by Geraldine O’Farrell CEng FCIBSE FIET FSLL
Geraldine is a Senior Building Services Engineer with Historic England, and before that its predecessor English Heritage, for the last 25 years. She is the author of Historic England’s guidance on Fire alarms, Internal and external lighting, Daylight harvesting, Surge and Lightning protection and has given webinars on all these topics, recordings of which can be found on the HE website under “Technical Tuesdays”.
Fire is probably the most destructive event that can happen to any building. Damage is not only caused by the heat and smoke but also the impact the water used to extinguish it can cause. Therefore, protection against and early warning of fire are two of the most important issues to consider regarding services to be installed within any building.
Historic structures pose more of a problem by virtue of the way some of them have been incrementally constructed, altered and added to over long periods of time. This can often produce hidden voids and routes through which a fire can spread unseen and undetected. There is also the unknown fire load, the lack of compartmentalisation and the associated problems with introducing any sort of passive fire measures such as fire doors.
Unfortunately fire not only occurs by accident but by arson attacks so it is important that any protection system gives as early a warning of fire to the owners, custodians and local fire services as possible.
As well as the concerns with historic construction methods there is the issue of ensuring that an automatic fire detection system is sensitively installed so that is not visually intrusive and in the case of large heritage buildings such as cathedrals and churches, capable of detecting smoke or flame within such large interior spaces which can often prove challenging.
Automatic fire alarm systems developed as early as the 19th century in America and in the early 20th century both the heat and smoke detector were discovered both by happy accidents but were not fully developed into the devices we know today until the 1940-50’s.
Modern fire alarm systems are covered by several guidance and regulatory documents including British Standard BS 5839 which defines eight individual fire categories, with each category falling under three different type of system, manual (M), life protection (L) and property protection (P).
As part of determining the type of system that should be used the building owner/custodian or their fire advisor must conduct a thorough risk assessment. In simple terms this means looking carefully at the building and the people who use it and understanding the risks.
Broadly speaking assessments are conducted in five key steps: -
• Identify the fire hazards
• Identify the people at risk
• Evaluate, remove or reduce the risks
• Record your findings, prepare an emergency plan and provide appropriate training
• Review and update the fire risk assessment regularly
Unfortunately, statistical evidence shows that a high percentage of fires in historic buildings have needed the local fire and rescue services to attend and Historic England research from 2019 shows that there have been the following number of incidents which have impacted: -
• 15 grade I listed buildings
• 47 grade II* listed buildings
• 343 grade II listed buildings
• 16 world heritage sites
• 554 conservation areas and locally listed buildings
which makes for startling reading.
Historic England suggests using a minimum of P1 fire alarm system within listed buildings as it provides the maximum protection to the building fabric. Our preferred recommendation is a L1/P1 system to provide maximum protection to both the listed/historic property and the occupants.
The main components of a modern fire alarm system are as follows.
1. Fire alarm panel which is the main point of reference for both the building occupants and the fire and rescue team. Panels are required on conventional, addressable and wireless systems. With addressable systems the panel will provide precise locations of the activated devices as each has its own unique electronic address. With wireless systems the panel uses a secure wireless connection between the sensor and the panel.
Wireless systems are a good option for listed buildings because this results in the minimum amount of cabling, chasing and hole drilling. It will however require a signal strength survey and booster aerials where needed but has a lot of advantages where installation time and disruption are concerned and in preserving historic fabric and interiors.
2. Detection heads can be for automatic sensing a variety of fire related symptoms such as smoke, heat, carbon monoxide. Under this heading also comes manual break-glass units where a person sounds the alarm upon discovering a fire.
3. Aspiration or air sampling smoke detection is an extremely sensitive form of detection often used in large spaces with very high ceilings where standard devices will not operate. It works by drawing air through a network of pipes, sampling the air for smoke particles. This enables very early detection and allows enough time for the building’s occupants to vacate the premises. This is often the best choice for cathedrals and other very large buildings where time to evacuate is essential given the quantity of people that could need to escape. These types of systems are known by a variety of names but the most well-known are VESDA (Very Early Smoke Detection Apparatus) and ASD (Air Sampling Detection). The biggest issue with this type of detection is that without proper maintenance the filters can become blocked with dust and dirt, rendering them less effective.
4. Beam detection is for those that do not wish to employ an aspiration system, the downside is that they will have a greater visual impact to a heritage interior and there is a restriction on how far apart the two component parts can be from each other. This distance varies from manufacturer to manufacturer but typically the detector and reflector plate must be a minimum of 40 metres apart and set down from the ceiling by between 475-600mm.
The best approach for installing any of this equipment within an historic interior is to initially establish what decorative and structural features such as beams, ornate ceilings, painted or stencilled finishes, panelling and decorative plaster work exist.
Then ensure that you locate a device where it still operates but is disguised by a building feature or is colour matched to blend in with a decorative ceiling. Any adjustments to colour or finish must be done in conjunction with the manufacturer to avoid nullifying any product guarantees or warranties.
This approach will often result in a design not entirely in accordance with the British Standard, but it should be remembered that these are advisory documents and not statutory.
For more detailed information see Historic England’s fire alarm guidance and technical webinar recording: -