NBS

PUBLICATIONS

A11104 053268

NBSIR 79-1755

Fire Accident Simulations with

Apparel Fabrics

A. W. Meierhoefer, E. Braun, J. F. Krasny and R. D. Peacock

Center for Fire Research

National Engineering Laboratory

National Bureau of Standards

Washington, D.C. 20234

June 1979

Final Report

U S. DEPARTMENT OF COMMERCE

100 NATIONAL BUREAU OF STANDARDS

,U56

79-1755

1979

C.2

NBSIR 79-1755

FIRE ACCIDENT SIMULATIONS WITH

APPAREL FABRICS

SCF&23 3 f

$\Ct

1980

C i fit mm

14'

A W. Meierhoefer, E. Braun, J. F. Krasny and R. D. Peacock

Center for Fire Research

National Engineering Laboratory

National Bureau of Standards

Washington, D C. 20234

June 1 979

Final Report

U S. DEPARTMENT OF COMMERCE, Juanita M. Kreps, Secretary

Jordan J. Baruch, Assistant Secretary for Science and Technology

NATIONAL BUREAU OF STANDARDS. Ernest Ambler. Director
)
TABLE OF CONTENTS

Page

LIST OF FIGURES iv

LIST OF TABLES iv

Abstract 1

1. INTRODUCTION 2

2. EXPERIMENTAL 4 2.1 The Apparatus 4

2.2 Data Acquisition and Computation 6

2.3 Fabrics 8

2.4 Simulation Procedure 8

3. RESULTS AND DISCUSSION 15

3.1 Total Heat Delivered to AFMA 19

3.1.1 Free-Hanging Mode 19

3.1.2 Reaction Mode 19

3.2 Injury Area 20

3.3 Maximum Rate of Increase of Injury Area 20

3.3.1 Free-Hanging Mode 20

3.3.2 Reaction Mode 20

3.4 Time to Ignite 21

3.5 Reaction Time 21

3.6 Overall Evaluation of Fabrics 21

4. FUTURE WORK 24

5. REFERENCES 24
LIST OF FIGURES

Page

Figure 1. Schematic view of AFMA 5

Figure 2. Time-heat curve for one AFMA sensor and

Derksen injury curve 7

Figure 3. Injury area-time history for 90 g/m2 (2.7 oz/yd 2

) PET/rayon fabric (no. 39) 16

LIST OF TABLES

Table 1. Fabrics which cause no reaction in AFMA simulation ... 9

Table 2. Heat transfer characteristics and ignition and

reaction times of fabrics which caused reaction 10

iv
FIRE ACCIDENT SIMULATIONS WITH APPAREL FABRICS

A. W. Meierhoefer , E. Braun, J. F. Krasny, and R. D. Peacock

Abstract

The objective of the work described here was

to continue earlier garment burn simulations and to

establish further background for the estimation of

the relative burn injury potential of flammable

apparel fabrics. The apparatus used was the Apparel

Fire Modeling Apparatus (AFMA) . The AFMA is a semicylinder almost completely covered with heat sensors.

It simulates part of a human leg or torso. Fabrics

can be burned on the AFMA in the free-hanging mode

or can be brought into contact with its surface after

a small amount of heat is sensed by the AFMA. The

burn injury potential of the fabrics can be evaluated

by such heat transfer characteristics as the total

heat transferred to the AFMA and the area of the AFMA

which would be susceptible to a second-degree burn,

as well as the rate of increase of this injury area. The results are related to fiber content, and weight

and construction of the fabrics. The fabrics used

were selected from a series used in the Cooperative

Program on Apparel Flammability sponsored by the

American Textile Manufacturers Institute.

Key words: Accident; apparel; burn injury; clothing;

fabric flammability; fabrics; fire; garments; heat

transfer; injury potential; simulation.

This work was done while Dr. Meierhoefer served as an NBS Research

Associate representing the Man-Made Fiber Producers Association.

Dr. Meierhoefer ' s current address is the American Enka Company,

Enka, North Carolina.

1
1. INTRODUCTION

The simulation of fire accidents has been recognized as an important

experimental approach to measuring the burn injury potential of fabrics

and garments. The results of such experiments are useful in the development of meaningful pass-fail criteria based on laboratory flammability

tests

.

