How Does a Sprinkler System Work?
A sprinkler system consists of a network of pipes filled with pressurised water connected to individual sprinkler heads. Each head contains a glass bulb filled with glycerine solution or a fusible alloy link that holds the head closed. When the ambient temperature rises to the head's rated activation temperature — typically 57°C to 79°C for standard commercial heads — the bulb shatters or the link melts, releasing the head and allowing water to discharge directly onto the fire.
A critical misconception is that sprinklers activate throughout the building when the alarm sounds. In reality, only the head(s) in the immediate vicinity of the fire activate. Typically, 90% of fires are controlled by a single sprinkler head. This precision dramatically reduces water damage compared to fire service hose line operations, and means sprinklers do not affect areas remote from the fire.
Types of Sprinkler System
- Wet pipe systems — the most common type; pipes are permanently filled with pressurised water, providing the fastest response. Used in all standard commercial and residential applications
- Dry pipe systems — pipes contain pressurised air or nitrogen; water rushes in only when a head activates. Used in unheated spaces where standing water would freeze
- Pre-action systems — a two-stage system requiring both detector activation and sprinkler head activation before water flows; used in data centres and archives where accidental discharge would be catastrophic
- Deluge systems — all heads open simultaneously when the system activates; used in high-hazard industrial applications such as aircraft hangars
Legal Requirements for Sprinklers in England
Following amendments to Approved Document B in 2020, sprinkler protection is required in all new residential buildings over 11 metres in England. Wales went further — requiring sprinklers in all new homes from 2016. For commercial buildings, BS EN 12845 sets the design requirements, and many insurers require sprinkler protection in high-value warehousing or storage facilities.
Sprinkler installation also provides design trade-offs under BS 9999 — in sprinklered buildings, it may be possible to increase travel distances, reduce fire resistance periods for certain elements, or justify a simultaneous rather than phased evacuation strategy.
Effectiveness
UK statistics from the Fire Sprinkler Association show that sprinklers operate in 94% of fires where they are installed, and in those cases they are effective in controlling or extinguishing the fire in 99% of activations. No deaths have been recorded in fully sprinklered buildings in the UK in a fire where the sprinkler system operated correctly. They remain one of the most effective life safety and property protection measures available.
