The Occupational Safety and Health Administration develops regulations for businesses and other workplaces in the United States. These regulations mandate the use of deadman switches in some machine processes.
The "Deadman" Switch
A deadman switch reverts automatically to the "Off" position when the user does not exert pressure. A deadman switch cannot be left in the "On" position if, for example, the operator becomes incapacitated or unconscious or dies while operating the machinery -- hence its name.
OSHA requires that all handheld power tools that cannot be operated remotely must have a deadman switch. This ensures that a power tool will not continue to function if the operator loses control of the power switch.
Crane hoists must also operate using a deadman switch or lever that returns automatically to the “Off” position on release. This measure prevents a crane from continuing to lift or drop a potentially dangerous load if the operator loses control of the hoist switch. This also applies to bridge cranes that carry overhead loads along horizontal tracks. The use of a deadman lever prevents the load colliding with the limit of the overhead track or boom in cases of operator negligence or incapacity.