Previous simulation work has usually involved the use of a mannequin. The underlying thought is that mannequins provide a reasonable

approximation of apparel fire accidents in which the complex shape of

the human body plays a role. Many simulations using simple mannequins

2 have employed photographic techniques [1] or simple heat sensors [2,3]

to estimate the burn injury potential of garment assemblies. More

completely instrumented mannequins, such as Thermo-Man, have been used

to establish detailed estimates of the injury potential of garments in

stationary situations [4]. The lack of movement in these experiments

removes one key element in simulations since some garment and body movements are generally associated with actual accidents.

Some simulation experiments which cover a variety of defensive

actions leading to extinguishment are described in the literature. Work

sponsored by the Consumer Product Safety Commission at the University of

Maryland and the National Bureau of Standards covered such extinguishing

modes as slapping [5,6], airflow, contact with heat sinks, and oxygen

depletion [6]. LeBlanc has also investigated airflow and slapping [7].

The Apparel Fire Modeling Apparatus (AFMA) which was designed at

the National Bureau of Standards and first used by Zawistowski, et al.,

is an attempt to include movement leading to body-fabric contact in the

fire accident simulation [8]. Basically, the AFMA is a semicylinder

which is almost completely covered with heat sensors. It simulates a

Numbers in brackets refer to the literature references listed at the

end of this paper.

2
leg or a torso. The specimen is ignited while hanging at some distance

from the AFMA surface. If it is allowed to remain in the original position, the experiment is called "free-hanging." In other experiments

called "reaction," the AFMA, upon sensing a certain temperature rise,

reacts by tilting and making contact with the burning specimen. It is

thus possible to simulate two extremes of what could happen in real-life

garment fires: the uninterrupted, free-burning of a loosely fitting garment and the behavior of a garment after it makes contact with a part of

the body which may serve to absorb heat and to exclude oxygen from one side of the fabric. This contact frequently leads to extinguishment of

the burning fabric.

While extinguishment of burning fabrics upon contact with skin has

been observed during in-vivo experiments [3], no claim is being made that

the present work where the contacting surface consists of copper sensors would give the same results as if skin had been exposed. However, the

relative ranking of the fabrics may be approximately the same for the

real-life fabrics and the present experiments independent of the heat

transfer properties of the medium receiving the heat.

The objective of this work was to continue earlier garment burn

accident simulations [8] and to establish further background for estimation of fabric burn injury potential. The fabrics used were chosen from

a larger number of fabrics which were used in the Cooperative Program on Apparel Flammability sponsored by the American Textile Manufacturers

Institute (ATMI) [9]. In this effort, 15 laboratories performed flammability tests or accident simulations with 65 fabrics furnished by ATMI.

The present report deals only with the results of the AFMA simulations;

future reports will relate these results to other laboratory tests and

Thermo-Man burn accident simulations.

3
2 . EXPERIMENTAL

2.1 The Apparatus

The AFMA is a vertically-mounted semicylinder, 60 cm (24 in) high

and 18 cm (7 in) in diameter (see figure 1). The lower end of the semicylinder is mounted on a fixed pivot which allows the AFMA to move

through an arc of approximately 20° . A fabric is mounted on a frame from

the top of the semicylinder, and ignited. At some point, the semicylinder

"reacts" (moves to a vertical position), bringing the burning fabric into

contact with the surface. The surface of the semicylinder is almost com- pletely covered by blackened copper sensors. The sensors are 7.6 x 2.5

cm, and are separated by 0.3 cm strips of mineral board. Heat transferred

to each sensor is recorded every 3 seconds. A more detailed description

of the AFMA can be found in an earlier publication [8]

.

Before work on the present series was started, three modifications

of previous procedures were introduced: a change in the criterion for

initiation of the reaction, closing the specimen on the top and sides so that heat would be trapped as in an actual garment, and introduction of

the "injury area" concept.

The monitoring circuit allows the AFMA to react to a specific heat

output rather than employing manual initiation for the reaction at a specific time from ignition or flame spread distance. This monitoring

circuit follows the temperature of four of the AFMA sensors located at

various heights in the center row. When any of these four sensors registers a temperature rise of 5° C (which would probably be perceived by a human), the AFMA "reacts"; i.e., swings, causing contact of specimen

and AFMA surface. The choice of a 5° C temperature rise is somewhat

arbitrary, but is probably in the range perceived by a reasonably alert

person

.

