Guide to Conversion of Traditional Buildings

2.15 Automatic fire suppression systems

Standard 2.15

Every building must be designed and constructed in such a way that, in the event of an outbreak of fire within the building, fire growth will be inhibited by the operation of an automatic fire suppression system.

Limitation:

This standard applies only to a building which:

a) is an enclosed shopping centre

b) is a residential care building

c) [SSI deletes text but does not amend letters assigned to following categories]

d) forms the whole or part of a sheltered housing complex

e) is a school building other than a building forming part of an existing school or an extension to a school building where it is not reasonably practicable to install an automatic fire suppression system in that building or extension

f) is a building containing a flat or maisonette

g) is a social housing dwelling,

h) is a shared multi-occupancy residential building, or

i) is a traditionally constructed residential building with 15 or more rooms used for sleeping accommodation

In this standard –

“traditionally constructed” means constructed by traditional construction methods, using permeable components, that promote the dissipation of moisture from the building fabric.

2.15.1 Type of standard

Mandatory Standard

In the case of conversions, as specified in regulation 4, the building as converted shall meet the requirement of this standard (regulation 12, schedule 6).

2.15.2 Commentary

Automatic fire suppression systems can not only detect and signal the outbreak of a fire but also extinguish or control it. The different automatic fire suppression systems available and the suitability of each type of system will depend on a range of factors, including the type of fire likely to be encountered in the protected space.

BS 9251: 2014 and 2021 provides guidelines for fire suppression systems in sheltered housing, residential care homes, and high-rise domestic buildings.

BS EN 12845: 2015 + A1 2019, details requirements for various non-domestic applications.

The types of buildings for which automatic fire suppression systems are required under the building regulations are limited. However, it is often necessary to consider such systems for other reasons. This may be for insurance purposes, or as part of a fire engineering solution to compensate for a failure to comply with other fire safety guidance within the standards. This second reason arises frequently in the conversion of traditional buildings.

The installation of an automatic fire suppression system is sometimes a practical way of overcoming difficulties in complying with normal requirements for escape routes, fire separation and the like. It should be noted that, if the system is installed for this reason, it might be necessary to make a detailed fire engineering case to show how the suppression system is able to provide the same level of protection to building occupiers as recommended in the Technical Handbook.

When fitting an automatic fire suppression system into a historic building, the risks posed to its fabric and character by the installation must be considered. If a building is listed, any alterations which affect its character as a building of special architectural or historic interest are likely to require listed building consent. The practitioner should aim to achieve a balance between life safety and fire protection needs and respecting the key characteristics of the building.

However, the process of conversion does provide the opportunity to plan for more sensitive installation of a fire suppression system as part of other works to the building. There will inevitably be some opening-up, which can be part of a planned process where the necessary pipes and other features can be hidden from view to minimise disruption to surface finishes. In the case of a badly dilapidated building, the installation of an automatic fire suppression system will be more easily accommodated within the building’s fabric as part of the restoration and repair works.

A further consideration is the provision of an adequate supply of water at the required pressure. If mains water is not available, or the pressure is inadequate, there will be a requirement for quite large water storage facilities, which may be very disruptive to a building if positioned internally. External storage tanks may be difficult to locate in a position that does not impact on the historic character or setting of the property. Where an underground tank is proposed, the tank and pumps should be housed within a concrete chamber that can be accessed via protected stairs.

Sprinklers required for life safety must be of the ‘wet pipe’ variety i.e. the pipework is permanently charged with water. Therefore, and where appropriate, precautions against freezing should always be taken.

2.15.3 Issues to be considered

Issue - Risks to historic / traditional buildings

1. Installation Poorly planned installation of pipes and related fittings may be damaging to historic character, features and fabric.

2. Devices Sprinkler heads and fire detectors may affect the character and damage the historic fabric and features of important ceilings.

3. Tanks and pumps Installation of pumps and tanks within buildings may require extensive structural and spatial alterations which may have a significant impact on a building’s character and fabric.

2.15.4 Recommendations to meet the standard

a) Suppression systems

Two main options for sprinkler installations are direct mains-fed systems and systems that have water storage and pumps.

i. The mains-fed system is significantly less expensive and less complex than the pumped system and requires less space. However, the mains water pressure and flow rate in the area must be such that the water supply can serve the sprinklers together with a degree of confidence in the continuity and reliability of the service. Scottish Water14 should be consulted regarding the flow rates and pressures to be measured near the intended connection point. Water pressures and available flow rates can fluctuate based on network demand, which needs to be considered. To meet the design guidance for these systems, the sprinkler installation must function properly at the lowest expected supply pressure.

ii. If the mains water supply is inadequate or does not exist (e.g. in a rural location where the building is served by a private water supply), then it may be necessary to use a system with a storage tank and pumps. Often a standby power supply or a pump driven directly by a diesel (or similar) engine is required for these systems so that the pumps can operate during a power failure. These requirements can become quite onerous in terms of the cost and space required to house the equipment and this is often problematic in older or culturally significant buildings. It may be possible to locate the central equipment (tank, pumps, standby power facility etc) outside of the premises served by the installation (underground, or in an outbuilding for instance) and pipe the sprinkler water into the building.

