6. Granular Flame Retarder for Railway Seats Using a Self-Extinguishing Resin for Reducing Fire Risk

Because railway seat cushions contain materials such as polyurethane foam, fire performance should be carefully considered from the standpoint of ensuring sufficient evacuation time for passengers and crew in the event of a fire.

To improve the flame resistance of these seats, a granular flame retarder using an intumescent-type (expansion-type) self-extinguishing resin was developed. By increasing the surface area through granulation, the material expands when exposed to fire, maximizing its self-extinguishing function by blocking oxygen and heat (Fig. 1).

Combustion tests were conducted using a full-scale seat in which the granular flame retarder, enclosed in a mesh bag, was inserted at a position 10 mm beneath the seat surface (Figs. 2-4). The results showed that during the first four minutes after ignition, which corresponds to the time required for passengers to evacuate to an adjacent vehicle, the total heat release from seat combustion (the integral of the heat release rate) was reduced to about half that of a conventional seat without the flame retarder (Fig. 5). This is expected to more than double the available evacuation time before smoke generated by the seat reaches critical levels.

By installing seats incorporating this granular flame retarder into vehicles, sufficient evacuation time for passengers and train crew can be secured, thereby reducing fire risk.