Combustion Characteristics of Polyurethane Foams Covered with Fabrics*—An SPI Research Project

Abstract

Combustion-modified polyurethane flexible foams can exhibit different flammability characteristics when covered with a fabric than when the foam alone is exposed to the same conditions. Recognizing this, regulatory and advisory agencies have turned to composite testing rather than component testing (e.g., the Boston Chair Test, California Technical Bulletin 133). It is doubtful that a small scale test could supplant the full scale tests; however, a method of screening composites would be very desirable.

The Society of the Plastics Industry's Flexible Foam Combustibility Commit tee previously reported a classification system for foams alone using ASTM E 906 as the test procedure. Using piloted ignition and an imposed flux of 1.75 Watts/cm², the foams could be partially classified. When the self-propagating flux values were added to the prior data, a classification system was developed.

As a continuation of this project, five laboratories participated in a round robin wherein four generic classes of fabric were tested in triplicate over seven different types of foam at 1.75 Watts/cm². The cumulative heat release at one minute intervals, the maximum rate of heat release, the time at which this oc curred and the percentage weight loss were the parameters studied.

The variability of the inter-laboratory data averages was too large to permit the development of a definitive classification system. If the wool/nylon fabric group (which gave the largest inter-laboratory variation but the lowest heat release results) is eliminated from consideration, the remaining composites (save one) could be classified into three categories based on the heat release at both three and four minutes.

This project indicates that it is possible to rank foam/fabric composites ac cording to their ability to resist combustion using ASTM E 906. However, fur ther work is necessary to define the causes of poor inter-laboratory agreement. Perhaps some other parameter not previously studied could aid in classifying foam/fabric composites.