Hazard On-board train systems
Knowledge and understanding
|On-board train systems||
Understand all associated hazard knowledge
Except for most heritage railways, trains are air-braked and most passenger vehicles have air suspension. Single or dual brake pipes will connect vehicles, and all vehicles will have reservoirs. Locomotives and some multiple unit vehicles will have compressors fitted. Modern electric traction will also have a rheostat brake in which the electric motor is effectively made to turn against itself, acting as a dynamo, and generating an electric current that can be returned to the overhead line equipment (OLE) (this is called regenerative braking), or passed with a large resistor to generate heat.
The hazards posed by pneumatic suspension units include:
- Projection or blast
- Entrapment due to chassis or axle dropping
- Compressed air
The hazards posed by a vehicle air braking system include:
- Unexpected movement
- Stored energy release
- Entrapment due to vehicle movement
Please note that when there is a loss of air (due to a ruptured brake line, for example) the brakes are automatically applied along the length of the train. This is most common in a freight train.
The length of a large freight train means that there can be a measureable period of time between the brake being applied by the driver and the pressure in the brake line rising sufficiently to apply the brakes.
Air conditioning systems
Trains are now regularly fitted with air conditioning units. On the majority of modern vehicles the units are roof mounted and so can be identified easily, while the equipment may be mounted on the underframe on older vehicles. Where windows can be opened on passenger carriages, it can be assumed that air conditioning is not fitted.
Air conditioning units will contain liquid refrigerant, which is hazardous and corrosive if the unit is ruptured or cut. The liquid easily vaporises to gas when exposed to small temperature increases or ambient temperatures.
There is an emerging type of rail vehicle which has a raised level of electromagnetic risk and crews should not go under the front driving carriages of these units without the antenna being switched off. This can be achieved by the driver operating a battery off switch. There is no danger when minimum clearance of one meter to the antenna is maintained. Fire and rescue services should identify if this type of rail vehicle is operating within their areas.