Another change was in the specimen configuration in order to make it

simulate a garment more closely. A backing fabric and a belt on top were

4
SPECIMEN

FRAME

+V7///A

C3

C_3

LU

Q—oo

5

Figure

1.

Schematic

view

of

AFMA
added, so that the specimen was part of an envelope enclosing the AFMA

rather than being open on the top and sides. The backing was a piece

of Nomex aramid fabric draped behind the AFMA and clamped to the specimen frame. The wire "belt" was placed around the top of the specimen

so it contacted the AFMA top. These changes were important to minimize

heat loss to the surroundings and to create a closed system resembling a garment

.

2.2 Data Acquisition and Computation

The data acquisition and computations were carried out similar to

the previous AFMA work [8] except for introduction of the "injury" concept. The heat sensors of the AFMA surface were scanned every 3 seconds

and the thermocouple outputs were recorded on magnetic tape. Subsequent

processing using NBS computer facilities gave equivalent heat flux values

for each sensor at 3-second intervals. The general calculations involved

determining the sensor temperature from the measured thermocouple millivolt output and then converting this to the quantity of heat transferred

using heat constants for each sensor arrived at by calibration as described in an earlier report [8],

In addition to the heat transferred to each sensor, an estimation

of "injury" was made for each sensor. The injury described here is an estimated incipient second-degree burn or deeper. The estimation is

based on the. work of Derksen [10], He exposed blackened rat skin to

square wave radiative heat at various rates, and established the relationship between total amount of heat and rate at which it was received,

to produce a second-degree burn. Stoll [11] showed this relationship to

hold true for human skin and convective as well as radiative heat. Figure

2 shows the Derksen curve, and a typical heat received vs exposure time curve for one AFMA sensor. The AFMA is considered "injured" where the

two curves intersect. The number of injured sensors was determined for

each 3-second interval from the time of ignition, and this was used to

calculate the "injury area" reported in the tables. This injury area

6
ical

thermosensor

05

CO

CD

LT3

CO

CM

CJ

03

CO

03

(jUI3/f) J8JSUBJ} )B8H

7

Figure

2.

Time-heat

curve

for

one

AFMA

sensor

and

Derksen

injury

curve
concept does not differentiate between second- and third-degree burns.

However, consideration of the injury area along with the total heat

delivered to this area permits a comparison of the depth of injury which

may be caused by the various fabrics. It must also be noted that the

AFMA heat sensors are blackened copper with thermal characteristics quite

different from those of human skin. The injury concept is thus only an approximation but, when used for comparative purposes, should permit

rough ranking of fabrics in terms of their burn injury potential.

2.3 Fabrics

The fabrics used in the AFMA simulation work were those supplied by

the American Textile Manufacturers Institute in the Cooperative Apparel

Fire Accidents Flammability Program [9]. The fabrics were representative

of the range of fiber and fabric types presently in common use but also

included a few experimental fabrics. The 58 fabrics used in this work

are described in tables 1 and 2. Table 1 shows the fabrics which did not

produce enough heat to cause reaction by the AFMA; i.e., did not raise

the temperature of four sensors located at various heights in the center

row of the AFMA more than 5° C. Table 2 lists the fabrics which caused

reaction, arranged by fiber content, and within each fiber content group,

by increasing weight. There were nine 100% cotton fabrics; 14 polyester/

cotton blends varying in polyester/cotton ratios from 76/24 to 15/85; seven fabrics containing acetate or triacetate alone or in blends with

nylon; nine fabrics containing acrylic or modacrylic fibers, some blended

with polyester; 13 fabrics containing thermoplastic fibers, nylon, or polyester; and five fabrics containing wool. Constructions ranged from lightweight wovens to denims, corduroys, terry towels, and included various

knits

.

