Fire Suppression Sprinkler Systems for London Commercial Premises
Automatic fire suppression sprinkler systems are required by building regulations in many categories of new and converted commercial building in London and are increasingly being retrofitted to existing buildings following updates to fire safety guidance. This guide explains how sprinkler systems work, the main system types used in London commercial premises, and the design and installation requirements.
How Automatic Fire Sprinkler Systems Work
An automatic fire sprinkler system consists of a network of pressurised pipework installed at ceiling level, with sprinkler heads positioned at regular intervals throughout the protected area. Each sprinkler head contains a heat-sensitive element, typically a glass bulb filled with a glycol liquid that expands and shatters the bulb when the surrounding air temperature reaches the activation temperature of the head. When the bulb shatters, the head opens and water flows from the head in a spray pattern designed to suppress the fire in its immediate vicinity. Contrary to a common misunderstanding, only the head or heads directly above a fire activate: the entire system does not discharge simultaneously.
Modern sprinkler heads are rated at a range of activation temperatures, with the most common being 68 degrees Celsius for standard residential and commercial applications, 93 degrees Celsius for areas with elevated ambient temperatures such as commercial kitchens, and 141 or 182 degrees Celsius for very high-temperature environments. The activation temperature is colour-coded in the liquid of the glass bulb, allowing instant visual identification: orange bulb heads activate at 57 degrees Celsius, red at 68, yellow at 79, green at 93, and blue at 141 degrees Celsius.
Sprinkler System Types for London Commercial Buildings
There are four main types of automatic sprinkler system used in London commercial buildings. A wet pipe system, the most common type, maintains the entire pipe network filled with water under pressure at all times, so that when a sprinkler head activates, water discharges immediately with no delay. A dry pipe system fills the pipework with compressed air or nitrogen rather than water, using a dry pipe valve to hold back the water supply; when a head activates, the air pressure is released and water fills the pipes before discharging. Dry pipe systems are used in areas where the pipework is at risk of freezing, such as unheated warehouses or car parks.
Pre-action systems combine elements of wet and dry pipe systems and are used in areas where accidental water discharge would cause significant damage, such as data centres or archive storage. A pre-action system requires both a heat detector signal and a sprinkler head activation before water is admitted to the pipes, providing two independent confirmations that a fire event is occurring before water is discharged. Deluge systems discharge water simultaneously from all open sprinkler heads in a zone when a fire detection signal is received, providing a high flow rate for suppression of high-hazard fires such as aircraft hangars or chemical storage areas.
Design Standards for London Commercial Sprinkler Systems
Fire sprinkler systems in London commercial premises are designed and installed to one of two primary British Standards. BS EN 12845 is the European standard for fixed firefighting systems, covering design, installation, and maintenance of automatic sprinkler systems in commercial and industrial buildings above a certain size threshold. BS 9251 is the British Standard for residential and domestic sprinkler systems, applicable to houses, flats, residential care homes, and similar smaller-scale residential applications.
The design of a commercial sprinkler system under BS EN 12845 involves classifying the protected building into a hazard class based on the nature of the occupancy and the fire risk present. Light hazard occupancies include offices, hotels, and retail premises; ordinary hazard occupancies are subdivided into three groups covering schools, hospitals, and light industrial uses; and high hazard occupancies include warehousing and manufacturing premises with significant fire loads. The hazard classification determines the design density of water application, the assumed area of operation used in hydraulic calculations, and the minimum water supply duration required.
Water Supply Requirements for London Sprinkler Systems
A fire sprinkler system requires a dedicated, reliable water supply capable of delivering the design flow rate and pressure for the minimum required duration. For smaller London commercial buildings, the system may be supplied directly from the mains water supply if the available pressure and flow are sufficient to meet the hydraulic design requirements. For larger systems, or in areas of London where mains pressure or flow is insufficient, a dedicated fire water storage tank and fire pump set must be installed to provide the required supply.
The connection to the public water main for fire sprinkler purposes requires a separate application to Thames Water for a dedicated fire main connection, distinct from the normal domestic or commercial supply. Thames Water have specific requirements for the design of the connection, including the provision of a Siamese inlet assembly for fire brigade use and the installation of a flow meter and check valve on the supply. Prestige Engineers work with specialist fire system designers and Thames Water to obtain the necessary consents for fire main connections in London commercial buildings.
Testing and Maintenance Requirements
Automatic fire sprinkler systems must be subject to a programme of regular testing and maintenance to ensure that they remain in effective working order. The maintenance requirements are set out in BS EN 12845 and BS 9251 and include weekly flow tests via a test valve to confirm system operation, quarterly inspection of all control valves and alarm devices, and annual inspection and test of the complete system by a competent sprinkler contractor. Sprinkler heads must be replaced after any activation and are also subject to a maximum age limitation, with heads in service for more than 50 years requiring replacement.
Prestige Engineers are experienced in the installation of BS EN 12845 and BS 9251 compliant sprinkler systems in London commercial and residential buildings, working alongside structural engineers and fire engineers to integrate the sprinkler system into the overall building design. We also offer planned maintenance contracts for existing sprinkler systems across London commercial properties.