Properties of Polymers

Polymers may have vastly different flammability characteristics depending on their chemical composition, the structure (e.g., the amount of cross linking or chemical bonding between adjacent polymer chains), and other factors. The investigator does not generally have information as to the specific polymers used in the vehicles examined. Therefore, investigators can simply examine the range of melting, decomposition and ignition temperatures possible and assess the circumstances accordingly.

The melting temperature, decomposition temperature, and ignition temperature for various polymeric materials commonly found in automotive applications are provided in the following table.

According to one source [2], PVC has a melting temperature as low as 167 degrees F. The authors consulted a materials scientist who works with polymers and two other sources [1,3] and were unable to confirm such a low melting point.

Polymeric gasoline tank from Explorer (pictured earlier). Note that though vehicle appeared to be a complete burn, there were some consumables remaining, including the majority of the fuel tank (which show drips of molten material in this view). The top of the tank was consumed, but a fluid level line inside the tank was visible when viewed from above. When the inside of the tank was inspected, the bottom portion was clean and top portion exhibited soot deposits, indicating that gasoline remained in the tank during the fire.

References

1. Tewarson, A., et al., “Characterization of the Ignition Behavior of Polymers Commonly Used in the Automotive Industry,” NHTSA-98-3588-71, 1998.
2. NFPA 921, Guide for Fire and Explosion Investigations, 2004 Edition.
3. Osswald, T. A., Menges, G., Materials Science of Polymers for Engineers, Hanser Publishers, 1996.