*

>*/2/,ce> This report has been prepared

for information and record

purposes and is~nat to be reference

ift-any-pubUoation

NATIONAL BUREAU OF STANDARDS REPORT

REVIEW OF FABRIC FLAMMABILITY TEST METHOD

A Progress Report

by

M, P» Vaishnav

and

M. W. Sandholzer

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

L

8671
THE NATIONAL BUREAU OF STANDARDS

The National Bureau of Standards is a principal focal point in the Federal Government for assuring

maximum application of the physical and engineering sciences to the advancement of technology in industry and commerce. Its responsibilities include development and maintenance of the national stand- ards of measurement, and the provisions of means for making measurements consistent with those standards; determination of physical constants and properties of materials; development of methods

for testing materials, mechanisms, and structures, and making such tests as may be necessary, particularly for government agencies; cooperation in the establishment of standard practices for incorporation in codes and specifications; advisory service to government agencies on scientific and technical problems; invention and development of devices to serve special needs of the Government; assistance

to industry, business, and consumers in the development and acceptance of commercial standards and

simplified trade practice recommendations; administration of programs in cooperation with United

States business groups and standards organizations for the development of international standards of

practice; and maintenance of a clearinghouse for the collection and dissemination of scientific, technical, and engineering information. The scope of the Bureau’s activities is suggested in the following

listing of its four Institutes and their organizational units. Institute for Basic Standards. Electricity. Metrology. Heat. Radiation Physics. Mechanics. Applied Mathematics. Atomic Physics. Physical Chemistry. Laboratory Astrophysics.* Radio Standards Laboratory: Radio Standards Physics; Radio Standards Engineering.** Office of Standard Ref- erence Data. Institute for Materials Research. Analytical Chemistry. Polymers. Metallurgy. Inorganic Materials. Reactor Radiations. Cryogenics.** Office of Standard Reference Materials. Central Radio Propagation Laboratory.** Ionosphere Research and Propagation. Troposphere

and Space Telecommunications. Radio Systems. Tipper Atmosphere and Space Physics.

Institute for Applied Technology. Textiles and Apparel Technology Center. Building Research.

Industrial Equipment. Information Technology. Performance Test Development. Instrumentation.

Transport Systems. Office of Technical Services. Office of Weights and Measures. Office of Engineering Standards. Office of Industrial Services.

* NBS Group, Joint Institute for Laboratory Astrophysics at the University of Colorado. ** Located at Boulder, Colorado.
NATIONAL BUREAU OF STANDARDS REPORT

ms PROJECT MBS REPORT

1002-12-4210120 April 13, 1965 8671

REVIEW OF FABRIC FLAMMABILITY TEST METHOD

A Progress Report

by

M. P* Vaishnav

and

M. W. Sandholzer

IMPORTANT NOTICE NATIONAL BUREAU OF S'

for use within the Government, and review. For this reason, tl whole or in part, is not authc Bureau of Standards, Washing

the Report has been specifically

Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST) on October 9, 2015.

ess accounting documents intended

5 subjected to additional evaluation

e listing of this Report, either in

le Office of the Director, National

y the Government agency for which

copies for Its own use.

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

REVIEW OF FABRIC FLAMMABILITY TEST METHOD

A Progress Report

by

M. Pw Vaishnav and M. W. Sandholzer

ABSTRACT

A study of the technical aspects of the fabric flammability test method of Commercial Standard 191-53 is in progress.

The results of a program of experimental work to determine the

importance of a number of possible variables in the test procedure

are reported. On the basis of these results, a standard test

procedure for use in further work with the method has been selected,

and a few recommendations relative to the test equipment developed.

A comparative classification of a wide range of clothing and

bedding materials by CS191-53 and NFPA, Standard 702, together with

data on their heat release behavior, will be presented in a later

report.

REVIEW OF FABRIC FLAMMABILITY TEST METHOD

A Progress Report

by

M. P. Vaishnav

and

M» W e Sandholzer

1. Introduction

The Federal flammable Fabrics Act, passed in 1953 , delegated to the

Secretary of Commerce the responsibility of presenting to the Congress,

appropriate legislative proposals at any time he might find the commercial

standards referenced in the Act (CS 191-53 and CS 192=53.) inadequate for the

protection of the public interest. With a view to fulfilling that responsibility, a review of those commercial standards and the operation of the

law, tejdate ,was initiated by the Secretary. As part of that review, the

National Bureau of Standards was asked to conduct a technical study of the

test procedures and equipment on which the standards are based, and their

application to current consumer fabrics.

Primary attention was centered on €8191=53, inasmuch as the present

use of plastic films (covered by CS 192=53) in clothing is very small.

