Permit to Work

Definition

A Permit to Work (PTW) is a written document that authorises a specific person or crew to carry out a specific high-risk activity in a specific location, during a specific time window, subject to specific controls. It is not paperwork — it is the last line of defence between an operation and the incident it is trying to prevent. The signature on the permit is the point at which someone with authority looked at the actual site, the actual equipment, and the actual people, and confirmed that it is safe to proceed.

Typical Permit Types

• Hot work — welding, grinding, flame-cutting.
• Confined space entry.
• Work at height beyond a defined threshold.
• Live electrical work or work near live conductors.
• Excavation in proximity to buried services.
• Isolation permits for mechanical, electrical, or process systems.
• Lifting operations above a defined weight or complexity.

What a Good Permit Actually Controls

The permit references the method statement and confirms it has been briefed to the crew. It lists the specific isolations, the tag numbers, the gas-test results (for confined space), the fire watch (for hot work), the rescue plan, the return-to-service procedure, and the time window during which the permit is valid. A permit that says "work at height in the north tower for the week" is not a permit; it is a filing exercise.

Real-World Example

On a substation upgrade, the isolation permit for a 33 kV bay listed six earths, three padlocked isolators, and the specific commissioning engineer authorised to remove them. Halfway through the shift the crew asked to extend the working area by one bay. The permit issuer refused and required a new permit. The extension took 90 minutes to authorise properly, including verifying that the adjacent bay was actually isolated. In the debrief the client's engineer noted that on the previous project, a verbal "just carry on" would have been given. On that previous project someone had died. The 90 minutes was the entire point of the permit system.

Practical Lessons Learned

• The permit issuer must be senior enough to say no. A junior forced to sign under pressure is not a control.
• One activity, one location, one time window. Elastic permits are worthless.
• Cross-check with the isolation register. A permit referencing an isolation that never happened is a fatality waiting.
• Close the permit deliberately. "Close" means the area is inspected, tools accounted for, isolations returned to service, and paperwork signed off — not the crew going home for tea.
• Audit random permits weekly. A live audit programme is the only way to know whether the system is working or being ticked-and-flicked.

Common Mistakes

• Blanket permits covering multiple activities across multiple days.
• Permit issuer signing without walking the site to verify the controls.
• No cross-reference to the isolation register or to the method statement.
• Extending a permit informally when the scope changes — silently invalidating every control on it.
• Fire watches leaving the area 10 minutes after hot work stops instead of the required 60.
• No independent gas testing before confined space entry — trusting a previous shift's reading.
• Treating the permit book as a filing exercise rather than a live safety control.

Expert Tips

• Colour the permit copy on the job. A permit that isn't visible at the work face isn't controlling anything.
• Time-box aggressively. A permit valid for 8 hours forces a mid-shift check. One valid for 5 days forces nothing.
• Independent verifier for high-consequence work. The person doing the isolation and the person verifying it should never be the same.
• Photograph the isolations. A phone photo of the locked-off isolator with the tag number ends every "I thought it was" argument.
• Rehearse permit refusals. Teach permit issuers how to say no under commercial pressure — because they will need to.

Key Takeaways

• The permit is a physical control, not an administrative record.
• One activity, one location, one time window, one signed-off crew.
• Isolations must be verified, tagged, and closable back to a live register.
• Elastic permits, informal extensions, and pre-signed blanks are how fatalities happen.
• The signature is a promise that the signer has walked the job — not just read the form.

Related Concepts

Interlocks with Method Statement, Commissioning Plan, Quality Gates, and Incident Management. Sample permit forms at PMMilestone.org.