Fire Safety and Technology Editorial
Automotive Fire Safety
At NFPA all hurdles to the development of NFPA 556, Guide on Methods for Evaluating Fire Hazard to Occupants of Passenger Road Vehicles, have been overcome and the first national consensus document showing the fire safety problems associated with cars and other passenger road vehicles. NFPA 556 was developed by the NFPA Technical Committee on Hazard and Risk of Contents and Furnishings, after eight years of development, overcoming abundant opposition from the automotive industry.
As most readers of this bulletin know, the only fire safety requirement for materials in passenger road vehicles in the US are that materials “within 13 mm of the occupant compartment air space” exhibit a flame spread rate of no more than 102 mm per minute when tested to FMVSS 302. FMVSS 302 is technically identical to both an ISO standard (ISO 3795) and a Japanese standard (JIS D 1201), and it is these test methods that are used for regulatory purposes in countries outside the US, with very similar (if not identical) requirements. The test method is a small Bunsen burner test where the test specimen is placed on a grid and the burner exposes it from underneath. The test, developed in the 1960s, was initially intended to solve the problem of smoldering ignition caused by cigarettes. It does not address heat release, smoke production, or melting of materials, including flaming drips. It is difficult to find thermoplastic materials that fail the test.
NFPA 556 states that FMVSS 302 provides some measure of fire growth from a match sized ignition source. However, since it involves only horizontal flame spread, it does not provide any direct measure of flame spread on a vertical surface. Moreover, it does not provide information on how a material might respond to the levels of external radiation input that inevitably occur as a fire grows larger and begins to involve multiple surfaces that exchange radiation. NFPA 556 continues to say that tests such as the cone calorimeter can provide these types of data, namely measures of ignition delay time and heat release rate as a function of the level of external radiative input.
NFPA 556 identifies as fire scenarios those in which the fires start inside the passenger compartment, in the engine compartment, in the trunk or load carrying area, from pool fires resulting from fuel tank failure and burning under the vehicle or from other external heat sources. In every case, the key issue is the penetration of the fire into the passenger compartment, since that is what is most immediately dangerous to the passengers, since time available for escape is minimal especially if the fire incapacitates occupants or decreases their ability to escape. Once a fire starts, fire spread depends on amount, composition, orientation, configuration and fire properties of compartment materials. A key concern is fires following collisions. Heat release test data is included in the guide on fire properties of all these types of materials, which tend to be poor fire performers.
Many more fires start in the engine compartment than in the passenger compartment, with flame spread occurring through the engine cover, ductwork or windshield, although collision damage can provide alternative paths for fire penetration into the passenger compartment. The other fire scenarios, all of which are studied in detail, are of much lesser importance than those starting in the engine or passenger compartment, due to their probability or severity.
NFPA 556 points out that the continued use of FMVSS 302/ISO 3795 as the sole fire safety tool is inconsistent with any expectation of significant decreases in vehicle fire losses. Some engineering design approaches can be used to mitigate the effects of fires on vehicle occupants (such as using proper barriers to separate the engine compartment or to prevent penetration from pool fires). However, the key means to decrease fire hazard is to use materials and/or products with appropriately improved fire properties, especially lower heat release.
Now, the publication, by a standards development organization (NFPA) of this consensus document, although a key first step, is nothing more than that. This document does not revise any regulation and it is likely to be ignored by both vehicle manufacturers and those regulators in charge of setting the requirements for road vehicle fire safety, which is NHTSA (National Highway Traffic Safety Administration). An international conference will be held in Sweden in September (Fires in Vehicles, see Calendar) where these (and other) issues will be aired and discussed. Research in Sweden has also shown this fire safety problem and hopefully this may be taken up by the European Union to change fire safety requirements in Europe.
In the US statistics show very high vehicular fire losses and that vehicular fire losses (dominated by passenger road vehicles) are in the same range as structure fire losses. The heat release rate from burning cars, in the range of 1.5 to 8.0 MW, is in the same order as that from fully involved rooms in homes.
In order for any change to occur in the US, a petition to that effect will have to be made to NHTSA to set any potential regulatory activity in motion. I hope that a petition to that effect be introduced soon to improve public fire safety.
Marcelo M. Hirschler
