Maintenance, shutdowns and brownfield installation all happen next to energy that can kill: pressurised process lines, rotating equipment, electrical supply, stored heat and hazardous atmospheres. A permit-to-work system and lockout/tagout (LOTO) are the controls that make that work safe. They matter to plant owners, maintenance planners and every contractor who works on an operating site. When they fail, it is rarely because the form was missing. It is because a step was skipped.
What a permit does
A permit-to-work is a written authorisation, issued by a competent person who controls the plant, that defines what work will be done, where, by whom, when, and under which precautions. It forces the issuer and the performing authority to agree on the hazards before work starts, and it creates a record of who is responsible at each stage.
Most plants use a general work permit together with specific certificates for higher-risk activities.
| Permit or certificate | Main hazards | Typical precautions |
|---|---|---|
| Hot work | Ignition of flammable gas, liquid or dust | Gas testing, removal or covering of combustibles, fire watch, extinguishers, spark containment |
| Confined space entry | Oxygen deficiency or enrichment, toxic or flammable atmosphere, engulfment | Isolation and blinding, purging and ventilation, continuous gas monitoring, standby person, rescue arrangements |
| Work at height | Falls of people and objects | Fall protection plan, scaffold tag, exclusion zone below |
| Electrical isolation | Electric shock, arc flash | Isolation by an authorised person, testing for dead, locks and earths |
| Excavation | Collapse, buried services | Service location, shoring or battering, barricading |
Isolation and lockout/tagout
Before mechanical or electrical work, every source of energy that could harm the people doing the work must be identified and isolated. That includes electrical supply, process fluids, pneumatic and hydraulic pressure, gravity, springs and residual heat. The isolation points are listed on an isolation certificate or isolation list, drawn from the P&IDs and single-line diagrams, and each point is secured with a lock and a tag.
For process lines, a single closed valve is often not enough. The isolation standard for the hazard may require double block and bleed, or positive isolation by spades, blinds or removal of a spool.
Verify before you work: the try step
An isolation is not proven until it has been tested. The try step confirms that the equipment cannot start or release energy:
- Isolate and lock every point on the list
- Release stored energy: drain, vent and depressurise, block or lower suspended parts, discharge capacitors
- Attempt to start the equipment locally, then return the control to off
- For electrical work, test for dead with a tester proven on a known live source before and after the test
- Confirm zero pressure at the bleed or drain points
- Only then sign the permit to allow work
Group lockboxes
On a shutdown, one isolation may protect dozens of people from several crafts. A group lockbox keeps that manageable. The isolating authority locks every isolation point, places the keys in the lockbox, and applies a control lock. Each person working under the isolation then applies a personal lock to the box. The keys cannot be recovered until every personal lock has been removed, so no isolation can be lifted while anyone is still exposed. Each person removes only their own lock.
Shift handover
Long jobs cross shifts, and handover is where permits most often fail. A good handover:
- Is done face to face at the work location, not only in the control room
- Confirms that the isolations, gas tests and work conditions on the permit still match the plant
- Transfers responsibility formally, with signatures from the outgoing and incoming performing authorities
- Repeats gas testing where the permit conditions require it
- Updates the permit if the scope has changed, or raises a new one
Close-out and return to service
At the end of the job, the performing authority confirms the work is complete, tools and materials are removed, guards are refitted and the area is clean. Personal locks come off, the isolating authority removes the isolations in a controlled sequence, and the plant owner accepts the equipment back before it is started. A permit closed on paper while people or tools are still inside the boundary is one of the most dangerous outcomes of all.
Common failures
- Isolation lists copied from an earlier job without checking the current drawings
- Skipping the try step or testing for dead with an unproven instrument
- Two permits overlapping on the same equipment without cross-referencing
- Scope creep: work done that was never assessed on the permit
- Gas tests done once and not repeated after breaks
- Locks removed by someone other than their owner
At Redsafe
Redsafe delivers maintenance, shutdown and turnaround work with in-house HSE management available on the same scope, including SACPCMO-registered, NEBOSH-qualified HSE personnel and ISO 45001 certified systems. Discuss your shutdown with us.
This article is general guidance. The site owner's permit-to-work and isolation procedures always take precedence.