2.4 Simulation Procedure

The samples were prepared and conditioned in a room maintained at

approximately 23° C and a relative humidity of 40%. The samples were then

8
Table 1. Fabrics which cause no reaction in AFMA simulation

ATMI

Number Description Weight

Total

Heat

g/m2 (oz/yd 2

) J

11 100% PET Woven 80 2.3 662

13 " " " fr 130 3.8 272

7

" " Knit 190 5.7 942

9

tl tl ft 240 7.2 360

8

II II It 240 7.2 214

4

II II II 245 7.3 3488

5

" " Woven 270 8.0 398

14 Nylon-6 Knit 30 0.9 176

15 II II II 80 2.4 502

68 " Nylon Knit 90 2.7 193

41 71/29 Modacrylic/Acrylic Knit 155 4.5 473

43 II II II 295 8.7 343

21 100% Wool Woven 205 6.0 377

54 " " " FR 195 5.7 452

53 It It II II 270 8.0 285

9
Table

2.

Heat

transfer

characteristics

and

ignition

and

reaction

times

of

fabrics

which

caused

reaction

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10

Asterisk

next

to

ATMT

No.

indicates

bottom

Ignition;

fabrics

did

not

Ignite

with

paper

tab

held

on

fabric

Number

after

slash

Indicates

quart

'le;

e.g.,

59500/3

means

result

Is

in

third

(next

to

highest)

quart

lie.
Table

2.

Ileal

transfer

charael

er

1st

icn

and

Ip.nltlon

and

ram- 1

Ion t

imen

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fnbrlca

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11

Asterisk

next

to

ATM1

No.

indicates

bottom

ignition;

fabrics

did

not

ignite

with

paper

tab

held

on

fabric

surface.

Number

after

slash

indicates

quart!

le;

e.g.t

59500/3

means

result

is

in

third

(next

to

highest)

quartiie.
Table

2.

Heat

transfer

characteristics

and

ignition

and

reaction

times

of

fabrics

which

caused

reaction

front

Inued

)

i

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12

Asterisk

next

to

ATM1

No.

indicates

bottom

ignition;

fabrics

did

not

ignite

with

paper

tab

held

on

fabric

surface.

Number

after

slash

indicates

quartile;

e.g.,

59500/3

means

result

is

in

third

(next

to

highest)

quartil**.
13
mounted on the AFMA. A paper tab was placed on the front of the specimen,

12 cm (A. 75 in) from the bottom edge. The back fabric and the wire belt

on the top were then attached. Upon ignition of the tab, a stopwatch was started to determine the time until the temperature of one of the four

monitored sensors increased by 5° C. This was called the reaction time.

At t lie instant of ignition of the tab, the data acquisition system

was started and allowed to scan the heat sensors at 3-second intervals

during the burning of the fabric and for about 15 seconds after the last

evidence of fabric combustion. For those fabrics which would not ignite

with surface ignition, a second attempt was made by ignition at the bottom

edge

.

After each experiment, the AFMA was cleaned, any adhering char or thermoplastic melt removed, and allowed to cool. The general procedure

was to let all heat sensors cool until the potential from the thermocouples was 0.02 mv or less.

Samples were tested either in the free-hanging mode or the AFMA was allowed to react to make fabric contact when the temperature on any one

of four sensors rose 5° C, as discussed earlier.

At the end of the series of experiments, the magnetic tape was processed to give the injury and heat data for each sensor. Copies of the raw data and the computer programs are on file at NBS

.

In addition to determining injury area, and total heat received by

this area, a measure of the probability of ignition of the fabrics was desired. Ignition time was measured on the Mushroom Apparel Flammability

Tester (MAFT) [12] . Cylindrical specimens were exposed to a methane flame

at a point 10 cm above their bottom edge. The ignition time was not measured for fabrics with low heat transfer characteristics.

14
3. RESULTS AND DISCUSSION

In the AFMA simulations, fabrics fall into two general classes,

those which caused the AFMA to react and those which did not. The determination of "reaction" was by heat transfer, so those which caused no reaction either did not ignite under the above described ignition procedure, or, if they did, transferred very little heat. Several examples were noted where large areas of fabric were destroyed but too little heat was transferred to the AFMA surface to initiate reaction.

Table 1 lists those fabrics which did not transfer enough heat to cause AFMA reaction. Included in this group are all but three of the

100% nylon and polyester fabrics; the two modacrylic/acrylic blends with

highest modacrylic content; and one untreated and two FR treated wool

fabrics. The only measurement made for these samples was the total heat

transferred to the AFMA sensors during the experiment which includes the

heat from the paper ignition tab. For all of these, ignition was attempted both on the surface and from the bottom edge.

