They allow work to start only after safe procedures have been defined and they provide a clear record that all foreseeable hazards have been considered. A permit is needed when maintenance work can only be carried out if normal safeguards are dropped or when new hazards are introduced by the work.
Examples are, entry into vessels, hot work and pipeline breaking.
While aimed primarily at the chemical industry the guidance provided may have application in other industries. Don't assume that your system is a good one just because you have not yet had a serious accident. You should critically review your system and ask yourself the following questions. It should be designed by the company issuing the permit, taking into account individual site conditions and requirements. Separate permit forms may be required for different tasks, such as hot work and entry into confined spaces, so that sufficient emphasis can be given to the particular hazards present and precautions required.