In many metalworking and other fabricating processes, machine guards are often required to protect workers against injury from hazardous points of operation.

Frequently, such guards must be opened to permit access to change tooling, load/unload material, clear jams, apply lubricant, and/or adjust process parameters.

To minimize the impact of movable guards on productivity, they are generally designed to be opened without the use of tools. Such ease of access dictates precautions be taken to protect the workers from exposure to hazards when the guards are open.

Interlock Switches
One commonly used precautionary technique is the use of interlock switches and sensors, which are intended to shut down the machine upon opening of the guard.

Traditionally, design engineers and plant operation personnel have interlocked movable guards with conventional position-presence-sensing devices.