gypsum wallboard and vinyl covered gypsum

I board, which burned only to a distance of 0.5 m (20 in) the elapsed times for

j flames travelling up the wall to reach the ceiling after ignition were found to

range from 20 to 50 seconds. The data also show that the rate of flame spread

along the ceiling was significantly lower than that across the wall surface and

strongly dependent upon the nature of the materials and constructions utilized

for the walls. As expected, these walls played a major role through generation

and transport of heat energy required for the spread of ceiling flames.

Most finish materials tested, except particle board and gypsum board, were penetrated by flames at times varying from 5 to 10 minutes. It is obvious that

the flame- through time is dependent on the fire properties and thickness of the

I material involved.
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132
In order to observe the time to full involvement of room contents in fires

three indicator specimens including ordinary newsprint, 0.19 mm (0.0075 in)

thick white cotton cloth and 6.4 mm (1/4 in) thick fir plywood commonly found in

dwellings were placed within the test compartment. These indicators, each

consisting of two 120 x 152 mm (4 x 6 in) sheets formed in a "L" shape, were

placed at two locations; near one of the room corners and at the room center,

respectively, at heights of 500 mm (20 in) and 100 mm (4 in) above the floor.

Visual observation indicated that these indicators were ignited at different

times depending on material type and location. In general the newsprint was

the easiest and the plywood the hardest to ignite. It was found that the time

to reach an average room temperature of 400°C (752°F) generally fell within the

range of time for ignition of these indicators and was considered a critical

point to the survival of occupants and property. As shown in table 2, the

elapsed times to attain this critical temperature are widely varied from about

5 minutes to infinity. The possibility of complete involvement of combustible

room contents was found to be significantly dependent upon the nature, amount

and construction of the lining materials involved.

The average maximum concentrations of smoke produced by painted gypsum

board, vinyl covered gypsum board and asbestos-cement board walls under fire,

condition were on the order of 0.25, 0.31 and 0.11 Optical Density/m (O.D./m)^

respectively. For all tests with interior linings the walls covered with fir

plywood panels generally produced the highest levels of smoke concentration and

the gypsum wallboard finished with latex paint the least. The time taken to

reach peak smoke levels was found to range from 4 to 8 minutes after initiation

of the test.

Flames emerging from door and window openings are conducive to the spread

of fires to the corridor or upper stories in the building. The elapsed time

until the flames emerged from the doorway was obtained from visual observation

and found to vary widely from approximately 5 minutes to infinity depending

upon material type and construction.

A comparison plot of average temperature versus time of air within the

compartment for fires involving several different types of finish materials is

shown in figure 5. Data on average room temperature from a blank test using

6.4 mm (1/4 in) thick asbestos-cement boards as wall and ceiling covering

materials were also plotted in the same figure for comparison. As shown in the

figure, the maximum temperature increased from 80°C to about 450°C for fir

plywood walls, and 650°C for fir plywood walls and acoustic tile ceiling when

combustible finish materials were substituted for gypsum boards. It was also

found that the complete involvement of combustible contents frequently occurred

immediately after rapid rise in the room air temperature.

Figure 6 shows the variation with time of the level of heat flux incident

at a horizontal plane located 225 mm (9 in) above the floor directly beneath

the center of the ceiling specimen. In these tests, portions of the two adjacent walls and the ceiling of a room corner were fitted with various types of

building boards, and the combustible load consisted of the standardized small

wood crib. The heat flux level increased more rapidly with a combustible

ceiling than with a painted gypsxam board ceiling and remained at a high level

until most of the linings had burned away. Combustible finishes for walls and

ceiling would result in a peak flux density of about ? W/cm^ at the floor

within 7 minutes after start of the test. This downward heat transfer rate

would cause ignition of typical combustible contents in dwellings.

5. COMPARISON WITH SMALL-SCALE TEST METHODS

In order to determine if useful correlation exists between laboratory and

full-scale methods the results obtained by corner fire tests on seven types of

interior finish materials were compared with those obtained by the existing

standard test procedures.

133
800

Figure 5, Effect of material

combination of wall and

ceiling linings on average room air temperature.

Legends on curves indicate

wall/ceiling material.

400

200

FIR/ACOUSTIC / TILE '

FIR/GYPSUM BD.

GYPSUM BD./GYPSUM BD.

ASBESTOS CEMENT BD./ASBESTOS CEMENT BD.

I |_ TIME (min.)

2.5

2.0

1.5

1.0

0.5

FIR/ACOUSTIi TILE

FIR /GYPSUM BO.

\

ASBESTOS CEMENT BD/ YPSUM BD./GYPSUM BD. ASBESTOS CEMENT BD.

Figure 6. Effect of type of

wall and ceiling materials

on downward heat flux incident near the floor. Legends

on curves indicate wall/

ceiling material.

TIME (min.)

134
5.1. Ease of Ignition

A small-scale ease of ignition test by flame impingement, recently developed at NBS [4] , was used to measure the ignition times of these lining materials

in sustained burning. The results of small-scale laboratory tests on ease of

ignition along with surface flame spread, heat release rate and smoke producing

properties for each interior finish material are summarized in table 1. Figure

7 shows the laboratory test results compared to the ignition times obtained

from the full-scale corner fire test. Excluding painted and vinyl covered

gypsum boards, which did not have sustained ignition during laboratory tests,

the correlation between the corner test and laboratory method for the lining

materials examined was generally fair.

I 5.2. Flame Spread

j The laboratory test methods used for evaluation of surface burning charV acteristics of these finish materials include the ASTM E84 tunnel and E162

i radiant panel standard methods. These tests are separately described in the

1 ASTM literature [5,6]. Typical curves showing the distance traveled by the

|; flame, which is normalized with total distance available for flame spread, as a

I function of time for two materials evaluated for surface flammability by corner

I and laboratory fire tests are presented in figure 8. For corner fire tests the

temperature records from thermocouples placed at the surfaces of test specimens were used for determining flame spread rate. Surface temperature in excess of

I a critical value at the test specimen face is considered to indicate the arrival

of the flame front. The value for this critical flame propagation temperature

was determined from both the observed ignition time and the surface temperature

records and found to be approximately 370 °C (698°F) for most lining materials

examined. As expected, materials had different induction periods, varying

linear rates of flame spread, and different distances traveled by the flames

, since the material properties, location and fire exposure level had a pronounced

f effect on material behavior. As shown in figure 8, the materials in the corner

] test generally had longer ignition times and higher rates of flame spread than

determined by the tunnel and radiant panel tests. This is attributed to lower

intensity of fire exposure to the materials in the early stage of the corner

test and increasingly severe heating of the materials through the exposing

flames and upward hot gas current in the development stage. A significant

phenomenon can be seen from the curve showing the spread of flames over the

wall surface in that the upper wall situated near the edge formed by the wall

and the ceiling usually ignited before flaming covered the entire wall. The

flame front would also progress down the surface for some distance. This is

primarily due to enhancement of energy transfer to the upper wall by increased

I forced convection through cross-flow of hot gas impinging on the corner and

flaring out radially beneath the ceiling.

) 5.3. Heat Release Rate

The heat release calorimeter being developed at NBS [7] was used to measure

the rates of heat release of these lining materials. The peak one minute

j average heat release rate values obtained as the result of this laboratory test

are plotted in figure 9 against the maximum average room temperatures from

i corner fire tests. As the intense heat produced by the fires within a room is

I considered a serious danger for safe evacuation, the average temperature of

j room air is a measure of both the magnitude and the duration of the heat released.

! 5.4. Smoke Generation

The smoke density chamber test method [8] was used to evaluate the smoke

producing properties of these interior finish materials. Figure 10 shows the

comparison between the maximum specific optical density obtained from smoke

I density chamber test measurements under both flaming and non-flaming conditions,

I 135
200-

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<

150

100

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A

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50„

MATERIAL TYPE

Acoustic Tile Lauan Plywood

Fir Plywood

Particle Board Melomine/Hardboard

Painted Gypsum Board Vinyl/Gypsum Board

T

_L I I

Figure 7. Comparison of the

results of ease of ignition

measurements by laboratory

and corner fire tests.

Arrow on top of the symbol

indicates no sustained

ignition in laboratory test.

50 100 150 200

IGNITION TIME (sec)-CORNER TEST

250

1.0

CO

UJO

CO

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I-COo

0.8-

0.6-

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TESTS

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Bd. Melamine/

Hordboord -0-"

war —A—

celling

I O

100 -6200 550 650

Figure 8. Flame spread data obtained by ASTM E-84 Tunnel, E-162 Radiant

Panel and Corner Fire Tests.

136
SMOKE DENSITY CHAMBER

NONFLAMING FLAMING WALL MATERIAL 0 • GYPSUM BD. PARTICLE BO, V T MELAMINE / HARD80ARD A A VINYL /GYPSUM BD. 0

FIR PLYWOOD

LAUAN PLYWOOD o • ACOUSTIC TILE

WITH ACOUSTIC TILE /

CEILING

NON-FLAMING

FLAMING

Figure 10. Comparison of the

results of accumulated smoke

measurement by smoke density

chamber and maximum observed

smoke level in the room during a corner fire test.

0.4 0.6 DCORNER (O.D./m)

0.8 1.0

137
and vertical photometric smoke measurements during the full-scale corner fire

tests. It should be noted that the chamber method measures the maximum accu- mulated smoke level under a closed system condition whereas the full-scale test

is a measure of the smoke accumulation in a room with an open doorway through

which a significant portion of the smoke leaves. The latter measurement

obviously depends upon the degree of ventilation and the intensity of the room

fire, and should not be considered unique. Despite this, correlation is fair

as indicated in the figure,

6. CONCLUSIONS

A reproducible fire with a standardized wood crib was found to be capable

of duplicating the essential features such as: temperature, heat flux and heat

output levels, and the size and shape of the flame of typical well ventilated

incidental fires.

The presence of combustible interior finish materials has a significant

influence on fire growth in buildings by shortening the time to reach full

involvement of combustible contents, enhancement of rapid spread of fire, and

increased generation of heat and smoke.

The potential fire hazard of interior finish materials can be measured by

use of a corner fire test in which the materials to be evaluated are installed

as the walls and ceiling in a typical full-size room. This arrangement permits

separate measurement of ease of ignition, flame spread rate, flame penetration,

and smoke producing properties during a single test.

7 . ACKNOWLEDGMENTS

The authors wish to thank Mr. C. F. Veirtz, Mr. T. F. Maher and Mr. B. E. Ramey for their assistance in the experimental work and Mr. J. W. Raines for

his help in modifying the computer program to process the outputs of the data

acquisition system. This work was supported in part by the United States

Department of Housing and Urban Development.

8 . REFERENCES

[1] Surface Flammability as Determined by the FPL 8-Foot Tunnel Method, U.S.D.A.

Forest Products Laboratory Report 2257 (1962) .

[2] Williamson, R. B. and Baron, F. M. , A Corner Fire Test to Simulate

Residential Fires, J. Fire and Flammability, Vol. 5, 99-105 (1973).

[3] Fang, J. B. , Measurement of the Behavior of Incidental Fires in a Compartment (to be published)

.

[4] Parker, W. J., The Development of a Test for Ease of Ignition by Flame

Impingement (to be published)

.

[5] Standard Method of Test for Surface Burning Characteristics of Building

Materials, ASTM E84-70, American Society for Testing and Materials,

Philadelphia, Pennsylvania (1970).

[6] Surface Flammability of Materials Using a Radiant Heat Source, ASTM E162-67,

American Society for Testing and Materials, Philadelphia, Pennsylvania

(1968).

[7] Parker, W. J. and Long, M. E., Development of a Heat Release Rate Calorimeter at NBS, ASTM STP 502, American Society for Testing and Materials

(1972) .

[8] Lee, T. G., Inter laboratory Evaluation of the Smoke Density Chamber Test

Method, Nat. Bur. Stand. (U.S.), Tech. Note 708, Appendix II (Dec. 1971).

138
NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 411, Fire Safety Research,

Proceedings of a Symposium Held at NBS , Gaithersburg , Md . , August 22, 1973,

(Issued November 1974)

A 30 X 30 X 32 inch enclosure was constructed to study the

fire build-up process in a room. Conductive and radiative heat

flux, temperature, air velocity, fuel supply rate, and oxygen

concentration were measured. In order to relate the phenomena

observed in the small enclosure to that in a full size room, the

possibility of small-scale modeling with combustible walls was

examined. This was done on a preliminary basis by comparing

the results of some corner fire tests conducted both in the model

and in a full size room. A preliminary examination was also made

of the effect of the fuel flow rate and the location of the burner

on the temperature and oxygen profiles in the enclosure. Since

the ceiling temperature closely follows the upper air temperature

the latter is a suitable measure of the degree of fire build-up

in the room. Any analysis of the fire build-up process must

account for this temperature.

Key words: Fire tests; flashover; heat release rate; scale

models; thermal radiation.

Proper selection of wall, ceiling, and room furnishing materials can prevent the build-up of a serious fire in a room. Unfortunately, the fire

performance of any material is difficult to assess on the basis of a single

test or even from a series of laboratory tests. The fire behavior of a material must be evaluated along with the room and its furnishings so that the

combination will have a low probability of full involvement in the event of an accidental ignition. Prerequisite to this approach, it is necessary to develop

an understanding of the growth and spread of fire in the room. Instrumented compartment fires on both full and reduced scales can provide

such information. However, smaller fires are more economical and manageable,

and can be used to explore variables in a more expeditious and systematic

manner. Reduced scale modeling methods for simulating the fire build-up in

compartments have been developed at the Illinois Institute of Technology Research

Institute (IITRI)[1] and at the Factory Mutual Research Corporation (FMRC) [2]

,

however, their potential usefulness for predicting the performance of real room

fires has not been thoroughly explored.

The IITRI technique requires a constant ratio of heat release rate to the

volumetric rate of air inflow in order to maintain the same temperature distribution in the enclosure. The volumetric rate of air inflow, V, is proportional to wh^/^ [1] where w is the width of the doorway and h is its height. If

the ratios of the width of the doorway to the width of the room (W) and the

height of the doorway to the height of the room (H) are kept invariant, then

The heat release rate, q, should be proportional to the floor area,

W^, where the width of the room is equal to its depth. Thus, if

FIRE BUILD-UP IN REDUCED SIZE ENCLOSURES

W. J. Parker and B. T. Lee

National Bureau of Standards, Washington, D.C.

1. INTRODUCTION

^1 ^2 — = — then

^31 ^2

3/2 3/2 2/3

2 2 (1)

W.1W,2

Sponsored in part by U.S. Navy.

139
where (VI ^Z"^-^) is taken to be the scale factor. Subscripts 1 and 2 refer to the

full-scale and the model rooms, respectively. With the scaling of height by the

/W2\5/3

3/2 power, the area of the wall, WH, scales as r;— | whereas the area of the

2 V^i)

floor scales as I — 1 . If it is assumed that the mass burning rate of a com- bustible wall is proportional to its area, then its heat release rate is proportional to w5/3 which violates the requirement that the heat release rate be

proportional to w2 . To summarize: when the horizontal dimensions of the prototype compartment are reduced by a scale factor, the IITRI modeling criteria

require that the vertical dimension should be proportional to the scale factor

raised to the two-thirds power and the rate of heat release be proportional to

the square of the scale factor. Using this technique for non-combustible walls,

IITRI found that the radiation flux, concentration, gas temperatures, and

wall surface temperatures measured at several locations within the compartment

were in fair agreement for both model and 10 x 10 x 8 foot room fires for model

sizes as small as 1/8 scale. However, as seen above, the technique breaks down 1 for combustible walls. I

I FMRC approached the scaling problem from dimensional analysis considerations.

Their findings indicate that the temperatures and gas compositions in a room

scale reasonably well for geometrically similar enclosures where the heat release

rates are proportional to the 5/2 power of the scale factor. This method assures that the ceilings of the model and the prototype are at geometrically similar

points of the convection column generated by the flames. If it is again assumed

that the burning rate of a combustible wall is proportional to its area, then it

is proportional to for geometric scaling, whereas, the burning rate required

by the FMRC modeling is proportional to w5/2. This scaling method also fails

to account for the contribution of combustible walls.

The objectives of the present study are to determine the degree to which

models can be used to scale the fire development in rooms with combustible

linings, and to develop a procedure for predicting the potential for full fire

involvement of a room based on measurements of the fire and thermal properties

of the materials comprising the linings and the furnishings. This work is only

in its initial stages.

This paper describes some tests conducted in accordance with the IITRI

scaling rules in a small enclosure which approximates a quarter scale model of

a 9.5 x 10.5 X 7.9 foot burnout room. It compares the results of some corner

tests in the model with those obtained from tests conducted in the full-scale

room. It includes a preliminary examination of the effect of the gas flow rate

and the location of the burner on the oxygen and temperature profiles in the

small enclosure.

2 . EXPERIMENTAL

2.1. Procedure

The model has a 30 x 30 inch floor area, a ceiling height of 32 inches

and a 6.8 X 27.4 inch doorway opening in the middle of one wall. The model

enclosure consists of a steel shell with a non-combustible interior lining of one inch thick asbestos insulation board (36 lbs/ft-^) (AIB) . Several preliminary experiments with a gas burner at the center of the

floor were conducted to assist in the selection, development and placement of

adequate instrumentation to characterize the fire behavior in the model as well

as to establish an overall energy balance. The latter not only contributes to an understanding of the fire behavior, but also checks on the accuracy of the

measured data.

140
The effect of burner location and elevation on the air temperature, oxygen

depletion, and thermal radiation was examined in the enclosure using AIB walls,

ceiling, and floor.

The model was then used to approximately simulate three prototype

corner fire tests [3] conducted in a 9.5 x 10.5 x 7.9 foot high room with a 35

X 80 inch doorway near one corner. The model was originally designed to be a quarter scale for a 10 x 10 x 7 foot compartment using the IITRI scaling rules.

Thus, the height of the room and the doorway dimensions were not scaled exactly

for these preliminary tests. All large-scale tests used a burning wood crib

in one corner of the room. The corner was formed by two 4x8 foot panels of

the sample wall material running from floor to ceiling where it joined the 4 x

8 foot ceiling panel that was to be tested. Three combinations of wall and

ceiling materials of interest used in the full-scale tests were: (1) 1/2 inch

thick gypsum board walls and ceiling, (2) 4.4 mm unfinished lauan plywood

paneling and gypsiam board ceiling and (3) 5/8 inch particle board walls and

gypsum board ceiling. One test of the first combination using AIB as a substitute material for the gypsum board, two tests of the second and one of the

particle board-gypsum board combination were done on the reduced scale. Panels

1 X 2.8 feet and 1x2 feet were used respectively for the walls and ceiling.

The thickness of the linings was not scaled down as the modeling uses real

time. In each of the model tests a gas burner was used with a rate of heat

release equal to 1/16 of that of the wood crib in the full-scale tests. The

natural gas was released through a 3 x 3 inch porous plate whose area was 1/16

that of the top surface of the wood crib. This provided essentially the same

gas flow rate per unit area in the two cases and thus, eliminated the forced

jet effect which results when the gas is delivered over a small area. The gas

flow rate was adjusted during the test to correspond to the changing burning

rate of the wood crib. The air for combustion of the gas was drawn in through

the doorway by natural convection. A heat release of 7,200 Btu was assumed for

each pound of wood consumed in the burning crib. This was based on oak with a moisture content of 13 percent.

2.2. Instrumentation

Measurements made to characterize the fire environment included heat flux

into the walls and ceiling; radiation incident on the floor; air, ceiling and

wall temperatures; air temperature and inflow velocity distributions in the

doorway, and the concentration of oxygen at the top of the doorway.

Heat transfer to the ceiling and walls was determined using seven simple

heat flux sensors consisting of 2 x 2 inch sections cut out from the ceiling or

wall. Thermocouples were inserted inside each section — one located near the

exposed surface and another positioned a short distance behind. The temperature difference between the thermocouples was calibrated in terms of heat flux

using commercial heat flux meters. The plugs were then put back into their

original locations and the seams were caulked over. Since the sensor was made

of the same material as the wall, the heat conducted through the sensor was the same as that through the wall. Conventional heat flux sensors would not give

the same readings due to their different surface absorptivities and thermal

properties. The thermal radiation incident on the lower portion of the room

was monitored with a water cooled radiometer. Indicator panels of cotton

fabric and plywood were placed at the center of the floor and at one back

corner of the compartment; their ignition signaled the occurrence of flashover.

The term, flashover, as used in this paper, means the condition in which the

radiant flux levels are high enough to ignite essentially all of the combustibles in the room. It is synonomous with the phrase, "full room involvement".

All temperatures and air inflow velocities were measured with AW6 No. 30

wire chromel-aliamel unshielded thermocouples and a hot-wire anemometer, respectively. An oxygen cell was used to measure the oxygen concentration of the

outflowing air by continuous sampling through a copper tube. No precautions

were taken against reactions in the tube.

141
3. RESULTS AND DISCUSSION

3.1. Preliminary Tests

In the preliminary tests with the model enclosure the overall energy

balance at 5 minutes, after introduction of a constant rate of heat input,

showed the following:

1. Energy in, Btu/min

a. gas burner - 800

2. Energy out, Btu/min

a. conduction through the hot upper walls and ceiling - 190

b. thermal radiation absorbed by the surface area below the hot and

cold fluid interface, and the thermal radiation carried out

through the doorway - 160

c. heat absorbed by the air and carried out the doorway - 450

The hot and cold fluid interface is the horizontal plane where the temperature rise is half of its value in the upper part of the room. In this case it was located at about 1/2 of the distance from the floor to the top of the

doorway. At five minutes, the temperature distribution across the ceiling

surface varied from 215 °C at the center to about 195 °C near the edge. This

finding, along with the data taken across the room at 4.5 inches below the

ceiling, indicated a fairly uniform horizontal distribution of temperature.

The temperatures gradually increased with elevation -above the mid-height of the

doorway up to 1 inch below the ceiling. The ceiling temperature was about 50°C

lower than the highest air temperature. Below the mid-height of the doorway

the temperatures fell off rapidly with decreasing elevation.

The energy balance indicated that by 5 minutes the heat radiated by the

hot upper surfaces of the compartment was nearly as much as the heat conducted

into them. It took approximately 30 minutes for the model compartment to reach

its equilibrium temperature, at which time the heat radiated from the upper

interior surfaces of the room was considerably more than the heat conducted

through them.

Following these preliminary tests with a gas burner on the center of the

floor, the model enclosure was used to simulate some full-scale corner fire

tests [3] . Whereas the prototype fires had a burning crib in one corner of the

room, the model used a gas burner in the same location. Although differences

existed between the prototype and the model enclosure, which was designed to

scale down a compartment, they were not major. The model doorway area was 30

percent too small and was not offset towards one corner as in the prototype for

proper scaling. In the first full-scale test gypsum board was used while the

model used AIB for its interior lining.

Figure 1 shows that the average temperature inside the model chamber was about the same as for the full-scale test. However, the inflow velocities in

the model were about 30 percent higher than the scaled-(iown velocities in the

prototype as shown in figure 2, so that the volumetric air flow was similar.

The scale factor which was taken to be equal to the square root of the ratio of

the doorway heights was 0.58. In figures 1 and 3 both temperature profiles at

the doorway and within the chamber showed that the hot and cold fluid interface

was lower for the model enclosure. This was also apparent from IITRI's data [1]

.

3.2. Comparison With Full-Scale Corner Tests

142
.70 I

1 1 1 1 1 1 r X

Figure 2. Velocity profile in

doorway at 10 minutes for full

and quarter scale enclosures.

The velocity data for the

full-scale test is scaled

down by the square root of

the ratio of the doorway

heights

AIR INFLOW VELOCITY (ft/min)

143
0 100 200

AIR TEMPERATURE (X)

Figure 3. Temperature profile at doorway at 10 minutes

for full and quarter scale enclosures.

Since the burning rate of a combustible wall is proportional to (W„/W, ) ^'^"^

,

2 whereas proper scaling requires that it be proportional to (W„/W, ) , the ratio

1/3 of the fuel produced to the fuel needed is proportional to {Vlj^/W^) • This

amounts to a 59 percent excess fuel for a quarter scale model. This non-scaling

of the wall lining is evident from figure 4, where the air temperature variation

with distance down from the center of the ceiling is shown for enclosures having

lauan walls and gypsum board ceilings. Except for a sudden upturn in temperature

close to the ceiling on the model, the temperature profiles are in fair agreement

at 3 minutes which is before active lauan burning. At 5 minutes the temperature

increase attributed to the burning of the lauan was about 70 percent greater

in the model than it was in the burnout room. After 10 minutes, when the active

burning of the wood panels was completed, the temperature was again similar in

the two tests.

The up-swings in temperature near the ceiling at 3 and 10 minutes, which

were also present with particle board, may have been due to the relatively

higher flames which flash partway across the ceiling in the case of the model.

This type of behavior was absent in the full-scale fire except at locations

close to the corner. Data taken from the full-scale test indicated that a sudden temperature rise near the ceiling occurred at a position two feet away

from each of the adjacent walls where the crib was located.

The data in figure 4 indicates that the hot and cold fluid interface

within the chamber is lower in the model. A comparison of the flow out of the

doorway for enclosures having non-combustible and combustible linings (figs 3 and 5) shows that the height of this interface at the doorway is also lower for

the model and is not strongly dependent on the heat release in the enclosure.

These results are in agreement with the theoretical finding by Thomas and

Heselden [4] that the vertical position of the interface is a weak function of

heat input.

144
I-X

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0

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0

FULL l/4th

SCALE SCALE

3min 3min

A 5min A 5min • iOmin O IOmin

200

4- 400 600 800

Figure 4. Air temperature

profile in center of

compartment for enclosure

having lauan plywood

walls and gypsum board

ceiling. Wall panels

start burning after 3 minutes

TEMPERATURE (°C)

Figure 5. Temperature profile

in doorway at 5 minutes for

enclosures having lauan plywood walls and gypsiim board

ceiling.

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MODEL

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AIR TEMPERATURE (''C)

800

145
Although data were not available for a direct comparison for the same wall

material, the radiant heat flux incident on the floor was similar for the model

with the lauan paneling and the full-scale room with the particle board walls

as shown in figure 6. The level of this flux is the main criterion for flash- over or full room involvement.

Tables 1 and 2 summarize some of the visual observations on the model and

prototype tests. The ignition times for the combustible linings are in good

agreement for the model and the full-scale fires. The pairs of ignition times

indicate the times at which the panel on each side of the corner ignited.

Ignition times of the cloth indicator panels for flashover were between 5 and 9 minutes for the particle board walls. Flashover did not occur for the fullscale lauan test and for only one of the model lauan tests. There was flame

out of the doorway for both full-scale and model for the particle board, but

only for the model in the case of lauan.