Running sprinkler pipework through a traditional building and locating the sprinkler heads can be problematic too. Pipework is typically quite large (in the order of 100mm diameter in certain parts of the installation). Finding vertical and horizontal routes for such large pipes in older buildings is usually difficult. Possible approaches to resolving the problems can include the following:

i. Flexible connections for fire sprinklers are now available and can enable connections to be made in difficult locations without damaging existing structures. Care should be taken to ensure the radius of the bend of the flexible pipe is not too acute as this might lead to premature failure.

ii. The problem of pipe size can be eased by utilising a network design for the distribution rather than a simple root and branch type design. A network design allows parallel routes for water to flow to a given sprinkler head, so reducing the size of each individual pipe.

iii. Having high pressures available also helps, as the higher the pressure the smaller the pipes can be to carry the same quantity of water. The available pressures can be adjusted when using a pumped system, but if using a direct main supplied installation, pressure in the system is governed by the reliable pressure at the main.

iv. Making significant alterations to a building or its structure to accommodate a sprinkler system should only be considered as a last resort. The system should be designed to reflect the construction and spatial arrangement of the building and pipework should be routed, wherever possible, through existing voids, ducts, spaces, such as ‘dumb waiters’, old chimneys and disused pipe ducts.

The location of sprinkler heads will require careful consideration in historically important buildings because of the aesthetic impact and/or making holes in historic fabric. Ornate ceilings present a particular problem since inappropriately located heads may damage plasterwork or detract from the special interest of the ceiling and its appreciation. It will be necessary for the sprinkler system designer to take special care when considering the style and location of heads to minimise the intrusion of the system while still meeting the functional requirements for coverage of the heads within the room.

The use of recessed and/or concealed sprinkler heads (rather than the traditional pendant type of fire sprinkler head) will be visually less obtrusive. Whilst care must always be taken to ensure fire sprinkler heads are not painted, they can be supplied in colours to suit.

Generally, the design of these systems will have to be carried out by a suitably qualified engineer or a specialist contractor with in-house design facilities. In either case, the demands of traditional buildings and any designation associated with buildings of special architectural or historic interest should be made clear to them at the outset, and enough time allocated to the design and installation processes in case this is more complex than in typical conversion projects.

b) Other fire suppression systems

Other fire suppression systems include the use of water mist and oxygen reduction suppression. The latter, while generally regarded as safer for fabrics found in some historic buildings, reduces the oxygen content of the air and is therefore a risk to occupants. Proprietary inert gas systems are now available that allow humans to continue to breathe where the mixture has been discharged. However, they are unsuitable for large areas due to the quantity of gas required and the difficulty of maintaining the appropriate concentrations of gas for the duration of the fire’s life.

They can be ideal, though, for smaller spaces, such as archive storage rooms or high-risk areas such as transformer chambers and switch rooms. The room being protected will require a pressure relief vent and possibly a duct to the outside

Water mist and fog type fire suppression systems are increasingly being used in domestic situations and have proved beneficial in safeguarding means of escape.

BS 8458 and BS 8489 are the two system standards for water mist in the UK. BS 8458 or BS EN 14972-17:2025 are for residential and domestic applications using wet pipe systems while BS 8489 is for commercial and industrial systems, irrespective of nozzle type. These standards specify requirements and give test methods for the construction and performance of open and automatic watermist nozzles for use in watermist systems. They do not cover the electrical actuation of watermist nozzles which should conform to BS 7273 Part 5 Code of practice for the operation of fire protection measures: Electrical actuation of watermist systems (except pre-action systems).

The guidance for these systems is not prescriptive like the sprinkler rules but relies on previous test data and a risk assessment process. The advantage of water mist systems is that the droplets are very much smaller than the droplets from a sprinkler system and turn more readily to steam which: -

• takes energy from the fire so reducing the temperature
• the steam replaces the oxygen in the atmosphere supressing the fire
• the fire also draws the mist towards it as it seeks oxygen, so the mist has a scouring effect on the smoke
• pipework is smaller diameter
• less water is used.

The disadvantages are: -

• More heads are required than a sprinkler system.
• Insurers prefer sprinkler systems as the sprinkler rules are prescriptive.

Even when sprinkler systems are required by building regulation standard 2.15, they may still be viewed as a compensating feature in a holistic building assessment.