Note. —All fabrics of natural or regenerated cellulose, as well as certain types of finished and unfinished fabrics made from other natural or synthetic fibers, are combustible. Some combustible fabrics, when used for clothing, are potentially dangerous to the wearer because of the speed and intensity of flame with which those fabrics burn and their ease of ignition, and because of the design of the garment. Two of these factors, the ease of ignition and the speed of flame spread, can be measured with the instrument described herein.

It is suggested that measurement of these two factors, together with visual observation of flame intensity, will permit the separation of various fabrics into three classes of flammability, thus assisting in a judgment of fabric suitability for clothing.

1.1 The purpose of this standard is to reduce danger of injury and loss of life by providing, on a national basis, standard methods of testing and rating the flammability of textiles and textile products for clothing use, thereby discouraging the use of any dangerously flammable clothing textiles.

2.1 The standard provides methods of testing the flammability of clothing and textiles intended to be used for clothing,¹ establishes three classes of flammability, sets forth the requirements which textiles shall meet to be so classified, and warns against the use of those textiles which have burning characteristics unsuitable for clothing.

3.1 Flammability.

3.1.1 Normal flammability, Class 1. —This class shall include textiles which meet the minimum requirements set forth in 3.1.1.1 or 3.1.1.2. Textiles meeting these requirements are generally accepted by the trade as having no unusual burning characteristics.

3.1.1.1 Textiles without nap, pile, tufting, flock, or other type of raised-fiber surface. —Such textiles in their original state and/or after being dry-cleaned and washed as described in 4.4 and 4.5, when tested as described in section 4, shall be classified as Class 1, normal flammability, when the time of flame spread is 4 seconds or more.

3.1.1.2 Napped, pile, tufted, flocked, or other textiles having a raised-fiber surface. —Such textiles in their original state and/or after being dry-cleaned and washed as described in 4.4 and 4.5, when tested as described in section 4, shall be classified as Class 1, normal flammability, when the time of flame spread is more than 7 seconds, or when they burn with a rapid surface flash (from 0 to 7 seconds), provided the intensity of the flame is so low as not to ignite or fuse the base fabric.

3.1.2 Intermediate flammability, Class 2. —This class shall include textiles which meet the minimum requirements set forth in 3.1.2.1. Textiles meeting these requirements are recognized by the trade as having flammability characteristics between normal and rapid and intense burning.

3.1.2.1 Napped, pile, tufted, flocked, or other textiles having a raised-fiber surface. —Such textiles in their original state and/or after being dry-cleaned and washed as described in 4.4 and 4.5, when tested as described in section 4, shall be classified as Class 2, intermediate flammability, when the time of flame spread is from 4 to 7 seconds, both inclusive, and the base fabric ignites or fuses.

3.1.3 Rapid and intense burning, Class 3. —This class shall include textiles which have burning characteristics as described in 3.1.3.1 and 3.1.3.2. Such textiles are considered dangerously flammable and recognized by the trade as being unsuitable for clothing because of their rapid and intense burning.

3.1.3.1 Textiles free from nap, pile, tufting, flock, or other type of raised-fiber surface. —Such textiles in their original state and/or after being dry-cleaned and washed as described in 4.4 and 4.5, when tested as described in section 4, shall be classified as Class 3, rapid and intense burning, when the time of flame spread is less than 4 seconds.

3.1.3.2 Napped, pile, tufted, flocked, or other textiles having a raised-fiber surface. —Such textiles in their original state and/or after being dry-cleaned and washed as described in 4.4 and 4.5, when tested as described in section 4, shall be classified as Class 3, rapid and intense burning, when the time of flame spread is less than 4 seconds and when the intensity of flame is such as to ignite or fuse the base fabric.

4.1 Test specimens.

4.1.1 Number and size of specimens required. —Five specimens, each measuring 2 by 6 inches, are required for each test.

4.1.2 For textiles without a raised-fiber surface the long dimension shall be that in which they burn most rapidly, and the more rapidly burning surface shall be tested. To establish the long dimension and the surface, preliminary tests are made as described in 4.7, with specimens cut in different directions.