The fire behavior for lauan and particle board walls were approximately

similar up to 5 minutes, after which only the heat release of the particle

board continued to increase due to its larger thickness.

3.0-1 1 1 1 1 1 1 1 1 1 r o

^ 2.5- 1/4 Scale enclosure Full scale enclosure having

' having lauan walls and particle board walls and

2 gypsum board ceiling gypsum board ceiling

01 23456789 10 II TIME (min)

Figure 6. Radiant flux to floor for two enclosure fires.

146
Table 1. Visual Observations for Enclosures Having Lauan Plywood Walls

Test Size

Ignition

Times for

Adjacent

Walls

(sec)

Flashover

Indicator

Panels

t j.ame— i ip

Height

Above Floor

(% Ceiling

Height)

Flame Out

Doorway

(sec)

Other Observations

Full-Scale 150

15U

All cloth and

wood panels at floor center,

scorched during the 660

sec test

30% at 30 sec . lUV/o at 180 sec.

none Strong hot flow

through top 1/3 of

doorway at 300 sec.

Small-Scale 90 150No ignitions

Cloth at corner

turning brown

at 360 sec. Wood panels at corner and at floor center smoking at 420 sec.

25% at 30 sec. 100%

at 165 sec.

315 Strong hot flow

through top 1/3 of

doorway and weak

flow out down to 1/2

of doorway at 360

sec

Small-Scale 95 Cloth at corner ignited at 343

sec.

25% at 30

sec. 100%

at 165 sec.

280 Same as previous

small—scale test.

Table 2, Visual Observations for Enclosures Having Particle Board Walls

Test Size

Ignition

Times for

Adjacent

Walls

(sec)

Flashover

Indicator

Panels

Flame-Tip

Height

Above Floor

(% Celling

Height)

Flame Out

Doorway

(sec)

Other Observations

Full-Scale

No. 407

140

140

Cloth at floor center ignited

at 323 sec. Cloth and wood

at room corner ignited at 455

sec. Vtood at floor center ignited at 456

sec.

50 at 60 sec

75 at 120 sec 435 Strong hot flow

through top 1/3 of

doorway at 360 sec.

Full-Scale

No. 411

155

160

Cloth and wood

at corner ignited at 315

sec. Cloth at floor center ignited at 412

sec. Wood at center ignited

at 415 sec.

60 at 60 sec

65 at 120 sec

342 Strong hot flow

through top 1/4 of

doorway at 420 sec and through top 1/3

at 450 sec.

SmallScale

147

147 All panelssmoking at 360

sec. Cloth at corner ignited

at 480 sec. Cloth at floor

ignited at 493

sec

60 at 60 sec 100 at 120 sec 228 Strong hot flow

through top 1/3 of

doorway at 360 sec.

147
3.3. Effect of Flame Height and Location

The effects of burner location, height, and flow rate on the temperature

and oxygen concentrations are shown in table 3 and demonstrated graphically in

figures 7 and 8. Figure 9 shows the location of the burner in the enclosure.

Table 3 indicates the flame height, the ceiling temperature, maximum air

temperature, maximum oxygen depletion, air inflow rate, and lowest elevation at

which a decrease in oxygen concentration is detectable. The air inflow rate is | calculated from the oxygen depletion and the gas supply rate. Observations of ' the air flow using smoke tracers and suspended materials in the outgoing gas , stream indicated a high velocity of the exhaust over the range of elevations at j which the drop in oxygen concentration was significant. Smoke tracers also

' indicated that through the zone between the mid-height of the doorway and the ' oxygen depleted air there was a mild outflow of intermediate temperature air i warmed by contact with the radiantly heated floor and lower walls. The pattern i emerging from these observations is sketched in figure 10. In this case the

burner is located at floor level adjacent to the center of the rear wall of the

enclosure. Air enters the lower half of the doorway and is pulled downward

toward the burner where it then moves upward through the flame or the region

immediately adjacent to it. It ascends into zone C and thence moves horizontally

out of the upper part of the doorway at high velocity. Reduced oxygen concen- trations and high temperatures are restricted to this zone. Part of the air in

the lower part of the enclosure is warmed by the radiantly heated surfaces,

rises through the stagnant air region on either side of the doorway to zone B and then travels horizontally out of the doorway at low velocity. The dashed

lines in figure 10 indicate 3 dimensional movement outside of the main flow

field. Smoke tracers at the doorway within an inch of plane AB exhibit random

changes in flow direction. The effect of increasing the flame height with the same gas flow rate is to raise the transition plane EC. This results in a decreased inflow velocity and thus, a higher upper air temperature. The flame

height is increased by moving the fuel source close to the wall where burning

can take place on only one side of the fuel stream. It can be increased still

further by locating the source in a corner. Thus, even the proximity of a couch to a non-combustible wall could influence the fire build-up potential

of the room. Increasing the gas flow rate without changing the flame height

increases the air temperature without affecting the height of the transition

plane or the air inflow significantly.

Table 3. Effects of Changing Burner Location and Gas Flow Rate

Elevation

Lowest

Elevation

Approx

.

Flame

Height Maximum Temperature

Test Location

of Burner

Surface

(in)

Flow

Rate

(CFM)

O2 Depletion

Maximum

(percent)

Air

Inf low

(CFM)

of O2 Depletion

(in)

Above

Floor

(in)

Upper

Air

CC) _

Ceiling

(°C)

A(°c)

1 Center 3 0.37 5 74 17 11 180 140 40

2 Rear Wall 3 0.37 8 46 21 18 240 190 50

3 Corner 3 0.37 12 31 23 29 265 215 50

4 Corner 11 0.37 19 20 25 Flames

impinge

on ceiling

320 250 70

5 Corner 11 0.68 33 21 25 Flames

impinge

on ceiling

450 410 40

148
UJX

o

o

u.o

z

o

I-o

<

-rt>--^ rCenter of room

Against rear wall

In corner D Elevated In corner A Elevated in corner

with high flow rate

Vertical temperature

s in the model for difburn locations and gas

Ltes. See figure 9 for

)n of burner with

: to floor plan.

0 100 200 300 400 500 600

TEMPERATURE('C)

I-X

o

UJX

a:o

o

o

o

O

<

U.

.U-^i /. —cr'

-6c

o Center of room

X Against rear wall

• In corner —Elevated in corner ^ Elevated in corner

with high flow rate

4- 4- 4- 4- 0.04 0.08 0.12 0.16 0.20 0.24 0.28 0.32

FRACTION OF OXYGEN DEPLETED

Figure 8. Vertical oxygen depletion profiles in the model for

different burner locations and gas flow rates. See figure 9 for position of burner with respect to floor plan.

149
3,4,5

THERMOCOUPLES

RADIOMETER

Figure 9. Burner locations in model for data in figures 7 and 8.

I nnni 1)1) 1)1 111)111 iiiiini))!)) Ill niiiiiiiiinninn)i))iimii))))iinni))h

FLAME

mnniiuuiiuiiuuTiliiuiunuiinluiniuiuiiiiiuTilTfunndiiiiiiuiuVi

Figure 10. Idealized air flow pattern in an enclosure with the burner on the

floor adjacent to center of rear surface. Dashed lines indicate flow in

regions at either side of the main flow field.

150
3.4. Determination of Fire Build-up Potential

The critical factor in establishing whether flashover conditions occur is

the achievement of a critical irradiance for spontaneous ignition of materials

in the lower part of the room. This irradiance is about 2W/cm in the case of

cellulosic materials. For large areas, such as carpets, it is only necessary

to exceed the critical flux for piloted ignition since the concentration of

pyrolysis products at that exposure level could be high enough some distance

from the source to be ignited by flames already present in the room. Assuming

a radiation shape factor of 1/2, the ceiling would have to radiate 4W/cm2 which

corresponds to a temperature of 650°C for a black surface and 700°C for one with

a total emissivity of 0.9 which is typical of non-metallic materials in this

temperature range. Note in figure 7 that with the AIB ceiling the temperature

drop between the upper air and the ceiling was about 50°C at equilibrium regardless of the flame height, location, and gas flow rate. This suggests a critical

upper air temperature of about 730 °C to induce flashover after fairly long times.

As seen in the last section, the locations, horizontal as well as vertical,

along with the burning rates of the combustibles, control the height of the

transition plane EC which to a large extent determines the rate of air inflow

for fixed doorway dimensions. The rate of air inflow, the burning rates of the

combustibles, and the heat losses determine the air temperature. All three

must be capable of estimation in order to build a prediction model for fire

build-up. The effect of the burning rate on the elevation of the transition

plane is through its effect on the flame height. The burning rate itself depends

on the material and its temperature and radiation environment.

In the case of the gas burner the heating time can be extended as long as necessary to attain the maximum air temperature and thus, the maximxam radiant

flux. In the case of combustible contents the initial fire may be burned out

before the wall and ceiling lining materials reach a sufficient radiating

temperature to induce flashover. The rate of temperature rise of the surfaces

of the walls and ceiling depends on the products of their thermal conductivity,

heat capacity, and density (KpC) . If the KpC is low the surface temperature

rises rapidly and radiation feedback increases the heat release rate of the

burning contents. This enhancement may be enough to induce flashover when it

might not otherwise occur. Thus, the KpC of the lining materials is very

important in predicting the occurrence of flashover.

4. SUMMARY

4.1. Heat Balance

A satisfactory heat balance could be obtained during the fire buildup phase in the model where about 60 percent of the heat produced was carried

out through the doorway with the exhaust gases and the remainder was distributed between heat conduction into the hot upper surfaces and heat radiation by

these surfaces into the lower part of the room or out of the doorway. The

portion radiated away increased with time up to about a half hour when steady

temperatures were attained using a gas burner with a constant fuel flow rate.

4.2. Simulation of Corner Tests

1. The elevation of the interface between the high and low temperature

air layers was lower in the model than it was in the prototype for

both combustible and non-combustible walls. In both cases it was above the mid-height of the doorway. It should be noted that the

doorway height was not scaled exactly.

151
2. The air velocities in the model were about 30 percent higher than the

product of the square root of the ratio of the doorway heights and

the measured velocities in the prototype. This may have resulted

from improper scaling of the doorway. At any rate, the volumetric

air flow rates were similar.

3. The upper air and ceiling temperatures in the model were similar to

those in the prototype when non-combustible walls were used.

4. In the case of combustible walls, the temperatures in the model were

higher than those in the prototype. This difference could be

accounted for by the relatively larger combustible area.

5. Radiation fluxes on the floor were roughly similar for combustible

walls. The higher ceiling temperatures in the model were partially

compensated for by a decreased radiation shape factor.

4.3. Flame Height and Location j

i 1. The high temperature air was confined to the region above a horizontal ] transition plane whose elevation was above the mid-height of the door- j way. The air from this region flowed out of the doorway at high , velocity. If a constant gas flow rate was maintained, the height of \ the plane increased with increasing flame height resulting from difj ferent burner locations within the enclosure. As the plane was raised

the air inflow rate decreased and the temperature of the outgoing air j increased.

2. The flame height increased as the constant fuel supply was moved j against a wall or placed in a corner.

j 3. There was a region between the mid-plane of the doorway and the high I temperature region in which warm air heated by contact with the

radiantly heated lower surfaces of the enclosure rose and passed out j of the doorway at low velocity.

j

I

i 4.4. Determination of Fire Build-up Potential j A prediction method for fire build-up potential must be capable of

estimating the ceiling temperature which controls the radiant flux level in ' the lower part of the room. When this level exceeds some critical value, full

[ involvement of the room occurs. This ceiling temperature is dependent on air | temperature which in turn is determined from the heat release rates of the i burning materials in the room, the heat losses, and the air inflow rate.

5. CONCLUSIONS AND RECOMMENDATIONS ! This preliminary work, investigating the usefulness of the quarter scale j model as a tool in the study of fire build-up in full sized rooms, is encour- , aging. However, the scaling rules used by IITRI, which work well for rooms j with inert walls, are not adequate to scale rooms with combustible walls. It

appears advisable to go to geometrical scaling (i.e., keep all dimensions pro- ! portional to the scale factor) in order to keep the heat release rate of the \ walls proportional to the area of the floor. At the same time it would be

necessary to alter the doorway dimensions in order to maintain a constant ratio j' of air inflow to floor area. Because of the importance of the region above the j, doorway it would be desirable to keep the height of the doorway proportional

j to the scale factor and let the width of the doorway vary to provide the proper | air flow. The ratio of heat release rate to volumetric air flow must be kept [ constant to maintain the same temperatures in the model and the prototype. ,

I
Geometrical scaling has the added advantage of keeping the radiation shape

factor constant. If the shape factors and the temperatures are the same, then

the radiation levels which are responsible for flashover can be duplicated in

the model.

The upper air temperature which is close to the ceiling temperature is the

most important indicator of the degree of fire build-up in the room. It was modeled satisfactorily for the corner fire tests using the IITRI scaling criteria up to the time of ignition of the walls. When the walls were burning

the rate of heat release in the model was too high for proper scaling of this

temperature. Although the times to flashover and the radiation levels on the

floor were roughly similar for the model and the prototype and the increase in

air temperature in the model could be estimated in terms of the relatively

greater surface area involved, satisfactory scaling for combustible walls

requires alterations in the scaling criteria.

It has been practical to keep the thickness of the room lining materials

constant between full and quarter scale and thus, maintain real time in the

model.

The upper air temperature was found to depend on the height of the flame

above the floor and the proximity of the flame to the wall, even when both the

walls and ceiling are non-combustible.

6. REFERENCES

[1] Waterman, T. E., Determination of Fire Conditions Supporting Room Flashover, Final Report IITRI Project M6131, DASA Contract No. DA-49-146-XZ475 (Sept. 1966).

[2] Heskestad, G. , Modeling of Enclosure Fires, Fourteenth Symposium (International) on Combustion, The Combustion Institute, 1021-1030 (1972).

[3] Gross, D. and Fang, J. B. , Contribution of Interior Finish to the Growth

of Fire in a Room, Fire Safety Research, Proceedings of a Symposium held

at the National Bureau of Standards, Gaithersburg , Md., Aug. 22, 1973.

[4] Thomas, P. H. , Helselden, A. J, M. and Law, M. , Fully-Developed Compartment Fires - Two Kinds of Behavior, Fire Research Technical Paper No. 18,

October 1967, Fire Research Station, United Kingdom.

153
NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 411, Fire Safety Research

,

Proceedings of a Symposium Held at NBS , Gaithersburg , Md . , August 22, 1973,

(Issued November 1974)

AN ANALYTIC MODEL FOR CALCULATING THE FIRE RESISTANCE

OF SIMPLY SUPPORTED PRESTRESSED AND REINFORCED CONCRETE BEAMS

Lionel A. Issen

National Bureau of Standards, Washington, D.C.

At present the fire resistance of concrete beams is determined

either by running a fire test or by interpolation from existing fire

test data. The second method can only be used if the data are for

beams that are closely similar to the object beam. Other ad hoc

empirical methods are equally limited. To overcome these difficulties an analytic model was developed for the rational analysis of

prestressed and reinforced concrete beams. This model will be

checked against available test data. A computer program based on

the analytic model is being tested and will be used for developing

graphical tools (graphs, nomograms, tables) for estimating the fire

endurance of simply supported prestressed and reinforced concrete

beams

.

Key words: Analytic methods; concrete; creep; elevated temperature;

finite differences; finite elements; fire endurance; fire tests;

isotherms; prestressed concrete; reinforced concrete.; steel.

1. INTRODUCTION

1.1. Requirement For Fire Tests

Structural elements such as beams normally carry a load. During a fire

the materials of which the beam is made degrade; that is, they lose strength,

they soften and flow as the beam is heated. The fire performance rating of a beam is related to the results of a standard fire test [1] during which the

beam is subjected to a prescribed time-temperature exposure representing a fully developed fire.

Major U.S. building codes have fire resistance rating requirements based

on these tests for the structural elements of buildings. These ratings may

depend on the proposed building size, occupancy classification and, in some cases, fire district classification.

These fire tests are relatively expensive ($5,000, plus construction of

the specimen in the test furnace) and in the case of concrete elements there

may be a waiting period of several months while the test unit dries.

To overcome the problems of cost and waiting time, alternative procedures

to the fire test have always appeared attractive. The alternative methods that

are usually considered are interpolation methods, small-scale models and analysis of mathematical models.

1.1.1. Interpolation Methods

In the interpolation method, as applied to estimating the fire resistance

of beams, an effort is made to interpolate between the results of tests on similar beams to provide an estimate of the fire resistance of a particular

beam. This method works best when the particular beam is similar to those

beams comprising the test data. By similar is meant similar shape, material

and load factor.

Experienced individuals can do this reasonably well. The process is not

objective, being dependent on judgement, intuition and experience and therefore

is not suitable for general use.

154
1.1.2. Small-scale Models

j, Small— scale models have long been considered an attractive tool in engiI neering analysis. Their attractiveness lies in the fact that they are usually

smaller, cheaper and easier to test than a prototype; the effects of a wide

range of loading conditions can be studied and a check can be provided for a quick analysis. Small-scale models for fire tests are not feasible at the

present state of furnace and material technology, because the thermal scaling

relationships [2] require that the rate of temperature rise in the furnace be

inversely proportional to the scale of the model. For instance for a 1/2 scale

model the furnace temperature must rise at twice the rate for a test with a full size prototype.

j The scaling relationships are difficult to satisfy exactly since the thermal

I and mechanical properties of materials, including concrete and steel, are not

I linear functions of tempefature, and heat transfer by radiation, convection and

conduction may not be in similitude

1.1.3. Mathematical Models

Analysis of mathematical models is a popular method for estimating or predicting the performance of structures. The use of this method is limited in

the case of thermo-structural analysis of structural elements because both the

thermal and structural properties of concrete and steel (the main structural

materials of interest) are non-linear with temperature and stress level. For

these reasons closed form solutions to either the thermal or the structural

parts of the problem have not been found and, therefore, it is necessary to use numerical methods.

The two methods of numerical analysis that are of interest here are the

I finite difference [3] and the finite element [4] methods.

The finite difference method is as old as the calculus; there is thus a long history of use and experience. In the method, the differential or integral

equation is replaced by a series of algebraic equations which are solved using

algebraic methods. Briefly described, the method divides the region of interest

into a grid (1-, 2- or 3-dimensional) , where the intersections of the grid lines

are called nodes or node points. The values of the process (in this case temperature, stress and strain) are calculated at the nodes by the finite-difference

equations which are comparatively easy to set up and solve. Difficulties arise

if the grid is not regular, if the boundary of the region is other than simple,

or if the material properties change with temperature or time.

The finite element method is quite recent, having been developed as a practical method in the late 1950 's in the aerospace industry. As with finite

differences the differential or integral equation is replaced by a set of algebraic equations. In the method, the physical body is divided mathematically

into a number of elements, hence the name finite element, and the conditions

along the boundaries of adjacent elements are matched up to give the values at

the nodes, or vertices, of the elements (usual shapes are triangles or quadrilaterals for two-dimensional problems) . The finite elements do not have to be

of uniform shape so that irregular boundaries can be closely matched by the

elements and varying temperature and time dependent properties can be easily

incorporated into the equations. For these reasons the finite element method

was selected for the thermal analysis.

155
1,2. Previous Work on Analytic Methods

NBS pioneered in rational analysis of structural fire resistance design.

In the middle 1950 's Robertson and Genensky analyzed transient heat flow in

fire-exposed reinforced concrete beams using a computer analysis^. At the time

the only thermal properties of concrete that were available were for temperatures below 150 °F. Since this work was never published except as an internal

NBS report, it never received the attention it deserved.

Other work^ has been done at the Portland Cement Association (PCA) [5,6,7],

the Technical University in Braunschweig [8] , the National Research Council of

Canada [9,10,11], and at other centers. Gustaferro [12] who was formerly with

PCA has sximmarized, in a set of graphs, existing test data on the fire resistance of beams and slabs. Gustaferro showed great ingenuity in arranging the

available data into a readily useable form. He also included suggestions for

extending the data to beams of different shapes. The graphs are probably best

suited for beam and slab configurations that are similar to the test specimens

and less effective for configurations that are dissimilar to the test specimens.

2. CURRENT WORK AT NBS

2.1. Thermal Analysis

In the fall of 196 8 a copy of the TRUMP [13] thermal analyzer program was acquired from the Lawrence Radiation Laboratory. This program is a large,

general purpose thermal analyzer^ which includes radiation and mass transfer

effects

.

There are several associated programs that may be used with TRUMP in order

to facilitate its use. In particular the user is referred to FED [14] and

TRUMP/XB2. [15]

The program can be run for 1-, 2- or 3-dimensional problems, though the

output format appears to be designed for 1-dimensional analysis. By judicious

numbering of the nodes, the output can be put into a form that will facilitate

interpreting the results of 2- and 3-dimensional analyses. Because of its

general purpose nature, the program may be used for corroborating other programs.

TRUMP was found to be a good general thermal analyzer and the calculated results

compare favorably with those from other similar programs.

The user is advised to obtain the latest version of the program and also

a copy of the current defect list. As with any large computer program, the

defects are uncovered by widespread use of the program. The Lawrence Radiation

Laboratory periodically issues a correction list and these are automatically

incorporated into subsequent issues of the program. There are, of course, other

general purpose thermal analyzers available and the user should examine them in

order to select the one most suited to his needs.

In 1971 the Building Fires and Safety Section of NBS acquired a modified

version of AMG065 [16] , a finite element thermal analyzer. This program was originally developed by Brisbane of the Rohm and Haas Corporation for the Army

Redstone Arsenal. For a detailed description of the program see reference 16.

^Unpublished report, 1956.

^This listing represents only a part of the work done in this field.

^A thermal analyzer computes the thermal distribution in a solid body. A

thermo-structural analyzer uses the output of the thermal analyzer to compute

the structural response to these temperatures.

156
The acquired version allowed the input of temperature-dependent thermal properties. The program was further modified at NBS for fire test problems by including

in the analysis heat transfer via Stefan-Boltzmann radiation, a power exponent

in the convection equation, and view factors.

The radiation equation for this analysis is given by:

q^ = BEAV(T J* - aTj) (1)

a. S rate of heat transfer by radiation

Stefan-Boltzmann constant

where

B =

E = emissivity_ of surface

A = surface area through which heat flows

V = view factor of surface

T = temperature (absolute) of furnace atmosphere

T = temperature (absolute) of surface

a = ratio of emissivity of furnace atmosphere to black body radiator.

The inclusion of the V term is necessary as experience has shown that the

amount of heat going into the side of a beam shape is less than that entering

through the bottom surface. Since the difference seems to be related to furnace

shape, this term includes the effect of furnace geometry. In this analysis V

was determined by estimating the view factor for points at the middle of the

bottom face of the beam and at the middle of the side surface of the beam.

This simple procedure has been found to give the correct relationship for the

differing amounts of heat entering through the bottom and sides of the beam.

The convection equation for this analysis is written:

q = hA(T^ - T^)"^ (2) c as

where q = rate of heat transfer by convection

h = heat transfer coefficient (different for vertical and horizontal

surfaces)

A = surface area through which heat flows

T^ = temperature of atmosphere

Tg = temperature of surface

n = exponent where l<n<2 (usual values are 1, 1.25, 1.33)

The above parameters may be in any consistent set of units. The values

of n are based on the Nusselt number at the specimen surface. The greater the

Nusselt number the higher the exponent (see for example [17]). For the rate

of heat transfer that occurs on the fire exposed faces of the beams the value

of n is of the order of 1.25 or 1.33. For the rate of heat transfer at the

unexposed face (top face) of the beam where the rate is much lower than on the

fire side, n is of the order of 1.0 or 1.25.

157
In the present NBS version of AMG065 eqs (1) and (2) are combined into a single quasi-convection equation, and with a = 1 for simplicity

or

= ^ ^c

= BEAV(Tas'*-T'*)+hA(Tas- T)'

A(T^ - T^) [BEV(T^2 +

rp 2) + t ) + h(T - T )" as "] a fc> as as

q^ = A(T^ - T^) [R + S] (3)

where q^ = total heat transfer

R = BEV(T 2 + T 2) (T + T ) a s a s

S = h(T - T )^ (positive real root only)

a s Eq (3) is the form used in the thermal analyzer.

The detailed theory for a finite element thermal analyzer program is adequately discussed elsewhere. [16] The fundamentals of heat transfer can be

found in Myers' book [18] which also discusses the finite element method in

heat transfer.

The capability of the program was extended to include a plotting program

which takes the output of the thermal analyzer and uses it to produce either

printer plots'* or line drawings (via a line plotter) of the isotherm contours

at selected time intervals. An example of these contours is shown in figure 1,

2.2. Structural Analysis

In 1971 the Building Fires and Safety Section initiated the preparation

of a thermostructural analysis computer program for simply supported prestressed

and reinforced concrete beams under fire test exposure.

Originally, it was thought that a normal temperature structural analysis

program could be modified without too much difficulty for this analysis. With

this in mind the listing of BEAMBUSTER [19] was acquired. This computer program

computes the ultimate capacity in bending of simply supported reinforced and

prestressed concrete beams at normal temperatures. The program is quite compact.

Though this program had to be discarded after several trials and a new structural analyzer prepared, several ideas on the sequence of the calculations

and the table search method were retained. The main difficulties encountered

were the inclusion of time dependent and temperature dependent material properties, the proper sequencing of the different parts of the calculations, incorporating thermal stresses and modifying differences in program logic that had

to be compatible.

The printer plotter subprogram came with the acquired version of the program.

158
EXPERIMENTAL CALCULATED

TIME 180 min.

NORMAL WEIGHT CONCRETE

Figure 1. Comparison of calculated with measured temperatures.

159
TIME,

t

CREEP PATH FOR A TEST AT CONSTANT STRESS

WITH SEVERAL TEMPERATURE CHANGES.

^,^3-AH/RT

REDUCTION OF CREEP CURVES AT SEVERAL TEMPERATURES

TO A SINGLE CURVE BY 6 PARAMETER.

Figure 2. Diagrammatic representation of Harmathy-Dorn theory.

160
The structural analysis program that is being developed includes a capability

l| of either computing the material property tables from room temperature values or

I reading in a full set of material property tables for the full range of temperatures.

The creep analysis in this program is based on the Harmathy-Dorn [10,11]

theory and on a modification of the time hardening rule^. [20] The thermal

properties of concrete and steel are based mainly on the comprehensive summary

in Bizri's thesis [21] and on Harmathy's recommendations. [9,11]

2.2.1. Outline of Creep Theory

The Dorn [22] theory states that if the creep curves for metals at the

same stress but at different temperatures are plotted against the temperature

compensated time, which is defined below, all the curves will be coincident.

