Emergency brake
Encyclopedia
On trains, the expression emergency brake has several meanings:
The emergency brake applies considerably more braking force than the standard full-service brake. The engineer, motorman or driver 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.
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 locomotive
s (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 he may not know it is due to the pulling of the alarm chain) and is expected to apply his brakes immediately also. It is possible for a driver to override the alarm-chain pull; this is 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 (master 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.
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 Railway network. Chain-pulling is rampant on Indian railways, where miscreants use it to make unscheduled stops near their destination. Penalties for misuse of this facility include a fine of Rs.
1,000 and/or a prison sentence of up to one year. Because of the rampant misuse of this facility, former President of India
APJ Abdul Kalam proposed an alternate method wherein a passenger in an emergency communicates with the guard and driver of the train.
s) will give about 1.5 m/s2 (0.15 g
) deceleration. The braking distance will be approximately 250 m (820.2 ft) at 100 km/h (62.1 mph) and 600 m (1,968.5 ft) at 160 km/h (99.4 mph). High-speed trains are usually equipped with a magnetic track brake, which can give about 0.3 m/s2 extra, and give braking distances like 850 m (2,788.7 ft) at 200 km/h (124.3 mph) and 1900 m (6,233.6 ft) at 300 km/h (186.4 mph).
by the Regulation of Railways Act 1868. Section 22 stated, "All trains traveling a distance of more than 20 miles without stopping are to be provided with a means of communication between the passengers and the servants of the company in charge of the train". At first, this means of communication was a cord running down the length of the train at roof level outside the carriages, connected to a bell on the locomotive. When the use of automatic brakes was made compulsory in the Regulation of Railways Act 1889
, the equipment was modified so that it operated the brakes; however, the term "communication cord" has survived. Until the 1970s a "cord" (by that time a chain) was still used, which ran the length of the carriage and connected to a valve at one end which opened the brake pipe. A butterfly valve
on the side of the carriage was used to reset the brake, and also made it easy for the train crew to see in which coach the cord had been pulled. Later designs used handles which were activated by pulling down; more recent types use buttons connected to a PassComm system. On modern trains with sliding doors the body-indicator light (BIL), usually used to show that doors on a carriage are open, will flash when the brake has been used.
Pulling the alarm chain on a British train will pull a lever connected to the brake pipe flaps. Pulling the alarm activates a piston, causing the flaps to be opened and all the air pushed out the air tube, forcing the brakes on. In the driver's cab, a buzzer and a light will tell that the alarm has been activated. In the guard's, van this is seen from a valve which shows loss of pressure in the brake pipe. In the UK, there is a fine of £25 for pulling the alarm chain without good reason.
built since the 1980s passenger communication handles (or PassComms) have been installed, which activate an alarm in the driver's cab when used. If the train is not in a safe place (in a tunnel
or on a bridge, for example) the driver has approximately three seconds to override the alarm by pressing a button before the brakes automatically apply. The driver may also speak to the person who pulled the handle via an intercom
mounted alongside the handle. On modern trains this is particularly useful, since the PassComm must be much easier to use and more accessible due to accessibility regulations; this makes accidental activation easier. On some modern trains, the PassComm in the accessible toilet is mounted such that it is often confused with the door or flush control; this sometimes leads to accidental activation.
s and other trains it is usually located near the doors, and sometimes in the middle of the car as well. A stop valve usually has a distinctive red handle. Turning the handle down (counter-clockwise) by about 90 degrees causes pneumatic
brakes to engage, due to pressure loss in the standard air-braking system. While primitive and not allowing any override such a system is effective, resembling usual train brake activation; it does not fail in emergency conditions. More complicated systems may not provide quick braking when needed, or during a communications failure. Emergency braking is somewhat risky; it is hard on passengers, and there is a risk of passenger injury if braking occurs at high speed. As a result, use of a stop valve without good reason is prohibited and may lead to fines. Depending on circumstances and consequences, authorities may even arrest a person for the incorrect use of a stop valve.
in tunnels and so on). It is dangerous to stop in a tunnel if a fire develops; an emergency exit could lead to electrocution by the third rail
(energized with 825 volts DC). Instead drivers try to reach the next station, even in an emergency. As a result, there are no emergency brakes directly visible to passengers. However, there are hidden stop valves and simplified train controls, allowing each car to act on its own in need. In an emergency, there are door-control handles (visible to passengers) which are intended to make the pneumatic train doors able to be opened by removing air pressure. Subway trains have mechanisms and alarms which prevent trains from moving if the doors are open, and alert the driver or engage the brakes if doors open while a train is moving. Penalties for misuse of emergency door-opening handles are similar to those for stop-valve misuse.