During the years since enactment of the law, a considerable amount of ex= perience in the application of CS 191-53 has been developed both in production

control laboratories and in government and commercial testing laboratories.

In preparation for the study, therefore, the Commodity Standards Division

of the National Bureau of Standards solicited comments on the standard from

the various organizations, agencies, and laboratories, interested in the

manufacture, distribution, and hazards of clothing fabrics. The experience,

problems, and suggestions on the technical aspects of the standard reported

in these comments were of value in development of a program of experimental

study of the test.

The present progress report presents the findings of an experimental

study of the influence of a number of variables on the results of flammability

measurements. A later continuation of this work will deal with performance

of a number of selected fabrics as tested by the procedures of the Commercial

Standard and the NFPA Standard No. 702. This later report will also include

data resulting from measurements of relative heat release behavior of the

fabrics
- 2 -

2. Factors Selected for Study

The description of the apparatus and procedure given in the standard

had not proved sufficiently explicit on several points to avoid some variation in interpretation and practice among different laboratories.

Incomplete definition, has also permitted modifications, apparently minor

but still possibly significant , of the test equipment by the manufacturer.

Although some of these differences had been the source of considerable

concern to several groups, thei'r actual importance in affecting the test

results was largely unknown, hence, the first part of the experimental

program was designed to determine which of the variations to which the

method was subject would significantly affect, the test results and

necessitate more precise definition of equipment and procedure.

A review of the comments received disclosed six points in the test

method where practice among laboratories commonly varied or where a decided modification of procedure was proposed. The sources and extent

of variation at these points, and the experimental approach followed in

exploring its significance in each instance, are outlined below:

1. Oven drying.

The commercial standard stipulates that the specimens shall be

dried in an oven for 30 minutes at 221 °F (105°C). The type of oven

is not specified and ovens differ widely in the time required to re- gain the specified temperature after introduction of a set of specimens.

Hence, the total time for which specimens may be held at a considerably

elevated temperature is highly variable, and the question of the possible

effect of this variable on the test results has been raised.

Tests were carried out using an oven equipped with farced air

circulation, which regained the specified temperature within two or three minutes after introduction of a set. of specimens. The effects

of holding specimens in the oven for 10, 15, 20, 30, and 60 minutes

were studied.

2. Desiccator cooling.

The standard requires that, upon removal from the oven, the

specimens be "placed over anhydrous calcium chloride in a desicator

until cool, but for not less than 15 minutes." No maximum time limit

is imposed. The rate of cooling depends on the number of specimens

stacked in the desiccator, as well as on ambient, conditions, and the

definition of "cool" will vary with different operators. Hence,

specimens may be left in the desiccator for periods ranging from 15

minutes to several hours.
- 3 ~

In studying the' effect of this variable on the test results.,

desiccator times of 0, 15, 30, and 60 minutes were used. The

specimens tested with no time in the desiccator were removed individually from the oven and tested immediately. Silica gel was substituted as a more effective and dependable desiccant than

anhydrous calcium chloride.

}

3. Thread height.

The thread guides ©n the specimen holder, which determine the

position of the stop cord over the specimen, are not precisely

described in the standard and have been subject to modifications

which resulted in differing heights of the thread above the fabric

surface. Specimen holders of both types are in use and the effect

of thread height on the test results is therefore of decided interest.

A set Of specimen holders was prepared with guides . which permitted threading the stop cord at various selected heights ranging

from 1/8 to 3/4 in. above the specimen surface. Primarily, however,

attention was centered on a comparison ©f the 1/8 in. and 3/8 in.

heights, the two heights appearing in commercially distributed

holders

.

4 . F lame length

•

Although the length of the igniting flame is specified in the

standard, the measurement of its lej^th depends to some extent on operator judgment and is slightly variable. In addition., the flame

length is sensitive to small changes in fuel pressure and some laboratories reported difficulty in maintaining proper adjustment.

Hence, information on how critical a factor the flame length might be

appeared important.

The standard stipulates a flame length of 5/S in. For the com- parative study flame lengths 1/2, 5/8, and 3/4 inches were used..

5. Taping of specimen.

S ome light-weight fabrics are so- thin that the smooth metal of

the specimen holders (which may also become slightly warped) fails to

grip the material. This permits the exposed area of the specimen to

sag slightly farther from the igniting flame in the case of soft,

limp materials; and fabrics which shrink and curl decidedly in a flame

fend to draw out of the specimen holder as they burn. To prevent such

behavior, the practice of securing the specimens of very thin materials

to the holder by means of an adhesive tape has been suggested. Taping

is sometimes used also, to hold iri a reasonably smooth, flat position,

the badly wrinkled specimens of materials which might be altered by

pressing.
= 4 »

To determine whether the practice of taping would be advisable,

tests were made on both taped and not-taped specimens of the same material. The taped specimens were secured to the back section of

the specimen holder by means of four short strips of masking tape, one near the top and one near the bottom of each side of the

specimen.