This immediately leads to a great simplification in analysis, as now only a single curve (and its associated equation) is needed to calculate creep strains

I at constant stress. This is shown in figure 2. Harmathy [10] extended the

I temperature range of the Dorn theory and added a term to account for the stress

I level. The term turns out to be the Zener-Hollomon parameter. [9,11,23] The

Zener-Hollomon parameter is the slope of the secondary portion of the creep

I curve when it is plotted against the temperature compensated time. This is

shown in figure 2. Thus, this parameter may be considered as a temperature

compensated creep rate and it is a function of stress only.

Harmathy [10] proposed the following equations for calculating the creep

in reinforcing and prestressing steels:

I de/dQ = coth2(e/eQ) (4)

Z which when integrated and rearranged gives

Ze/E^ = e/z^ - tanhCe/E^) (5)

where Z = Zener-Hollomon parameter (function of material and stress; (fig. 2)

e = temperature compensated time (function of temperature and material)

= e-AH/RT^

and AH = activatior energy of creep [10]

R = gas constant

T = absolute temperature

t = time

e = creep strain

= intercept of the secondary portion of creep curve plotted

against the temperature compensated time (function of

material and stress; see figure 2).

The restriction on eqs (4) and (5) is that either the stress is constant

or at most the stress is slowly changing with time. Under the conditions of a fire test, this restriction is satisfied.

^This is in conformity with Harmathy's theory which is discussed below.

161
In order to solve for creep using eq (5) , an iterative procedure must be

used.

Thus, Harmathy's recoiranendations greatly simplify the computation problems

for estimating the creep in the steel, since varying temperature level and

moderately varying stress level are included in a single equation. It is

assumed that since the creep of the concrete in the compressive zone of the

beam is much smaller than the creep in the steel, it may be neglected in the

analysis of simply supported beams. The ass\imption is based on the fact that

in most fire tests the average temperature of the concrete compressive zone is

generally within the range of elastic or elasto-plastic behavior.

2.3. Outline of Structural Analysis Program

In the structural analysis program, the calculations are controlled by

two program elements. These are designated MAIN and BEAMB, MAIN controls the

reading in of the problem data, the preparation of tables of material properties,

the initializing of the problem, controlling the time sequencing of the problem

and reading in the temperature data that had previously been prepared by AMG065.

BEAMB controls the structural calculations within each time cycle and calculates

either the ultimate normal temperature capacity of the beam section, the stresses

and strains in the concrete and steel under working loads (required for initializing the creep calculations) , or the capacity of the beam section during the

process of a fire test exposure. These two program elements also call other

sxibprograms which perform specific calculations during a run, such as setting

the temperature of each element, calculating or reading in the temperatures of

each bar, creep calculations and so forth.

2.4. Verifications of Structural Analysis

The structural analysis computer program will be verified by comparing the

analytic results with available test data. In this, some discrimination is

necessary as it has been found that test results from different laboratories

vary.

3. FUTURE DIRECTION

The computer programs will be used to generate fire performance information

for a variety of beam shapes. These data will be used to develop design aids

such as graphs, tables, and nomographs for use by designers, architects,

building code officials and other interested users. Based on experience with its use, the computer program will be modified.

Possible modifications are: inclusion of creep in concrete, calculation of

available strength at selected fire exposure times and testing of alternative

creep algorithms.

4 . ACKNOWLEDGEMENT

This work was sponsored in part by the Ptiblic Building Service, General

Services Administration. Isotherm data were provided by the Portland Cement

Association.

162
5 . REFERENCES

[1] Standard Methods of Fire Tests of Building Construction and Materials,

American Society for Testing and Materials Designation E119, American

Society for Testing and Materials, Philadelphia, Pa. (1973).

[2] Issen, L. A., Scaled Models in Fire Research, Journal of the PCA

Research and Development Laboratories, Vol. 8, No, 3 (Sept. 1966).

[3] Hamming, R. W. , Numerical Methods for Scientists and Engineers (McGrawHill Book Co., New York, 1962).

[4] Zienkiewicz, O. C, The Finite Element Method in Engineering Science

(McGraw-Hill Book Co., New York, 1971).

[5] Issen, L. A., Gustaferro, A. H. and Carlson, C. C, Fire Tests of Concrete Members: An Improved Method for Estimating Thermal Restraint

Forces, Fire Test Performance ASTM STP 464, American Society for Testing

and Materials, Philadelphia, Pa. (1970).

[6] Abrams, M. S,, Gustaferro, A. H. and Salse, E. A. B. , Fire Tests of

Concrete Joist Floors and Roof, Research and Development Bulletin

RD006.01B, Portland Cement Association, Skokie, 111. (1971).

[7] Gustaferro, A. H. , Abrams, M. S. and Salse, E. A. B. , Fire Resistance

of Prestressed Concrete Beams Study C: Structural Behavior During Fire

Tests, Research and Development Bulletin RD009.01B, Portland Cement

Association, Skokie, 111. (1971).

[8] Ehm, Herbert, A Contribution to the Design 'of Fire Endurance of Reinforced Concrete Beams and Similar Structural Elements, Doctoral Thesis,

Faculty of Structural Engineering of the Carolo-Wilhelmina Technical

University in Braunschweig (West Germany) , 196 7, translated by K. F. Zaluda, Portland Cement Association Foreign Literature Study. 545.

[9] Harmathy, T. Z., Thermal Performance of Concrete Masonry Walls in Fire,

Fires Test Performance ASTM STP 464, American Society for Testing and

Materials, Philadelphia, Pa (1970).

[10] Harmathy, T. Z., A Comprehensive Creep Model, Transactions A.S.M.E.

Journal of Basic Engineering, Vol. 89, American Society of Mechanical

Engineers, New York, N.Y. (1967).

[11] Harmathy, T. Z. and Stanzak, W. W. , Elevated-Temperature Tensile and

Creep Properties of Some Structural and Prestressure of Steels, Fire

Test Performance ASTM 464, American Society for Testing and Materials,

Philadelphia, Pa. (1970).

[12] Gustaferro, A. H. , Fire Endurance of Concrete Slabs and Beams, unpublished proposals to the American Concrete Institute Committee, No. 216

(1973) .

[13] Edwards, A. L. , TRUMP: A Computer Program for Transient and SteadyState Temperature Distribution on Multi-dimensional Systems (available

from the NTIS, Springfield, Va. , Report No. UCRL-14754, Rev. II).

[14] Schauer, D. F., FED: A Computer Program to Generate Geometric Input for

the Heat-Transfer Code TRUMP (available from the NTIS, Springfield, Va.

,

Report No. UCRL-50816)

[15] Edwards, A. L. , TRUMP/XB2: A Computer Program for Processing the TRUMP

Thermal Property Data Computation (available from the NTIS, Springfield,

Va., Report No. UCRL-50663)

163
[16] Brisbane, J. J., Heat Conduction and Stress Analysis of Solid Propellant

Rocket Motor Nozzles (available from the NTIS, Springfield, Va. , Report

No. AD848594)

.

[17] Perry, Robert H. , et ai , John H. Perry's Chemical Engineers Handbook,

4th Edition (McGraw-Hill, New York, 1963).

[18] Myers, G. E. , Analytic Methods in Conduction Heat Transfer McGraw-Hill

Book Co., New York, 1971).

[19] Hansen, N. , BEAMBUSTER: Program Solves for the Moment-Curvature

Relationship of a Reinforced Concrete Cross-Section Subject to Axial

Load and Bending, Portland Cement Association, unpublished (1971).

[20] Leckie, F. H. , Some Structural Theorems of Creep and Their Implications,

Advances in Creep Design, in Chapt. 4, A. I. Smith and A. M. Nicolson,

Eds. (John Wiley and Sons, Inc., New York, 1971).

[21] Bizri, H. , Structural Capacity of Reinforced Concrete Columns Subjected

to Fire Induced Thermal Gradients, Report No. UL SESM 73-1, Structural

Engineering Laboratory, University of California, BerTceley, Calif. (1973)

[22] Dorn, J. E., Mechanical Behavior of Materials at Elevated Temperatures,

esp. Chapt. 14, Creep Under Non-steady Temperatures and Stresses, by

S. S. Manson (McGraw-Hill Book Co., New York, 1961).

[23] Zener, C. and Hollomon, J. H. , Effects of Strain Rate on the Plastic

Flow of Steel, Journal of Applied Physics, Vol. 15 (1944).

164
NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 411, Fire Safety Research,

Proceedings of a Symposium Held at NBS , Gai thersburg , Md . , August 22, 1973,

(Issued November 1974)

SMOKE AND CARBON MONOXIDE GENERATION

FROM BURNING SELECTED PLASTICS AND RED OAK

Thomas Y. King^

Armstrong Cork Company, Lancaster, Pennsylvania

This paper presents preliminary results of simultaneous smoke

and carbon monoxide measurements from burning selected plastics

and red oak in the smoke density chamber. An attempt was made to

correlate smoke optical density with mass concentration of smoke.

Particulate shape and approximate size range of the smokes were obtained using a scanning electron microscope.

Key words: Carbon monoxide; electrostatic precipitation; particulate mass; scanning electron microscope; smoke.

1 . INTRODUCTION

A material's flammability (i.e., flame spread, ease of ignition, etc.) has

in the past been the primary consideration in fire safety evaluation. Now with

a greater understanding of those factors which contribute to fire injuries and

deaths, smoke and toxic products are becoming of increasing concern. Even a relatively good flame retardant or thermally stable material, which by itself

would not ordinarily propagate a flame, should be considered in the total com- bustible system. In most actual fire situations other more flammable material

will be available which could result in partial or full involvement of materials

of low flammability.

The deleterious effects of smoke in a fire result from decreased visibility , both for the escaping occupant and the rescuing firefighter; inhalation of

particulates which restrict respiration and can induce panic; and the toxic

gases that accompany the smoke and account for a large fraction of fire deaths.

A study of the physical and chemical parameters which affect the smoke

generating potential of various materials is important not only in assessing

possible hazardous materials, but also in determining the means by which the

hazard can be reduced.

This paper presents preliminary results of measurements of smoke and gaseous combustion products from selected materials in a smoke density chamber.

Since the research described has recently been started, this paper is designed

primarily to introduce the overall program and indicate its likely direction.

2. SMOKE AND CARBON MONOXIDE GENERATION

Smoke can be defined as the solid particulate and/or liquid aerosol generated from the incomplete oxidation of organic materials and the release of

certain inorganic materials during the burning process. The gaseous combustion

products are not included in the above definition of smoke. Factors which can affect the smoking tendency of materials include: composition, density and

thickness, heat flux, air flow, oxygen availability, pressure, surface characteristics, and geometry. Carbon monoxide is formed from the incomplete oxidation

of the decomposition products, and the same factors which affect smoke production might be expected to influence carbon monoxide generation.

The author was a Research Associate at the National Bureau of Standards,

Washington, D.C. when the work reported here was performed.

165
In this paper, smoke was measured using the National Bureau of Standards'

Smoke Density Chamber. [1] This is an 18 cubic foot enclosed chamber in which

a vertically positioned photocell measures the amount of light absorbed (or

scattered) from the smoke emanating from burning a vertical 3" x 3" sample.

In the standard test method, the sample can be exposed to heat under either a flaming (2.5 W/cm^ of radiant heat plus piloted ignition) or smoldering (radiant

heat only) type exposure. The specific optical density is a measure of light

obscuration for a specimen of given thickness and density, and is specific for

the sample area exposed.

Although normally only the maximum specific optical density (D^) is

reported, other measured parameters of interest include: the time at which D^^ occurs (Tj^) , the time at which the specific optical density equals 16 (T = 16) , and the maximum smoke production rate averaged over a two minute period (Rj^) . Carbon monoxide (CO) was measured continuously and simultaneously with the

smoke using an infrared analyzer connected to the chamber (fig. 1) . Results

are reported graphically in parts per million (ppm)

.

Throughout these studies the flow rate from the chamber to the infrared

analyzer was maintained between 1 to 1-1/2 liters/min. A delayed response time

due to dead air spaces (dry ice trap, particulate filter assemblies, and sample

lines) for 90-95 percent CO response in the analyzer was approximately 30

seconds. None of the carbon monoxide curves shown in this paper were corrected

for this factor.

SECONDARY

FILTER

ASSEMBLY

DRY ICE TRAP

PRIMARY FILTER

ASSEMBLY

INFRARED CO

ANALYSER

vacuum

SMOKE

DENSITY

CHAMBER

I

PARTICLE

MASS

MONITOR

PHOTOMETER

OPTICAL

DENSITY

Figure 1. Smoke analysis system.

166
2.1. Sample Design

Samples for this study (table 1) included: red oak, acrylonitrilebutadiene-styrene (ABS) , and rigid and plasticized polyvinylchloride (PVC)

(Polystyrene and a polyurethane will be included later in the program.) These

materials were chosen to represent typical cellulosic and polymeric materials.

The plastics, however, are not truly representative of actual building and

furnishing compositions since they contain no fillers and only a minimum amount

of the other components necessary for fabrication. This allowed the comparison

between different materials without undue concern for fillers, flame retardants,

and other components which in practice could comprise a large percentage of the

actual composition and have a significant effect on the results. Since smoke

and carbon monoxide concentration would be expected to increase with sample

weight, the samples were compared at approximately the same weight (4.1 to 4.4

grams) . Sample weights were relatively small so that the heat transfer into

the sample and resultant smoke generation would occur rapidly without allowing

excessive time for particulate deposition to occur during the build-up stage.

The maximum specific optical density (D^^) can be regarded as the point at which

equilibrium exists between smoke production and particulate deposition.

Table 1. Materials Studied

Material

Approximate

Thickness (in)

Approximate

Density (g/in^)

Rigid Polyvinylchloride^ 0.023 20.3

Plasticized Polyvinylchloride^ 0.022 21.2

Acrylonitrile-ButadieneStyrene^ 0.031 15.1

Red Oak 0.045 10.4

^Materials were specially prepared for this study.

2.2. Effect of Composition on Smoke

and Carbon Monoxide Generation

The relationship between smoke (dotted curves) and carbon monoxide (solid

curves) with time for red oak, ABS, and rigid and plasticized PVC samples

burned under non-flaming exposure is shown in figure 2. The curves shown were averaged from three separate determinations. At a heat flux of 2.50 W/cm^

,

rigid and plasticized PVC and ABS generate carbon monoxide very slowly (1-2 ppm/

min) at a constant cumulative rate over the time interval described. Since

there is little difference in the rate of CO build-up for these three materials,

but a substantial difference in the maximum smoke densities, one can conclude

that no simple relationship exists between smoke and carbon monoxide for

materials under these conditions. Carbon monoxide appears to be liberated in

each case only after a substantial amount of smoke has been generated. Whether

this is due to the slow oxidation of carbonaceous char and/or smoke and gaseous

decomposition products is not yet clear. The six-fold increase in smoke obtained

from burning plasticized PVC compared to rigid PVC can be attributed to the

significant contribution of the plasticizer to the non-flaming smoke evolution.

Comparatively, red oak liberates large quantities of carbon monoxide under

smoldering conditions. The rate, however, was slow initially until the onset

of glowing combustion, then rapidly increased (approximately 80 ppm/min)

167
450n

400-

350-

V) 300-

uio

SMOKE

CARBON MONOXIDE

AVERAGE OF TRI PLICATE TESTS

SMOLDERING EXPOSURE (2.50 W/cm^)

SAMPLE WX AVG.(gms)

RED OAK 4.29

RIGID PVC 4.22

PLASTICIZED PVC 4.20

ABS 4.35

P-PVC

Figure 2,

,-1400

1200

1000 Z

Q.

I biO 800 X

o

-600

o

m

o: 400 o

-200

^R-PVC

—ABS

^P-PVC

TIME, MIN.

Smoke and carbon monoxide concentration for various materials.

Figure 3 illustrates similar curves for the four materials under flaming

conditions. Under this exposure the carbon monoxide generated from the pilot

burners was subtracted from the actual CO curve measured from the material.

With the exception of red oak, more smoke and CO are produced under flaming

compared to smoldering exposures. After the maximum smoke density had been

reached the carbon monoxide curves for red oak and ABS reached a plateau which

was consistent with the observation that little char remained at that point.

For rigid and flexible PVC there appear bo be two distinct slopes on the

CO curves, one corresponding to the rapid rate of CO generation until the maxi- mum smoke density has been reached, the other occurring after the smoke begins

dissipating which apparently results from carbon oxidation of the remaining

char

.

2.3, Sample Probe Position

In the previous studies continuous sampling for carbon monoxide had been

accomplished from the top of the chamber. It is conceivable that under certain

circumstances the convective heat flow might be such that the gases would tend

to stratify at the top of the chamber before mixing. To determine this, CO was monitored at the middle and bottom in addition to the top to represent a cross sectional area of the chamber. The CO produced from red oak and rigid PVC

samples was evaluated under flaming exposure at these three positions (fig. 4).

Results indicated that there was a carbon monoxide concentration gradient only

during the first few minutes of the test. After this initial time period con- centration was essentially uniform throughout the chamber.

168
SMOKE

CARBON

MONOXIDE

AVERAGE OF TRIPLICATE TESTS FLAMING EXPOSURE (2.50 W/cm2)

-1200

SAMPLE WTAVG.(gms) _ RED OAK 4.30

RIGID PVC 4.13 PLASTICIZED PVC 4.15 ABS 4.42

rl400

16 20 24

TIME, MIN.

-1000 f

UJa

-800 g

z

o

s

-600

-400

-200

Figure 3. Smoke and carbon monoxide concentration for various materials,

1200-1

T TOP OF CHAMBER

M MIDDLE OF CHAMBER

B BOTTOM OF CHAMBER

AV6.0F DUPLICATE RUNS

CURVES CORRECTED FOR

PILOT BURNERS

TIME. MIN.

Figure 4. Effect of probe position on carbon monoxide concentration from red

oak and rigid PVC (flaming exposure)

169
2.4. Heat Flux

Smoke and carbon monoxide concentrations from burning rigid PVC samples were studied as a function of heat flux (flow rate of energy across or through

a surface). Radiant heat flux levels were varied from 1.87 to 3.07 W/cm^ under

flaming type burning conditions while the gas and air mixture to the ignition

burners was constant. As shown in figure 5 as the heat flux increased the

maximum specific optical densities were increased, the maximum rates of smoke

and carbon monoxide generation were increased, and the times to reach D^^ were decreased. The marked two-fold increase in maximum smoke density resulting

from increasing the radiant heat from 1.87 to 3.07 W/cm^ can be attributed in

part to a greater total weight loss (ca. 70 percent and 84 percent respectively)

.

Other factors which could contribute might be that less time for particulate

decomposition on the chamber surface is available and there are possibilities of

different reaction pathways which favor more smoke production at higher temperatures .

3. SMOKE MASS

Smoke mass density has been related to optical density measurements in the

smoke chamber by using frequency monitored electrostatic precipitation. The

change in frequency during a given time interval is directly proportional to

the total particulate mass. In this study smoke was sampled at a point half

way up the chamber wall under steady state conditions after reaching the maximum

smoke density. A plot of smoke optical density per meter versus smoke mass density (milligrams per cubic meter) for red oak (flaming and smoldering

exposure) and ABS, and rigid and plasticized PVC (smoldering exposure) is shovm

in figure 6.

450-r

SMOKE

CARBON MONOXIDE

3.07 W/cm^

2.50 W/cm^

3.07 W/cm|

1.87 W/cm^

-rl400 —1200

-1000 2

Q.

Q.

I liJ -800 I

o

-600 ^

o

m

IT -400 o

--200

20

TIME, MIN.

Figure 5. Effect of heat flux on smoke and carbon monoxide

generation from rigid PVC samples (flaming exposure)

.

170
0 50 100 150 200 250 300 350 400 450 500

MILLIGRAMS/ CUBIC METER

Figure 6. Optical density vs. smoke mass density.

Initial sample weights were varied by changing the sample area exposed, keeping

thickness constant, to obtain a range of optical densities in the chamber.

With the exception of red oak and ABS under non-flaming burning conditions,

smoke mass density was found to be linearly related to optical density over the

range explored. The non-linearity observed with the red oak and ABS specimens

under smoldering conditions is not fully understood. It might result from the

particular properties of the pyrolysis products contributing to more rapid agglomeration. However, by varying the sample area and therefore weight, a possibility exists that edge effects and heat flux gradients could have led to the

observed results. It is interesting to note that in the case of red oak a con- siderably lower smoke mass to optical density ratio was found under flaming

compared to non-flaming burning conditions.

4. PARTICULATE SIZE AND SHAPE

To complement the smoke optical density and mass studies, scanning electron microscope pictures were taken of smokes from rigid and plasticized PVC

,

red oak, and ABS (figs. 7 to 10 respectively) under flaming burning conditions.

Samples were prepared by electrostatic precipitation (aerosol sampler) of the smoke particles from the chamber on an electro-polished titanium metal surface.

By using a pulsed precipitating electric field in the sampler, smoke deposition

was relatively uniform without preferential size separation.

171
Figure 7. Rigid PVC "flaming exposure" smoke particulate, scanning electron

microphotographs

.

172
Figure 8. Plasticized PVC "flaming exposure" smoke particulate, scanning

electron microphotograph

173
174
6.0 //m

Figure 10. ABS "flaming exposure" smoke particulate, scanning electron

microphotograph

175
I

I

I

I Particle shapes ranged from "stringer" type smokes containing discrete ; spherical units forming chains for rigid PVC and ABS to the elliptical shaped | liquid residue for red oak. Through a knowledge of the magnification of the | scanning electron microscope photographs, typical particle sizes were estimated i as follows:

Estimated

Minimum (ym)

0.15

0.10

0.30

0.15

No attempt was made at this time to estimate particle size distributions.

It is interesting to note , however, that there appears to be a noticeable

difference in shape between rigid and flexible PVC smoke particles, the former

containing relatively long aggregated chains while the latter has a greater

number of smaller aggregates more spherical in nature.

5. FUTURE STUDIES I The research described in this paper has recently been started and represents only a part of the overall program. The program will be limited to the i six materials described earlier and will consist of three phases: [

1. The determination of the effects of heat flux, oxygen depletion, j material composition, and weight loss on smoke and carbon monoxide

evolution.

2. The determination of the relationship between optical density and

smoke mass density for each material under both flaming and non- flaming burning conditions. j

3. The determination of smoke particulate shape and size distribution i (if possible) for each material under flaming and smoldering exposures.

The study is designed to provide information relating to the following | questions

I 1. What are the relative smoke and carbon monoxide generating character- . istics of these six materials and do they change significantly with j higher temperatures and oxygen deficiencies?

2. From a knowledge of weight loss, heat flux, and oxygen availability ! can the maximum smoke densities and CO generation rates be estimated \ on samples of similar composition to those studied? \

3. After experimentally determining the relationship between optical ; density and smoke mass density over a narrow range can these data be ! extrapolated to include higher optical densities so that one might ; predict total airborne smoke mass?

4. How does smoke particle shape and size vary with material composition ' and burning conditions? i

I

Estimated

Composition Maximum (ym)

rigid PVC 15

plasticized PVC 24

red oak 2 ABS 3 0

176
II 6. CONCLUSIONS

I Based on the limited study to date, carbon monoxide accompanies smoke

j development in the flaming combustion process, but there does not appear to be

a unique relationship between the two products for materials of different composition.

In the case of red oak, it is possible to produce considerable amounts of

CO without much smoke if the burning process remains in the flaming mode. The

rate of carbon monoxide evolution for the plastic materials studied under nonflaming conditions was observed in all cases to be relatively low.

The complex interrelationship between smoke mass, optical density, and

particulate size and shape appears to be strongly dependent upon material com- position .

7 . REFERENCES

[1] Lee, T. G. , Interlaboratory Evaluation of Smoke Density Chamber, Nat. Bur.

Stand. (U.S.), Tech. Note 708 (Dec. 1971).

[2] Gross, D., Loftus, J. J. and Robertson, A. F., Method for Measuring Smoke

from Burning Materials, Symposium on Fire Test Methods -- Restraint and

Smoke 1966, American Society for Testing and Materials, Philadelphia,

Pa. , 1967, pp. 166-204.

177
NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 411, Fire Safety Research,

Proceedings of a Symposium Held at NBS , Gaithersburg , Md . , August 22, 1973,

(Issued November 1974)

A FIELD STUDY OF NON FIRE-RESISTIVE MULTIPLE DWELLING FIRES

Francis L. Brannigan^

Montgomery College, Rockville, Maryland

A field study was made of structural and building design

factors contributing to the spread of fire in more than 40 non fire-resistive, multiple occupancy dwellings, typically "Garden

Apartments". Most deficiencies could be corrected by preserving

the integrity of a gypsum board sheath serving as a fire barrier.

Examples are given of penetrations and openings in fire barriers

which permitted substantial fire spread.

Key words: Apartments; building codes; fire; fire walls; garden

apartments; gypsum board; insurance; livability; multiple dwellings.

1. INTRODUCTION

From January 1971 till the present the author has been under contract to

the National Bureau of Standards to investigate serious multiple dwelling fires

to determine what structural elements or practices contributed to the extension

of fire beyond the area of origin.

Several local fire department radio channels are routinely monitored by

the author, and he responds to fires of interest. In addition, he keeps in

close touch with fire officials in the local area, and is notified of fires of

interest. All investigations were made either while the fire department was still in possession of the premises, or if later, accompanied by a fire official

and with the permission of and access provided by the owners' representative.

Wherever possible firefighters early on the scene were interviewed.^ A few

observations are based on examination of buildings under construction.

No attempt was made to determine the extent to which any particular

building conformed to the code in effect at the time the particular building

was built. Obviously, not all the defects cited exist in all jurisdictions,

or in all structures examined.

Each report provides a capsule description of the building, the fire, the manner in which the fire spread from the point of origin, appropriate 35mm

slides, and any recommendations the investigator might have on how modifications

of present practices might improve the fire containment design of similar

buildings. The reports are circulated to the appropriate staff members and

provide a body of information which aids the staff in developing and supporting

improved building design.

Through other channels the investigator shares his findings and fire

tactical recommendations with firefighting forces. If a fire department is

well aware of the defects of a building or types of buildings it may be possible

to "plug the gap" tactically and reduce the consequences of the designers' errors

.

Mr. Brannigan serves as a consultant to the Program for Fire Control - Construction, Programmatic Center for Fire Research, National Bureau of

Standards, Washington, D.C.

Appreciation is expressed to the Montgomery County Department of Fire and

Rescue Services and the Fire Departments of Bethesda, Kensington, Silver

Spring, Rockville, Gaithersburg, Prince Georges County, Anne Arundel County,

Clarkesville and Annapolis in Maryland, Arlington and Fairfax Counties in

Virginia and the District of Columbia.