4.1.3 For textiles having a raised-fiber surface, the direction of the lay of the surface fibers shall be parallel with the long dimension of the specimens. For this type of textiles with varying depths of pile, tufting, etc., the specimens are taken from that part and tested on that surface which has the fastest rate of burning.

4.1.4 If the specimens in the preliminary test, when tested as described in 4.7, do not ignite or are very slow burning, or should leave a fire-retarding finish, a swatch large enough to provide the specimens required for the test, with allowance for shrinkage in dry cleaning and washing, is subjected to the dry cleaning and washing procedures described in 4.4 and 4.5. The specimens for the flammability test are then taken from it.

4.1.5 The specimens required for testing, each 2 by 6 inches, are marked out on the back (or under side) of each sample with the long dimension in the direction in which burning is most rapid, as established in the preliminary trials. The end of the specimen toward which and on the face of which burning is most rapid is identified by attaching a staple to it. The specimens are then cut out.

4.2 Flammability tester.³—The flammability tester consists of a draft-proof ventilated chamber enclosing a standardized ignition medium, sample rack, and automatic timing device.

4.2.1 Draft-proof chamber with vented top (A, fig. 2). —This metal chamber prevents air circulation around the specimen rack and flame, but permits free ventilation for rapid oxidation. The chamber is 14½ inches wide, 8½ inches deep, and 14 inches high. There are 12 half-inch holes equidistant alone the rear of the top closure. A ventilating strip is provided at the base of the sliding glass door in the front of the apparatus.

4.2.2 Specimen rack (B, fig. 2). —The specimen rack provides supports for the frames in which the specimens are mounted. The angle of inclination is 45°. Two guide pins projecting downward from the center of the base of the rack travel in slots provided in the floor of the chamber so that adjustment can be made for the thickness of the specimen in relation to the flame front. A stop is provided in the base of the chamber to assist in adjusting the position of the rack.

4.2.3 Specimen holder (C, fig. 2). —The specimen holder consists of two ¹/₁₆-inch matched metal plates with clamps mounted along the sides, between which the specimen is fixed. The plates are slotted and loosely pinned for alinement. The two plates of the holder cover all but 1½ inches of the width of the specimen for its full length. The specimen holder is supported in the draft-proof chamber on the rack at an angle of 45°. Five specimen holders are provided.

4.2.4 Indicating finger (D, fig. 2). —The forepart of this finger touches the specimen when the rack is adjusted. By means of this finger the thickness of the specimen is compensated for in the throw of the gas nozzle.

4.2.5 Control knobs (not shown). —There are two of these knobs which hold the rack in test position. The knobs can be reached under the stage of the cabinet and permit forward and backward movements of the rack when loosened.

4.2.6 Ignition medium (F, fig. 2). —The ignition medium consists of a spring-motor-driven gas jet formed around a 26-gage hypodermic needle. A trigger located in the front of the apparatus serves to wind the spring-motor when the machine is placed in operation. The gas jet is protected by a copper shield.

4.2.7 Stop cord (G, fig. 2). —This cord, stretched from the spool (P, fig. 2) through suitable thread guides provided on the specimen frame and chamber walls, permits the lacing of the cord in the proper position exactly 5 inches from the point where the center of the ignition flame impinges on the test Specimen. The stop cord consists of a No. 50 mercerized sewing thread and measures the rise and spread of the flame from the test specimen.

4.2.8 Pulley or eye (H, fig. 2). —The pulley or eye is the support and guide for the stop cord.

4.2.9 Stop weight (I, fig. 2). —The weight, attached by means of a clip to the stop cord, in dropping actuates the stop motion.

4.2.10 Slide door control (J, fig. 2). —This knob moves the catch mechanism used to hold the sliding door in an open position for insertion of test specimen racks.

4.2.11 Slide door (K, fig. 2). —A glass door in its normal position slides in the grooves at the front of the cabinet.

4.2.12 Fuel-control valve (L, fig. 2). —This valve consists of a sensitive control device for regulating the fuel supply at the tank. The valve ends in a ½-inch male connection for attachment to the standard butane tank of 2 pounds capacity.

