The lock standard
- One worker, one lock, one key.
- No spare keys; keys do not open each other's locks.
- The key cannot be withdrawn while the lock is open.
- Insulating locks are used on electrical work.
- Only the person who fitted the lock and tag may remove them; the authority cannot be delegated.
The group box
In group work the authorised person puts all isolation keys into a box and fits their own lock to it. Every worker on site adds a personal padlock. The box opens only when the last padlock is gone — as long as one person is still inside, energy cannot be restored.
Shift handover
The outgoing worker removes their own lock and the incoming worker fits theirs. If the job continues, the shift supervisor also fits a lock to the hasp. Passing a lock or a key from hand to hand is what the rule forbids without exception: the lock represents the person, and a person cannot be handed over.
Colour coding is not universal
| Colour | In the system we measured |
|---|---|
| Yellow | Contractor |
| Blue | Mechanical maintenance |
| Red | Electrical maintenance |
| Green | Thermal and hot work |
| Orange | Personal |
That mapping is specific to the site; we measured no common standard across colour codes. What matters is not the colour but that everyone on site knows the same mapping.
Issued equipment
Lock and tag equipment was issued personally against signature and inspected annually. Without an issue record there is no answer to "whose lock is this", and the lock removal process stalls at its very first step.