Lockout/tagout — how to secure a system before you work on it

Some of the most serious industrial accidents occur when a system or machine starts while someone is working on it. Lockout/tagout is the systematic method designed to prevent exactly that: an energy source being inadvertently activated while a colleague has their hands inside the system.

Lockout means that a power source is physically locked off — typically with a personal padlock, which only the person performing the work has the key to. Tagout means that a clearly visible label is placed on the locked equipment, warning that the system is under work and who has locked it. The two parts go together: the lock physically prevents restart, the label tells everyone else why.

• 01Identify all energy sources to the system — electricity, pressure, hydraulics, steam, gravity and moving mechanics
• 02Inform relevant colleagues that the system is being shut down for work
• 03Stop the system according to the normal, fixed procedure
• 04Isolate and disconnect each energy source in one place for all
• 05Lock and label each isolated energy source with name and purpose
• 06Relieve or conduct away remaining energy, such as spring tension, raised loads or pressure in pipes
• 07Verify that the system is actually de-energized — for example with a zero test — before work begins

It is a classic mistake to only think about electricity. A system can also contain pressure in pipes and containers, hydraulic or pneumatic energy, mechanically stored energy in springs or raised parts, chemical energy, and thermal energy from hot surfaces or steam. A safe lockout/tagout takes all the energy forms that are relevant for that particular equipment into account.

The requirement for safe shutdown and securing of technical equipment before work is performed on them is part of Danish regulation of machinery and machinery installations, mentioned among other things in the Occupational Safety and Health Authority's AT guidance B.1.3, and is based on EU Directive 2009/104/EF on workers' use of work equipment, which in Denmark is implemented in the rules on the use of technical equipment.

The history in industry is full of accidents where one step in the procedure was skipped because it went faster that way, or because one was sure the system was stopped anyway. It is precisely that situation where lockout/tagout is supposed to protect you — not against what you know, but against what you think you know.

“A system you think is off is not safe. The one you have locked depressurised and checked is.”