178
2. PRIVATE HOMES VS. MULTIPLE DWELLINGS

i "A man's home is his castle" is a long established principle of our

I common law. This principle is carried forward into statute law such as building

codes, in that fire protection aspects of building codes bear very lightly on single family dwellings. Regulations calling for masonry exterior walls and

spacing between buildings limit one's "right" to burn down his neighbor,

though recent relaxation of rules against wooden shingles have restored this

"right" in some areas. Generally, inspection laws don't give the Fire Inspector

access to private dwellings. The principal impact of the statutes is in the

regulation of the initial installation of electricity and heating appliances,

but there is generally no warrant for reinspection to determine that instal1 lations have not been substantially altered after initial approval. Even when

I requirements are upgraded, usually no attempt is made to apply them retroj actively to existing dwellings. For example, current efforts to legislate

installation of combustion products detectors in one-family homes are limited

! to new homes; little thought is given to ordering installation in existing homes.

I It is impossible to house each family in the United States in its own

j individual "castle". Multiple dwelling units are necessary.

! In the multiple dwelling unit there is an interaction between a fire in

I any unit, and the safety of the occupants in all the other units. In addition,

j multiple dwelling units contain common areas accessible to all occupants, and

I to varying degrees, to any outsider. A fire in the common area threatens all

I the occupants.

Historically, multiple dwellings in many cities were created by the subdivision of large one-family homes into smaller units as the former owners

moved away and neighborhoods deteriorated. In cities like New York, the supply

of deteriorated housing was insufficient to meet the needs of hordes of immigrants, so tenements were built to house several family units, structurally

indistinguishable from the multi-story one-family house of the well-to-do (the

typical New York " Brownstone" )

The first official recognition of any special fire safety problem was the

requirement that outside fire escapes (vertical ladders, with a platform at

each floor level) be provided. Terrible losses of life occurred in these tenements (now "old-law" tenements in New York parlance)

^

About 1903, as a result of sociological pressures, sweeping tenement house

legislation was passed in New York giving rise to the "New Law" tenement.

Though not so stated, the principle which underlay the requirements was that

no person should lose his life due to a fire which started outside his apartment. The entire thrust was towards easy escape of the occupants, and for

many years there was no loss of life in such a building due to extension of fire.

While the fire protection emphasis was almost exclusively directed towards

safe escape, requirements for life safety also tended to limit extension of fire.

Fire resistive stairways, self-closing fire resistive apartment doors and similar

requirements for dumbwaiters together with the universal complete plastering of

all interior surfaces, served to contain almost all fires to the apartment of

origin, for many years. The provisions for easy escape of occupants lightened

the burden of rescue operations so that firefighters were available to swiftly

check for, and suppress, any extension of fire. Exterior fire escapes provided

direct secondary access to all apartments.

^For a further discussion of the circumstances of the New York City Tenement

House Act see Brannigan, F. L. , "Building Construction for the Fire Service",

National Fire Protection Association (1971) , pp. 146-150.

179
Unfortunately, building codes are parochial and so as communities shift

from individual to multiple dwellings, the same error of regarding a multiple

dwelling as simply a larger version of a single family house is repeated.

Typically, in 1966 the District of Columbia asked the National Bureau of

Standards to investigate possible methods of improving, in situ, the fire

resistance of existing wooden apartment doors. Tests indicated that improved

fire performance was an attainable but costly solution; a simple alternative

was to remove the door and frame and substitute metal, a determination made

two-thirds of a century earlier in New York.

The multiple dwellings in which the fires were investigated are of a post

World War II type known generally as garden apartments. The exterior structural

walls are of solid masonry or of brick veneer over platform wood frame. ^ In some cases portions of the exterior surface, typically the spandrel spaces

directly between vertical lines of windows are of wood. No completely wooden

exterior buildings were involved in any of the fires studied. The usual

nominal height is limited to three stories, but by taking advantage of terrain

the building can be four stories on one elevation.

Balconies are customary, either extended or reentrant, and variously of

combustible or noncombustible construction. Common gable roof attics usually

extend over the entire structure, broken in area only to the maximum permitted

by the local code when the building was built, and by barriers as inadequate

as the code or inspections will permit.

Regardless of exterior construction the interior construction is almost

totally of wood, using identical construction techniques to those used in one- family homes. The addition and stacking of units multiplies many times fire

extension potentials which are inherent in current construction techniques.

Bathrooms provide an excellent illustration. Years ago, the bathroom was fully plastered and the bathtub stood independently on "feet". "Glamorizing"

the bathroom brought about the development of the built-in bathtub. Because

of its contours, such a tub interconnects the void spaces of one wall, the

void spaces of the wall at right angles, and the void spaces under the floor.

These void spaces are interconnected with vertical voids which must be of substantial dimensions to accommodate waste and vent piping. In the layout of

the apartments the plumbing facilities are consolidated for economy. This can result in four bathrooms being located in four quadrants around a point.

Vertical and horizontal voids three or four stories high are, thus, fully

interconnected. In installing plumbing fixtures, it is often the practice to

cut and, thus, weaken structural members. The result is that any fire which

starts in or penetrates this void will extend rapidly to as many as 16 family

units, and the attic above. In one fire, interior collapse occurred very early

in the bathroom area. The weight of fixtures, cutting of structure for accomo- dation of plumbing, and the air supply due to interconnected voids would make

early collapse not unexpected. The contrast between the potential ultimate

effect of an initially identical fire in a one-family ranch house and a garden

apartment is startling, yet no code provision really takes this into account.

"Fire stopping" even if mandated is usually nonexistent, or at best ineffectual.

^Shoub, H. and Gross, D. , Nat. Bur. Stand. (U.S.), Bldg. Sci. Ser. 3, "Doors

as Barriers to Fire and Smoke (March 1966)

.

^See Brannigan, "Building Construction...", p. 93, for a discussion of the

impossibility of distinguishing brick veneer from brick masonry by exterior

observation in modern construction.

^See Brannigan, "Building Construction...", pp. 64-65, for a discussion of the

difference between "Inherent" and "legal" f irestopping

.

180
3. THE INTERIOR FIRE RESISTIVE SHEATH

A few years ago New York subway riders were startled to read "car card"

ads which urged them to "Keep New York Plastered". Many tried, in more than

one sense, but their effort failed. The reference was to the fact that the

city was about to embrace a new building code which would permit the use of

gypsum board or "drywall" for interior finish. Prior to this, wet plastering

had been required. The all plaster, essentially continuous sheath of the wood

lathed "New Law" tenement provided (until the plaster deteriorated with age) an almost complete and usually adequate barrier to the extension of fire to

the combustible inner structure of the building.

Today, almost universally, interior finish is of "drywall" or gypsum board.

Gypsum board consists of a layer of gypsum, sandwiched between two sheets

of paper. It is offered commercially in sheets from 3/8 to 5/8 inch thickness,

4 feet in width and 7 to 10 feet long. By including vermiculite or glass fibers

in the gypsum, the time a given thickness of gypsum will resist fire can be

increased. If thicknesses greater than 5/8 inch are desired, successive layers

of gypsum board are used.

Gypsum itself provides negative Btu yields of as much as -580 Btu per

pound, measured by the "bomb" calorimeter method.

Underwriters' Laboratories "Fire Resistance Index" (see fig. 1) contains

a number of fire riesistive (combustible) wall and "floor and ceiling" assemblies

tested and rated according to the standard fire test, ASTM E119. In most cases

the essential protective element is gypsum board.

The test assemblies are simple structures. Walls are of vertical wood

studs, without any offsets, and are fire stopped: Floor and ceiling assemblies

are usually on 2 x 10 inch wood joists fire stopped.

Building codes contain various requirements for fire resistive (combustible

construction

The "as built" wall and floor ceiling assemblies are far more complex than

the test assemblies. It appears that builders, building officials, and inspectors are quite unfamiliar with all the details of the assemblies which passed

the tests and were rated.

One of the most persistent and dangerous errors is the assignment of the

fire resistance rating to the gypsum board itself rather than to the assembly

as erected in the test facility . Another error is the failure to understand

the meaning of "combustible" when added to a fire resistance rating.

Gypsum board walls and ceilings competently installed under the watchful

eye of inspectors who understand the full installation requirements can and

have performed remarkably well. An excellent example can be found in the

Harbour House project in Annapolis. There, at least 11 fires have made substantial attacks on the gypsum sheathing, but in no case was the sheath penetrated. (An aluminum soffit permitted an "end around" extension.)

Up to this point the author has, artfully he supposes, led the reader to

believe that there is such a concept as a continuous fire resistive sheath

protecting the combustible structure from a fire in the contents. In fact,

there is apparently no such conception on the part of those who build, regulate,

supply materials or test. The building is simply never looked at as a whole.

This is another example of component testing as opposed to systems safety.

While the chief problem appears to be the failure of continuity of what

could be an adequate protective sheath, there are some other areas of design

construction and layout features which contribute to the extension of a typical

confinable fire, to a building conflagration (see fig. 2).

181
Design No. L506

(Formerly Design No. 1—46 Mln.) Unrestrained Rotirtg—% Hr. Combustible

Finish Rating—See Item 6.

Nominol Dimension

1. Finish Flooring—1 by 4 in. T&G : laid perpendicular to joists, or %-in. plywood, minimum grade "underlayment," with T&G long edges, and conforming with PS 1-66. Face grain of plywood to be perpendicular to joists with joints staggered.

2. Bnilding Paper—Commercial rosin-sized, 0.010 in. thick.

3. Sabflooring—1 by 6 in. T&G. fastened diagonally to joists, or %-in. plywood, minimum grade "standard," with exterior glue, and conforming with PS 1-66. Face

grain of plywood to be perpendicular to joists with joints staggered.

4. Cross-Bridging—1 by 3 in.

B. Wood Joists—2 by 10 in., spaced 16 in. O.C. P.restopped.

6. WaUboard, Gypsum*—% in. thick. Sheets of wallboard installed with long dimension

perpendicular to joists and fastened to each joist with 1% in. long Dd, cement-coated

nails spaced 6 in. O.C. Big Horn Gypsnm Co.—Type A (finish rating 18 min). Type B (finish rating

20 min) or Type C (finish rating 15 min).

Flintkote Co.—Type III (finish rating 20 min).

Repoblic Honsing Corp.—Type HG-1 {finish rating 15 min) or RG-3 (finish rating 20 min).

Finishing System—Fiber tape embedded in compound over joints and exposed nail heads covered with compound, with edges of compound feathered out. As an alternate, nominal 3/32 in. thick gypsum veneer plaster may be applied to the entire surface

of Classified veneer baseboard. Joint reinforced. *BeariDg U.L.I. Classification Marking.

Attic Access

7.

Figure 1. Design L 506 P 265 i Underwriters' Laboratories ^ Fire Resistance Index, Jan. i 1973. "The firestopped ' 2" X 10" joists, the spacing i and setting of nails and the I taping of joints are all j essential elements of the

rating achieved by the floor ; and ceiling assembly. It ' appears that in the field,

the gypsum board is con- sidered to be the essence

of the fire resistance

rating, and the other

equally important elements : are ignored." I

Extension Voids

Exterior Wood Trim

Heal Duct

Plumbing Access

Kitchen Soffit

Kitchen Vents

Gas Service

Soffit

Insufficient Nailing

Non-Closing Door

Hollow Double Walls

Wooden Doors

Sliding Doors

Floor Design

Electric Service

FEW OF THE PINHOLES

Figure 2. Sketch of garden apartment house showing all pinholes in the

sheathing. "Any lack of continuity in the sheathing permits fire to

enter the interior voids of the building where it can spread unchecked."

(Courtesy of Montgomery College, Learning Resources)

182
The various modes of failure are interrelated, but it is possible to break

down the discussion into a few headings for convenience.

1. Ways in which fire penetrates the gypsiim sheath and enters the inner

structure of the building.

2. Fire spreading substantially in combustible voids, within the inner

structure of the building, usually interconnected with the huge com- bustible void of the attic.

3. Fire extension through or around fire walls and barriers between

buildings

While loss of life was not very common in the fires studied, a few observations of life safety, both of occupants and firefighters are warranted.

4. FIRE PENETRATION MODES

1. Inadequate nailing, particularly of ceilings is common. At times,

entire 4' x 8' panels of gypsum board fell early in the fire, before the board

should have failed by fire exposure. Examination showed that nailing was short,

as little as 12 inches on centers versus the 6 inches usually required.

2. The only U.L. listed standard for floor and ceiling assemblies using

trusses rather than joists, requires two 1/2 inch layers of gypsum board.

Ceilings nailed to gusset plate trusses are nailed only on the 24 inch spacing

of the trusses rather than 16 inch spacing. Single layer 1/2 inch or 5/8 inch

ceiling constructions permitted under trussed roofs appear to be unwarranted

extrapolations from the tested constructions.

3. Gypsum board was found of less than the required thickness , 3/8 inch

in some cases.

4. Two (gypsum board) layer construction in which the underlayer was made

up of incomplete "scraps" with large areas uncovered, was noted.

5. Plywood panels are used to cover openings. The commonest example is

the omnipresent wooden panel which gives access to the bathtub plumbing. Many

access panels to attics are of plywood. Most of the buildings involved were

heated by hot air heat. In one case hot or chilled water was delivered to convectors. One convector in an interior wall between two bedrooms served the two rooms. A3' x 4' plywood panel gave access to the convector for maintenance.

A typical "child set" fire in the bedroom entered the wall space through the

plywood, extended upward through the walls along the water pipe openings to

the next floor level, broke through the corresponding plywood panel. The

extended fire did more damage to the upper apartment, than to the apartment of

origin

6. An attractive pass through between the kitchen and dining area could

be closed off by sliding louvered doors. The doors slid back into a space

provided by doubling the wall, much like old fashioned sliding doors. The fire

entered the wall space through the opening, and extended to other apartments

by interconnected voids. A picture taken at the time the fire department was "turning out" shows that the smoke was already coming from two other apartments.

7. In a number of cases fire penetrated the drywall sheath around hot

air heat register openings, and light fixtures.

8. Penetrations were noted around door frames.

9. The basement areas of garden apartments are used for utility meter

rooms, rubbish rooms, coin laundry rooms, and storage rooms. The typical

storage room has a series of wire cages, one per tenant, individually locked.

183
The storage area particularly can represent a substantial fire load. These

areas are arranged to be usually locked with a key provided to each tenant,

but are often found open. They are a common point of origin of incendiary

fires.

10. Because of many utility openings, the integrity of the gypsum sheath

on the basement ceiling is particularly dubious.

11. Utility meters are commonly grouped for convenience. In one case

the gypsum ceiling was cut short 2 inches from the wall. The gap was made up

by a piece of wood 1" x 2". The electric cables passed upward through holes

drilled in the wood. The fire extended upward by burning out the wood.

12. The difficulty of fitting gypsum around the gas pipes caused the area around the gas meters to be left unprotected. The fire extended upward through

the unprotected area.

13. Oversized holes for plumbing pipes, or unclosed openings in the ceiling

for repairs also permitted extension.

14. Fire came into a building following the main electrical service. The

fire department sized the fire up as an electrical fire. Following cables,

which went up through an opening in the ceiling, the fire extended upward through

the building and involved a dozen or more apartments.

15. Access plates are sometimes provided in basement ceilings for access

to plumbing. In one incendiary fire it was believed that an access plate had

been deliberately opened to permit extension of the fire.

16. The built-in metal bathtub "substitutes" for the drywall sheath.

In one fire, studied before this investigation, it was evident that fire

extended into the apartment from the wall by conduction through the bathtub.

At least one building code requires that drywall be complete behind a plastic

bathtub, but I have not seen sheathing behind a steel or cast iron tub.

17. A wooden floor joist with plywood nailed on top and gypsum nailed on

the bottom (the ceiling) serves as a stop to the spread of fire at right

angles to the joist. In earlier construction practices, a double joist was placed under each partition wall to carry the weight of the plaster. This

practice is not necessarily followed in current construction. Floor joists

are laid on 16 inch centers and the partitions of the floor above are laid out

as directed by the architect. As a result a partition wall between apartments

may rest on the plywood floor, between two joists. In two cases a fire starting

in one apartment close to the partition wall burned down through the floor to

the joist void, which was common to the next apartment."^ The fire then burned

up into the next apartment. In one case this was how the fire was discovered.

18. Plywood surfaces are installed for decorative effect. Often the plywood is the only wall sheath, and thus, the void space is quickly penetrated.

Walls of hardboard decorated to look like plywood have also been noted.

19. More expensive detailing does not necessarily produce greater fire

safety. In low cost work the walls are finished and then kitchen cabinets are hung on the wall. In more costly work, soffits are built down from the ceiling

^The entire testing concept of "fire-resistive combustible" floor and ceiling

assemblies is open to question. The test fire attack is made only against

the gypsum board ceiling. No assemblies are tested by a fire attacking the

wooden floor. Fires in fact burn downward through floors quite readily.

Those constructions which provide huge voids under the floor, such as trussed

floors, provide a potential for disaster when the floor is penetrated from

above

.

184
Figure 3. Kitchen cabinets. These "built-in" cabinets are attractive in

appearance, but the only barrier between a kitchen fire and the inner

voids of the building may be 1/8 inch of hardboard forming the top of

the cabinet.

line. Gypsum board is applied to the ceiling and the vertical surface of the

soffit. The bottom of the soffit is left open. The cabinets are then installed.

The only barrier between a kitchen fire and the void spaces is the thin top of

the kitchen cabinet, often 1/8 inch hardboard (see fig. 3) . The determining

factor in the confinement of a kitchen fire to the kitchen is often, whether the

cabinet doors are open or closed. Where kitchens are back-to-back these

soffits are common voids. Soffits are also provided to conceal heat ducts.

Along interior apartment partition walls they are often back-to-back creating

another void common to two or more apartments. These voids are often interconnected to vertical voids discussed further on.

20. Fire extended through the narrow vertical void formed by gypsum board

furred out from a masonry wall on 1" x 2' strips.

21. While no fire extension has been noted, some apartments are built

with "sunken living rooms". The offset between the rest of the apartment

floor and the living room floor is covered by a vertical board nailed in

place. It appears likely that this would pass fire sooner than a floor all in one plane. There is no listed construction of this type.

5. ATTIC AND OTHER CONCEALED VOIDS

1, In a few cases nominally flat roofs are used. Even such a roof has

interconnected void spaces because a pitch must be provided to run the rain

off the roof. The difference between the pitched roof and the horizontal

ceiling joists creates openings so that the roof joists do not serve as fire

stops. In one case there was no void (see fig. 4) . The roof was of plank on beam construction and the interior followed the room pitch. It did not fail

structurally, but fire charred the entire surface, possibly due to the use of

a high flame spread finish.

2. The usual attic is a high pitched gable roof, of sheet plywood on lightweight gusset plate trusses. When the attic is invoJ.ved the fire is

spectacular (fig. 5) , and often is stopped only by a true fire wall or by the

end of the building.

The attics are provided only for heat relief, architectural effect and

sometimes utility services. They are not used for storage. Access is usually

by a scuttle hole in the top floor stairway ceiling.

Fire can reach the attic in several ways.

185
Figure 4. Penetration of the attic void permits fire to attack the top floor

ceiling from the upper side - note the burning on the bottom chords of the

roof trusses. Water required to extinguish the fire causes the ceiling to

drop. Water damage down through the building is often severe.

Figure 5. A typical garden apartment fire. The combustible attic makes a spectacular show, for the passerby, but not for the many families victimized by incompetent design.

186
Requirements for attic ventilation are often met by the provision of a screened opening along the soffit under the roof overhang. In one fire, a top

floor tenant returned home late at night, started cooking, fell asleep, and awoke

to find the kitchen in flames and the apartment filling with smoke. He opened

the balcony door (this probably saved his and his father's life). This gave

the fire immediate access to the attic as flames rolling out of the living room

engulfed the vent. Other tenants fleeing the building found pieces of the roof

falling on their heads as they came out of the stairway.

3. Little attention is given to fire resistance of the roof overhang

soffit. Soffits are constructed variously of plywood, hardboard, and aluminum.

Flame pouring out a top floor window or balcony doorway, and even from the floor

below the top floor, have attacked and penetrated such materials with ease. Balcony overhangs are a particular problem. In the case of reentrant

balconies, there are varying practices. Wire lath and plaster, with the customary nullifying attic ventilator has been noted. In some cases gypsum board

painted with a moisture resistant has been used. In most cases plywood or ^

hardboard is used. Most jurisdictions have laws against the use of charcoal

grills on balconies, as much for the protection of those passing below as a fire protection measure. The enforcement of the law is usually in response to

complaints, and the transgressor righteously points to the caution on the charcoal bag that it not be burned indoors. In one fire the top floor tenant

apparently accelerated his fire with gasoline and then went in to prepare the

food. On arrival the fire department found a full blown attic fire which burned

off the entire attic. Necessary water damage made the lower floor apartments

uninhabitable

In another case children playing with matches and charcoal lighter fluid

on a top floor balcony started a fire which entered the attic via a plywood

soffit with ventilation opening. The attic was fully involved on arrival of

the fire department.

4. "Noise Pollution" is not a new complaint. Over half a century ago the

double wall to prevent noise transmission between apartments was developed.

This is an arrangement of a double row of studs; alternate studs are offset

so that the separate wall surfaces do not share the same stud. Earlier, sea grass was inserted for a sound deadener. Currently, mineral wool or glass fiber

is used. This arrangement, of course, negates the "fire stopping" which is an integral part of the "rated" dry wall-wood stud construction.

At the top floor ceiling, the channel between the two stud walls is open

to the attic. Fire in the void space extends into the attic.

5. Earlier in the paper we noted the use of vertical channels for plumbing

piping; these often serve the purpose of double walls for soundproofing.

When kitchens are installed in the interior of the building, vertical

exhaust ducts are provided leading to the roof. The voids for these ducts are often interconnected with soffits above the kitchen cabinets, and soffits

around heat ducts so that there is a truly huge amount of interconnected void

space, all of which is connected to that big overall void, the attic.

6. When extension of fire through vertical voids is considered by fire

departments, it appears that attention is devoted almost exclusively to the

very evident potential for upward extension. In fact, in addition to the

traditional "conduction-convection-radiation" ^ methods of fire extension,

fires often extend by flaming material, moving upward, downward, or laterally.

^These are more accurately the methods of heat transfer, not the mechanism of

fire spread.

187
An electrical defect started a fire within such a void between two first

floor apartments. Flaming material fell out onto an upholstered chair in the

basement. First arriving volunteer fire units assiamed that the chair fire was

the full extent of the problem; additional responding units were returned to

quarters by radio, and it was necessary to recall them when fire was detected

coming from the attic.

6. FIRE WALLS

The use of masonry walls to limit the spread of fire is as old as the

republic. The first building code of the City of Washington, signed by

President Washington, required that the outer walls of all buildings be built

of brick or stone. "Trade-offs" were not unknown even then; the wall was directed to be a "party wall"^ and the second person sharing the use of the

wall was required to reimberse the original builder of the wall.

Fire walls or barriers are intended to provide a physical limit to the area involved in a fire.

The ideal fire wall is free standing masonry wall, parapetted through the

roof, projecting through the exterior wall, or tightly joined to an exterior

masonry wall which is unpierced for a distance of several feet on either side

of the fire wall. Such a wall should be capable of stopping the extension of

fire independent of the operations of the fire department.

The following deficiencies have been noted. For most of them specific

examples of fire extension are contained in the reports.

1. Fire wall used as bearing wall. Main wooden girders of adjacent

townhouse were lodged in common wall sockets. In one case these were photographed before a fire had occurred. When a fire occurred over 2 0 units were

destroyed. A perhaps apocryphal story quotes an official of the construction

company as saying, "Those fire walls were terrific; they were the only thing

left standing" (see fig. 6)

.

2. Fire walls complete only to the underside of the roof. There is

rarely a "meeting of the minds" between the masons and the carpenters as to

where the underside of the roof will be. The gap has been seen to be as much

as four inches. Given the basic gas relationship of Temperature, Volume and

Pressure, it is obvious that pressurized heated gases will pour through this

void, but few building inspectors or tradesmen are familiar with elementary

chemistry.

3. Lewis Mumford called the Mansard the "crowning indignity of the seventies", and that was a hundred years ago. The Mansard provides a fire path around

the end of the fire wall, unless a cantilevered beam supports a masonry extension of the wall.

4. Where officials are stern supporters of fire wall integrity, utilities

are installed in trenches parallel to the buildings and each building is served

by laterals. At times the easier method of running the utilities through the

fire walls is permitted, thus, providing a hidden fire extension path. In one case the gas main passes through the attics and service is dropped down into the

apartments. The fire walls in this case extend only to the top floor ceiling.

The attics are overlapping truncated wooden pyramids, and the opening around the

gas main provides a fire path from attic to attic.

See Brannigan, "Building Construction...", p. 119, for a discussion of the

fire deficiencies of the party walls.

188
Figure 6. The firewalls were all that was left.

5. This matter of fire walls extending just to the top floor ceiling line

has a history. As "New Law" apartment houses of larger size were being built

in New York during the 30 's, the limitation of building area was maintained.

Larger buildings were created by joining together two or more units with a common ground floor lobby. The concept of life safety was paramount and thus,

it was felt necessary to extend the fire walls only to the top floor ceiling.

In several disastrous fires, fire spread through the common "cockloft" (shallow

attic) . Eventually fire walls were required to be parapetted.

6. In some cases one common facility such as the laundry may be under

one unit, while the storage rooms may be under the next. To provide all weather

access, swinging fire doors are provided in the fire wall between units. These

are almost invariably found propped open. While no fire extension was noted

due to this defect, in one case smoke in dangerous quantities filled the stairway of the next unit. The occupants were rescued from balconies. In hindsight this risky operation was unnecessary but it is difficult to explain this

fact to a panicky citizen threatening to jump.

7. Soffit roof overhangs are constructed beyond fire walls, thus providing a fire path out of access of hose streams and out of sight.

8. Fire barriers in attics are often constructed of gypsum on studs.

Defects include failure to construct barrier in the overhang, failure to fit

tightly to the roof, failure to tape and set nails, and openings cut by maintenance personnel for passage from unit to unit. In one case the inadequate fire

stop did serve to hinder the extension of the fire, but the fire did extend to

the roof over the adjacent units on each side. Necessary water use and the

partial damage to the roof made 12 apartments uninhabitable in addition to the

6 directly affected by the fire.

189
9. In rolling terrain the roof line of the lower unit may be several feet

below the top of the masonry wall of the next and higher unit. The fascia

board on the sloping edges of the higher roof has been ignited by fire coming

through the lower roof.

