09 September 2020

The ethos for automatic gaseous fire protection systems is fast detection and rapid extinguishing. There is a balance between prompt activation and allowing intervention. Guidance is available in the relevant standards namely BS 5839-1 Fire Detection, BS 6266 Protection of electronic installations, and BS 7273-1 Actuation of systems. This paper is intended to act as an aide-memoire and introduces some additional considerations relevant today. The Standards recommend coincidence fire detection (two fire detectors have to alarm, giving the first stage with the initial detector and second stage when two or more alarm) followed by up to 30 seconds time delay before the discharge of the extinguishant. Other measures may be necessary and in exceptional circumstances, a longer discharge delay may be desirable. After careful consideration of all the factors, the logic – “cause and effect” – and justification shall be documented and agreed with all stakeholders. We trust that stakeholders reading this will appreciate the thought pattern that has gone into the logic of the actuation of a fire extinguishing system and that prescriptive standards have their limitations.It is important to avoid the wrongly adopted approach of unnecessarily switching the system into the ‘Manual Only’ mode of operation, which is likely to be outside stakeholder and insurer agreement and has further potential for user error, such as a system left in its ‘Manual Only’ mode when the premises are unoccupied, or no personnel are present; leaving the risk unprotected.