Control of Work (COW) is the integrated management of business critical maintenance processes, made up of hazard identification and Risk Assessment (RA), Permit to Work (PTW) and Isolation Management (IM).

Instructions or procedures are often adequate for most work activities, but some require extra care.  A Permit to Work system is a formal system stating exactly what work is to be done, where, and when.  A responsible person assesses the work and checks safety at each stage; the staff doing the job sign the permit to show that they understand the risks and precautions necessary.

Permits are effectively a means of communication between site management, plant supervisors and operators, and those who carry out the work. Examples of high-risk jobs where a written permit to work procedure may need to be used include hot work such as welding, vessel entry, cutting into pipes carrying hazardous substances, and work that requires electrical or mechanical isolation. It is also a means of coordinating different work activities to avoid conflicts.