Table 2 shows fabric construction and the results of the freehanging and reaction simulations for the fabrics which caused a reaction

by the AFMA. Fabrics which did not ignite with a burning paper tab

attached and were ignited at the bottom edge to the surface are indicated

by an asterisk next to the ATMI number in the table.

Figure 3 shows injury area as a function of exposure time for the

free-hanging and reaction modes for a lightweight, polyester/rayon fabric

(No. 39). The first reading of heat rise on the AFMA was at about 7 seconds; at 9 seconds, 5° C heat rise was registered and the AFMA reacted

to make contact with the burning specimen. After this, the area of the

simulated body which was considered to be the "injury area" (i.e., it

received heat in the amount and at the rate which, according to Derksen,

would cause a second-degree burn) increased rapidly. Soon afterwards,

the rate at which the injury area increased slowed down and almost leveled

15
TYPICAL

AFMA

INJURY

HISTORY

FOR

A

LIGHT

CELLULOSIC

FABRIC

CD

C/5

CO CO CM

z

uio V3UV AUOPNI

16

Figure

3.

Injury

area-time

history

for

90

g/m 2

(2.7

oz/yd

2)

PET/rayon

fabric

(no.

39)
out at about 12 seconds, indicating extinguishment. The free-hanging

specimen transferred heat at the initial rate for about the same time.

When the flames reached the top and started to spread horizontally, the

rate of injury area increase slowed down. The total injury area caused

by the free-hanging specimens was about 2-1/2 times that of the reaction

specimen. (About 30% of the AFMA area could be considered injured in the

reaction mode, and 75% in the free-hanging mode.)

Two columns of table 2 show the total heat received by the AFMA during the whole duration of the burns for the free-hanging mode and for the

reaction mode. Where the fabric extinguished soon after reaction (because

of the heat sink effect and the exclusion of oxygen by the AFMA surface),

the reaction heat was lower than the free—hanging heat. In some cases

the reaction heat was higher, indicating that either no (or slow) extinguishment took place or that more heat was transferred to the AFMA because

of closer specimen—AFMA surface distance than in the free—hanging mode

(e.g., fabric 5b, terry cloth, and several acetate fabrics, group 1,

table 2).

The next column of table 2 shows "injury area," that AFMA area con- sidered to have undergone the equivalent of an incipient second-degree

or deeper burn, as discussed earlier . Only the reaction mode results

list ed because the free—hanging specimens were burned almost entirely

and there was little difference in injury area results between the various

fabrics

.

The "maximum rate of injury area increase" in the free-hanging and

reaction modes is the maximum increase in injury area measured during any

3-second period during the burn. For many free-hanging fabrics, especially cellulosic fabrics (those which contain rayon or cotton, alone or m blend with other fibers) which burn primarily upward, the flame spread

rate may increase till the fabric burns a considerable distance from the

point of ignition before it levels out [13]. The values reported here

for free-hanging mode burns thus are in many cases considerably below

17
the possible maximum. In the reaction mode, the listed rate sometimes

occurred during the early part of the burn and sometimes during or after

contact of the burning fabric with the AFMA surface.

The times to ignite cylindrical specimens of the same fabrics on the

MAFT [11] are also listed. Of two fabrics with similar heat output characteristics, the one with the longer ignition time may be considered less

hazardous

.

Finally, table 2 shows the "reaction time," the time from the application of a match to a paper tab on the outside of the specimen to the

time at which one of four sensors registered a 5° C temperature rise.

Such a heat rise would probably be recognized by a reasonably alert person, who may react defensively (in the "reaction" simulation, it is

assumed that the reaction leads to fabric-body contact) . It is not quite

clear whether a short or long reaction time is preferable. Short reaction

times are generally associated with two types of fabrics: lightweight

cellulosics which ignite readily and burn rapidly, and thermoplastics

which melt in the flame impact area but usually burn slowly. Long reac- tion times are associated with heavy, thick fabrics which burn on the

outside before sufficient heat is transferred to the inside to cause a reaction. Such flaming could be well developed before the heat rise is

felt by a wearer in real-life situations. On the other hand, the chances

of visual detection and defensive action before the skin is endangered

by the heat are increased when the heat transfer to the body is slow.

