Deadman switch

[derekleffew]

A safety device that must be held engaged by pressure from a human in order for something mechanized to operate. So named because if the operator drops dead, the switch releases and the motion stops. A good control system will perform a "Freddy check" to ensure that the switch is operating properly, and hasn't been taped down or otherwise defeated (apparently a guy named Freddy disliked holding the switch).

A deadman may also be termed an enable. Many pyrotechnics systems will not fire without the operator, as well as another person on an Enable switch, thus guaranteeing two sets of eyes watching for issues.

A deadman switch is what is termed by NFPA 79 - Electrical Standard for Industrial Machinery as an Enabling Control:

9.2.5.7.1 An enabling control function incorporating the use of an enabling device shall, when activated, allow machine operation to be initiated by a separate start control and, when deactivated, stop the machine and prevent initiation of machine operation.

Enabling controls are required to be of the momentary type:

9.2.5.7.3 An enabling control shall automatically return to its off function when its actuator is not manually held in the enabling position.