- The maximum brake force available to the driver/engineer from his conventional braking system, usually operated by taking the brake handle to its furthest postion, 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 situation, either operating the brakes directly or sending an alarm to the driver so that he can stop the train
The emergency brake applies considerably more braking force than the standard full-service brake. The engineer, motorman or driver will only use the emergency brake as a last resort, since it may cause damage; even with modern wheel slide protection
Wheel slide protection
Wheel slide protection and wheel slip protection are railway terms used to describe automatic systems used to detect and prevent wheel-slide during braking or wheel-spin during acceleration. Analogous to ABS and traction control systems used on motor vehicles....
, a train may develop wheel-flats, and the rails themselves can suffer profile damage.
Possible consequences of operating the Emergency brake
Putting the engineer'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 brakingDynamic brakingDynamic braking is the use of the electric traction motors of a railroad vehicle as generators when slowing the Locomotive. It is termed rheostatic if the generated electrical power is dissipated as heat in brake grid resistors, and regenerative if the power is returned to the supply line...
- 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
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 alarm - 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 he chooses a safe place to stop the train. Severe fines are in place to dissuade 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 vacuumVacuum brake
The vacuum brake is a braking system employed on trains and introduced in the mid-1860s. A variant, the automatic vacuum brake system, became almost universal in British train equipment and in those countries influenced by British practice. Vacuum brakes also enjoyed a brief period of adoption in...
or air brakes
Air brake (rail)
An air brake is a conveyance braking system actuated by compressed air. Modern trains rely upon a fail-safe air brake system that is based upon a design patented by George Westinghouse on March 5, 1872. The Westinghouse Air Brake Company was subsequently organized to manufacture and sell...
), 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 locomotive
Locomotive
A locomotive is a railway vehicle that provides the motive power for a train. The word originates from the Latin loco – "from a place", ablative of locus, "place" + Medieval Latin motivus, "causing motion", and is a shortened form of the term locomotive engine, first used in the early 19th...
s (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
Conductor (transportation)
A conductor is a member of a railway train's crew that is responsible for operational and safety duties that do not involve the actual operation of the train. The title of conductor is most associated with railway operations in North America, but the role of conductor is common to railways...
may also notice the loss of brake pressure (although he may not know it is due to the pulling of the alarm chain) and is expected to apply his brakes immediately also. It is possible for a driver to override the alarm-chain pull; this is 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 (master 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.
India
Indian rupee
The Indian rupee is the official currency of the Republic of India. The issuance of the currency is controlled by the Reserve Bank of India....
1,000 and/or a prison sentence of up to one year. Because of the rampant misuse of this facility, former President of India
President of India
The President of India is the head of state and first citizen of India, as well as the Supreme Commander of the Indian Armed Forces. President of India is also the formal head of all the three branches of Indian Democracy - Legislature, Executive and Judiciary...
APJ Abdul Kalam proposed an alternate method wherein a passenger in an emergency communicates with the guard and driver of the train.
USA
In some passenger train cars, the emergency brake is a cord that passengers may pull to activate. In the cabs of light-rail cars the emergency brake is often a large red button, which the train crew refers to as the "mushroom"; this also activates the magnetic track brakes. The mechanism of an emergency brake may differ, depending on railcar design. Emergency-braking a train (without track brakeTrack brake
Track brakes are a form of brakes unique to railborne vehicles. The braking force derives from the friction resulting from the application of wood or metal braking shoes directly to the tracks...
s) will give about 1.5 m/s2 (0.15 g
G-force
The g-force associated with an object is its acceleration relative to free-fall. This acceleration experienced by an object is due to the vector sum of non-gravitational forces acting on an object free to move. The accelerations that are not produced by gravity are termed proper accelerations, and...
) deceleration. The braking distance will be approximately 250 m (820.2 ft) at 100 km/h (62.1 mph) and 600 m (1,968.5 ft) at 160 km/h (99.4 mph). High-speed trains are usually equipped with a magnetic track brake, which can give about 0.3 m/s2 extra, and give braking distances like 850 m (2,788.7 ft) at 200 km/h (124.3 mph) and 1900 m (6,233.6 ft) at 300 km/h (186.4 mph).