For convenience in the evaluation of the relative standing of the

various fabrics, the measured heat and area values listed in the columns

in table 2 were classified according to quartiles; i.e., into four groups,

each containing the same number of values. The quartile assigned to the

numerical result is noted in the table as in the following example:

59500/3, the first entry in the total heat free-hanging column means that

the total heat measured by all sensors for this fabric was 59500J and that

this result is in the third (the second highest) quartile. By comparing

18
the quartile notations for any one fabric, one can readily establish

whether a fabric ranked high in all listed properties, or, e.g., high in

the free-hanging but low in the reaction mode.

In most cases, only one specimen was examined in the free-hanging

mode and one in the reaction mode. When duplicates were run, results for

all properties listed in table 2 generally differed by 20% of the first

value or less.

3.1

Total Heat Delivered to AFMA

3.1.1

Free-Hanging Mode

As might be expected, the total heat delivered to the AFMA from

fabrics when burned in the free-hanging mode generally increased with

increasing fabric weight. For a given weight, the results for cotton,

polyester/cotton, and the 100% acrylic fabric were similar. Blending of

modacrylic with acrylic reduced the total heat delivered. The acetate

woven fabric delivered less heat than the cellulosic fabrics of similar

weight; the knitted acetate fabrics and the polyester and nylon fabrics were generally in the lower quartile.

3.1.2

Reaction Mode

Most fabrics extinguished soon after making contact with the AFMA

in the reaction mode. These fabrics delivered considerably less heat

to the AFMA in the reaction mode than in the free-hanging mode. However,

in some cases, good contact was prevented by the surface characteristics

of the fabric, such as the pile of the double face terry towel, No. 56, or the fabrics curled away from the AFMA surface and continued to burn,

such as most acetates and acrylics (also observed by Zawistowski [8]).

If the fabric continued to burn after reaction, the total heat delivered

to the AFMA tended to be larger than in the free-hanging mode because of

the closer proximity of the flame to the sensors.

19
3.2 Injury Area

Table 2 only lists the injury area for the reaction mode. In the

free-hanging mode, most fabrics caused injury areas of over 80% of the

total and thus there was little difference between fabrics.

The injury area did not exceed 65% of the total surface area for

any of the fabrics tested in the reaction mode. The larger injury areas were generally caused by the fabrics which continued burning after the

reaction, i.e., the terry towel, the acrylic knit, one acrylic/modacrylic

knit, and the majority of the acetate fabrics. Relatively large areas were also found for two lightweight polyester/cotton blends which burned

rapidly. At the point of reaction, most of their surfaces were already

aflame and thus transferred heat over a large area. Presence of modacrylic fiber or wool in blends with nylon or polyester resulted in

relatively small injury areas.

3.3 Maximum Rate of Increase of Injury Area

3.3.1 Free-Hanging Mode

The maximum rate of increase of injury area—the maximum increase

in injury area measured during any 3 seconds during the burn—was highest

for the lightweight cellulosic fabrics, the single and double-faced terry,

the woven acetate, and the acrylic knit fabrics. It was relatively low

for the nylon, polyester, and the three triacetate/nylon blends, the FR

cotton, a heavy denim, two of the knits containing acrylics, and, inexplicably, one heavy polyester/cotton twill (similar fabrics were considerably higher)

.

3.3.2 Reaction Mode

In the reaction mode, relatively high rates were again found in the

lightweight cellulosics and the acetate satin. Most other acetates were

20
in the middle range. Relatively low rates were again registered by the

nylon, polyester /wool blend fabrics and some of the acetate and acryliccontaining knits.

In most cases, the injury rate in the reaction mode was lower than

in the free-hanging mode.

3.4

Time to Ignite

Time to ignite increased generally with fabric weight for the cellulosic fabrics, except the terry towel, which exhibited a short ignition

time. It was generally short for acetate and long for acrylic-containing

fabrics

.

3.5

Reaction Time

Reaction time also generally increased with fabric weight for the

cotton fabrics. The relationship for polyester/cotton blends was similar

but less regular and fabrics with a pile structure, such as terry and

corduroy, had reaction times which were somewhat shorter than expected

on basis of weight only. Reaction time of acetate-containing fabrics was generally in the lower quartile, indicating little time before the

flames from the burning paper tab penetrated to the fabric side facing the

AFMA. The acrylic group tended to be in the middle range and apparently

was little affected by weight. The polyester and nylon fabrics had the

longest reaction times, indicating the low heat output from such fabrics even though they were readily penetrated by the flames.

