Three test methods commonly referenced to define flammability of film:
Oxygen Index (ASTM D 2863-77) - This test measures the minimum concentration of oxygen (O2) in a nitrogen/oxygen (N2 /O2) mixture that will just support combustion. With films, a U-shaped vertical frame is used to hold the film within a "chimney".
NBS Smoke Density (ASTM E 662-79) - The density of smoke generated by the burning sample is measured via light transmission, under controlled conditions.
U.L.94 - A vertical one-half inch diameter tube of film is ignited and the following data reported:
duration of flaming after a three (3) second burner application;
duration of flaming after an additional three (3) second burner application;
duration of flaming plus glowing after the second three (3) second burner application;
whether or not specimens burn up to a five (5) inch mark;
whether or not specimens drip flaming particles which ignite a bed of dry cotton underneath the sample.
ASTM has issued the following disclaimer for methods (A) and (B) above:
"These standards should be used to measure and describe the properties of materials, products, or assemblies in response to heat and flame under controlled laboratory conditions and should not be used to describe or appraise the fire hazard or fire risk of materials, products, or assemblies under actual fire conditions. However, results of these tests may be used as elements of a fire risk assessment which takes into account all of the factors which are pertinent to an assessment of the fire hazard of a particular end use."
Underwriters Laboratories also states the following concerning U.L.94:
"The final acceptance of the material is dependent upon its use in complete equipment which conforms with U.L. standards applicable to such equipment. The flammability classification considered for a material may vary, depending on the equipment or device involved and the particular use of the material. The performance level by these methods should not be assumed to correlate with its performance in end-use application".
"The requirements of U.L.94 do not cover plastics when used as materials for building construction of finishing."
From the above statements, it is clear that flammability data for a given material is not nearly as important as data for the total construction in which it is used. Therefore, care should always be exercised in reporting such data and cautions given concerning implied fitness for use.
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