United Kingdom
Emergency brakes were introduced in the United KingdomUnited Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...
by the Regulation of Railways Act 1868. Section 22 stated, "All trains traveling a distance of more than 20 miles without stopping are to be provided with a means of communication between the passengers and the servants of the company in charge of the train". At first, this means of communication was a cord running down the length of the train at roof level outside the carriages, connected to a bell on the locomotive. When the use of automatic brakes was made compulsory in the Regulation of Railways Act 1889
Regulation of Railways Act 1889
The Regulation of Railways Act 1889 was an Act of the Parliament of the United Kingdom of Great Britain and Ireland...
, the equipment was modified so that it operated the brakes; however, the term "communication cord" has survived. Until the 1970s a "cord" (by that time a chain) was still used, which ran the length of the carriage and connected to a valve at one end which opened the brake pipe. A butterfly valve
Butterfly valve
A butterfly valve is a valve which can be used for isolating or regulating flow. The closing mechanism takes the form of a disk. Operation is similar to that of a ball valve, which allows for quick shut off. Butterfly valves are generally favored because they are lower in cost to other valve...
on the side of the carriage was used to reset the brake, and also made it easy for the train crew to see in which coach the cord had been pulled. Later designs used handles which were activated by pulling down; more recent types use buttons connected to a PassComm system. On modern trains with sliding doors the body-indicator light (BIL), usually used to show that doors on a carriage are open, will flash when the brake has been used.
Pulling the alarm chain on a British train will pull a lever connected to the brake pipe flaps. Pulling the alarm activates a piston, causing the flaps to be opened and all the air pushed out the air tube, forcing the brakes on. In the driver's cab, a buzzer and a light will tell that the alarm has been activated. In the guard's, van this is seen from a valve which shows loss of pressure in the brake pipe. In the UK, there is a fine of £25 for pulling the alarm chain without good reason.
Override
In most rolling stockRolling stock
Rolling stock comprises all the vehicles that move on a railway. It usually includes both powered and unpowered vehicles, for example locomotives, railroad cars, coaches and wagons...
built since the 1980s passenger communication handles (or PassComms) have been installed, which activate an alarm in the driver's cab when used. If the train is not in a safe place (in a tunnel
Tunnel
A tunnel is an underground passageway, completely enclosed except for openings for egress, commonly at each end.A tunnel may be for foot or vehicular road traffic, for rail traffic, or for a canal. Some tunnels are aqueducts to supply water for consumption or for hydroelectric stations or are sewers...
or on a bridge, for example) the driver has approximately three seconds to override the alarm by pressing a button before the brakes automatically apply. The driver may also speak to the person who pulled the handle via an intercom
Intercom
An intercom , talkback or doorphone is a stand-alone voice communications system for use within a building or small collection of buildings, functioning independently of the public telephone network. Intercoms are generally mounted permanently in buildings and vehicles...
mounted alongside the handle. On modern trains this is particularly useful, since the PassComm must be much easier to use and more accessible due to accessibility regulations; this makes accidental activation easier. On some modern trains, the PassComm in the accessible toilet is mounted such that it is often confused with the door or flush control; this sometimes leads to accidental activation.
London Underground
When London Underground began converting trains for one-person-operation during the 1970s and 1980s, the original emergency brake systems were replaced by an alarm and a passenger-communication system. On earlier systems the brakes were not applied automatically (being under the control of the driver), whereas later systems have an override as above. On older systems, marker boards showing an exclamation mark were provided on departure from each station at the point where the rear of the train would no longer be at the platform. Normally, if the alarm was activated before the board the driver would stop the train, and otherwise continue to the next station. These boards were replaced by a number of boards counting up the number of cars that are beyond the end of the platform; for example, on a line with six-car trains the boards show 1, 2, 3, 4, 5, 6. When a train has stopped, they help the driver to see how much of the train is at the platform. With the help of passenger communication and available station staff, the driver can then decide whether to deal with the situation as it is, continue to the next station or possibly reverse back into the station (after consulting with line controllers and proper safety measures). During hot summer weather passengers are warned against using the emergency alarms if feeling unwell, since it can delay trains and increase the problem; they are instead instructed to leave the train at the next station and get some fresh air or a cold drink.Russia
In Russian trains there is usually an emergency brake known as a "stop valve" . In elektrichkaElektrichka
Elektrichka is an informal word for elektropoyezd , a Soviet or post-Soviet regional electrical multiple unit passenger train. Elektrichkas are widespread in Russia, Ukraine and other countries of the former Soviet Union....