3.6

Overall Evaluation of Fabrics

The fabrics listed in table 1 are those with a low burn injury

potential. While some of these ignited and continued burning, the heat

developed was insufficient to cause even as little as a 5° C heat rise

on one of four heat sensors on the AFMA surface. Thus, these fabrics

21
did not cause a reaction of the AFMA and were not brought in contact

with the AFMA surface.

Table 2 lists the fabrics which caused a reaction, i.e., developed

a 5° C rise and were brought in contact with the AFMA surface. They vary

widely in (a) the total heat measured in the free-hanging and reaction

modes, (b) injury area in the reaction mode, (c) maximum rate of increase

of the injury area for the free-hanging and reaction modes, and (d) ignition time. The longer the time to ignite, the higher the probability

of fabric ignition in many garment burn situations. (The other major

effect on this probability of garment ignition, looseness of garment fit,

is not considered here but has been discussed in an earlier paper [12].)

A review of the quartile designations for each fabric indicates that some fabrics rank high or low in all characteristics while others vary

greatly in their relative positions. No attempt was made to assign a weight to these characteristics in order to develop a "hazard index,"

nor to evaluate relative importance of the characteristics measured in

the reaction or the free-hanging modes. In every real-life garment burn, some of the garment will be free-hanging and some will come into contact

with the body. The relative amount of free-hang and contact of a garment

will depend on garment fit and the motion of the wearer. The AFMA reac- tion simulation is specific for a garment part changing from free-hanging

to contact. The reaction and free-hanging simulation represent two

extremes, but no prediction can be made as to their relative frequency of

occurrence in real-life garment fire incidents.

The fabrics which ranked lowest in heat transferred are listed in

sections D, E, and F of table 2. They had similar fiber compositions to

those listed in table 1: nylon, polyester, wool, or 40-50% modacrylic.

As indicated by the asterisk placed near the fabric number, many of them

did not even ignite from the burning paper tab attached to the surface

but ignited at the bottom edge. Their ignition times were long.

22
On the other end of the scale, the cellulosic fabrics weighing less

than 170 g/m2 had short ignition times and tended to be in the highest or third quartiles of the heat transfer characteristics measured on the AFMA.

Also in this group were the two terry towels, which were considerably

heavier. Their pile ignited in 1/2-second, and they ranked high in all

heat transfer characteristics. Only their maximum rate of injury area was relatively low in the reaction mode. Apparently the outer pile burned

first, followed by the rest of the fabric, resulting in high heat output

burn in spite of contact with the AFMA but with the heat spreading over

the AFMA at a relatively low rate.

Fabric 63 was a cotton fabric treated with a low-level of FR agent.

It ranked low in total heat but quite high in the reaction maximum rate

of increase in injury area and total injury area. Other investigators

have found that many cotton fabrics with low-level FR treatment develop

a rapidly spreading flame on the surface along a narrow path [14].

The cellulosic fabrics weighing more than 270 g/m 2 generally ranked

high in total heat, free-hanging, but were in the intermediate ranking

in the other characteristics, especially in the reaction mode. Apparently

all extinguished in this mode upon contact with the AFMA surface.

The fabrics containing acetate or triacetate differed markedly from

the cellulosics. They ignited readily and the woven acetate sateen ranked

high in most heat transfer characteristics. The six other fabrics, all

knits, transferred generally little heat in the free-hanging mode. In

the reaction mode they did not extinguish, but the edges of the previously

burned area curled away from the AFMA and continued to burn. The injury

area generally did not increase in size after 15-30 seconds, but additional heat was delivered to it for up to 90 seconds. This resulted in

relatively high total heat in the reaction mode. These fabrics are some- what thermoplastic in nature, melt ahead of the flame, and shrink and

shrivel in the burning area. The flame flickers considerably more than

in cellulosic fabrics [8].

23
The heavy acrylic and polyester/acrylic knits ranked high in most

heat transfer characteristics. Acrylic, like acetate, has been found to

continue to burn in the reaction mode, forming a foam-like substance

which does not fully make contact with the AFMA surface [8]

.

The lighter

polyester/acrylic knit, however, ranked quite low.