10. One Florida condominium could have been an excellent building, but

there were two weaknesses. The building was of concrete block construction,

the floors were of reinforced concrete, and the units were separated by block

walls, to the top floor ceiling. Unfortunately, the attic fire stops were of

gypsum applied to the sides of the trusses, where they happened to be located.

Thus, the fire stop did not continue the vertical plane of the fire wall

between units. No matter, the fire barriers extend only to the building line,

and do not penetrate the overhanging void.

7. EXTERIOR EXTENSION

Combustible balconies figured in several vertical fire extensions. Combustible separators between two adjacent apartments sharing the same balcony

have also provided an extension path.

1. Plastic shutters burned and extended fire downward to shutters below.

2. Wooden paneling in the spandrel space between windows permitted

extension to the floor above.

3. Fire lapping out the window passed a masonry spandrel and entered

the floor above. As noted elsewhere fire lapping out of second floor window

bypassed the third floor and entered the attic via the soffit vent.

4. In one case a concrete balcony was credited by the fire department

with preventing extension to the floor above of a particularly severe fire.

5. In one group of apartments, second floor windows project beyond the

first floor. The underside of the projection is plywood. A first floor fire,

rolling out the windows will probably soon enter the second floor through the

plywood.

In one group of wood frame apartments the sheathing is of gypsum. This

is defeated, however, by huge two story "dormers" which create a monstrous

unfirestopped , inaccessible, combustible void on the exterior of the building.^

For some unaccountable reason, codes often require true fire walls between

separately owned row units, but permit common attics over similar "townhouse"

units (apartment with rooms on two floors) being rented. The conversion of

rental to condominium units has required building alterations to provide fire

separation between units.

In one case related to the writer, a selective insurer refused to write

contents insurance for a tenant of a garden apartment due to lack of fire walls.

A local fire marshal was examining the housing authority's plan for "townhouses". The fire separations conformed to the code for rental housing. He

convinced them to install fire walls between each dwelling by arguing that at some future date they might want to sell them to the occupants.

Both of these were noted outside the area in which the fire investigations

were made. This author is not aware as yet of any fires in which these

designs are a factor.

190
Permitted distances between separations are usually stated in square feet,

not in number of dwelling units. It is up to the ingenuity of the designer to

see how many units he can cram into one fire subdivision. This is a menace to

all in the area, and in some cases a loss of "livability" , if not direct fire

damage to all units, is an almost predictable result of any fire which involves

so much as one room. If this situation is to remain unchanged, perhaps the

victims of official neglect should at least be warned.

8. LIFE SAFETY AND FIREFIGHTING

1. Only a few fatalities occurred in the fires investigated and none could

be directly attributed to any building defect; however, there were some injuries

and "near misses".

2. Non self-closing doors permitted smoke or fire to escape into the

stairway from the apartment of origin. This often forces other occupants to

the refuge of the balconies. Rescue efforts slow down the control of the fire,

and ladder rescues are always hazardous.

3. Fire involving the attic can soon cause roof overhang structures to

fall on persons escaping from the building.

4. While nominally three stories high, garden apartments are often four

stories high on one side due to rolling ground. When this fourth floor is in

the rear it is inaccessible to truck mounted aerial ladders. The raising of

a 40 or 50 foot ground ladder requires the efforts of a well drilled crew of

several men which has worked together. This is not often delivered early in

a fire by volunteers, and paid departments often do not have enough men in

ladder companies.

5. Complicated street layouts and cul-de-sacs may improve the livability

of garden apartments, but if the first due fire unit commits itself to the

wrong driveway, the building can be lost. Fire departments expend great effort

to get maps of all projects and to drill drivers, but direction signs do not

take fire problems into consideration, and building numbers follow no standard

pattern.

6. A fire hydrant is a useless obstruction until a fire piimper hooks into

it, but hydrant locations are rarely coordinated with firefighting procedures.

7. In a number of cases substantial quantities of smoke were distributed

through hot air ducts and the void spaces around them.

8. Current design developments feature economy of material, often by

substituting geometry for mass. Gusset plate roof trusses are now commonplc.ce. Standard firefighting

procedures, based on the reserve strength in conventional wood rafters, often

call for men to get onto a roof to open it to release pent up heat ("ventilation" in fire parlance). To the best of the writer's knowledge, no firefighter

has been injured carrying out this practice on the fast to collapse, truss roofs.

The usual reason assigned is that fire is "through the roof" on arrival.

Recently we have seen floors made of wooden gusset plate trusses (see

fig. 7) . These provide a common unf irestopped void over (and under) the

entire area of four apartments on each floor. If, as is probable, the voids

are interconnected by vertical voids, the entire building can be involved in

fire very rapidly (see fig. 8) . The possibility of early structural collapse

cannot be discounted.

"I" beams rolled of steel develop their characteristic shape from the

flanges provided to resist the maximum compression (found in the top) and tension

(found in the bottom) . Until recently, there was no wooden "I" beam. Now such

191
Figure 7. These trussed floors permit a combustible void over and under the

four apartments on a floor. Vertical channels may interconnect the several

voids. In such a structure it is possible to envision collapse not long

after fire penetrates the void.

Figure 8. The combustible attic forms a vast horizontal flue.

192
beams are offered; 2" x 4" lumber forms the top and bottom flanges; the web is

plywood. Such a beam may carry the same load as its sawn counterpart, but it

appears self-evident that it could not make the same contribution to a fire

resistive (combustible) assembly as a solid sawn beam.

9. Many gas meters are often located in one room for ease of reading. In one case the twenty or so lines leading to apartments were grouped together

overhead in the passage between storage cages. They were supported by horizontal

pipes attached to the joists by pipe strapping. The failure of one nail dropped

all the pipes on advancing firefighters and caused a massive gas leak. A serious

tragedy was narrowly missed.

10. In one fire extensive areas of brick veneer fell off during the fire.

This falling masonry is hazardous both to escaping occupants and firefighters,

even though the building is not impaired structurally.

9. CONCLUSIONS

A meeting of builders is hardly complete without a speaker who raises the

shibboleth, "Buildings would cost far less if we didn't have those terrible

specification codes. New performance codes would let us use imagination and

technology." Here is a suggested "performance code":

"A combustible multiple dwelling should be so designed and

built that the "design basis fire" will be confined to the area of origin for 30 minutes."

The design basis fire would be a typical garden apartment fire based on a study

of fire loads. Such a requirement would lead to the elimination of many penetrations of the protective gypsum sheath. Where openings are necessary, there

would be a demand for listed devices to provide openings equivalent to the

protective sheath in fire resistance. Sociologically, the requirement should

have great appeal. Since each of us is entitled to do "his own thing" in his

apartment, the living conditions of others are equally entitled to be protected

(see fig. 9) . To have the tenants barely escape alive is no longer an adequate

design criterion.

What can be done to improve existing buildings to deliver the right to

"livability" to their occupants?

Work should be done to determine whether a few strategically placed high

temperature sprinklers, fed from readily available domestic water, could not

create a steam condition within vertical and horizontal voids which would act

to control the free movement of fire through these areas. A lightweight field foamable gypsum would provide a ready means of fire

stopping voids, after the installation of all utilities. No such material is

known to exist.

Retroactive^ legislation should require:

1. The installation of supervised automatic sprinklers fed from the

domestic system in all laundry, storage, rubbish and similar rooms. Fire officials are unanimous as to their effi-cacy.

2. The equipping of all apartment doors with door closers.

3. Renailing of poorly nailed gypsum, particularly ceilings.

1 "Retroactive" safety legislation is not "ex post facto" legislation and is

constitutional

193
Figure 9. Xmas Tree. The tenants of this apartment lived 200 feet away from

the apartment where the fire started. Should not the building "system"

protect them from the other tenant? "Fire Prevention" will not help these

innocent victims. Architectural awareness, adequate code requirements, and

competent enforcement are required to assure the right to live in peace.

4. Elimination of all plywood not mounted on gypsum board.

5. Elimination or adequate firestopping of all voids common to more than

one apartment.

6. Elimination of all exterior wood balconies, sheathing and soffits.

7. Painting of all combustible attics with fire retardant coating.

Greater efforts should be made to educate fire departments in the deficiencies of these buildings. Adequate education, leading to realistic prefire

planning, should contribute to cutting off the extension of a fire closer to

the origin.

Questioning of tenants discloses that probably less than half have personal

property fire insurance. Such insurance is usually quite cheap, so there is

little incentive to anyone to "sell" it. If the owner was required to provide

a personal property insurance policy up to some limit for each tenant, the

insurer would now be examining a much larger risk, and there might be some pressure from this quarter for improvement. This is not a foregone conclusion;

without a doubt, the buildings are insured.

In summary, since most of our population must be housed in multiple

dwellings, the constitutional right of a citizen to be secure in his apartment

home must be extended to protect him from a fire caused by his neighbor exer- cising his "constitutional right to be careless".

194
NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 411, Fire Safety Research,

Proceedings of a Symposium Held at NBS , Gaithersburg , Md . , August 22, 1973,

(Issued November 1974)

THE CURRENT STATUS OF FIRE DETECTION

George Sinnott

National Bureau of Standards, Washington, D.C.

The status of residential fire detection systems is presented

in terms of the major problems encountered in their use. This

includes a discussion of risk benefit considerations, false alarms,

and the effectiveness of alarms. The impact of these considerations

on acceptance standards for residential fire detection systems is

pointed out.

Key words: Alarm communications; false alarms; fire alarms; fire

detectors; risk benefit; smoke detectors; standards.

Common to much of what you have heard here today is the high expectation

of the ability of technology to solve many social, hiiman problems, even those

created by contemporary technology itself. This is so much in us that we find

ourselves surprised, for example, when what seemed like routine engineering

problems years ago have yet to come to fruition. This is true not only of the

so called "big" problems like breeder reactors or automated transportation systems but also of specialized ones like automatic fire detection. A nxamber of

articles and testimony before the National Commission on Fire Prevention and

Control, and before Congress have described the potential benefits of modern

fire detectors and hav.e expressed disappointment that for some reason fire detectors have not become widely used. I want to describe here what might be

called a "hangup analysis" of fire detection. That is, I want to explore the

hangups, those untoward social and technological side effects, that have prevented the wide acceptance of residential fire detectors.

A good place to' start is with an appraisal of the risks that one runs of

fire at home. Of the 12,000 fire deaths in the United States each year, a little over half occur in homes. There are about 700,000 residential fires

each year and since there are about 65,000,000 residences in the country this means that as an overall national average the mean time between fires per re- sidence is about 100 years. This gives us the first hint of a problem. There

are very few devices commonly used by man with a mean time between failure of more than 100 years. We must then face the situation of installing in our home

(or requiring others to do so in theirs) devices that have a much larger chance

of failing than of being useful, or else of creating devices of exceptional re- liability by any standard. What's more, these exceptionally reliable devices,

as we shall see later, must be exceptionally cheap.

The two ways of looking at the statistics, then, is perhaps thf first

hangup. At meetings like this we discuss the 6,000 lives lost and perhaps 10

times that many injuries and $874,000,000 direct financial loss each year.

Fire is nevertheless a rare occurrence for any one family. The average family

perhaps intuitively senses the 10,000 years mean time between fire caused death

per residence or the annual average $14 financial loss per residence and relegates fire well down on its hierarchy of fears. However, three major model

building codes in the country as well as the Department of Housing and Urban

Development's minimum property standards do now or will soon require fire detectors in residences. How alarmed should a person be at this hazard? Are

there rational implications as far as public policy is concerned? That is, is

there a statesmanlike position somewhere between being cynical and hysterical?

Some rather nice insights to this problem have been presented in recent years

in several articles by Chauncey Starr. [1,2] The argument here is put in terms

of the risk of fatalities even though injuries are certainly an important con- sideration. The problem with discussing injuries is that the severity of injuries is difficult to measure and the statistics are haphazard.

195
Natural disasters (floods, earthquakes, tornadoes, and storms — "acts of

God") cause 5 to 10 deaths per million population per year. Over the years,

the human attitude has adjusted itself to this so that this tends to set a base

level for noticeable risk. Man-made risks at this level can be considered almost negligible. On the other hand, fatalities due to disease are the major

cause of man's mortality and a hazard of this magnitude appears to represent

the level of a fearful risk. As indicated in figure 1, that is about one per

hundred years on a population average. (There are 8,766 hours in a year or

114 years per million hours) . Starr adduces evidence that on a per hour of ex- posure basis, society adjusts its activities in terms of risk and perceived

benefits in a rather consistent manner and notices a factor of a thousand difference in the apparent level of acceptable risks between those activities that

an individual voluntarily undertakes and those activities forced on him by the

makeup of the economy, that is those activities undertaken collectively. The

two levels of risk, disease, and natural disasters, are indicated by the dashed

lines in figure 2. The two lines indicate Starr's conjecture on society's riskbenefit trade off levels for voluntary and involuntary activities. I will not

go into his calculation of the benefits of the various indicated activities. [1,2]

With this point of view as background, then, let us look into the riskbenefit situation for fire detectors. It has become part of the folklore of

fire* protection that fire detectors could save about a third of the residential

fire fatalities. This is based on some studies done more than 10 years ago. [3]

This is probably a reasonable estimate, but it is complicated by some unfortunate correlations with senility, alcoholism, and other disabilities. For example, the Baltimore City Medical Examiner and the Johns Hopkins Applied

Physics Laboratory in Howard County have some preliminary statistics based on detailed autopsies conducted on fire victims in that area that indicate that

many of the victims had significant levels of blood alcohol. It is not easy

to determine how much good fire alarms would do in many of these situations.

Nevertheless, let us assume that fire detectors in every residence in the

country would prevent 2,000 fatalities per year, which is to say that the risk

of fire fatality would be lowered by about 2 x 10"^ per person per hour at

home. Or in other words we can estimate one life will be saved per year for

every 30,000 installed detector systems.

We can compare the added risks of not having a fire detector in a home

to the benefit of not having to pay for such a detector. The only present

voluntary standard for fire detection systems in homes is the National Fire

Protection Association #74 which requires heat sensors throughout the house

and a smoke detector in a central hall. A system meeting this standard is an expensive one often costing more than $1,000. Amortizing this, adding for

maintenance and assuming each system protects three people you arrive at an annual cost of about $40 per person. On the other hand, a good single station

smoke detector very we]l might give almost as much protection at an annual

cost of $5 per person. Over on the left hand side of figure 2, in the region

of small risks and costs, I have located fire detectors. The model codes and

the Department of Housing and Urban Development are all going in the direction

of single station detectors because of the low cost. Presumably sporting types

such as hunters and skiers and even smokers would conclude that not having a single station smoke detector in the house is a foolish risk considering the

small cost. A member of the Bureau staff is now chairman of this NFPA committee that maintains #74 and they will be looking into appropriate changes in

that standard. I hope that I have made the point that the problem of benefit

versus costs places severe restrictions on the proposals that one can entertain for new improved fire detection methods.

The cost of installation, however, is not the only cost that has to be

considered for fire detection systems. There is also the question of false

alarms, perhaps hangup number two. Good statistical information on this is

unavailable. As an example of field experience, however, tables 1 and 2 present

some data compiled in England. [4] The general experience is that there are somewhat more than 10 false alarms per real fire. The English data are for

196
4.0 X 10-6

3.5x10-6 -

MORTALITY

Figure 1. The overall mortality

rate provides a reference

against which particular

hazards can be compared. For

simplicity, in this paper, we refer only to the population

average

20 30 40 50

AOE GROUP ( YEARS)

RISK TOLERANCE

AVERAGE ANNUAL BENEFIT/PERSON INVOLVED (DOLLARS)

Figure 2. With the exception of fire detectors, this figure is taken from

Starr [1] . The location of fire detectors on the graph indicates the

lowered risk of fatality provided by fire detectors compared to their

cost. The NFPA Standard #74-1972 does not allow for a range of tradeoffs by the consumer. (This has been modified in the 1974 edition of

the Standard.)

197
commercial systems and are not directly applicable to residential situations.

The reasons for false alarms will be different in residential situations,

however, our general experience is that there are a lot of them. This limits

the application of fire detectors in homes to modes where the cost of responding to an alarm is very low. One handle that we have that can be used to

improve detectors and their false alarm problems is standards.

Historically, fire detection has been associated with the melting of fusible links or other mechanical, temperature-sensing devices. Getting the re- quired speed of response and sensitivity in these devices is a design problem

and the standards that have evolved over the years have been primarily sensitivity standards. These standards have also been directed towards the free burning open fire that produces a lot of heat and develops rapidly. These fires are characteristic of some of the industrial and commerical hazards, but the

pattern of loss in homes is quite different. Forty percent of residential

fire casualties come from fires that start in bedding or mattresses or upholstery. [5] These fires are not the kinds of fires that we are accustomed to

thinking about, but these represent the hazards that potentially might be

reduced by detectors. These fires develop very slowly, giving off smoke and

carbon monoxide but little heat. The detectors that are effective for this

kind of fire are the electrically-operated, smoke detectors. These detectors

can easily be made with virtually any sensitivity, limited only by their incidence of false alarms. Deciding on a figure of merit and an acceptance standard

for this kind of detector requires the incorporation of the concept of signal

to noise ratio into the standard, A research associate from Underwriter's

Laboratories will be with us for the coming year to make use of our facilities

and resources in the generation of performance standards relevant to these

needs. It is a technical task of no mean proportions. There are two levels

of trade off involved. First, there is sensitivity to fire versus false alarm

rate. Then there is the false alarm rate versus effectiveness of response.

That is, there are situations where it would be advantageous to have a less

sensitive, slower responding detector in exchange for a more effective response

such as alerting the entire apartment house or one's neighbors when it did

alarm.

Smoke aerosols are very complicated, being a mixture of organic liquids

and tars, carbon particles, water, etc. Undoubtedly, there are many subtle

ways - composition, droplet structure, size distribution - by which the aerosol

maintains some clues to its origins. At present there are two types of smoke sensors in common usage. One is the so called ionization type. It consists

of a small ionization chamber where the air is kept weakly ionized by a radioactive source, usually on the order of a microcurie of americium 241 or radium

226. An electric field produced by two electrodes in the chamber induces a current on the order of a nanoampere which is monitored. The magnitude of this

current is determined by the competition between collection of the ions by the

electrodes and gas phase recombination. Diffusion of gaseous ions to the surface of any aerosol particles that are present alters this balance in favor of

recombination and reduces the collected current. This type of detector has a sensitivity bias towards very small particles. On a per mass of aerosol basis,

the sensitivity is proportional to one over the particle radius squared for

particles of 100 k diameter and up.

The other common type of smoke aerosol sensor is the optical type. This

type sends a pencil beam of light into a chamber that is protected from stray

light but where smoke is allowed to enter and detects the presence of aerosol

particles via the scattered light. This type has a maximiim sensitivity for

particles whose diameter is of the order of the wavelength of light with

decreasing sensitivity for larger or smaller particles. Further development

of these devices as well as possibly the invention of new detection principles

in the future, may well exploit some of the subtle characteristics of smoke

aerosols to greatly improve the discrimination against false alarms by smoke

detectors

.

198
Table 1. Summary of Calls Received

No. of calls to fires No . of False calls

Type of system By system By other false per

installed means calls fire calls

All types 489 288 5,440 11.1

Heat 193 105 2,146 11 .

Smoke 101 37 1,429 14.1

Sprinkler 101 125 1 , 04 8 10.4

Manual 55 10 243 4.4

Mixed 18 6 137 7.6

Heat and smoke 18 2 410 22.8

Unspecified 3 3 27 9.0

Note: There was also one false call from gas detector equipment.

Table 2. Summary Table of Reasons For False Calls

Reasons for false calls

Totals (all types

of equipment)

No. Percent

Ambient conditions

Extraneous heat and smoke 951 17.5

High ambient temperature 233 4.3

Condensation, snow, rain, etc. 153 2.8

Low ambient temperature 37 0.7

Steam, vapor 29 0.5

Draught, high wind 7 0.1

Total 1,410 25.9

Mechanical and electrical

Defective wiring on control unit 602 11.1

Defective head 539 9.9

Surge in mains 411 7.6

Miscellaneous (e.g. broken pipe) 293 5.4

Direct impact on head 244 4.5

Vibration of system 215 4.0

Shock (e.g. falling weight) 151 2.8

Voltage drop, power cut 42 0.8

Defective push button, etc. 10 0.2

Total 2,507 46.1

Communication

Testing, maintenance not notified 478 8.8

G.P.O. activity 335 6.2

Defect in connection to brigade 88 1.6

Total 901 16.6

Unspecified and vmknown 62 3 11.5

Total (all reasons) 5,441 J.«0

199
The last and m a way the most wide open problem is what should happen

when the fire sensor senses a fire. It has a sort of an E.T.I.P, (Experimental

Technology Incentives Program) kind of flavor in that it is a question of stimulating the invention of, the testing and evaluation of, and finally the

implementation of suggestions for new modes of alarm. I think that this is a very important technical problem in fire detection.

As an example, consider a telecommunications aspect. It is widely recognized that it would be better to alert the fire department or the neighbors in

addition to a potential victim near the fire rather than only having a local

alarm. Many of these schemes require some kind of telephone communication.

This normally now requires a leased telephone line which often is by far the

most expensive part of the system. The cost of the leased telephone line, in

fact, usually makes these schemes impractical. But dedicating a telephone

line to this service is something like building a separate set of highways for

exclusive fire truck use. It is much cheaper to pre-empt existing roads for

emergency use with a siren. For telephone lines this would require the availability of a control function or what is known in the computer trade as an interrupt capability. What prevents this is not so much the technical problem

but rather the absence of an economic or social pressure to advocate this provision in the telephone tariffs.

In summary then, there are three major points that must be kept in mind

when attempting to make progress in the business of fire detection and alarms.

One is the dilute nature of the hazard. This is a fact of life in the fire

safety business that we must learn to live with gracefully. I present it not

as a source of discouragement but as a challange to our cleverness. Lest we find ourselves tilting at windmills, action in this area must be based on a more thorough analysis of our fire loss experience.

The second is that the sensitivity or quickness of fire alarms is limited

by our tolerance of false alarms. Improvements in this regard require either

that we envision ways of being more tolerant of false alarms or that we develop

detectors that produce fewer false alarms. In this latter category are those

nice gadgeteering types of activity where we in the science-engineering fraternity feel so much at home.

The third is the observation that, as can easily be shown in the laboratory, ringing a bell does not in itself put out a fire. The effectiveness of

an alarm must be viewed in terms of some series of actions, if any, that the

alarm initiates. It is possible that effort spent on devising alarm systems

that trigger more constructive responses to the emergency might be among the

most promising opportunities that we have to make improvements in fire detection systems.

REFERENCES

[1] Starr, Chauncey, Social Benefit versus Technological Risk, Science, Vol. 16

1,232 (1969).

[2] Perspectives on Benefit-Risk Decision Making, National Academy of Engineering (1972)

.

[3] McGuire, J. H. and Ruscoe, B. E., The Value of a Fire Detector in the

Home, Fire Study #9 of the Division of Building Research, National

Research Council, Ottawa, Canada (Dec. 1962).

[4] Fry, J. F. , The Problem of False Alarms from Fire Detection Systems,

Problems of Automatic Fire Detection, Institut fur Elektrische Hachrichtentechaik, Technischen Hoshschule, Aachen, Germany, Conference Proceedings , 37 (Oct. 1972)

.

[5] Pingree, Daniel, Material Ignited and Fire Casualties, Fire Journal, Vol.

65, No. 3, 8 (Mar. 1971) . 200
NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 411, Fire Safety Research,

Proceedings of a Symposium Held at NBS , Gaithersburg , Md . , August 22, 1973,

(Issued November 1974)

SEQUENCING THE PURCHASE AND RETIREMENT OF FIRE ENGINES

Patsy B. Saunders and Richard Ku

National Bureau of Standards, Washington, D.C.

A mathematical model and solution method are presented for the

problem of determining an "optimum" manner of sequencing the purchase

and retirement of fire engines. The method calculates that stream

of "buy and retire" decisions which, subject to certain natural con- straints (such as limits on annual acquisitions) , minimizes the

operating cost of the fleet of engines over a prescribed planning

period. Implemented as an efficient computer program, the model has

been applied to illustrative data from the Washington, D.C. Fire

Department. The approach carries over to problems dealing with the

replacement of other types of items (e.g., ambulances, small fleets

of aircraft, typewriters) whose reliability-maintenance becomes increasingly expensive with age.

Key words: Dynamic programming; equipment replacement; fire engines.

1. INTRODUCTION

This paper describes a method to determine an "optimum" manner of sequencing

the purchase and retirement of fire engines (hereafter simply called "engines")

,

with specific application to the Washington, D.C. Fire Department. The model

developed, however, has more general applicability as regards both the equipment type and the fire department. Because of the apparent similarity of the

present problem to conventional equipment replacement problems, we first will

review briefly some of the ideas in the equipment replacement literature.

Equipment replacement problems have a long history in industrial engineering

and operations research. The reader is referred to [1] for a comprehensive

bibliography on this subject. One class of equipment replacement problems

balances the cost of failures against the cost of planned replacements [2]. If

units are to operate continuously over some time period [0, t] and are replaced

upon failure, then typically the expected cost C(t) during [0, t] may be given

by

C(t) = c^E[N^(t)] + C2E[N2(t)], (1)

where

= per unit total cost resulting from a failure and its replacement,

= per unit total cost of replacing a non-failed item {c^ < c^)

,

N^(t) = the number of failures in [0, t] , a random variable,

N2(t) = the number of replacements of non-failed units, a random variable,

and E denotes expected value. The problem is to minimize eq (1) over the

possible replacement procedures available within a given policy of replacement.

Examples of replacement policies are: strictly periodic replacement, random

periodic replacement and sequentially determined replacement. Electronic com- ponents typify the equipment to which this well developed mathematical theory

applies.

201
A second class of equipment replacement problems, called "preparedness"

problems, ass\ames that a piece of equipment is kept in a readiness state for

use in case of emergency. The objective is to maintain the equipment in a state of operational readiness at minimal cost. Thus, a sequence of inspection

and replacement actions that minimizes the ratio of expected cost per unit time

to proportion of "good"^ time, would constitute an "optimal" decision stream

[1,3] . Large military hardware provides examples of the type of equipment to

which this class of models may be applied.

One of the basic underlying concepts of the two classes of equipment

replacement models discussed so far is that of a reliability function^ . This

is the probability R(t) that the equipment is "good" at time t (measured from

a time at which the equipment is considered to be "new") and is exemplified by

the negative exponential form

R{t) = exp (-Xt) . (2)

A closely related concept is the failure rate, defined for any reliability

function R(t) as p (t) = -R'(t)/R(t), where the prime denotes the derivative.

