Escape routes, open areas and high-risk task areas
Commercial premises usually contain all three categories and each has a different requirement. A defined escape route — a corridor, a stairwell — needs a minimum of 1 lux along its centre line. An open anti-panic area, meaning any open space larger than about 60 m² where people may need to reach an escape route, needs at least 0.5 lux across the empty floor. A high-risk task area, where a process must be shut down safely before evacuation, needs 10% of normal illuminance and never less than 15 lux — think a commercial kitchen with live fryers, a workshop with rotating machinery, or a laboratory. Buildings that change use are the ones most often caught out: an office converted to a workshop inherits lighting designed for the wrong category entirely.