4.2.13 Flow meter (V, fig. 2). —A flow meter is used to bring the fuel supply to test level by means of the control valve. The flow meter consists of a U -shaped glass tube cut into the gas line in a manner to register the gas pressure delivered to the microburner. Attached to the case wall behind the flow meter is a movable metal plate with two parallel horizontal lines properly spaced for the desired flame length. When the pressure is off, the plate is so regulated that the liquid level in both sides of the U -shaped tube meets the lower line. When the test is made the pressure is so adjusted that the higher liquid level in the U -shaped tube meets the upper line.

4.2.14 Butane, c. p., container⁴(M, fig. 2).—This fuel supply is a No. 4 cylinder of c. p. butane.

4.2.15 Stop watch and timing mechanism (N, fig. 2). —This watch, by means of special attachments, is actuated to a start by connection with the gas jet (F, fig. 2). A driving mechanism on rear of cabinet (S, fig. 2) moves the gas jet to its most-forward position and automatically starts the timing at the moment of flame impact. The falling weight (I, fig. 2), when caused to move by severance of cord (G, fig. 2), stops the watch. Timing is read directly.

4.2.16 Starting lever (O, fig. 2).—This lever is operated from left to right in one stroke and is released to operate the gas jet.

4.2.17 Cord supply (P, fig. 2).—This supply, consisting of a spool of No. 50 mercerized cotton sewing thread, is fastened to the side of the chamber and can be withdrawn by releasing the thumbscrew holding same in position.

4.2.18 Cord loop (Q, fig. 2).—At a point behind the stop cord (G, fig. 2) on the rear panel, there is installed another loop to draw the cord away from directly over the flame.

4.2.19 Draft ventilator strip (R, fig. 2).—A draft ventilator strip is placed across the front opening, sealing the space between the sliding door when in lowered position and the base on which the grid rack is attached.

4.3 Brushing device.⁵

4.3.1 This device consists of a baseboard over which a smaller, carriage is drawn. This carriage runs on parallel tracks attached to the edges of the upper surface of the baseboard. The brush is hinged with pin hinges at the rear edge of the baseboard and rests on the carriage vertically with a pressure of 150 grams.

4.3.2. The brush consists of two rows of stiff nylon bristles mounted with the tufts in a staggered position. The bristles are 0.016 inch in diameter and 0.75 inch in length. There are 20 bristles per tuft and 4 tufts per inch. A clamp is attached to the forward edge of the movable carriage to permit holding the specimen on the carriage during the brushing operation.

4.3.3 After the specimen has been put in place on the carriage and fastened by means of the clamp, the brush is raised, the carriage pushed to the rear, and the brush lowered to the face of the specimen. The carriage is then drawn forward by hand at a uniform rate.

4.4 Dry cleaning.—A swatch from each sample, as mentioned in paragraph 4.1.4, shall be subjected to the following dry-cleaning procedure.

4.4.1 Apparatus. —The apparatus is a cylinder, preferably of metal, approximately 13 inches high and about 8 ¾ inches in diameter (capacity 3 gallons). The cylinder is mounted in a vertical position on an axis which is inclined 50° to the axis of the cylinder, and is rotated about this axis at a speed of 45 to 50 revolutions per minute.

4.4.2 Cleaning procedure. —The apparatus is filled approximately one-third with perchlorethylene to which is added 270 ml of dry-cleaning soap.⁶ The swatches and sufficient suitable worsted cloth,⁷ in pieces of approximately 12 by 12 inches, to make a total dry load of 1 pound are placed in the apparatus. It is operated for 25 minutes. The solution is poured out, the apparatus refilled to approximately one-third with fresh perchlorethylene without soap, and the apparatus is operated for an additional 5 minutes. This last operation is repeated three times. The swatches are then removed and the excess solvent removed from the swatches by any convenient means, such as rolling them between two layers of turkish toweling or between two layers of absorbent paper. They are then permitted to dry at room temperature.

4.5 Washing procedure. —The swatches, after being subjected to the dry-cleaning procedure (par. 4.4), shall then be immersed and worked gently for 5 minutes in a bath of soft water in which 0.5-percent neutral chip soap has been dissolved. The volume of the bath shall be 30 times the weight of the swatches and the temperature shall be between 95° and 100° F. The swatches shall then be rinsed twice in water at 80° F., extracted, and dried. The individual specimens, each 2 by 6 inches, are then cut out as described in 4.1.5 and tested as described in 4.6 and 4.7.