For the negative exponential, the failure rate is the constant X. A third class of equipment replacement problems deals with the replacement

of items that deteriorate. Mathematical models to solve this class of problems

typically trade off the increasing operational and maintenance costs (and decreasing resale value) of an aging item against the cost of a new purchase, i.e.,

the "optimal" replacement time is that time at which these opposing forces are equalized. Dreyfus [5] used a dynamic programming approach to solve this problem under the additional complication of technological change.

The main concern of this paper is the development of a model to determine

purchase and retirement decisions over a planning period, subject to certain

constraints, which would minimize the cost of operation of a fleet of engines

during that period. The concern of the Washington, D.C. Fire Department was not

with the cost of failure or the distribution of failures of fire engines per se

,

primarily because of the negligible n\imber of engine failures and the inability

to measure the "cost" of a single engine failure. The model developed may be

regarded as an extension of the ideas represented by the third class of equipment replacement problems discussed above.

Section 2 describes a simple calculation, which serves to introduce the

data at hand and compares the results of this calculation (as applied to

Washington, D.C.) to those of a study [6] from which the data were obtained.

A dynamic programming (DP) model is formulated and given illustrative application in section 3, and directions for further investigation are suggested in

section 5. Section 4 lists formulas for computing upper and lower bounds on

the variables of the dynamic programming model. For the derivation of these

bounds, as well as for an integer programming analog to the DP model, the

reader is referred to [7]

.

2. INITIAL CONSIDERATIONS

Aside from personal communications with members of the staff of the

Washington, D.C. Fire Department, the main source of data was a report by

Balcolm [6] . That report also proposes a model for determining the life-span

of an engine, which will be described later.

^It is implicitly assumed that the equipment is either in a "good" or a "failed" state.

^See [4] for a discussion of the statistical theory of reliability.

202
A linear relationship between engine age and maintenance cost was used in

[6], and least-squares regressions yielded three sets of coefficients, corresponding to "high usage," "medium usage," and "low usage" engines. Balcolm

then obtained a "composite" equation — a weighted average (by the number of

engines in the three categories) — which this paper also uses. This equation

is of the form:

= Uq + U-^a, (3)

engine age,

the maintenance cost of an engine entering its a^^ year of service,

24.17,

122.46/year.

Values of u^ are listed in table 1. This relationship was adopted as the basis

of the data for maintenance cost since it was felt that a more complex function

could not be supported by the observed cost figures.

where

a =

U„ =

Table 1. Data For the Dynamic Programming Model

a Qa -a* t=l

(1971)

t=2

(1972)

t=3

(1973)

t=4

(1974)

t=5

(1975)

1 4 147 14,474 8,684 5,211 3,126 1,876

2 0 269 8 ,477 5,086 3,052 1,831 1,099

3 10 392 4 ,961 2,977 1,786 1,072 643

4 5 514 2,902 1,741 1,045 627 376

5 0 636 1,696 1,018 611 366 220

6 5 759 991 595 357 214 128

7 10 881 578 347 208 125 75

8 0 1,004 337 202 121 73 44

9 5 1,126 197 118 71 42 25

10 5 1,249 114 69 41 25 15

11 3 1,371 67 40 24 14 9 12 4 1,494 39 23 14 8 13 4 1,616 22 13 8 14 4 1,739 13 8 15 5 1,861 8 Values have been rounded to the nearest dollar.

A linear relationship was also used in [6] for the purchase price of a new engine, given by

= Pq + P^ (t - 1900) , (4)

where

Pq = -16258.18,

P, = 576.87.

All monetary quantities are expressed in dollars.

203
Values of are given in table 2. The choice of the "base" year 1900 is not

explained, but it accounts for the surprising (negative) value of Pq. The index

t refers to the year for which a value of the purchase price is desired.

Table 2. Purchase Price of a New Engine

t

1 (1971) 24700

2 (1972) 25276

3 (1973) 25853

4 (1974) 26430

5 (1975) 27007

*Values have been rounded to the nearest dollar.

Using these data, simple calculation can be made to determine an "optimum"

life-span for a single engine. Assuming a zero salvage value (for simplicity)'*

and a constant purchase price P, the accumulated total cost of keeping an engine

for n years is

n TC(n) = + U^a) + P a=l

n nU. + U, a + P

^ a=l

nUg + [n(n+l)/2] + P, (5)

Thus the average annual cost of keeping an engine for n years is

AC(n) = TC(n)/n

•= Uq + [(n+l)/2]U3^ + P/n. (6)

Clearly, the longer an engine is kept, the longer the time to amortize the

price P, so that portion of the cost per year will decrease with n. However,

the maintenance costs increase year by year. Thus, with the "optimum" lifespan defined as that value of n which minimizes eq (6) , the standard calculus

technique of setting the derivative of (6) equal to zero and solving for n yields

(d/dn) [AC(n)] = 03^/2 - P/n^ = 0,

whence

n = (2P/Ui)-'-/^. (8)

Since P > 0 and n > 0, the second derivative 2P/n is positive so that the

value of n given in eq (8) ensures a minimum value of eq (6) . Figure 1 indicates contours of the optimum value of n in the (U-, , P) -plane.

''Constant salvage values (with respect to age) can be represented by subtracting them from Uq.

204
Figure 1. Contours of the optimum engine life.

For Washington, D.C., using the 1969 purchase price, eq (8) yields n = 19.6,

considerably larger than the present life—span of 15 years. Balcolm [6] recommends a life-span of 10-11 years, depending on the number of years over which

an engine is linearly depreciated, using as his criterion the equality of

current (resale) value and accumulated repair cost, i.e., n is chosen so that

n

P - n(P - S)/N = ^ U^,

a=l

where N is the number of years over which an engine is depreciated and S is the

salvage value of an engine after N years. (Note that Balcolm assumes that the

number of years over which an engine is depreciated (N) and the number of years

it is kept (n) need not be the same.) No rationale for this criterion is

offered in [6] , but the large difference between the "optimum" life-span in

[6] and the one derived from the present calculation [eq (8)] indicates a significant difference between the two models.

3. A DYNAMIC PROGRAMMING MODEL

The dynamic programming (DP) model described in this section takes a some- what different approach to the problem of equipment replacement. Instead of

determining an "optimum" life-span which would be applied to all engines, the

DP model begins with the existing scenario and prescribes purchasing and

retiring decisions over a T-year planning horizon. (The index t = 1,...,T is

used in this model and appropriate notation changes are made in the relevant

formulas presented in section 2.) In this sense, the model may be "tailored"

to fit the initial state of affairs of any urban fire department. The reader

interested in DP in general is referred to the text by Nemhauser [8] . For

other DP formulations of equipment replacement problems, see [9] and [10].

205
In accordance with the concerns and objectives of the Washington, D.C. Fire

Department, the DP model determines the purchases and retirements to be made

during the planning horizon such that the total cost incurred during this period

is minimized. The model accounts for various constraints with which a fire

department must operate, e.g., constraints on the number of purchases and/or

retirements which may be made in any year, the total fleet size and the maximum

allowable engine age.

The DP "state variables" (those which describe the system at each stage, or year in this case) are

^It ~ number of engines in the initial fleet which remain in year t-1,

^2t ~ number of new engines purchased in years l,...,t-l,

= the maintenance cost in year t-1 on engines purchased in years 1,...,

(Note that x, . + x„ is the fleet size in year t-1.) The "decision variables"

6.2^ = the number of engines purchased in year t.

It should be emphasized that retirements are made only from engines in the

initial fleet, i.e., none of the engines purchased during the planning period

are considered for retirement. Since the- Washington , D.C. Fire Department indicated interest in a planning horizon of at most five to ten years, restriction

to retiring engines from the initial fleet only is not considered a limitation.

The data required by the model are D^ = the minimum number of engines required during year t (checked against

the fleet size after year t's decisions have been made)^,

= the maximum number of engines which may be purchased in year t,

= the maximum number of engines which may be retired in year t,

R = the age by which engines must be retired,

P^ = the purchase price of a new engine in year t,

= the number of a-year-old engines in the initial fleet.

t-1.

are

dIt the number of engines retired from the initial fleet in year t.

a

u the maintenance cost of an engine during its ath year of service.

a

^That D^ adequately measures the demand for fire service is a simplification.

206
V . = the resale value in year t of an engine which was initially of age

at e _'

= the age of the i^'^ youngest engine in the initial fleet (e.g.,

a-j^ is the youngest) .

As in the simple model of section 2, the maintenance costs are calculated as

u^ = Uq + U^a,

with the values of Uq and U^^ , as indicated earlier. The linear relationship

leads to a recursive definition of u^,

= Uq + U^a + U-,^

= u + U, . a 1 Letting = (x-,^^, x^^, x^^) , eq (9) may be used to obtain, as the stage

transformation formula,

^t+1 = (^It - ^It' ^2t + ^2t' ^3t ^ ^l^t "l'^2t^- ^1°)

The transformation for x, and x is clear. The value of x. . , ,

, the maini-t 2t J , t+i

tenance cost in year t on engines purchased in years l,...,t, is obtained by

adding to x^^ both the cost of the first year of maintenance for engines purchased in year t

(^]^<^2t^

incremental increase in maintenance cost on engines purchased in the preceding years (U-iX ), the latter deriving from

eq (9). 2^

The "stage return" is the cost of operation in year t. With the notation

d^ = (d^^, d2^) , the stage return is calculated as

^It-^lt ^It y ItK^V = (Pt ^ ^1^^2t ^ "a.-Ht - 1=1 1 i=x-|^^-d^^+l . 5 4.1 %t1

-^^ V2f

(11)

^The convention is adopted that an a-year-old enginfe in the initial fleet

enters its (a+l)st year of service at t=l . It is assumed, for simplicity,

that decisions are made at the beginning of a year, and that a >_1

''whenever the lower limit of a summation exceeds the upper limit, the summation

is taken to be zero. This is a standard notational convenience.

207
The components of eq (11) have the following interpretations:

(P^ + Uj^)d = the cost of purchasing engines in year t

^ and maintaining them during the first year of

service.

^It-^lt

1=1 i

a.+t = the maintenance cost in year t on engines which

remain from the initial fleet.

^It— T ^a +t = the revenue from retiring the d. oldest

i=Xl4.-dT,+l 1 . , • T J. • jfllt It It engines not previously retired",

X- + U X = the maintenance cost in year t on engines

purchased in years l,...,t-l.

The linear form of the maintenance cost yields the pleasing result that

the values of x^^ are all exact multiples of . ^ This, together with the fact

that x^^ and x^^ are integers bounded by the constraints, makes it computationally feasible to consider all of the combinations of values that the state

variables may assume in any stage. It follows that the optimal solution is

exact, rather than involving the sort of discrete approximation typically found

in DP problems. This characteristic is explicitly noted here as a favorable

feature of the model.

The recursive equations of the DP model are

f^(x^) = min [I^{x^,d^) + f (x^^^ ) / (1+r ) ]

,

*^t (12)

f^{x^) = min I^(x^, d^) .

The quantity r is a discount rate, so that division by (1+r) in the first

relation of eq (12) renders f^(x^) as the minimum present value cost of operations from years t through T, given that the state of the system in year t is

x^. Since the initial state is known to be x^ = (m,0,0), f-|^(m,0,0) is the

optimal value of the objective, i.e., the minimum total cost of operations in

years 1 , . . . ,T

.

The constraints of the DP model are straightforward from the definitions

of the variables and parameters:

0 ^

d^^ ^ (t=l,...,T), (13)

0 1 ^2t - \ (t=l, . . . ,T) , (14)

X + x^^ 1 D^_^ (t=2, . . . ,T+1) , (15)

t-1

E d. . > n (t=2, . . . ,T+1) (16)

j=l ID - t ^This assumption of retiring "oldest first" is supported by the Washington, D.C.

Fire Department.

^The proof of this can be found in [7]

.

208
where n = Q is the number of engines which must be retired prior to

^ a>R-t+l ^ year t because of the age limitation R. Note that by. definition the initial

conditions are: x^-,^ = m, x^^ = 0, x^^ = 0 and n^ = 0. With the definition

Dq = m, eqs (15) and (16) automatically hold for t = 1.

The constraints (13) - (16) and the relationships among the state and

decision variables lead to interesting and computationally useful results which

are detailed in [7] . Section 4 lists the bounds derived from these relationships. Suffice it to say here that a special computer code,^° developed as a part of this effort, takes advantage of these results to make it possible to

i solve larger problems than could be handled by a general purpose DP code.

I Furthermore, experience thus far has indicated that computer running times are

I significantly shorter using the special code. For example, one of the runs to

I be discussed below took 12 seconds using the special code, while the general

j purpose code^^ took 227 seconds. (Both codes are written in FORTRAN V and runs were made on the National Bureau of Standards' UNIVAC 110 8 computer under the

EXEC II Operating System.

)

In exercising the DP model, the maintenance costs and purchase prices were

the same as those discussed previously (cf., section 2). The purchase price

function was modified to

I P^ = Pq + P^ (70 + t) , (17)

so that t = 1 would correspond to 1971. The values of P^ and P^ are unaffected

by the modification and remain as listed under eq (4). The resale values v^^ were calculated on the basis of eq (17), assuming an annual depreciation rate p, using

^at = (1 - P)^"^^"""" [Pq ^ Pi(70-a+l)]. (18)

This allows the resale values of engines in the initial fleet (purchased prior

to t = 1) to be calculated from the appropriate purchase prices. -^^ Finally,

values of Q were obtained directly from the Washington, D.C. Fire Department's

a inventory of engines. These data are given in tables 1 and 2 with T = 5 (a

five-year planning horizon)

^

For the remaining data specifications , it was suggested by members of the

Fire Department staff to take R = 15 (the present maximum engine age in

Washington), D^ = 64 for t = 0,...,5 (i.e., constant minimum required fleet size

equal to the present fleet size) , and M.^. = N.^ = 6 for t = 1,...,5 (constant and

equal purchase and retirement ceilings)

A base run was made with no discounting, i.e., r = 0, and the resultant

"optimal" decisions were to purchase and retire 6 engines in each of the first

three years and to purchase and retire 2 engines in year 4, i.e., d^^ = = 6 (t=l,2,3), d . = d^. = 2, d = d„^ = 0. Note from the age distribution Q in

14 24 ' 15 25 a ^°A listing of this code can be found in [7],

^^This code is an extension of the code documented in [11].

^^A geometric depreciation is not required by. the model. It is incorporated in

the code, but can easily be modified with minor coding, changes.

^ ^Members of the Fire Department staff advised that a planning period of more

than five years is unreasonable.
table 1 that 20 engines reach the mandatory retirement age by year 5 (i.e.,

ng = 20) . Since the maximiim niimber of retirements permissible is 6 in each

year, the optimal policy is to retire the 20 engines as soon as possible (ASAP

policy) , replacing them with new engines to meet the minimum required fleet size.

The above results are not surprising in view of the discount rate r = 0. Increasing maintenance costs, decreasing salvage values and increasing purchase

prices all indicate early retirement. The same policy is optimal in the extreme

case where the purchase price is always zero. It is intuitively obvious that in

this situation the ASAP policy is optimal regardless of the value of r, since

the newly acquired (free) engines are operated at a lower maintenance cost than

are the old ones.

In order to study the effect of the discount rate r on the optimal decisions, a series of runs was made with as a parameter, taken from 62.46 to

162.46 in increments of 10.00. (Recall that the "nominal" value of \J-^ is

122.46.) Initially, r was varied from 0.0 to 0.5 in increments of 0.1 (a very

rough grid) , and based upon these results, smaller ranges with finer increments

were studied for certain values of U-j^. The following observations were made

consistently from the outputs of all the runs:

1. The only engines retired were the 20 which reach their maximum age

during the 5-year planning period.

2. In every year, the numbers of purchases and retirements were the same. This may be attributable to the constant demand and to the constant and

equal values of and over all t.

3. For those values of r considered, there was a value r^ such that for

r <_ the ASAP policy was optimal, and a value r^^ such that for

r >^ rj^ the optimal policy was to retire as late as possible (ALAP

policy). (The ALAP policy has d-^-^ = = 5, d^^ = d2^ = 4 (t=2,3,4), d^^ = d^^ = 3 for this particular problem.)

4. The values of r , r and r^ - r„ are monotonically increasing functions

of Uj^.

E L L E

The values of for which the behavior of the optimal policy, as a function of r, was studied in greater detail are listed in table 3 together with

the relevant results. All other values of U-^ considered gave rise to values of

r^ = 0.0 and r-|^ = 0.1 in the initial runs. It can be seen from table 3 that the

finest analysis with the smallest increments for r was made for the "nominal"

value of Uj^ = 122.46. For .080 < r < .089 the optimal decisions were "mixed",

i.e., neither an ASAP nor an ALAP policy. For example, with r = .085, the

optimal decisions were

^11 "'^21"^' ^^12 = ^22 = ^'

^13 = ^3 = ^' ^^14 = ^4 = ^'

^15 = ^25 = 0-

The "critical" range of r (.080, .089) is quite small, but it should be noted

that the values = = 6 do not permit a drastic difference between the ASAP

policy and the ALAP policy.

210
Table 3. Results of Finer Variation of r For Certain Values of the Parameter

"l Range of r Increment

62.46 .01 - .10 .01 .05 .06

122.46 .08 - .09 .001 .080 .089

152.46 .01 - .20 .01 .09 .11

162 .46 .01 - .20 .01 .10 .12

It is clear that if a value of r is specified, then the DP model may be run to determine the optimal policy. If r cannot be specified, then the values

of r„ and r^ may be determined for the given value of U, • Then one need only ill Li 1 specify whether r <^ r^ or r >_ r^^ to conclude that the ASAP policy or ALAP

policy, respectively, is optimal.

One run was made with = = 10 for all t, with the other data re- maining the same. With r = 0, the ASAP policy resulted; in this case

'11 = d23_ = d^2 = ^22 = ^It = St = ° (t=3,4,5). Unfortunately, lack of

time prevented further study of this case. Intuitively, one might expect a greater "critical" range of r since the larger values of and give rise

to a greater difference between the ASAP and the ALAP policies.

4. BOUNDS ON DP VARIABLES

Dynamic programming models are frequently subject to criticism because

although the formulation can be accomplished, the numbers of states and decisions to be considered make the model computationally unfeasible. Fortunately,

for the model described in this paper, there are relationships among the variables which make it possible to examine a limited number of states and decisions

for which the stage return ^^^^t'^^t^ calculated. Although technical in

nature, this aspect of the problem is of great importance to computational feasibility in the sense that computer storage requirements and running time depend

on the n\imber of states and decisions that the algorithm must consider.

This section will simply present the set of formulas to be used in calculating upper and lower bounds on both the state variables and the decision

variables. The full derivations and explanations of these formulas are given

in [7] . Before presenting the bounds, certain notational conventions should be

explained. Notations of the form X (x^^) and vi (x^^) will denote the greatest

lower bound (GLB) and least upper bound (LUB) of ^-^^^r respectively. Notations

of the form (x^^; Xj^^, X2^) will denote the GLB of X2^, given specific values

of X, and x„ . , namely x^ ^ = x, and x„ = x^ . As in section 3, it is underIt 2t' It It 2t 2t

stood that whenever, the lower limit of a summation exceeds the upper limit,

the summation is taken to be zero. With these notational conventions in mind,

table 4 lists all of the formulas needed to calculate' the ranges of the variables used in the dynamic programming model.

211
Table 4. Formulas For Ranges of the

Dynamic Programming Model Variables

T-1 t-1

X{x, .) = max {0, max [D ^ - E M. - N.]}

l£T<T+l j=l ^ j = T

^

T-1

y (x ) = m - max [n " X] ^ t<T<T+l j=t ^

A (x ; X ) = max {D - V M . - min [y (x ) , x + V N.]}

2t It 1<T<T+1 j^t ^ 1^ It jf-: :

-1 - t-1

t-1

p(x2t) = E M.

j=l ^

t-1

'^^3t' ^It' ^2t^ = "t-T (^2,T+1 - ^2t^

t-1

^2t = "^^^ f^2T' ^2t - ^j^

0-1

X* = max [D - X*, - E M ] ^ l<a<t ]=T J

t-1

X* = min [y (x^J , x^^ + E N . ]

y(x^^; x^^, X2^) = Ut-x(^2,T+l " ^2t^

T-1

E M, for l<T<a

j=l ^ 2t

x^^ for cr'<T_<t

k-1

0 is the largest value of k such that > E M.

j=l ^

A(d^^; x^^) = max [0, x^^^ -

212
Table 4. (Cont'd)

y(d^^; x^^, x^t) = {^t' ^It " '(^l,t+l^' '^It ^2t ^ \

T-1 t . - max [D^ - E M - X: N ] 1<T<^T+1 j=t+l j=T ^

'

X(d2t; x^^, x^^, d^^) = max [0,XU^^^^^; x^^ - d^^) - X2^]

y (d-^) = 2t t

5. CONCLUDING COMMENTS

It should be emphasized that the DP model has considerably greater generality than was indicated in the limited application to Washington, D.C. The

only model constraint on the data is that they be self -consistent (e.g. , M^ and

must be consistent with D^) . If, for example, an urban fire department sees

fit to reduce its fleet size because of overkill capacity or perhaps because

of declining demand, and the values of and N^ fluctuate because of a fluctuating budget, then a greater portion of the model's generality could be exploited.

The interactions among the variables and parameters of the model which are evident in section 4 should support this contention.

On the other hand, time limitations prevented any attempts to examine the

model with particular relationships among the parameters. It seems reasonable

that certain conditions, e.g., M^ = N^ = constant, or = a constant for all

t, could lead perhaps to closed-form optimal solutions, or at least might simplify the necessary DP calculations. Further research along these lines is

recommended. In addition to these basic issues, there is a need for further

sensitivity tests, with respect to the discount rate and the value of U-j^, for

other values of the parameters M^, N^, D^ and R. For instance, the optimal

values of the objective f-j^ira, 0, 0) could be compared for different values

of R (in some reasonable range of maximum ages) , leading to an "optimal" value

of R (i.e., one which minimizes f^^ (m, 0, 0)). Finally, runs with depreciation

rate p varying, or using a different (perhaps linear) depreciation policy,

would be desirable.

6 . REFERENCES

[1] McCall, J. J., Maintenance Policies for Stochastically Failing Equipment:

A Survey, Management Science, Vol. 11, No. 5, pp. 493-524 (1965).

[2] Barlow, R. E. and Proschan, F., Planned Replacement, Studies in Applied

Probability and Management Science, K. J. Arrow et al (eds.) pp. 63-87

(Stanford University Press, Stanford, Calif., 1962).

213
[3] Radner, R. and Jorgenson, D. W. , Optimal Replacement and Inspection of

Stochastically Failing Equipment, Studies in Applied Probability and

Management Science, K. J. Arrow et al (eds.) pp. 184-206 (Stanford

University Press, Stanford, Calif., 1962).

[4] Zelen, M. (ed.). Statistical Theory of Reliability (The University of

Wisconsin Press, Madison, Wis., 1963).

[5] Dreyfus, S. , A Generalized Equipment Replacement Study, JSIAM, Vol. 8,

No. 3, pp. 425-435 (1960)

.

[6] Balcolm, R. D., A Systems Analysis for the District of Columbia Fire

Department Dealing with the Replacement of Wagon Pumpers, report to the

Washington, D.C, Fire Department (1970)

.

[7] Ku, R. and Saunders, P. B. , Sequencing the Purchase and Retirement of

Fire Engines, Nat. Bur. Stand. (U.S.), NBSIR 74-513 (to be published).

[8] Nemhauser, G. L. , Introduction to Dynamic Programming (John Wiley & Sons,

New York, 1967)

.

[9] Ackoff, R. L. , Progress in Operations Research (John Wiley & Sons, New

York, 1961).

[10] Britten, A. A., Decision Making in Vehicle Management, Report No. S.15,

Local Government Operational Research Unit, Reading, England (1971)

.

[11] Bellmore, M. , Howard, G. and Nemhauser, G. L. , Dynamic Programming

Computer Model 4, The Johns Hopkins University, Baltimore, Md. (1966).

214
NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 411, Fixe Safety Research,

Proceedings of a Symposium Held at NBS , Gaithersburg , Md . , August 22, 1973,

(Issued November 1974)

FIFI — FIRE INFORMATION FIELD INVESTIGATION

F. James Kauffman and Martin E. Grimes

National Fire Protection Association, Boston, Massachusetts

The Research Phase of FIFI defined and evaluated those stateof-the-art investigation techniques used at the scene of fires to

report on the cause and circumstances of those fires. The two most

significant conclusions reached during the research phase were

(a) that very little literature is available to an officer interested in studying methods of general fire cause determination, since

most existing literature is arson oriented, and (b) that standardized training programs in systematic investigative practices do not

exist. The Development Phase of the project isolated the most valid

of the investigative techniques evaluated in the research phase, and

synthesized them into a new, simplified, logical, process-ofelimination investigation sequence known as HEP (Hexagonal Elimination Process) based on the NFPA Standard 901, Coding System For Fire

Reporting . Two prototype training packages were developed; designed

to aid firefighters in carrying out the systematic HEP investigation sequence in their initial, on-scene, routine fire investigations. The prototype training packages were field tested in six

fire departments of varying sizes and types.

Key words: Field investigation; fire information; fire investigations; fire training; programmed instruction.

1. THE PROBLEM

The National Fire Protection Association (NFPA) has maintained and published statistics and information on fire and its effects for many years. The

information received is used by NFPA's technical committees in the preparation

and evaluation of codes and standards. It is made available to any organization

engaged in fire research. However, it has been quite apparent that much of the

information on fire received by NFPA from various sources is deficient due to

lack of adequate field investigaticin and that the reports received frequently

do not contain material pertinent to research needs.

Recognizing this, NFPA employs investigators and utilizes its specialists

to make field investigations of special incidents. This must, of necessity,

be limited. If a higher standard of reporting from primary sources were available, its usefulness would be reflected, not only in NFPA's operations, but

also in providing a sound basis of data for all research workers in fire protection .

In order to make progress towards a uniform national reporting system and

with the obvious need for basic information for research purposes, a greater

emphasis on sound information gathering in the field is essential.

2. PRIME DEFICIENCY

Fire research requires an input of valid qualitative and quantitative data

on fire behavior.

^This work was done under a contract with the National Bureau of Standards.

215
The information required must include such items as cause, propagation,

development, growth periods, contributory acts or omissions, performance of

materials, and other factors, in order to provide a meaningful basis for research

and statistical analysis.

The validity of fire data depends on consistent accuracy and quality ioy

the primary reporting source. The Fire Service attends by far the majority of all fires occurring and,

considering the large number of incidents, would seem to be the most practical

and economical source of quantitative basic information. This does not preclude

reporting from other sources as a supplement. There is a need for separate indepth studies of incidents of special research interest and regional studies

for sociological and demographical purposes.