6. Type of ignition.

Among suggestions for change to the Federal law, has been the

proposal that CS191-53 be replaced by National Fire Protection

Association Standard 702 as the basis for defining hazardous

flammability. The two standards employ basically the same test

equipment but differ in test procedure, the most notable difference

being the method of igniting the specimen. In CS 191-53, the igniting flame is applied to the surface of the specimen for one second.,

while in NFPA 702, it is applied to the edge of the specimen until

ignition has occurred. The effect of this change in ignition

procedure on the test results was included in the study.

In addition to the difference in procedures outlined above, the com- ments included several suggestions for modification of the apparatus.

Most frequently mentioned was a possible advantage from the substitution

of an electrical timing system for the mechanically operated stopwatch

described in the standard. Some operators felt that an electrical system

would provide more precise measurement and be more convenient and dependable in operation as well. To develop experience and information on the

question, an electric timer was incorporated in the apparatus in such a way that it and the stopwatch were activated by the same devices and

provided simultaneous records.

Another point on which some question was raised involved the positioning of the specimen in the specimen holder. The usual practice of most

operators appears to have been to place the lower end of the 6- in. specimen

even with the lower end of the back plate of the specimen, holder. Inserted

thus, the igniting flame should impinge on the surface of the material at a point 1/2 in. from the lower end of the specimen. However, this 1/2 in.

spacing (which may be further reduced by only slight deviations in flame

or specimen adjustment) is small enough that fabrics subject to severe shrinkage in a flame may draw the edge up to produce essentially edge

ignition. Throughout the present study, the specimens were positioned about

1/8 in. lower in the holders in order to slightly increase the distance

between the point of flame impingement and the specimen edge. This was accomplished by cutting the specimens 6 1/4 inches in length and positioning

the upper end even with the top of back plate.
- 5 -

One of the modifications which have developed in the apparatus

since the original design, appears in the rack which supports the specimen

holder during test. In the early machines , the metal support on which the

bottom of the specimen holder rests was a continuous bar running across,

the full width of the rack. In the currently produced machines , however,

the bar has become discontinuous supporting the specimen holder at the corners but leaving the center open. While these arrangements are equally

satisfactory for support of the holder, the Conditions of air flow around

the bottom edge of the fabric specimen will be affected by the presence

or absence of the partial obstruction of the bar across the center of the

rack. Although the effect of this modification was not studied extensively,

sufficient comparison was made to show that it does influence the burning

times of some fabrics, and should be standardized in all machines.

3. Organization of Experimental Program

Inasmuch as the test results for different types of fabrics may be

affected differently by a given procedural variation, the program

necessarily included a fair number of materials, although only fabrics

which ignite in the one-second flame exposure would be useful. In all,

eleven fabrics were used in the study of test method variances, but none was carried through every comparison.

In order to avoid unnecessary and excessively prolonged experimentation,

a program of factorial experiments was designed under the. guidance of the

Applied Mathematics Division of the Bureau. After some preliminary trials

to study the characteristics of the problem and determine the number of

repetitive specimens required, one general plan for the individual series

of tests was adopted. For the most part, each series of tests compared

four different variables in test procedure at two levels on three different

fabrics. For example, one series might, compare the effect, of oven times

of 15 and 30 minutes, thread heights of 1/8 and 3/8 inches, edge and surface

ignition, and flame lengths of 5/8 and 3/4 inches on three fabrics.

Duplicate, specimens were tested in each instance so that such a series

employed 32 specimens in all, and each comparison was based on averages of

16 determinations. While the schedule of tests was adjusted in some series

to study more than two levels of a variable at one time, or develop a point

of particular interest, care was taken to maintain a meaningful number of

determinations in each comparison. Twenty- two such series of tests were

made

.
- 6 -

4. Test Results and Selection of Standard Procedure

The results of the test series are shown in Table 1. The overall

mean burning time for the series is given in the fourth column. Each

of the following columns shows the difference in burning time obtained

under the comparative conditions indicated in the heading. Thus,

referring to colunn 6, the average burning time for silk I was 0.26 sec. longer with a thread height of 1/8 in than with a thread height of 3/8 in.

Differences which proved to be significant under statistical analysis at

the § 5% confidence level, are indicated by an asterisk.

