Permit To Work

Permit To Work (PTW) refers to management systems used to ensure that work is done safely and efficiently. These are used in hazardous industries and involve procedures to request, review, authorise, document and most importantly deconflict tasks to be carried out by frontline workers.

PTW is a core element of ISSOW systems that along with Risk Assessment and Isolation Planning, enable As Low As Reasonably Practicable (ALARP) reduction of unsafe activities in non-trivial work environments. PTW adherence is essential to achieve Process Safety Management.

PTW implementations usually utilise incompatible operations matrices i.e. preclude one workgroup welding/grinding in the vicinity of another venting explosive/flammable gases. The PTW system is for work being performed in accordance with preapproved procedures and that has been macro scheduled, the purpose is to deconflict short term activities of different frontline workgroups to prevent mutually hazardous interference.

Once a PTW has been issued to a workgroup, a tag-out or lock-out system is used to restrict equipment state changes such as valve operations until maintenance is complete. Since the PTW is the primary deconflictation tool all work activities in high risk environments should have a PTW, specific hazardous operations will then have a second permit for activities such as Confined Space or Hot Work. Here the Hot Work permit is minimising the risk of the individual task, the PTW is minimising the risk of simultaneous activities.

PTW system permit authorisation and its trace-ability are crucial if it is to be beneficial. Ideally one person should be delegated with this responsibility at any one time and all workers at that facility should be fully aware of who that person is and when the responsibility is transferred.

Generic PTW form contents

A permit to work form typically contains these items.^[1]

• Specifies the work to be done, the equipment to be used and personnel involved
• Specifies the precautions to be taken when performing the task
• Specifies other workgroups to be informed of work being performed in their area
• Authorisation for work to commence
• Duration permit is valid
• Method to extend permit for additional period
• Witness mechanism that all work has been complete and the worksite restored to a clean, safe condition
• Actions to be taken in an emergency

Historical examples

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.^[2]

HMS Artemis a submarine of the Royal Navy sank alongside when activities of ballast management and watertight integrity were uncontrolled and without oversight^[3]

Despite having a Permit To Work system, Occidental Petroleum's Piper Alpha platform was destroyed by explosion and fire after a shift reinstated a system left partially disassembled by the previous shift. 167 men perished in this incident due to failure to properly communicate permit state at shift handover.^[4]

Legislative and Industry Association guidelines

United Kingdom: Health and Safety Executive - Permit to Work Systems^[5]
Australia: Commonwealth Law - Offshore Petroleum Safety Case contents^[6]
United States: Occupational Safety and Health Administration - Process Safety Management^[7]
Petroleum and natural gas industries: ISO 17776:2000^[8]
European Industrial Gases Association: WORK PERMIT SYSTEMS - Doc. 40/02/E^[9]

References