Most fire departments complete reports on fires attended, usually for local

record purposes. There is no uniformity and very few departments ascertain

information reliable enough for research purposes. This is partly due to lack

of demand on a local basis but is also due to the fact that fire department

personnel have not been indoctrinated or oriented to the need for such information.

The high incidence of fire has placed fire departments under pressures

which have resulted in undermanning and a need to reduce time spent at the scene

of a fire. As a result, officers often make only a cursory investigation of the cause and effect.

Special investigators are called in when arson is suspected, but they generally concentrate on the criminal aspects of the incident. They rarely get

involved with infoirmation necessary for research purposes. It is impractical

for specialist officers, such as fire prevention staff who might be better able

to report, to visit every fire.

There are several logical reasons why the fire departments should be the

primary field collectors of fire information. The firefighter, present at an early stage of the fire, sees much of its development and spread. He, of

necessity, removes or disturbs much that is relevant to determining the circumstances of the fire. The firefighter sees, but is not aware of, many indicators

that might be research potential. The officer charged with the responsibility

of completing the fire report could, if trained in a systematic approach and

with the assistance of properly oriented fire crews, easily obtain meaningful

basic information with a minimum of time expended.

Further, if special interest studies are to be carried out, it will be

vital that prompt notification be given in order that specialist investigators

of interdisciplinary teams can respond. Properly oriented fire personnel could,

in effect, provide reconnaissance to alert such investigators of incidents of

probable research value.

In general, little or no training is given to alert fire personnel to the

methods and value of identifying and collecting such information. They are certainly not yet oriented as to what might constitute research potential.

This is also probably true of other agencies involved in fire reporting.

3. RESEARCH PHASE

Four tasks were designated as necessary research activities prior to the

development of an optimum investigation system and training course:

TASK A: Review the availability of technical, scientific and

educational resources to support project.

216
TASK B: Survey current practices in training and methods for

field collection and investigation.

TASK C: To determine required information (quantitative and

qualitative) at each of the levels necessary.

TASK D: Identification of problems associated with current field

investigative techniques and establishment of criteria to

be used as a basis for development of systems.

3.1. Task A — Information Sources

Task A was a review and compilation of information available to support

the development of sound fire information field investigation practices. This

involved a complete search of the literature, files, and records of NFPA; a survey of those educational institutions which offered fire service courses and

degrees; and a survey of allied organizations such as the American Insurance

Association, Factory Insurance Association and the Federal Aviation Administration, for reference materials and procedures that they use in fire investigation . We also sought information suitable for the development of a systems

approach to fire investigation and fire investigation training.

3.1.1. Literature

A comprehensive literature search yielded 103 candidate books, articles,

and papers numbering approximately 4,000 pages. Of these, 65 were considered

reflective of the state-of-the-art in fire and arson investigation and were selected for further evaluation in Task D.

All reference materials and existing literature were found to be extensively arson oriented, with determination of fire cause becoming critical only

if it was suspected that the fire cause was something other than natural or accidental

3.1.2. Educational Establishments

One hundred fifty-two (152) colleges and universities in the U. S. offer

courses in fire investigation or fire related subjects. Details on the type

of training offered by these institutions is contained in the final contract

report^

3.1.3. Allied Organizations

Ten agencies or organizations are, or were at one time, engaged in fire

investigation and fire cause determination. Examination of their methodologies yielded useful information.

3.2. Task B -- Survey of Current Practices

Task B surveyed existing practices in fire investigation and available

training in methods of fire investigation. To accomplish this, a mail survey

of 2,268 fire departments was conducted. The data received from the 1,401 fire

departments who returned the survey form indicates that thorough investigations

^National Fire Protection Association, FIFI-Fire Information Field Investigation,

Phase I, Final Report, July 1972.

217
were mainly conducted on those fires which were suspicious or involved fatalities or major dollar loss. It also showed that fire department line officers

are generally responsible for conducting the initial investigation. Special

investigators responded only if requested. Formal training in investigative

procedures is conducted in very few departments. Those having training programs generally rely on the lecture method by an "experienced" fire investigator

since printed texts and publications are not widely available except in the

limited scope of arson determination. State Fire Marshal agencies are heavily

relied upon for assistance when special investigators are required, but very

seldom are outside specialists such as engineers, chemists, etc. utilized in

fire cause determination.

In addition to contacting the individual fire departments, all 42 State

Fire Marshal Offices were surveyed by mail. Fire Marshal survey tabulations

indicate a heavy emphasis on arson or on those fires regarded as suspicious,

those involving fatalities, or those constituting large monetary loss. Fire cause and damage determination appear to be the main objectives of such investigations. Details of fire spread and contributing acts are often a secondary concern of the investigation. Outside specialists are seldom used in state

fire marshal investigation activities.

In an effort to summarize the existing formal training in fire cause determination, 191 universities, colleges, and State Fire Service Training organizations were contacted by mail. Investigation courses offered by the respondents to the survey were very limited in scope or fire investigation was given

only as part of another course. Courses were generally taught by individuals

who had fire service backgrounds but not necessarily educational backgrounds or experiences. The advent of the community college has increased the availability

of formal education in fire science or fire protection technology. However,

very few courses are offered exclusively in fire investigation and those that

are offered are highly arson oriented. Reference materials for such courses generally consist of texts with supplementary material occasionally developed

on a local basis.

In our surveys of fire departments and the other agencies or institutions,

several procedures which appeared to warrant detailed study were brought to

light. These procedures were found in the San Diego, California; Portland,

Oregon; Houston and Dallas, Texas; and Ashtabula, Garfield and Shaker Heights,

Ohio fire departments. Special field visits were made to these fire departments

to gather on-site material and for personal evaluation of methods and procedures

practiced by the fire department personnel. Summaries of these field trips and

the information obtained are included in the final report.

3.3. Task C — Evaluation of Existing

Fire Information Collection Systems and Methods

In order to determine the scope and extent of information that any system

developed in the project should provide, a study was made of existing fire

information collection systems and other relevant factors.

Lack of uniformity and absence of a national reporting system presented

a problem of considerable proportion. Currently, reports of fires are entirely

a local prerogative, depending mainly on the decision of the individual fire

department as to extent of detail and quality of information. In some states

fire departments are required to submit reports to a state level agency — in some cases a State Fire Marshal, in others, an Insurance Commissioner. The

variations in required information for fire reports, when viewed nationally,

are wide ranging.

218
Increased interest and recognition of the need for collection of fire

information has led to the development of reporting systems utilizing automatic data processing and in most such systems NFPA Standard 901, Coding

System for Fire Reporting , is used as a basis.

The design of a system and training package on field fire information

collection which would be compatible with the multiplicity of systems and

repgrt forms currently in use appears to be an almost impossible task unless

it is based on a number of elements common to most systems.

Examination of a number of systems and forms in use indicated that if the

required information was based on elements contained in Standard 901, even if

used in conjunction with other coding systems, there would be enough commonality to make the systems compatible. The descriptors in 901 were such that

even if used narratively without any coding, as is the case presently in the

majority of fire reports, they would be satisfactory. Additionally, it was

felt that use of the descriptors of 901, either coded or narratively, would

assist in standardization and generally improve fire reporting nationally.

In reviewing 901, it was obvious that additional information relating

to actual firefighting operations and other similar factors pertinent to the

suppression of a particular fire should be available. As the means for reporting

such information were so varied and well within the capability of local determination and reporting, they were considered as options and were not included

in this program. In this respect, the Uniform Fire Incident Reporting System

(UFIRS) , developed by NFPA under contract to the Department of Housing and

Urban Development, is a system which is based on 9 01 with additional information

of particular value for local use. This system could ultimately become the

basis of a national fire reporting system.

The type of fire information required by other research, code making,

insurance, and allied organizations was also considered to be necessary input

for this project. The final report contains statements of the requirements and

statistical research information considered desirable by these agencies. In

most cases the information desired was not suitable for mass collection and

quantification. Rather, it would lend itself more suitably to separate studies.

The Report Summary and Recommendation of a Committee Appointed to Study

the Arson Problem in California (Appendix Q of the Final Report) is a good

treatise on the establishment of a state-wide fire investigation team. The

report shows the financial considerations and the problems encountered when

trying to establish such a team on a state-wide basis — notwithstanding the

problems that could be encountered in establishing such a team on a national

basis

Another part of this task was to explore the feasibility of the Interdisciplinary Team concept for in-depth investigation of fires of special

interest. Our research indicated that some of the preconceived theories

regarding this concept might not be practical. Meetings with the sponsor

of the project, the National Bureau of Standards in Washington, D.C. , further

confirmed that any nationwide network of such teams at this time would be

premature and unworkable.

3.4. Task D — Problem Identification

and Establishment of System Criteria

The principal goal of this task was to establish criteria for developing

a system to identify problems associated with current fire investigation

techniques. An evaluation was made of all current techniques employed by fire

departments in the recognition and preservation of evidence as well as general

methods of investigation. These studies led to the development of the objectives for the FIFI training package.

219
3.4.1. Usefulness of Existing Literature on Fire Investigation

Generally, the existing texts and publications all place a heavy emphasis

on the arson-oriented investigation. Techniques to determine accidental fire cause are given a relatively minor role in most of these publications.

Close to 400 published articles and texts are listed in the International

Association of Arson Investigators bibliography of investigation resource

materials. Those titles considered to be most appropriate for our task of

teaching practical investigation procedures were weeded out and subjected to

closer review by FIFI project workers who had practical experience in fire

investigation

.

3.4.3. Materials Produced In-house by Fire Departments

Of the 1,401 fire departments who returned our questionnaire, 127 indicated that they used or printed their own investigation manuals, and 85 departments said they would send us a copy. Only 21 departments, however, actually

sent copies of their own in-house fire investigation training materials. It

is felt that the number of departments who actually use their own or locally

produced training materials is closer to the percentage reflected by the "21"

figure

.

1. The vast majority of the 1,4 01 U. S. fire departments who replied

to our questionnaire stated that they do not use any of the published articles or textbooks as direct teaching material for their

firefighters or investigators.

2. Of the relatively few departments which use a published text for

teaching investigation, the same four or five titles seem to be

cited

.

3. At least 21 of the 1,4 01 departments replying to our survey felt

so strongly about the need for some practical fire investigation

instructional material that they packaged their own. Because much

of the content of these locally produced training materials is

taken from well established and authoritative arson investigation

textbooks, it is obvious that these textbooks were perceived by

fire departments as authoritative but impractical teaching devices.

At the same time, however, in their desire for a more streamlined,

practical approach to teaching investigation, it is evident that

most of these 21 locally-produced, mimeographed handbooks have

serious gaps in content since they reflect the specialized needs or interests which pervaded each department at the time of their booklet's birth.

In short, there are 4 or 5 popular, authoritative, knowledgeable, and

complete textbooks on arson investigation. They are , excellent for gaining

perspective on the art and science of fire investigation, and they are excellent for reference purposes, but, they fail as an instructional tool.

3.4.2. Published Articles and Textbooks

3.4.4. Conclusions

220
A textbook, by its format, allows for little or no rehearsal or use of

the information read and processed by the student. Reading the textbook or looking at pictures in the textbook bears little resemblance to required onthe-job performance or behavior. Merely reading about a procedure or technique does not quarantee that the student will be able to retrieve that information at the appropriate time on the job.

What is needed is a programmed approach to teaching fire investigation.

By programming we mean certain learning units or learning experiences set

into meaningful arrays in order to achieve stated objectives. Typically, it

is a format which forces the student to interact with the material just learned

in a manner very much like the way he will have to interact with the material

on the job. This was the philosophy which governed the instructional design

of the prototype training package we developed.

3.5. Conclusions of Research Phase

1. Most emphasis has in the past been placed on field fire investigation

when cause and circumstances are suspicious.

2. Little specialized training has been given to the firefighter on the

role he can play in fire investigation.

3. Line fire officers have generally not been trained or given guidance

which will expedite their work in obtaining information for fire

reports

4. Motivation of the firefighters to observe and preserve the scene is an essential factor in fire information collection.

5. The process of elimination is the only satisfactory method to use in

fire investigation.

6. The elements of cause and circumstances of fire incidents contained

in NFPA Standard No. 9 01 provide a satisfactory descriptor basis even when used in a narrative form.

7. Little use is made of specialists (structural engineers, chemists,

etc.) to support routine fire investigations.

8. Very few qualified persons are available to carry out fire investigations .

9. Persons with a knowledge of fire behavior are vital to investigation.

10. A national network of interdisciplinary fire investigation teams is

not yet feasible.

11. There are wide variations in fire reporting when viewed nationally.

12. A national Uniform Fire Reporting System would materially improve

the availability of data on fires; in addition, it would initiate a greater interest and quality in routine fire investigation.

13. Any improvement in routine fire investigation would enhance the

detection of arson.

221
4. DEVELOPMENT PHASE

The next four tasks utilized the information gathered in the research

phase of the project and were concerned with establishing an appropriate

training methodology and the development of a working prototype training

package. The development tasks were:

TASK E: Develop systems approach techniques for use in training firefighters and fire officers.

TASK F: Develop systems approach techniques for use in training interdisciplinary fire investigation teams.

TASK G: Develop learner-centered training program and job aids for firefighters and fire officers.

TASK H: Develop program and job aids for interdisciplinary team investigation seminars.

The objective of Tasks E and F was to establish group behavior characteristics (skill clusters, performance objectives) of the projected study body

in simulated fire incident situations. These findings provided justification

for the technical approach used in Tasks G and H.

4.1. Task E — Training Techniques For Firefighters and Fire Officers

In this task, various approaches to training system development were evaluated and the most appropriate training system design chosen. One of

the first efforts needed to accomplish this was to establish a step by step

sequence of events and decision points typically encountered by people involved

in a fire occurrence. When viewed as a total system, the flow of information

from person to person and from the scene to a national data collection agency

becomes a very vital link. The development of such a system approach also

clearly establishes the interrelationships of the various tasks which must be

developed and taught in a training package.

4.1.1. Methods of Fire Loss Determination

The one factor for which there are no established criteria at the present

time, except in some isolated local instances, is determination of dollar fire

loss. A survey of existing practices and a realization of the complexity of

such a task, clearly indicates the necessity for a separate in-depth study.

Present methods for determining dollar fire loss are quite varied, localized

and generally unreliable.

4.2. Task F -- Training Techniques For Interdisciplinary Teams

Originally this task was to develop a systems approach to the fire investi

gation techniques for use at the C-level (Interdisciplinary Team) . Some preliminary work was accomplished, but the decision to delay recommendations for

establishment of the interdisciplinary teams deprived this task of practical

significance

.

4.3. Task G -- Learner-Centered Training Program

In essence, this task represents the central goal of the project: the

development of a prototype learner-centered training program which will make

fire cause determination an easier and more reliable task. Materials, guides

and aids developed for the training program are briefly discussed in the follow

ing paragraphs.

222
4.3.1. Training Package Audience

In keeping with our earlier objectives as defined in Task D, the training

programs were divided into two basic levels: the Basic Unit (Level A) for

firefighters and the Officer's Unit (Level B) for fire officers. Both packages

' can be used for small groups as well as large group instruction -- although

small group instruction, by its nature, affords greater instructor attention

I to individual student comprehension. The programs are designed to be administered by a fire officer acting as instructor. Field testing suggests that

I any fire officer, properly motivated, can perform adequately in the role of

I instructor, regardless of formal training. It is intended that all fire service

i personnel will participate in the Basic Unit (Level A) training program and

j that fire officers or other fire personnel responsible for completing fire

; reports and making fire cause determinations will take the Officer's Unit

I (Level B) of the training program as well. The Officer's Unit can be given by

itself, but the student will be missing some of the basic material concerning

observing and preserving the fire scene which was covered in the Basic Unit.

Field testing suggests that greater insight and motivation for fire scene observation and preservation can occur if the firefighter is also exposed to

the Officer's Unit (Level B)

4.3.2. Contents of Prototype Training Package

The Basic Unit (A-Level) training program includes an Instructor's Guide,

a cassette tape, a set of slides, and a participant workbook. The Instructor's

Guide gives the instructor a detailed, written script of the contents of the

tape to enable him to sequence the visuals (slides) with the recorded script.

The Officer's Unit (B-Level) includes an Instructor's Guide, a cassette

tape, a set of slides, a participant workbook, the Investigating and Reporting

Guide which contains the HEP^ Checklist and FIFI Field Notes, and the HEP

Chart which includes the Officer's Handbook. Since this level of instruction

is directed at the fire officer who will be completing the fire report and who

will be required to make a preliminary fire cause determination, there has

been extensive development of visuals and aids which can assist in this task.

In addition to a script of the contents of the tape cassette, the instructor's guide in both training packages contains statements of the philosophy and

objectives of each lesson being given, as well as suggesting what supplementary

information or materials might be added to enhance each particular learning

exercise. Including this information with each learning exercise is designed

to encourage the fire service officer conducting the course to include specific

supplementary information from his own experience, or the students' (i.e., war

stories) which illustrate the instructional point being made, in order to

preserve the spontaneity of the group and keep the instructor feeling useful

without letting him wander off the point at hand.^

4.3.3. Instructional Philosophy and Design

The instructional design of the training program takes advantage of the

intuitive reasoning capabilities of the students. It is designed to emphasize

the knowledge that the firefighter students already have concerning fire behavior and its effects.

Hexagonal Elimination Process: a simplified sequence of investigation developed during this project.

There is considerable evidence to suggest that using subject matter experts

(such as experienced fire investigators) merely as "button-pushers" for canned

mechanical presentations can have disastrous results. The hostility built up

in the instructor alone is often enough to completely sabotage the program.
In short, our philosophy towards the firefighter is this:

You already know quite a bit about fire behavior. We are about to expose you to a sequence of investigation, emphasizing

those things you already observe at a fire which will enable you

to draw some pretty exacting conclusions about the fire cause,

its point of origin and whether or not it was accidental.

Once the firefighter has learned to be suspicious and vaguely hostile

towards the incidence of fire, his natural mechanical aptitude (a characteristic of most firefighters) coupled with his first-hand (even if limited)

experience with the way fire behaves, will enable him to intuitively ask

and answer appropriate questions about a fire.

In administering the package, students are encouraged to draw conclusions

and answer questions before formal instruction in that particular topic is

given so that a degree of competitive interaction and useful involvement with

the subject matter will be maintained. This is done by presenting case histories and asking for conclusions before any instruction is given. For

example

Was this window locked or unlocked at time of fire?

Was this door opened or closed?

Those who answer questions, such as the above, without formal instruction, are not branched onto a faster instructional track as is common in many packages

where students show prior knowledge. This is for two reasons:

1. Students who are able to draw conclusions to investigative evidence

are valuable class resources. They give out answers, create arguments, and promote a subtle air of in-class competition.

2. It increases student interaction and involvement — a key to the success of any instructional design.

Likewise, it is hypothesized that firefighters who come up with answers

to investigative questions in class will encourage similar mental speculation

among peers about the causes and circumstances of the fires they are fighting

once they return to the firehouse. This has been shown to be the case in

several cities studied during the project.

Wherever possible, students are taught by example (several examples equal

a concept) so that they will generate their own definitions of the concept —

the only definition which we can be assured they understand. Validity of

their own definitions will be checked many times throughout the training

program since students will be required to apply their "learned" definitions

to problem situations as they go along.

In short, the on the job instructional design used in the development

of this package is intended not merely to "create an awareness" of the cause

and circumstances of the fires they are fighting, but also to interest firefighters in assuming a detective-like posture when fighting fire. Our goal

is for firefighters and fire officers to begin to value their firefighting

environment (the fire building itself) as an intimate interaction with the

evidence which they will be required to work with soon after extinguishment.

224
4.3.4. Job Aids Developed

The fire officer has many tasks to accomplish on the fireground. His

I primary task is to direct the men under his command in their efforts to effect

I rescue, limit fire spread, extinguish the fire, and prevent unnecessary water

I and smoke damage. This is a large task and requires much of his time and his

I decision making processes. However, if fire data collection and prevention

efforts are to have any meaning and validity, the officer's focus of attention

must shift to determining fire cause as well.

The Hexagonal Elimination Process (HEP) was a system developed to

give the fire officer a simplified sequence of steps to take in determining

j all the facts required for reporting a complete fire cause. HEP was also

developed around the NFPA No. 9 01, Coding System for Fire Reporting , in an effort to make the training program as universal as possible. The six steps

of HEP are the basic informational requirements of fire cause determination

required by NFPA No. 901.

The role of the fire officer, both in the fire station and on the fireground, was carefully analyzed in the development of FIFI training and job

aids

4.3.5. The HEP Chart

The HEP Chart is designed to graphically relate the six steps of HEP

to the proper recording of the fire cause determination. The Flip Chart

method gives the fire officer an easy reference to all of the descriptors

established by NFPA No. 901.

4.3.6. The Officer's Handbook

The Officer's Handbook is a detailed, step by step procedure manual on how to obtain the information necessary for determining each of the six steps

of HEP on the fireground. The size of the booklet was designed for easy

use as a pocket reference if the fire officer so desires. Common pitfalls

which can lead to wrong fire cause determination are pointed out in the Officer

Handbook in an effort to maintain accuracy and realism.

4.3.7. Investigating and Reporting Guide

Each officer is equipped with an Investigating and Reporting Guide , a note

book designed to fit into his fire coat. It is a condensation of some of the

tips and instructions (fig. 1) contained in the Officer's Handbook and contains

space for making notes (fig. 2) at the fire scene.

4.3.8. Present Training Package a Prototype

It is important to note that the development of any training package is

incomplete without appropriate validating field tests. The product developed

under this contract must be validated in the field for content clarity, content

applicability, desired performance outcome, and teachability.

5. SUMMARY AND CONCLUSIONS

FIFI (Fire Information Field Investigation) was a one year Research and

Development Project conducted by the National Fire Protection Association under

contract to the National Bureau of Standards.
H.E.P. CHECK LIST FOR DETERMINING FIRE CAUSE

LP Gas Natural Gas

Fuel oil Gasoline Keiosene Cooking nl

Tai Car grease Paint Wax Metal Plastic Wood Polish Food

fiadioadive materials Leather RubtKr Lumber

Grass Hay Tree Sawdust Paper Rag

Cardboard Shrub Wood shavings Canvas

Linoleum Treated paper

Fabric Clothing Other

AREA OF ORIGIN 1-2-3-3

Commenis: ObscmlioDs:

Fire dispatcher Smohe stains Rre discoverer Meiled items

Fire fighter Alarm sjfstems Occupant(s) 'V pattern Bystander Char depth

Light bulb

Other

Sidiii, Trii Root Eave Sotfit Interior. Wall surlace

Ceiling Floor covering

Floor Insulation Structural member

Furniture Cabinets Beddmg Dry goods

Curtain Linens Luggage Mattress

Pillow Clothing Food. Magazine Paper Toy Decoration Other

1-2-1-9-10 ACTOROMISSIOH

Pan lailure Control laiiure Design detiaency

Child vnth matches Smokers carelessness Carelessness with Flam Uq.

Other

ReassanUe rmm of ongin Erimpment in area oT unpa

ts equipment soum 61 beat? Equipment not tmotved Type of equipment Normal use ot eqiapment Equipmenl remmed id omliail

Furnace Bdler Firctriace Qumoey Ranee Oven

Electrical iring Fuse Appliam Motor Othei

Flame PiM light Spaili Ember Malcfa Slwrl artuit Overload Wire down lim ballast Srmlung materials Cutting o> welding Candle Spontaneous bgh) bulb Uolten metal Lightmng Flying brand

Radiated tsal Open frie Fricbon FirewDfks Incendnry device Otl»

Figure 1. The HEP Check List is one of the forms contained in

the Investigating and Reporting

Guide. It is a condensation of

the instructions contained in

the Officer's Handbook.

(1) For Queslioti Areas, A. B. C. D. E. and F, recoid what i! ALREADY KNOWN ataul fite (Intefview Dispatcher. Fife Discoverer. Firefighlers. Occupants. Bystanders).

(2) Verity ttiis inlormation by examining scene.

IF KNOWN INFORMATION IS INSUFFICIENT TO DETERMINE ALL SIX CAUSAL

FACTORS, BEGIN SEQUENCE BELOW:

(3) Find AREA OF ORIGIN (A). Work Irom

area o( no damage to area ol mosi severe damage (read fire language; reassemble re mams if necessary).

(4) Find EQUIPMENT (B) in area ol origin. (Did Ignition begin as result ol equipment, or did fire spread to equipment?)

(S) What FORM OF HEAT (C) caused ignitini of surrounding material?

(C) What MATERIAL (D) >ras first igniledi

(7) Ho* was MATERIAL (E) used or

(9) What ACT OR OMISSION (F) broueht

together HEAT OF IGNITION and MATERIAL

IGNITED'

(9) Complete Fire Report

(10) II Incendiary, Suspicious, or Undetermined, notily appropiiate'authonty.

Figure 2. This form gives the

officer space for recording

information on the fireground which will be needed

later to complete his fire

report. It asks for the

basic information necessary

for completing any fire

report form known to be in

existence at the present

time.

FIFI FIELD NOTES

INCIDENT NO.: DATE 1

INCIDEia ADDRESS:

OCCUPANT(S) NAME(S):

OWNER:

OWNER'S ADDRESS: .

INCIDENT: Fire Rescue False Alarm Public Service Other

BUILDING: Type Heighl Floor Area

VEHICLE: Year Make Model Style

DISPATCHER INFORMATION:

OBSERVATIONS ON ARRIVAL:

FIRE DISCOVERER: Name Address

COMMENTS.

WITNESSES: Name Address

Name Address

miURIES: Type Name Address

Type Name Address

DEATH(S): Name Address

AREA OF ORIGIN: Floor Room Pt. w in Room

SOURCE OF IGNITION : Equipment Form o( Heat

IF EQUIPMENT: Year Make Model

MATERIAL IGNITED: Type Form

ACT OR OMISSION:

FACTORS CONTRIBUTING TO FIRE SPREAD: Non fire Stopped Walls

Open Shatts

Poor Water Supply

METHOD OF EXTINGUISHMENT:

FORCIBLE ENTRY: Door

VENTILATION. Dooi

ESTIMATED VALUE: Building

ESTIMATED FIRE LOSS: Building

INSURANCE; Agent

Type ot fuel Slock Arrangement

Design Defiaencies

No. & Sire ol Streams

Window

Window

Root

Root

Contents

Contents

Address

Other

Other

Equipment

Equipment

Amount

226
5,1. Research Phase

The objective of the research phase of FIFI was to define and evaluate

those state-of-the-art investigation techniques used by piiblic fire agencies at

the scene of fires to report on the cause and circumstances of those fires.

