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, de-conflict tasks to be
carried out by front line workers. Permit to work is an essential part of control of
work (COW), the integrated management of business critical maintenance processes.
Control of work is made up of permit to work, hazard identification and risk
assessment (RA), and isolation management (IM)
Permit to work is a core element of integrated safe system of work (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.
Permit to work adherence is essential in process safety management.
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 should assess the work and check safety at
each stage. The people 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, diving in the
vicinity of intake openings, and work that requires electrical or mechanical isolation. It is
also a means of coordinating different work activities to avoid conflicts.
A permit to work is not a replacement for robust risk assessment, but can help provide
context for the risk of work to be done. Studies by the UK Health and Safety Executive
have shown that the most significant cause of the maintenance related accidents in the
UK chemical industry was a failure to implement of effective permit to work
systems.[1] Common failures in control of work systems are a failure to follow the permit
to work or isolation management procedures, risk assessments that are not suitable and
sufficient to identify the risks, and/or the control measures and a combination of the two.
Permit to work implementations usually use incompatible operations matrices. For
example, to preclude one workgroup welding or grinding in the vicinity of another
venting explosive or flammable gases. The permit to work system is for work being
performed in accordance with pre-approved procedures and that has been macro
scheduled, the purpose is to prevent conflicting short term activities of different
workgroups to prevent hazardous interference.
Once a permit to work has been issued to a workgroup, a lock-out tag-out system is
used to restrict equipment state changes such as valve operations until the work
specified in the permit is complete. Since the permit to work is the primary de-
conflictation tool all work activities in high risk environments should have a permit to
work, 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 permit to work is minimising the risk of simultaneous incompatible
activities.
Permit to work systems that permit authorisation and its traceability are necessary if they
are to be beneficial. Ideally one person should be delegated with this responsibility at
any one time and all workers at the facility should be fully aware of who that person is
and when the responsibility is transferred.
A permit to work form typically contains these items.
· The work to be done, the equipment to be used and personnel involved
· Precautions to be taken when performing the task
· Other workgroups to be informed of work being performed in their area
· Authorisation for work to commence
· Duration that the permit is valid
· Method to extend the permit for an 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
