On trains, the expression emergency brake has several meanings: The maximum brake force available to the engine driver from the conventional braking system, usually operated by taking the brake handle to its furthest position, through a gate mechanism, or by pushing a separate plunger in the cab. A completely separate mechanism from the conventional braking system, designed to stop the train as quickly as possible. A handle or plunger which may be applied by a passenger in an emergency, either stopping the train directly or sending an alarm to the driver so that they can stop the train.
Industry vernacular for when the emergency brake is applied is go into emergency, as in phrases like "the train may fail to go into emergency" or "the ability of the train to go into emergency is paramount".Railroad Accident Report. USA: National Transportation Safety Board, 1977.
The emergency brake applies considerably more braking force than the standard full-service brake. The engine driver or motorman will only use the emergency brake as a last resort, since it may cause damage; even with modern wheel slide protection, a train may develop wheel-flats, and the rails themselves can suffer profile damage.
Possible consequences of operation Putting the engine driver's brake handle into the emergency position may also: Shut off traction power On an electric train, drop the pantograph if the power supply is overhead-wire traction current, or raise the pickup shoes where the supply is third rail traction current Disable dynamic braking Prevent the brakes from being released until the train has stopped Connect the brake wires to ground, to prevent a "false-feed" voltage from releasing the brakes Send an emergency radio signal, if the brake handle has been in the emergency position for over 30 seconds Activate the sander Activate the train horn until the selector is placed out of the emergency position
Passenger-applied brakes Trains often have a facility in each car to enable passengers to apply the brakes in case of emergency. In many modern trains, the driver is able to prevent brake activation when a passenger operates the emergency alarmSoutheastern Traction Manual - Class 465/6: Passenger Communication Equipment - an audible warning is sounded, and the driver is then able to talk to the person who activated the alarm on the intercom and see them on an internal CCTV. The driver can press an override button and hold the brakes off whilst they choose a safe place to stop the train. Because of possible serious problems, severe fines and/or imprisonment penalties are in place to deter people from activating the brake without good reason.
Mechanism on locomotive-hauled stock with brake pipe The alarm chain in a passenger coach is designed to create a break in the continuity of the brake pipes (whether vacuum or air brakes), immediately resulting in a loss of brake pressure (or vacuum) and thereby causing the train brakes to be applied. With vacuum brakes, a clappet valve is provided, which is released by the pulling of the alarm chain; with air brakes, there is a similar passenger emergency valve which can vent the brake pipe to the air.
In most locomotives (in addition to a warning lamp or buzzer being sounded) the master controller undergoes auto-regression, with the notches falling to zero rapidly as the locomotive's motive power is switched off. The guard may also notice the loss of brake pressure (although they may not know it is due to the pulling of the alarm chain) and is expected to apply their brakes immediately as well. It is possible for a driver to override the alarm-chain pull; this is sometimes done where it is known that miscreants resort to pulling the emergency chain solely to get the train to stop at a point convenient for themselves. However, such an act by the driver (or guard) of deliberately ignoring an indication of alarm-chain pulling is a serious matter.
In recent years locomotives have been fitted with emergency flashers on the roof of the cab, and these flashers are also activated when the brake pipe pressure is lost for any reason other than the driver's application of the brake valve. This alerts drivers of oncoming trains of the possibility of a derailed or parted rake which may foul other tracks (since brake pressure may have been lost for those reasons as well); at the locomotive, it is not possible to tell whether the loss of brake pressure is due to the pulling of the alarm chain.
ACP (alarm chain pulling) also causes a small lever to be released near the emergency brake valve (usually mounted near one end of the coach), which does not retract to its normal position even when the chain is released. This allows the driver (or guard) to find out in which coach the ACP actually occurred. When the coach is isolated, the lever needs to be manually reset. Until this is done, the lamp and buzzer in the locomotive cab are continuously activated. A circuit breaker controls the lamp and alarm bell in the locomotive cab; in cases where defective equipment causes the lamp and bell to go off, the driver can disable them by placing the MCB (miniature circuit breaker) in the "Off" position. Despite the obvious safety hazards, sometimes this is resorted to by drivers when driving trains through sections where spurious ACP incidents are very common.
Around the world
Germany
The Regelung B009 NBÜ Rev 3.1 defines a set of nested state machines in the chapter “Anlage 1: Phasen einer Zugfahrt“, reflecting a very wide range of use cases, including platforms, tunnels, etc. and is applicable for subways, trams, metros(S-Bahn), as it implements appropriate actions for all use cases occurring in rail transportation. These state machines represents the state of the art in Germany, it is highly recommended to be implemented or retrofitted to avoid the problems experienced at the S-Bahn Rhine-Neckar.
