[1] It involves procedured request, review, authorization, documenting and, most importantly, de-conflicting of tasks to be carried out by front line workers.
Examples of high-risk jobs where a written permit-to-work procedure may need to be used include hot work (such as welding), confined space entry, cutting into pipes carrying hazardous substances (breaking containment), diving in the vicinity of intake openings, and work that requires electrical or mechanical isolation.
Studies by the U.K. Health and Safety Executive have shown that the most significant cause of maintenance-related accidents in the U.K. chemical industry was a failure to implement effective permit-to-work systems.
[6] USS Guitarro, a submarine of the United States Navy, sank alongside when two independent work groups repeatedly flooded ballast tanks in an attempt to achieve conflicting objectives of zero trim and two degree bow-up trim; a result of failing to have a single person aware of and authorising all simultaneous activities by a permit to work system.
[7] HMS Artemis, a submarine of the Royal Navy, sank alongside when activities of ballast management and watertight integrity were uncontrolled and without oversight.