Emergency Lighting Is Tested by the One Event Nobody Rehearses

Emergency lighting has one job, and it only ever does it on the worst day of a building's life. The mains fail, the corridors go dark, smoke may already be in the air, and every person inside needs to see the route out. For the rest of its life the system does nothing at all, which is exactly why it is so easy to find in poor condition.

How emergency lighting fails quietly

The weak point is almost always the battery. A self-contained emergency luminaire keeps its battery on permanent charge, and the indicator light on the fitting shows that it is charging — not that it can deliver its rated duration. A battery that has lost most of its capacity will still show a healthy green light, and will still come on when someone flicks a test key. It simply goes out after ten minutes instead of the hour or three hours the building depends on.

In hot climates this happens faster. Battery life shortens sharply with temperature, and fittings mounted in ceiling voids, plant rooms or under metal roofs age far quicker than their datasheet suggests.

What testing should actually cover

• A short functional test at regular intervals, simulating mains failure so every fitting and exit sign is seen to switch over to battery.
• A full-duration test at least once a year, running every fitting on battery for its complete rated period. This is the only test that finds tired batteries.
• Coverage, not just function. Escape routes change as buildings are refitted. New partitions, racking and doors can leave a stretch of corridor or a stair landing with no emergency light at all.
• Exit signs that point the right way. After a layout change, a sign that is working perfectly may be directing people towards a door that is now locked or blocked.
• A written log of each test, each failure found and the date it was put right.

Plan the full-duration test properly

A full-duration test leaves the batteries flat for hours afterwards. Run it at a time when the building can tolerate that, such as at the end of a working day, or test alternate fittings on alternate occasions so the building is never left without cover.

The question to ask

When did every emergency light in the building last run for its full rated time on battery? If nobody can answer with a date, the system is working on trust, and trust is not something you can see by in a smoke-filled stairwell.