The two most significant conclusions reached as a result of this research were:

1. That most existing literature and practices were arson oriented; and

2 . That*^ standard investigative practices and training programs do not

exist.

5.2. Development Objectives

After defining and evaluating the state-of-the —art of the many fire investigation techniques used in the field, the development phase was initiated with

two objectives in mind:

1. To increase the probability that the firefighter will recognize and

preserve useful fire scene information by enhancing the firefighters

ability and willingness to observe those events and actions which

assist in determining the cause cuid circumstances of the fire.

2. To improve the fire officer's effectiveness in determining the cause

and circumstances of a fire and to assist him in the early identification and notification of research potential incidents.

5.3. The Products of the Development Phase

In fulfillment of these objectives, the development phase of the FIFI

project:

1. Synthesized the most valid standard investigation techniques into a new, simplified, logical, 901-based^ process of elimination investigation sequence. This system of investigation, entitled HEP (Hexagonal

Elimination Process) , was developed to give the fire officer a simplified sequence of steps to follow which enable him to determine all

the facts required for reporting a complete fire cause. In an effort

to make the system compatible with an existing reporting standard, HEP was developed around NFPA Standard 901, Coding System for Fire Reporting . By design, the six steps of HEP constitute the basic informational

requirements of fire cause determination required by NFPA Standard 901.

2. Two pilot training packages were developed, designed to aid firefighters in carrying out the systematic investigation sequence known

as HEP in their initial, on-scene, routine fire investigations.

5.3.1. Summary Description of Pilot Training Packages

Each of the two training packages consists of a series of slides accompanied by a 33 minute tape cassette containing instructional material sequenced

with the slide progression. However, since there is no sense in turning qualified fire department instructors or fire service officers into button pushers

for canned mechanical presentations, the Instructor's Guide gives the instructors

suggestions for adding supplementary material with each slide shown, in order

to enhance the concept being presented at any one time during the package

sequence. This usually adds a minimum of 4-6 hours to each 33 minute core

package.

^Standard 901, Coding System for Fire Reporting , NFPA, 1971.

227^
For example, when the slide-tape program is explaining how the color

of window panes can be used to gauge the heat of the fire and help in finding

the area of origin of the fire, the Instructor's Guide states the learning

objective as: "Given two pieces of glass, students will be able to pick .the one closest to the hottest part of the fire". The Instructoi? ' s Guide also

encourages the instructor at this point to bring in actual samples of cracked,

syrupy glass which the students can examine at their leisure. The format is

flexible enough so that at this point -- during the session on using window

glass as heat indicators for instance -- the instructor is free to spend the

whole day or a couple of days tackling the subject.

Our intention in formatting the package this way was to take advantage

of the best of two possible worlds: the world of the fire service officer,

who is often armed with a good theoretical base of knowledge as well as years

of specialized experience in fire behavior — and the world of the audiovisual

package, which insures that all important concepts in fire investigation are covered in logical sequence, and as such, functions as a tool for the instructor.

5.3.2. Principle Objectives of Package #1

The principle objectives of the Basic Unit for firefighters are:

1. To convince the firefighter that he is a most valuable source of

fire intelligence information; that he is a most valuable person in

the whole scheme of valid fire incident reporting.

2. To create in the firefighters' mind an awareness of their firefighting

environment to the extent that they begin to assiime a detective-like

posture when fighting fire; to be aware of the investigative signifi- cance of everything he sees during the course of the fire he is

fighting

.

3. To encourage the firefighter to preserve, insofar as possible, the

original configuration of the fire scene, so that investigation is

made easier for the fire officer who will be investigating the fire's

cause. He will learn to value the fire building itself as evidence

which he and his fire officer will have to work with soon after the

fire is contained.

5.3.3. Principle Objectives of Package #2

The second training package is designed for fire officers (although

firefighters find it useful) after they have been through package #1. The

following objectives focus on the task of arriving at a fire cause determination, which is usually the job of the fire officer:

1. The fire officer will become familiar with the HEP sequence of investigation, a method whereby a process of elimination can be used to dis- cover the cause and circumstances surrounding the fire he has just

contained

.

2. Although the package itself does not make a fire officer into a skilled

fire investigator, it gives the student just enough practice in solving

investigation problems to whet his appetite for practicing his investigative skills "on the job" which, realistically, is the only place

where proficiency in fire investigation can occur.

228
In short, the training package provides the motivational setting as well

as a step-by-step sequence of investigation to follow while he is practicing

on the j ob

229
NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 411, Fire Safety Research,

Proceedings of a Symposium Held at NBS , Gaithersburg , Md . , August 22, 1973,

(Issued November 1974)

NATIONAL SCIENCE FOUNDATION RANN PROGRAM

Ralph H, Long, Jr.

National Science Foundation, Washington, D.C.

The fire research effort at NSF is part of the Research

Applied to National Needs (RANN) Program of NSF, which provides

funds for problem-oriented research on selected problems of

national importance. The current effort is funded at $2 million

and about 20 projects are under way. An outline of the thrust of

the total program will be given. Also, several projects which

are closely related to interests of the National Bureau of

Standards will be indicated. Related activities within NSF will

be mentioned.

Key words: Fire programs; fire research; National Science

Foundation; RANN; research grants.

1 . INTRODUCTION

The fire research effort of the National Science Foundation (NSF) is

part of the Research Applied to National Needs (RANN) Program which was initiated early in 1971. It involves problem-oriented research rather than

just meritorious research in a field of science or engineering.

2. RESEARCH OBJECTIVES

Without citing available data, a quotation from the National Fire Protection Association summarizes well the national situation: "In a word, the fire

problem is that too many people die or are injured by fire and that the social

and economic losses are an unnecessary burden on the American people." The

general objectives of the Fire Research Program, within the Division of Advanced

Technology Applications, are to reduce deaths, injuries and property damage due

to unwanted fires and also to reduce the costs and improve the effectiveness

of fire control.

Research is supported which develops understanding of mechanisms of ignition, fire spread and extinguishment sufficient to improve significantly fire

safety in homes and urban areas, including special problems of tall structures.

Some backup research is supported to complement efforts of the U.S. Forest

Service on forest fires.

3. STRATEGY

The fire problem has several components; in effect, it consists of a series

of interrelated problems. The spectrum covers public ignorance and apathy,

combustibility of environment, building deficiencies, effectiveness and cost

of fire protection and adequacy of fire statistics.

The proper NSF role in fire research is dependent on and complementary to

the activities and interest of mission agencies, particularly the National

Bureau of Standards, the Department of Housing and Urban Development, the

General Services Administration and the Forest Service. The research needs

outstrip the abilities and interests of any one agency, so a coordinated

Federal approach is required.

The research emphasis of the program is directed at the fire problems of

cities, where the losses occur, although some funds go to research that complements that of the Forest Service on forest fires. The general thrust addresses

problems connected with the means to provide adequate fire protection for

230
i

I buildings. The research will lead to safer buildings through the improvement

of design practices and of the test methods and standards for materials.

i The research efforts focus on the understanding of the ignition of various

materials, the fire spread mechanisms and extinguishing methods. Included are

the modeling of fire propagation, effectiveness of fire fighting systems and

I the deleterious effects of smoke. Research that will improve the detection and

I suppression of fires will be supported. The NSF effort provides the research

I base that can be effectively addressed primarily by university researchers in

I many critical areas of importance to other Federal agencies and the fire

protection community.

As the research base is improved and new technology developed, it will con- tinue to be necessary to devise methods to make the fire protection community

aware of the progress and induce cooperative experimentation in order to upgrade

the system. Greater efforts will be exerted to initiate projects related to the

direct needs of the fire services, including fire equipment technology where

there is sufficient economic incentive.

The Foundation's research effort provides support for four comprehensive

(multidisciplinary ) fire research groups on projects where special competence

is needed and for a larger number of smaller research grants.

li 4. ADVICE

The goals and strategy reflect advice from several qualified organizations

; and individuals, including the National Academy of Sciences-National Research

Council Committee on Fire Research. Recommendations from meetings and workshops which were concerned with specialized areas are also considered.

' Research proposals form the vehicle for implementation of the program,

i; The advice of several experts is sought for each proposal and forms the basis

I; for a decision.

I 5. SIZE OF FIRE RESEARCH PROGRAM

The RANN Fire Research obligations for fiscal year (FY) 1972 and FY 1973

are given in table 1. When RANN was formed early in 1971, nine existing grants

(totaling $670,000 on an annual basis) were administratively transferred to the

i| new Fire Research Program, two from the former Office of Interdisciplinary

Research on Problems of Our Society and seven from the Engineering Division.

Currently there are 24 active grants. Four multidisciplinary groups

li' (Harvard-Factory Mutual Research Corporation; Applied Physics Laboratory of

Johns Hopkins University; University of California, Berkeley; and University

of Utah) have major support, which ranges from $247,000 to $399,500 per year.

There are 16 other research grants which average about $36,000 for a year and

four special grants.

I Table 1. RANN Fire Research Obligations^

FY 1972 FY 1973

No.

Funding

(Thou.$) No.

Funding

(Thou. $)

Multidisciplinary

3 912 4 1,156'='

Research Grants . . . 9 508 14 791

Special Grants. . . . 2 35 4 164

Total 14 1,455 22 2,111

3-Note all grants do not have the same duration.

^Figure includes $113,000 from HUD.

231
6, AREAS OF FIRE RESEARCH

Seven sub-program areas will be briefly described. Some projects include more than one area and at times the classification of a particular grant may be

a bit arbitrary.

6.1. Structure and Solid Materials Flammability

In order to improve fire safety, a fuller understanding must be developed

of the conditions needed for ignition to occur on solid materials and structural

components, including the effects of flame retardants. Results will be used to

improve design practices and fire tests.

Empirical studies have been conducted for some time and have provided some knowledge of ignition, however, proper scientific understanding is lacking.

Research that is being supported will lead to the use of materials and design

of structures in a manner to provide improved fire protection. Moreover, improved bases for the setting of realistic ignition tests are being pursued.

Both chemical and engineering research efforts on pyrolysis of cellulose, wood

and polymers are under way.

6.2. Fluid and Fuel Flammability

This area deals with the development of the knowledge base concerning the

fire potential and propagating characteristics of fuels and volatile fluids.

The ongoing effort consists of an experimental and analytical effort at

Princeton and a complementary analytical program at Cornell University. A

detailed understanding of the mechanism of flame spreading across liquid fuel

is being sought. The research has advanced to the point where both gas phase

and heat transfer aspects can be included simultaneously in the analysis.

6.3. Fabric Flammability

Research is being conducted in fabric flammability and the associated

hazards for use by the National Bureau of Standards in setting flammability

standards

.

A two-year coordinated program with NBS has been completed. The effort

included NSF funded research at Georgia Institute of Technology and Massachusetts

Institute of Technology (MIT) and projects at Gillette Research Institute and

Factory Mutual Research Corporation with funds from three industrial associations. A Government-Industry Research Committee on Fabric Flammability was formed to monitor the group of projects. The MIT project terminated during

FY 1973 as did the ones at Gillette and Factory Mutual, Additional research

was funded at Georgia Tech on the ignition of composite systems. The purpose

of the analytical and experimental work is to relate the hazard from burning

garments to laboratory test methods on fabrics for use in setting reasonable

fabric flammability standards. The work is designed to lead to the prediction

of the probability of garment ignition under given exposure.

A grant was recently made to the Textile Research Institute (TRI) to establish, in rigorous quantitative terms, the thermal and flammability characteristics of multicomponent fibrous polymer-systems. The research is complementary

to the applied research normally done by TRI and funded by industry. The goal

is to provide guidelines for the development of textile materials that will

minimize the flammability hazards to the ultimate consumer.

232
6.4. Chemical and Physical Properties of Flame Propagation

A fuller understanding of the mechanism of flame spread, including cheinical

and physical properties, is needed in order to lead to improvements in building

design and methods for combating fires. Results will also be used to improve

flame spread tests. The movement of gases within structures is also included,

as it is important in connection with fire safety and detection. This area

includes research on fire spread in materials and systems, the role of radiation

and the fluid mechanics of combustion products.

Brown University is conducting an experimental and analytical study of

flame spreading over cylinders (round and rectangular cross-sections made of

wood and plastic) . A major long-range objective of the research being conducted at Harvard is to develop the capability to predict the history of fire progression from an assumed ignition point in a house. Under a subcontract from

Harvard, the Factory Mutual Research Corp. is determining the range of application for a pressure method of modeling building fires and for approximate

atmospheric pressure methods for modeling fires. Complementary research at

Berkeley is directed at understanding a standard wall furnace fire endurance

test. Another task is the prediction of the structural response to fire for

reinforced concrete frames. A two-dimensional model has been developed which

gives a realistic prediction of the stress history under different fire conditions. The convective flows of combustion products in building fires are being studied at California Institute of Technology. A recent grant to the

University of Notre Dame has the primary objective to provide the foundation

for the development and use of theoretical predictions for describing fire and

smoke spread in corridors. The analyses will be coupled with small-scale ex- periments at Notre Dame and with data from the NBS corridor facility.

6.5. Fire Fighting Systems and Human Behavior

Here the aim is to develop knowledge that will contribute to controlling

fires more effectively and that will reflect the human response to a fire

situation

Studies on the extinguishment of fires include the behavior of water droplets in a fire plume and the action of metal powders on flames. A project at

the University of Washington, with participation from the University of California, San Diego and Washington State University, and in cooperation with the

U.S. Forest Service, is directed at determining a rational understanding of

wildland fire response to fire suppression measures for use in the development

of proper equipment, attack strategies and management techniques that will

minimize costs. Research at the University of California, Riverside is directed

at some statistical problems connected with the development of a basic simulation model, for forest fire control, by the Forest Fire Laboratory of the Pacific

Southwest Forest and Range Experiment Station of the U.S. Forest Service.

At Johns Hopkins' Applied Physics Laboratory, the development has proceeded

on an economical and practical tactics case for use by fire departments. It is

being tested at the Hillandale, Maryland Volunteer Fire Department, and several

improvements have resulted. The case was a major element in the NSF/RANN Fire

Research exhibit at the May 1973 Annual Meeting of the National Fire Protection

Association in St. Louis. Plans call for further testing in several fire

departments in the next few months. Efforts will be made to locate an organization for the manufacture and distribution of the case if an adequate potential

market emerges.

At the University of California, Berkeley, part of the project is directed

at the development of a computer simulation model of the unwanted fire process

for use as a design tool for fire protection and fire control. In conjunction

233
with this, field studies have obtained fire incident and human response data

applicable to the simulation model. Using engineering psychology approaches,

analyses and experimental studies of hiiman response in fire situations will be

made. The data obtained will be useful in practical fire safety and control

design.

6.6. Smoke Effects

The effects of smoke on people are being studied so that attention can be

concentrated on the most critical points that offer a payoff in the reduction

of deaths and injuries.

Little information is available on the exact cause of death of fire

victims, except in cases where severe burns, heart attacks or fractures have

occurred. The clinical and pathological mechanisms are not understood when a person dies from the effects of by-product agents of a fire.

Under a grant at the Applied Physics Laboratory of the Johns Hopkins

University, a cooperative program has been initiated with the Baltimore City

Medical Examiner's Office and the School of Hygiene and Public Health of Johns

Hopkins University. The project includes the post-mortem examination of fire

victims in Maryland, chemical analyses of the lung tissues and fluids, and

investigation of the fire scene in order to determine the sequence of events

leading to death. In addition, the effects of the fire environments on fire

fighters are being studied.

A related program at the Flammability Research Center of the University

of Utah is directed at the physiological and toxicological aspects of smoke

produced during the combustion of polymeric materials. The research team

includes medical staff members at the University of Utah. The Salt Lake City

Fire Department, the Fire Marshal of the State of Utah and the National Bureau

of Standards are cooperating with the university group. The program is con- cerned with the problems connected with the burning of polymeric materials

such as fabrics, elastomers and cellular plastics. Laboratory studies of the

effect of smoke on rats are included. The research will provide the fundamental information necessary to develop improved materials and to devise better

testing procedures to evaluate material hazards under realistic conditions.

6.7. Technology and Information Transfer

There is also a need to develop greater facility for the transfer of fire

research knowledge between various sectors concerned with fire protection and

control

.

There are special problems in getting fire research knowledge into a form

that will ensure use by the fire services community. Through increased communication and education, the process of updating fire codes and standards can be

accelerated and the public can become more aware of fire safety.

An information dissemination plan is part of each research proposal. For

a large grant, an advisory committee, including potential users, is formed to assure coupling to the user communities. Specialized meetings and workshops

are arranged to facilitate information transfer, often in cooperation with other

groups such as NBS . For example, a conference was held July 18-2 0, 1973, on "Firesafety for Buildings, Research-Practice-Needs" involving most RANN grantees

and organized jointly by NSF, NBS, GSA, and HUD. Contact has been established

with several associations, such as the National Fire Protection Association,

the Society of Fire Protection Engineers and Society of the Plastics Industry

(SPI) . SPI is providing funds to supplement the NSF grant at the University of

Utah on the toxicology of smoke from polymers.

234
7. OTHER NSF FIRE RELATED ACTIVITIES

Within the Engineering Division of the Research Directorate there is a special program for tall buildings. Some effort is directed at structural problems resulting from fire. While some combustion research is supported within

the Division, research on unwanted fires is not.

Within RANN in the Social Systems and Human Resources Division, the

Municipal Systems, Operations, and Services effort includes the delivery of

fire protection. Two grants were recently made under Program Announcement

NSF 73-4 for evaluation of policy-related research in fire protection with

respect to technical quality, utility for policy-makers and potential for

codification and wider diffusion. The result will be a synthesized base of

evaluated information for potential use by agencies at all levels of government .

8 , SUMMARY

The NSF Fire Research Program covers the spectrum from basic to applied

research and is directed at critical elements of the nation's fire problems.

Through close coordination with other Federal agencies, a research effort has

resulted which is complementary and often permits study on longer term payoff

areas than is usually possible in a mission agency. Projects contain utilization plans, coupling with potential users and periodic progress reviews in

order to accelerate the transfer of research results to useful purposes and to

provide the research people with a knowledge of needs of practitioners.

235

APPENDIX. LIST OF ACTIVE NSF RESEARCH GRANTS

AND PRINCIPAL INVESTIGATORS, AS OF AUGUST 1, 1973

1. Brovm University, Division of Engineering, Merwin Silbiikin, Flame Spreading

Over Solid Surfaces.

2. California Institute of Technology, Division of Engineering and Applied

Science, Edward E. Zukoski, Convective Flows of Building Fires.

3. Cornell University, Department of Thermal Engineering, Kenneth E. Torrance,

Flame Spread Over Liquid Fuels.

4. Georgia Institute of Technology, School of Mechanical Engineering, Wolfgang

Wulff, Ignition of Fabrics.

5. Harvard University, Division of Engineering and Applied Physics, Howard W.

Emmons (with Raymond Friedman, Factory Mutual Research Corp.), The Home

Fire Project.

6. Johns Hopkins University, Applied Physics Laboratory, Robert M. Fristrom,

Fire Problems Research and Synthesis.

7. National Academy of Sciences-National Research Council, Committee on Fire

Research, Nelson T. Grisamore.

8. National Bureau of Standards, Conference on Firesafety For Buildings:

Research, Practice, Needs, Joseph E. Clark.

9. New York City-Rand Institute, Edward H. Blum, Fire Research Needs and

Priorities

10. Northwestern University, Department of Mechanical Engineering, M. C. Yuen,

Behavior of Water Droplets in Fire Plume.

11. Princeton University, Guggenheim Laboratories, Irvin Glassman, Flame

Spreading Across Liquid Fuels.

12. State University of New York, Binghamton, Department of Chemistry,

Walter E. Kaskan, Extinction of Flames By Metal Powders.

13. State University of New York, Department of Mechanics, Richard S. L. Lee, Fire Whirl and Firebrand in Mass Fires.

14. Student Competitions on Relevant Engineering, Charles M. McCuen, Students

Against Fires.

15. Textile Research Institute, Bernard Miller, Thermal and Flammability

Behavior of Multicomponent Fibrous Polymer Systems.

16. University of California, Berkeley, Department of Civil Engineering,

R. B. Williamson, Firesafety in Urban Housing.

17. University of California, Riverside, Department of Statistics, F. N. David, Forest Fire Statistical Problems.

18. University of California, San Diego, Department of Applied Mechanics

and Engineering Sciences, F. A. Williams, Fire Propagation Along Solid

Surfaces.

19. University of Maine, Department of Mechanical Engineering, Ashley S. Campbell, Fire Rate of Spread in Paper Arrays.

237
20. University of Montana, Wood Chemistry Laboratory, Fred Shafizadeh,

Chemistry of Cellulosic Fires.

21. University of Notre Dame, Department of Aerospace and Mechanical

Engineering, J. L. Novotny, Fire and Smoke Spread in Corridors.

22. University of Utah, Department of Chemical Engineering, Norman W.

Ryan, Mechanism of Fire Propagation on Polymer Surfaces.

23. University of Utah, Flammability Research Center, Irving Einhorn,

Physiological and Toxicological Aspects of Smoke Produced During the

Combustion of Polymeric Materials.

24. University of Washington, Department of Mechanical Engineering, R. C. Corlett, Mechanisms of Wildland Fire Suppression.

238
APPENDIX - CONTRIBUTING AUTHOR INDEX

Robert H. Barker

Clemson University

Clemson, S. C. 29631

John W. Hastie

Inorganic Materials Division

National Bureau of Standards

Washington, D.C. 20234

M. M. Birky

Programmatic Center for Fire Research

National Bureau of Standards

Washington, D.C. 20234

Francis L. Brannigan

Montgomery College

51 Manekee Street

Rockville, Md. 20850

Emil Braun

Programmatic Center for Fire Research

National Bureau of Standards

Washington, D.C, 20234

Benjamin Buchbinder

Programmatic Center for Fire Research

National Bureau of Standards

Washington, D.C. 20234

Laura Baker Buchbinder

Res. Assoc. - The Cotton Foundation

Programmatic Center for Fire Research

National Bureau of Standards

Washington, D.C. 20234

Clayton Huggett

Programmatic Center for Fire Research

National Bureau of Standards

Washington, D.C. 20234

Lionel A. Issen

Programmatic Center for Fire Research

National Bureau of Standards

Washington, D.C. 20234

Takashi Kashiwagi ' Programmatic Center for Fire Research

National Bureau of Standards

Washington, D.C. 20234

F. James Kauffman

National Fire Protection Association

60 Batterymarch Street

Boston, Mass. 02110

Thomas King

Armstrong Cork Company

Research and Development Center

Lancaster, Pa. 17604

I. N. Einhorn

The University of Utah

Salt Lake City, Utah 84112

Richard Ku

Technical Analysis Division

National Bureau of Standards

Washington, D.C. 20234

J. B. Fang

Programmatic Center for Fire Research

National Bureau of Standards

Washington, D.C. 20234

« Paul Gottfried

Consumer Product Safety Commission

5401 Westbard Avenue

Bethesda, Md. 20016

Martin E. Grimes

National Fire Protection Association

60 Batterymarch Street

Boston, Mass. 02110

D. Gross

Programmatic Center for Fire Research

National Bureau of Standards

Washington, D.C. 20234

M. L. Grunnett

The University of Utah

Salt Lake City, Utah 84112

B. T. Lee

Programmatic Center for_ Fire Research

National Bureau of Standards

Washington, D.C. 20234

Ralph H. Long, Jr.

Advanced Technology Application Div.

National Science Foundation

1800 G. St. , N.W.

Washington, D.C. 20550

Bernard Miller

Textile Research Institute

Princeton, N.J. 08540

S. C. Packham

The University of Utah

Salt Lake City, Utah 84112

W. J. Parker

Programmatic Center for Fire Research

National Bureau of Standards

Washington, D.C. 20234

239
J. H. Petajan

The University of Utah

Salt Lake City, Utah 84112

James Quintiere

Programmatic Center for Fire Research

National Bureau of Standards

Washington, D.C, 20234

J. A. Rockett

Programmatic Center for Fire Research

National Bureau of Standards

Washington, D.C. 20234

Richard W. Roberts, Director

National Bureau of Standards

Washington, D.C. 20234

Patsy B. Saunders

Applied Mathematics Division

National Bureau of Standards

Washington, D.C. 20234

J. D. Seader

The University of Utah

Salt Lake City, Utah 84112

George Sinnott

Programmatic Center for Fire Research

National Bureau of Standards

Washington, D.C. 20234

James A. Slater

Programmatic Center for Fire Research

National Bureau of Standards

Washington, D.C. 20234

Allan Vickers

Programmatic Center for Fire Research

National Bureau of Standards

Washington, D.C. 20234

F. Karl Willenbrock

Institute for Applied Technology

National Bureau of Standards

Washington, D.C. 20234

James H. Winger

Programmatic Center for Fire Research

National Bureau of Standards

Washington, D.C. 20234

240
kll4A (REV. 7-73)

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BIBLIOGRAPHIC DATA

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1. ITHI.K A riON OR l< l- I'OK 'l' NO. NBS S^- 411

2. Cov't Accc S-s ion No.

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TITl.F AND SllH i lTl.l-:

Fire Safety Research

5. I^u bl i c .It ion Date November 1974

6. Performing Organization (ode

, AUrilOR(S) Mary Jo Butler and James A. Slater , Editors

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i. ABSTRAC/r (A 200-word or less factual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here.) A Symposium on Fire Safety Research was held at the National Bureau

)f Standards (NBS), on August 22 , 1973. The Symposium's participants

fere NBS staff as well as outside contributors affiliated with the NBS

Eire program including representatives from private industries, universities, government agencies, and the National Fire Protection Association.

The papers covered topics in hazard analysis, standards develO;_ ent,

flame chemistry, fire modeling, fire detection, physiological eifects of

fire, fire services, effect of fire on building materials, and field ini^estigation methods for firefighters. Specifically included were papers

Sealing with the development of the Children's Sleepwear Flammability

Standards and mandatory sampling plans, mechanisms of flame retardants,

^lame spread and radiant panel test methods, contribution of interior

finish materials to fire growth, a field study of non fire-resistive

multiple dwelling fires, the Research Applied to National Needs (RANN)

Program of NSF, and other related topics.

I^ey words: Apparel fires; carbon monoxide; concrete beams; field investigation; FIFI; fire; fire buildup; fire detection; fire engines; fire

growth; fire research; fire retardants; fire safety research; firefighter

training; flame inhibition; flame spread; flames; flammable fabrics

standards; hazard analysis; injury severity; interior finishes; mandatory

standards; modeling; multiple dwelling fires; oxygen; physiological

effects of fire; polymeric materials; radiant panel; RANN; red oak;

smoke; standards; test methods; textile testing; thermal decomposition;

toxic effects of fire.

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