4.6 Brushing and drying specimens. —Each specimen having a raised-fiber surface, in its original condition or after dry cleaning and washing, is placed on the brushing device carriage (par. 4.3) and drawn under the brush once against the lay of the raised-fiber surface (see fig. 4). Other specimens do not require brushing. All specimens are clamped individually in the specimen holders of the flammability tester (par. 4.2.3), with the staple on top and the stapled end at the closed end of the holder. They are then dried in a horizontal position in an oven for 30 minutes at 221° F (105° C), removed from the oven, and placed over anhydrous calcium chloride in a desiccator until cool, but for not less than 15 minutes.

4.7 Procedure for testing flammability.

4.7.1. Adjust the position of the rack of the flammability tester (par. 4.2.2) with a holder and trial specimen (not a prepared specimen) in position, so that the tip of the indicator finger touches the face of the specimen.

4.7.2 Open the control valve in the fuel supply. Allow, approximately 5 minutes for the air to be drawn from the fuel line, ignite the gas, and adjust the flame to a length of ⅝ inch, measured from its tip to the opening in the gas nozzle.

4.7.3 Remove the mounted Specimen from the desiccator and place it in position on the rack in the chamber of the apparatus.

4.7.4 See that the stop cord (No. 50 cotton sewing thread) is strung through the guides in the upper plate of the specimen holder across the top of the specimen, and through the guides at the rear of the chamber over the guide ring, and that the weight is hooked in place close to and just below the guide ring. Set the stop watch at zero. Close the door of the apparatus. Conduct the test in a draft-free room with the apparatus at room temperature.

4.7.5 Bring the starting lever over to the extreme right and release it. This starts the timing mechanism and applies the flame to the Specimen for a period of 1 second. This should be done within 45 seconds of the time the specimen was removed from the desiccator. Timing is automatic, starting upon application of the flame and ending when the weight is released by the burning of the stop cord.

4.7.6 Record the time of flame spread (reading of stop watch) of each specimen and note whether the base of each specimen having a raised-fiber surface is ignited or fused to a point where the damage is apparent from the bottom of the specimen.

4.7.7 Results.

4.7.7.1 Time of flame spread.—The time of flame spread of the textile is taken as an average time for 5 specimens. Results of tests of specimens before and after dry cleaning and washing shall be recorded and reported separately. If the time of flame spread is less than 4 seconds or if the specimens do not burn, test 5 additional specimens. The time of flame spread is then taken to be the average time for the 10 specimens or for as many of them as burn.

4.7.7.2 Base fabric ignition or fusing. —Base fabric ignition or fusing of textiles having raised-fiber surfaces shall be reported when the base fabric of more than 1 of the 5 (or 2 of the 10) specimens tested ignites or fuses.

4.7.8 Reporting results. —The reported result shall be the flammability before or after dry cleaning and washing, whichever is the lower; and, based on this result, the textile shall be placed in the proper classification as given in section 3.

5.1 The methods of test and classifications outlined herein agree with all essential requirements of the Standard Test Method for Flammability of Clothing Textiles, of the American Association of Textile Chemists and Colorists.

6.1 Having been passed through the regular procedure of the Commodity Standards Division, and approved by the acceptors hereinafter listed, this Commercial Standard was issued by the United States Department of Commerce, effective from January 30, 1953.

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It has been brought to the attention of the Commodity Standards Division of the office of Technical Services, and to the Standing Committee for the Commercial Standard CS 191-53, that certain provisions of the Standard are not entirely clear. In a number of cases two or more interpretations are possible.

The Standing Committee met in New York on December 11, 1953 to consider these sections and after a thorough discussion drew up this Appendix. A copy of it was sent to the Federal Trade Commission on December 15, 1953 for their information in interpreting the Standard. Since such explanation might also prove beneficial to all segments of the trade concerned with meeting the legal requirements of the Flammable Fabrics Act, the Commodity Standards Division is releasing the full text of the Appendix to the trade and to all acceptors. The Appendix lists the sections of the Standard which have been questioned and contains statements which clarify the intent of those who originally prepared the Standard.

