Safety on the subway

Fires in underground train tunnels can be catastrophic because the heat and smoke have nowhere to escape. A new coating for suspension components may help buy the crucial few minutes necessary for the train to get to the safety of the next station.

Ever since the devastating fire at London’s King’s Cross Station in 1987, railways around the world have made fire safety a priority. Fire safety is particularly important in urban systems, where most of the tracks run below ground.

The challenge with railway tunnels is the environment. A restricted cross-section means that, although heat rises, there is not enough space for smoke and heat to rise above the passengers. Meanwhile, the risk of rapid spread of fire is increased through convection and radiative feedback.

Most urban underground transit systems have relatively short distances between stations in the tunnel sections. In the London Underground, a train is on average no more than four minutes away from a station. In the event of an onboard fire, train drivers are required wherever possible to drive the train to the nearest station before evacuating. This means that in an ideal situation, there should be measures in place to buy time. With a train fire, a few minutes can make the difference between life and death.

The most important elements in minimising the risk of an underground tunnel fire are limiting the use of combustible materials and, when such materials are essential in tunnels and on trains, treating them with effective fire retardants.

For the past 10 years, with the help of a Spark award, designed to link larger UK companies with universities, engineers at Trelleborg have collaborated with university researchers to develop a unique solution - a flexible coating for all primary and secondary suspension fittings and antivibration components. The coating is durable, fire retardant and, under certain circumstances, self-extinguishing.

Rod Holroyd, Trelleborg’s Global Market Manager Rail, explains: “The challenge was to develop a flexible coating that could be applied to a flexible component. DragonCoat is a unique response to a potentially life-threatening situation - a train fire inside a tunnel. Our solution is a polymer-based, fire-retardant coating that can be applied to suspension components.

The extreme flexibility and durability of DragonCoat ensures that it maintains its integrity despite constant movement of suspension components. It has a life expectancy that matches that of the suspension component, and it’s also highly resistant to environmental factors - rain, snow, heat, cold and the materials used in under-train cleaning. DragonCoat provides that vital few minutes of delay of the release of toxic gases, smoke, flame and heat, allowing a train driver to get the train and passengers to a station for evacuation and also providing a delay that allows firefighters safer access to the source of the fire.”

Bill Mortel, Director of Advanced Technologies for Trelleborg’s industrial antivibration systems, comments: “Although many of the natural and rubber components used in primary and secondary suspension components don’t cause fires, they are essentially fuels that will feed a fire. DragonCoat has no effect on the performance of a natural rubber spring; in fact, it enhances a component’s oil resistance. Combined with Trelleborg’s Metacone and Chevron primary suspension springs and the hourglass secondary suspension springs, we can deliver a unique, long-lasting product that makes a real contribution to fire safety on railway systems.”