In Switzerland the equivalent system is called 'safety control' (Sicherheitssteuerung).[2]
Description
Sifa is short for Sicherheitsfahrschaltung, German for "safety driving circuit". It is usually a pedal and/or large press button, which monitors the alertness of the driver. The driver has to repeatedly press a button after a fixed interval; if they fail to do so, the train will carry out an emergency stop. It complements the external train safety systems: PZB, LZB and ETCS.[3]
In Europe the Zeit-Zeit-Sifa (time-time Sifa) is common. In this system, the engine driver holds a pedal or button down for 30 seconds and must then briefly release the pressure. Thus the system can confirm that the driver is still able to react. If the driver does not react after 30 seconds, the system warns the driver, at first optically, then for a few seconds acoustically. After a further short period of time without any reaction the train is automatically stopped. The Zeit-Weg-Sifa (time-distance Sifa) system takes account of the distance travelled, as well as time, since the last activation.
In electric trains such as those working on U- and S-Bahn lines the Sifa has for a long time been combined with the driving switch. This is where the concept of the dead man's switch first arose. If the button was released (due to the driver becoming incapacitated) the train was automatically stopped.
Drivers must carry out a Sifa test before using a train, to check that the automatic braking is functioning correctly.
Following some serious accidents in which drivers fell asleep but somehow the pedal was still being activated, the Deutsche Reichsbahn in East Germany introduced a special type of Sifa (Sifa86). Here the driver has to acknowledge, by pressing a button, an optical signal given at random times and distances.