In each of the above paragraphs, the following statement appears: “Such textiles in their original state and/or after being dry-cleaned and washed. . . .” As written, this statement requires that either the subject textiles shall be tested both in their original state and after being dry-cleaned and washed, or indicates that there is an option as to whether said textiles shall be tested in their original state or after being dry-cleaned and washed.

This was not the purpose of the Standing Committee in developing the above requirements. The intent was that all fabrics should be tested in their original state, and in that state meet the requirements set forth. The dry-cleaning and washing provision was provided for use whenever a fire-retardant finish might be present in the subject textile, in which case, after dry-cleaning and washing, the flammability might be greater than in the original state. Conversely, when the testing is carried out by the fabric manufacturer, who knows that no fire-retardant finish is present, and that no other condition would make the material more flammable after dry-cleaning and washing, it was not intended that the expensive dry-cleaning and washing operation should be carried out.

In summary, the textiles to which these sections refer would always be tested in their original state as described in Section 4. In the absence of proof that a fire-retardant finish has not been applied, they would also be tested after dry-cleaning and washing as described in Paragraphs 4.4 and 4.5.

The terminal phrase in each of these three paragraphs is related to flame-intensity, one of the factors recognized to bear directly on possible or potential hazard in a combustible textile fabric. Through an oversight, this phrase in Paragraph 3.1.2.1. remains the same as in the April 3, 1952 draft of the Commercial Standard, then identified as TS-5131. In Paragraph 3.1.3.2 this phrase was changed from “. . .the base fabric is ignited or fused” to “and when the intensity of flame as to ignite or fuse the base fabric”. This brought that terminal phrase into agreement with that in 3.1.1.2 which read “provided the intensity of the flame is so low as not to ignite or fuse the base fabric.”

The intent of the Standing Committee to have 3.1.2.1 conform in the above respect with 3.1.3.2 should be understood. However, even the modified sentences do not fully clarify the purpose of these references to flame intensity. A brief description of the manner in which the specified fabrics born will make the Committee's intent clear.

When a fabric having a napped, pile, tufted, or other raised-fiber surface burns, two things may occur: (1) a flame may move across the raised fibers, generally rapidly, and (2) the base fabric itself may be ignited, if the flaming of the raised filers is of sufficient intensity to cause that effect. However, in some cases, the igniting flame itself may set fire to the base material, causing it to burn rather slowly after the surface flashing of the material has terminated. In such a case there exists a combination of two types of burning which are generally considered to constitute no unusual hazard. There is a non-hazardous surface flash which has not enough intensity to ignite the base fabric itself, and there is a rather slow burning, or normal combustion of the fabric resulting from ignition by the flame of the tester. The real danger from a fabric with a raised-fiber surface results from a rapidly spreading flame which has sufficient intensity to cause the fabric to ignite the base structure over a wide area. This latter effect can easily be observed in the tester, and should not be confused with occasional freak ignitions of the base fabric as described above, where the surface flash may leave little volume or intensity.

The intent can be seen in Paragraphs 3.1.1.2 and 3.1.3.2, where the final sentence says “provided the intensity of flame is such. . .”

Therefore, in testing fabrics as directed in Paragraphs 3.1.1.2, 3.1.2.1, and 3.1.3.2, the observation of flame intensity should be to establish the fact of whether or not the flaming of the raised-fiber surface causes the base fabric to ignite.

This paragraph directs that, when specimens “do not ignite or are very slow burning, or should have a fire-retardant finish”, additional specimens shall be carried trough the dry-cleaning and washing procedure and then re-tested.

There are many fabrics which, in their untreated state, will not ignite in the Flammability Tester, or if ignited, will burn slowly. It was not the purpose of this paragraph to require that such materials be carried through a dry-cleaning and washing procedure. Instead, the intent was to require that any fabric which might have received a fire-retardant treatment be carried through the dry-cleaning and washing procedure as an assurance that such a finish would not be readily removed in service. In other words, this is another case of the dry-cleaning and washing provision being incorporated as a safeguard against fugitive fire-retardant finishes, with no intent that the dry-cleaning and washing should be a testing requirement if it is known that the fabric has not been given a fire-retardant treatment.

In summary, this section has the same intent as Section 3, which was reviewed above. All textiles will be tested in their original state, and testing after dry-cleaning and washing will only be carried out in the absence of proof that a fire-retardant finish has not been applied.