The significantly longer burning times for surface ignition than for

edge ignition are to be expected of course. The only materials unaffected

by the type of ignition were those subject to a rapid surface flash

initiated by the first touch of a flame. It is clear also that the height of

the thread above the fabric is generally a significant factor in the test

results and should therefore be standardized and specified. Although, for

the most part, taping the specimens to the holder appeared to give slightly

shorter burning times, the difference did not prove significant in any

instance. This indicates that taping should be an acceptable procedure

in situations where it would facilitate positioning the specimen. The

absence of the metal strip across the bottom width of the specimen holder

support rack permitted, in some instances, flame travel around the lower

edge with resulting rapid propagation up the lower surface of the specimen.

The flame length comparisons suggest that, the flame length is critical

chiefly as it affects the distance between the flame and the fabric, not

with respect to heat output. Thus, significant differences occurred only

with the shorter flame length where the tip of the flame was slightly

farther from the fabric. The length of time the specimens were held in the oven had no significant effect over the range of 10-60 minutes. The period

of cooling in the desiccator proved unimportant after the first 30 minutes;

although the specimen holders were still warm at this time. This suggests

that the time required for the desiccant to absorb the moisture introduced

by a change of air, is the critical factor in the desiccator time rather

than the temperature of the specimens and holders. This view is supported

by continuous humidity records obtained from a humidity sensor hung in the

top of the desiccator, which showed that the humidity in the closed desiccator closely approached its equilibrium level in about 10-15 minutes,

while it required more than an hour for the holders and specimens to cool

to room temperature. Experience with the electrical vs. mechanical timing

devices suggest that, provided proper adjustment is maintained, either

method may be used with satisfactory results. The time resolution with the

electrically-timed system is, of course, much finer, but the need for this

precision is questioned.
On the basis of these findings the following standardized procedure

was selected for use in further work with the test method. The oven conditioning of 30 minutes at 105 °C was retained and a uniform period

of 30 minutes in the desiccator was adopted. Specimen holders with a bent-pin type of thread guides providing a uniform thread height of

3/8 in. across the specimen were used. This was facilitated by the

installation of a new guide in the cabinet above the spool. The practice

of positioning the specimen 1/8 in. lower in the holder was continued.

The support rack on which the specimen holder rested during the test, was used with a discontinuous support bar as provided in currently-produced

machines. The flame length was maintained at 5/8 in. and checked frequently,

with particular care to avoid variations toward a shorter length. Use of

the electric timer concurrently with the mechanical stopwatch was continued.

5. Comments on the Test Apparatus

As noted earlier, some variations in the test method have resulted from

changes in the manufacture of the equipment, which influence the procedure

although they do not violate the specifications of the standard. To avoid

further such inadvertent modifications, it is recommended that the drawings

be adopted as part of the commercial standard, or as a subsidiary requirement

of the Secretary of Commerce, and that all future revisions should be subject

to approval by the Secretary of Commerce. Before such adoption, however, it

is recommended that the following clarifications and additions be incorporated

in the drawings;

1. At the base of specimen rack 1 ) Drwg D453, change 3/8 dimension

on 45° line to 5/16.

2. Revise thread guide 3

N

’ in right elevation, Drwg D453, of specimen

holder assembly. There should be a tolerance on height of guides

above top plate, perhaps ± O.Ol in.

3. Add additional thread guide, 10 of D453, to cabinet, D450, above

thread spool, at a point 8-1/4" above floor and 5-1/4" from back.

Include dimensioned positions for all thread guides.

4. Make counterweight 3 on Drwg D452 of brass or increase the size

of steel weight to 1" dia x 1-1/2" long. (The specified dimensions

in steel do not provide sufficient weight).

5. On Drwg D454, part 25, dimension of weight diameter is indicated as changed to 3/4 in. Current production, however, involves 5/8 in', dia

weight as was used in our tests. This weighs about 33 gms . The

weight should be specified.

6. The drawings should include dimensions of the flame length gage and

the sheet metal specimen shim and block.

Fabric

Difference

in

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by

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Mean

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of

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on

Oven

Time

Desiccator

Time

Burning

Ignition

Height

in

Holder

Flame

Length

Support

Rack

(in

minutes)

(in

minute

c)

Material

Construction

Weight

Time

(edge-surface)

(1/8-3/8")

(Taped-Not

taped)

(1/2-5

/

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(5/8-374")

(1/2-3/4")

(Strip-No

strip)

(

10-20)

(

15-30)

(30-60)

(0-

15) (

15-60)

(30-60)

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significant

at

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confidence

level

of

957

c

or

greater