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Flammability testing of car interiors

Burning tests are essential for assessing the flammability properties of car interiors.

Motor vehicles contain a number of components that can burn if subjected to a large enough ignition source. These include seating, headlining and carpeting. Several test methods have been developed by the motor industry to assess burning behaviour. Materials used within the passenger compartment need to have a degree of burn resistance so that occupants have time to escape the vehicle in the event of a fire.

Safety standards such as FMVSS 302 (USA), BS AU 169a and ISO 3795 (all similar standards) have been developed to help reduce deaths and injuries to occupants caused by vehicle fires, especially those originating in the interior of the vehicle from discarded cigarettes and matches.

In some cases manufacturers have also developed their own specifications based on these standards. FMVSS 302 is a mandatory requirement for all materials used in the interior of motor vehicles sold in the USA, and the BS and ISO standards are generally specified for other markets, although not always as a legal requirement. The standards are not only applicable to passenger cars, but also lorries, trucks and coaches as well as agricultural and forestry vehicles.

The standards cover all materials used in the seating compartment of a vehicle, including such components as seat cushions, seat backs, seat belts, headlining, convertible tops, armrests, all trim panels, compartment shelves, head restraints, floor coverings, sun visors and airbags. The standards also cover curtains and mattress covers. The standards detail a common test method suitable for testing materials individually or as composites up to 13mm thick.

Testing is carried out in a small combustion chamber typically 370mmm long by 200mm wide and 350mm high, incorporating holes in the floor to allow air ingress and a ventilated clearance at the top. A glass observation window enables the tester to monitor the progress of any ignition, after the samples have been inserted via a hinged door on the side – samples of material measuring 356mm x 100mm are mounted horizontally in a U-shaped holder, which is slid onto rails within the chamber. When fully inserted, the end of the sample is situated above a Bunsen burner with a 10mm tube diameter, exposing the free end of the material under test to a small natural gas flame. Measurement of burning time is completed when the flame either extinguishes or completes its travel to the last measuring point. The burning rate per minute can then be calculated.

For general applications a burn rate of no more than 100mm per minute is acceptable, although some vehicle manufacturers have tightened requirements to stipulate slower burn rates.

These tests only take into account flammability considerations and do not address issues relating to the generation of noxious fumes.

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The tests detailed above for car interior burning behaviour are just some of the many automotive related methods carried out at SATRA. Email automotive@satra.com for more information concerning flammability or other automotive products and materials testing.