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Interpretation ID: nht93-2.24

DATE: March 23, 1993

FROM: John Womack -- Acting Chief Counsel, NHTSA

TO: L. J. Sharman

TITLE: None

ATTACHMT: Attached to letter dated 11-18-92 from L. J. Sharman to NHTSA, Department of Transportation (OCC 8089)

TEXT: This responds to your letter of November 18, 1992, regarding the test procedure in Standard No. 302, FLAMMABILITY OF INTERIOR MATERIALS. Your questions and the answer to each follows.

Question 1.

MVSS-302, in Section S5.3(e), states that the timing for each specimen be started when the flame from the burning specimen reaches a point 1.5 inches from the open end of the specimen and, in section S5.3(f), is stopped when the flame progresses to a point 1.5 inches from the clamped end of the specimen. Further, the Standard, in Section S5.2.2, states the specimen is oriented so that the surface closest to the occupant compartment air space faces downward on the test frame. The question that has been raised is whether the timing is started and stopped when the flame reaches the designated points on the surface of the specimen closest to the occupant compartment air space (the surface facing down during the test), or when the flame reaches the designated points on the surface of the specimen facing away from the occupant compartment air space (the surface facing up during the test).

You suggest that the timing should be started and stopped when the flame reaches the designated points on the surface facing up during the test. As explained below, NHTSA disagrees.

Section S4.3(a) of Standard No. 302 states: When tested in accordance with S5, material described in S4.1 and S4.2 shall not burn, nor transmit a flame front across its surface, at a rate of more than 4 inches per minute. However, the requirement concerning transmission of a flame front shall not apply to a surface created by the cutting of a test specimen for purposes of testing pursuant to S5.

Any surface not created by the cutting of the test specimen, including the surface oriented downward pursuant to S5.2.2, is required to comply with the burn-rate requirement of S4.3(a). Surfaces created by the cutting of the test specimen were excluded from this requirement in a final rule published on March 31, 1975 (40 FR 14318). The reasons for the exclusion were stated in the notice as follows:

(C)utting certain materials to the prescribed thickness produces a tufted surface upon which a flame front may be propagated at a faster rate than it would be upon the surface of the material before cutting, thereby creating an artificial test condition.

Because of this exclusion, the surface facing upward pursuant to S5.2.2 is not required to comply with the burn-rate requirement of S4.3(a) if the surface was

created by cutting the material to be tested to the prescribed thickness.

In addition, I note that S5.3(b) requires the test specimen to be placed in the center of the cabinet. Therefore, it should not be any more difficult to observe the progress of the flame on the surface facing down than the surface facing up.

Question 2.

MVSS-302, in Section S5.3(f), states that the flame progression be measured to a point 1.5 inches from the clamped end of the specimen under test. The standard does not specify actions to be taken after timing has stopped. Some laboratories put out the flame using a small amount of water from a spray bottle. The question has been raised as to whether using a small amount of water from a spray bottle to put out the flame is an acceptable procedure.

You are correct that Standard No. 302 does not specify a procedure to extinguish the flame after the test. Therefore, spraying a specimen with a small amount of water to extinguish the flame would be acceptable.

However, please bear in mind that S5.1.2 states

Prior to testing, each specimen is conditioned for 24 hours at a temperature of 70 degrees F. and a relative humidity of 50 percent, and the test is conducted under those ambient conditions.

After spraying a specimen in the test cabinet, it would be necessary to ensure that the ambient conditions in the cabinet conform to those specified in S5.1.2 before conducting any additional tests.

I hope you find this information helpful. If you have any other questions, please contact Marvin Shaw of my staff at this address or by phone at (202) 366-2992.