In Machine Guarding: The Second Alternative, equipment expert witness Albert Rauck, P.E., CSP, writes on machinery safety devices:
The second alternative can, when used in conjunction with the design consideration, be very effective in eliminating the dangerous condition. Safety devices include the whole range of machine guarding techniques such as fixed or automatic mechanical guards, safety mats, light curtains, safety gates, machine interlocks etc. Care must be taken to assure that machines guards are not removed for maintenance and not reinstalled or the guards are not defeated by workers in an effort to speed up the process.
The third alternative should be employed when the first and second alternatives cannot be used to eliminate the dangerous condition. The provision of warning devices should alert the exposed people to the specific danger and be consistently applied. These devices include signage, warning alarms (horns and lights), warning strips and ropes etc.