In Germany, passenger vehicles “must have easily visible and reachable emergency brake handles”.§ 23 paragraph 3 sentence 1 EBO It is allowed that the emergency brake can be reset,§ 23 paragraph 3 sentence 2 EBO on S-Bahn vehicles (i.e. Classes 420, 423, 425, 480 or 481) it's allowed to only result in a display when used outside of platforms. The implementation of the S-Bahn's emergency brake however does currently not reflect the state of the art in Germany, it has failed in practical use at least in one instance 2015, as a driver lost consciousness completely, but still accidentally triggered the vigilance device. Unlike the System NBÜ2004, which is used in conventional trains, the brake was not activated, because it is only an indicator light and a sound, while the train is running on the track. Without ATP enabled or over-speed, the described incident may have been leading to fatalities and substantial damage, as the passengers noticed the unconscious driver, but could not stop the train by pulling the emergency-brake-handle. Using the NBÜ2004, as used in regional- and long-distance-trains, this would have been prevented, a "overwrite" response is needed, typically the "FÜ"(Filling) position of the automatic brake-lever, otherwise the trains brake-computer will perform an emergency-brake after 10 seconds.
Equipment for this override (NBÜ) is necessary in tunnels above 1000 m. For regional trains, UIC 541-5 is not sufficient since 2011, long distance trains must at least be equipped with UIC 541-5.EBA-Tunnelrichtlinie chapter 3.2 (long and very long tunnels being defined in chapter 1.2) The sections where not to stop are marked with yellow bars on the kilometer signs. Regional trains, except MUs, are usually equipped with NBÜ 2004, which results in a display and a break a few seconds later if the train driver doesn't respond. For DB Regio, the rules for the staff are given in Ril 494. Long distance trains are mostly equipped with system DB, which uses the UIC 558 control wire, which results in conflicts with some door control systems and is therefore not used in regional trains. In MUs, usually a special implementation is used.
For trams, emergency brakes are also necessary.§ 36 paragraph 9 sentence 1 BOStrab In tunnels and track sections without safety area, using them outside a station may stop the tram at the next platform instead of immediately.§ 36 paragraph 9 sentence 2 BOStrab
India
Chain-pulling is the act of pulling a cord that activates the train's emergency brakes to stop a train, whether for a genuine emergency or (often) illegally for someone to get on or off the train on the Indian Railways network. Illegal chain-pulling is a serious problem on Indian Railways; where miscreants do so to make unscheduled stops near their destination, which delays trains. Penalties for misuse of this facility include a fine of Rs. 1,000 and/or imprisonment up to one year. In an effort to improve the service, former President of India Dr. A. P. J. Abdul Kalam proposed an alternate method wherein a passenger in an emergency communicates with the guard and driver of the train.
United States
In the United States, an emergency stop cord is not used. Any visible cord running within the body of a railway car would have been what was known as the "communicating cord". This was a method of signalling the engine operator (known in the US as the "engineer"). Unlike other countries, it was never intended for use by passengers. It had its own code of signals, similar to engine whistle signals. Drivers receiving an unusual, or unidentifiable, communicating signal might stop the train, perhaps as a "normal stop" or an "emergency application", at their discretion. A long, continuous signal would usually prompt a driver to make an emergency stop. Emergency brake valves are always located on the bulkheads, inside the body of the car next to its end doors. The emergency brake valve is covered by a metal or clear plastic shield labelled "Emergency Only". Sometimes there was also a communicating signal handle on the inside bulkhead, labelled "signal".
Mistakenly identifying the communication cord as the emergency brake can lead to confusion about how emergency braking works on US trains. Once an emergency brake valve is opened, all of the air in the braking system, except those of the locomotive(s), which are equipped with brakes controlled separately (independent brake) from those of the cars, is evacuated, immediately placing the train cars' brakes into emergency, just as if there had been an uncoupling of cars (a "separation"). All available pressure from the Equalizing Reservoir will go into the brake pipe, thus running the length of the train, actuating the train brakes on each car. No action is required (or even possible) on the part of the engineer. The train will stop no matter what they do, and there is no override. Once the train has stopped, the braking system will not recharge (pressurize) until the emergency valve has been closed. This means a member of the train crew must locate the open valve, and ascertain that there is no problem which would make it unsafe to release the brakes and proceed.