4 . FUTURE WORK

The flammability of fabrics discussed here has been investigated

in 14 other laboratories by a variety of test methods and apparel burn

accident simulations. Analysis of this extensive amount of data is in

progress, with special emphasis on the apparel burn simulations on the

motionless Thermo-Man, instrumented mannequin. The AFMA and Thermo-Man

data will be compared with the MAFT classifications and results from our laboratory flammability tests. Consideration will be given to results of

extinguishment experiments being carried out presently at NBS (measuring

the AFMA heat transfer characteristics of fabrics exposed to various

levels of airflow) and earlier experiments at the University of Maryland

[6], The present attempt of ranking fabrics according to flammability

hazard will thus be greatly enlarged. Hopefully, the advantages and

limitations of various laboratory methods in predicting these hazards

will be established.

5. REFERENCES

[1] Galil, F. and Lomartire, J., Flammability assessment in apparel

fabrics, part 1: the product parameter technique, Textile Chemist

and Colorist, Vol. 8, No. 8, 22-27 (August 1976).

[2] Finley, E. L., Summers, T. A., Carter, W. H., Cochran, B. J., and

Farthing, B. R., Flammability characteristics of multi-layer

24
clothing. Journal of Fire and Flammability, Consumer Product

Flammability, Vol. 2, 170-187 (June 1975)

.

[3] Krasnv, J. F. and Fisher, A. L., Laboratory modeling of garment

fires, Textile Research Journal, Vol. 43, 272-283 (May 1973).

[4] Bercaw, J. R., Industry apparel flammability program. Proceedings

of the Sixth Symposium on Textile Flammability, New York, New York

(April 19, 1978), sponsored by LeBlanc Research Corporation, East

Greenwich, Rhode Island 02818.

[5] Krasny, J. F. and Francis, J. B., Ranking extinguishability of

burning fabrics, Textile Chemist and Colorist, Vol. 6, No. 6, 36-37

(June 1974)

.

[6] Spivak, S. M. , Block, I., Smith B. F., Yeh, K., Bhat , G. R., Sun,

R. L., Miles, L., Fairall, P., and Potthoff, P., Extinguishability

as a component measure of the flammability hazard. Final Report,

Department of Textiles and Consumer Economics, University of

Maryland, to the Center for Fire Research, National Bureau of

Standards, NTIS P.B. 269489.

[7] LeBlanc, R. B. and DiCarlo, J. P., Tests for ease of extinguishment.

Proceedings of the 5th Symposium on Textile Flammability, New Orleans,

Louisiana (April 1977), sponsored by LeBlanc Research Corporation,

East Greenwich, Rhode Island 02818.

[8] Zawistowski, E. R., Krasny, J. F., Braun, E., Peacock, R. D., and

Williams, N. , The measurement of fabric flammability parameters in

experiments simulating human movement in burn accidents, Nat. Bur.

Stand. (U.S.), NBSIR 77-1236 (June 1977).

25
[9]

Bercaw, J. R. , Industry program on Thermo-Man and its relation to

MAFT and other predictive apparel flammability tests: status

report, Proceedings of the 10th Annual Meeting, Information Council

on Fabric Flammability (December 1976)

[10] Derksen, W. L. , Monahan, T. I., and DeLehery, G. P., The temperature associated with radiant energy skin burns, in temperature—its

measurement and control in science and industry, Vol. 3, Part 3,

p. 171 (1961).

[11] Stoll, A. M. and Chianta, M. A., Heat transfer through fabrics as related to thermal injury, New York Academy of Sciences,

Transactions, Vol. 33, No. 7, 649-670 (November 1971).

[12] Braun, E., Cobble, V. B., Helzer, S., Krasny, J. F., Peacock, R. D.,

and Stratton, A. K., Back-up report for the proposed standard for

the flammability of general wearing apparel, Nat. Bur. Stand.

(U.S.), NBSIR 76-1072 (June 1976).

[13] Miller, B., Martin, R. , and Meiser, C. H., Jr., Measurement of

burning rates of unrestrained fabrics. Textile Chemist and Colorist,

Vol. 7, No. 4, 30-34 (April 1975).

[14] Pete, J. A., Evaluation of fyrol treated fabrics using the mushroom

apparel flammability tester. Textile Chemist and Colorist, Vol. 9,

No. 8, 160-162 (August 1977).

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NBS-114A (REV. 9-78)