s and other trains it is usually located near the doors, and sometimes in the middle of the car as well. A stop valve usually has a distinctive red handle. Turning the handle down (counter-clockwise) by about 90 degrees causes pneumatic
Pneumatics
Pneumatics is a branch of technology, which deals with the study and application of use of pressurized gas to effect mechanical motion.Pneumatic systems are extensively used in industry, where factories are commonly plumbed with compressed air or compressed inert gases...
brakes to engage, due to pressure loss in the standard air-braking system. While primitive and not allowing any override such a system is effective, resembling usual train brake activation; it does not fail in emergency conditions. More complicated systems may not provide quick braking when needed, or during a communications failure. Emergency braking is somewhat risky; it is hard on passengers, and there is a risk of passenger injury if braking occurs at high speed. As a result, use of a stop valve without good reason is prohibited and may lead to fines. Depending on circumstances and consequences, authorities may even arrest a person for the incorrect use of a stop valve.
Subways
In subways, derailment is usually less dangerous (speeds are lower, trains cannot jackknifeJackknifing
Jackknifing means the folding of an articulated vehicle such that it resembles the acute angle of a folding pocket knife. If a vehicle towing a trailer skids, the trailer can push it from behind until it spins round and faces backwards. This may be caused by equipment failure, improper braking, or...
in tunnels and so on). It is dangerous to stop in a tunnel if a fire develops; an emergency exit could lead to electrocution by the third rail
Third rail
A third rail is a method of providing electric power to a railway train, through a semi-continuous rigid conductor placed alongside or between the rails of a railway track. It is used typically in a mass transit or rapid transit system, which has alignments in its own corridors, fully or almost...
(energized with 825 volts DC). Instead drivers try to reach the next station, even in an emergency. As a result, there are no emergency brakes directly visible to passengers. However, there are hidden stop valves and simplified train controls, allowing each car to act on its own in need. In an emergency, there are door-control handles (visible to passengers) which are intended to make the pneumatic train doors able to be opened by removing air pressure. Subway trains have mechanisms and alarms which prevent trains from moving if the doors are open, and alert the driver or engage the brakes if doors open while a train is moving. Penalties for misuse of emergency door-opening handles are similar to those for stop-valve misuse.
External signaling
The common signal to apply the emergency brake is to shake a highly-visible object vigorously near the track. This can prevent a collision if the signaling person has had time to run some distance from the obstacle, giving more room for the train to stop. Penalties for misuse are the same as those for applying the brakes from inside the train.Images
See also
- Air brake (rail)Air brake (rail)An air brake is a conveyance braking system actuated by compressed air. Modern trains rely upon a fail-safe air brake system that is based upon a design patented by George Westinghouse on March 5, 1872. The Westinghouse Air Brake Company was subsequently organized to manufacture and sell...
- Air brake (road vehicle)Air brake (road vehicle)Air brakes are used in trucks, buses, trailers, and semi-trailers. George Westinghouse first developed air brakes for use in railway service. He patented a safer air brake on March 5, 1872. Originally designed and built for use on railroad train application, air brakes remain the exclusive systems...
- Dead-man's brake
- Hydraulic brakeHydraulic brakeThe hydraulic brake is an arrangement of braking mechanism which uses brake fluid, typically containing ethylene glycol, to transfer pressure from the controlling unit, which is usually near the operator of the vehicle, to the actual brake mechanism, which is usually at or near the wheel of the...
- Hand brakeHand brakeIn cars, the hand brake is a latching brake usually used to keep the car stationary, and in manual transmission vehicles, as an aid to starting the vehicle from stopped when going up an incline - with one foot on the clutch , the other on the accelerator In cars, the hand brake (emergency brake,...
- Pulled tailPulled tailPulled tail is the act of a guard or conductor of a railway to apply the emergency brakes where something untoward has been noticed. This could be an excess of speed in a section of line known to have a lower speed, or strange noises and shaking that might indicate that the train has derailed or...