As noted, the intensity or volume of flame in a burning textile fabric was recognized by the Standing Committee to be one of the important factors relating the manner in which the fabric burns to its potential hazard when used as a garment. It was felt that a flame which had insufficient intensity or volume to ignite the base material itself would not transmit sufficient heat, or flame, through the fabric to the body. Therefore, the committee provided that, to be considered hazardous, a fabric must not only exhibit rapid flame spread, but also must show sufficient intensity or volume of flame so that the basic fabric structure itself will be ignited by that flame.

Paragraph 4.7.6 shows how base fabric ignition is to be observed. The purpose here was to examine the fabric on the reverse side from the face to which the testing flame was applied. Any evidence of scorching or fusing of fibers on the opposite face to that which was ignited would be considered evidence of base fabric ignition.

The term “bottom of the specimen” is confusing; the term “back or reverse side” would be preferable since the 45° mounting of the specimen permits another interpretation of “bottom”.

In summary, the purpose of 4.7.6 is to require the notation of whether the fabric is ignited or fused by the spreading surface flame to a point where the damage is apparent on the surface of the specimen opposite to that which was ignited.

This paragraph requires that, where the time of flame spread is less than 4 seconds, or where the specimens do not burn, five additional specimens shall be tested. There are two parts of this requirement, and since the intent was different for each part, they will be explained separately.

The basic purpose of this section is to provide for the testing of additional specimens in case of doubt as to the proper classification of the fabric. It is expected that very few fabrics will be hazardous and burn in less time than 4 seconds, because manufacturers will avoid such constructions. When such an unusual fabric is encountered, however, it was deemed advisable that an additional five specimens he tested to provide a better basis from which an average time of burning could be obtained. Furthermore, sometimes fabrics which burn with rapid surface flash will show a “freak” ignition of the base fabric. If such ignition occurs in only one or two of the specimens, the additional five specimens are provided for to show whether or not such base fabric ignition is indeed a characteristic of the fabric.

The second part of the requirement in 4.7.7.1 states that “if the specimens do not burn, test five additional specimens.” This was not intended to apply to any fabric in which none of the specimens burned. There are a great many fabrics which will not burn in the Flammability Tester and there is no point in testing ten strips when none of the first five burns. This provision was intended for those cases in which one to four of the first five strips burn. In many cases a reliable average burning time cannot be obtained, so an additional five strips are taken to provide the basis for a more satisfactory average. This is made clear at the end of the paragraph, in the statement “The time of flame spread is then taken to be the average time for the ten specimens or for as many of them as burn.”

The first sentence in Paragraph 4.7.7.1 indicates that the standard number of specimens required for a test is five. This is also pointed out in Paragraph 4.1.1, which states that five specimens are required for each test. Five additional specimens are only required where the presence of a fire-retardant finish is suspected, where some but not all of the first five specimens burn, and where the burning time is less than 4 seconds.

To summarize, then, two conditions call for the testing of an additional five specimens. First, if the first five show a burning time of less than 4 seconds with one or two strips showing base fabric ignition. Second, if some but not all of the first five strips burn, and when the burning time of the strips that do burn is close to the 4-second limit, so that an additional five strips would be desirable as the basis for a more reliable average.

The testing of fabrics under Commercial Standard 191-53 and under the Flammable Fabrics Act will necessarily be an expensive operation for certain textile manufacturers. A misunderstanding of the Commercial Standard, which would require testing 10 or 20 specimens instead of the 5 which were deemed adequate in many cases, would impose an unjustified burden and expense on such manufacturers. Therefore, it is important that the intent of the Standing Committee, in formulating the sections of the Standard listed above, and of the industry in approving the Standard, be clearly understood.

The Standing Committee on Commercial Standard 191-53 agrees that the above statements are in accordance with its intent and purposes in formulating the Standard. Members of the Standing Committee, whose names appear below, request that this document of clarification be made an official supplement of Commercial Standard 191-53, and that it be brought to the attention of the Federal Trade Commission for use in reference to the Flammable Fabrics Act.

Subsequently endorsed by:

Mrs. E. H. Daniel, General Federation of Women's Clubs

Mr. C. W. Dorn, American Retail Federation and National Retail Dry Goods Association

FTC L-3781