BCD 2019

147 C AT H E D R A L C O MM U N I C AT I O N S T H E B U I L D I N G C O N S E R VAT I O N D I R E C T O R Y 2 0 1 9 HEATING & LIGHTING SERVICES 4.2 factor in maintaining the original layout and use of a historic building, and hence preserving its historical and cultural significance. The Lygon Arms in Broadway has a pre- world war two fire sprinkler system (illustrated above), which has enabled the hotel to retain its existing doors and wooden ceilings despite the advent of the Fire Precautions Act 1971 and Fire Safety Order 2005 . An automatic sprinkler system consists of a series of sprinkler heads, positioned normally at ceiling or roof level or at a high level on a wall, connected by pipework to a water supply via a control valve system. The general operation of an automatic sprinkler system is that the sprinkler heads react to heat from a fire beneath them and automatically release water onto the fire. Only the sprinkler heads above or adjacent to the fire will operate initially, releasing water onto the fire and wetting the area immediately surrounding it. Statistics reveal that 26 per cent of fires in buildings in which sprinklers are installed are controlled by the opening of a single head. Water is discharged from a sprinkler head at a rate of between 30 and 100 litres per minute. This compares with about 350 litres per minute from a hand-held fire brigade hose and about 1,700 litres per minute from a monitor operated from a hydraulic platform or turntable ladder. If a fire is allowed to develop, considerably greater quantities of water would therefore be used by the fire brigade to extinguish it. It has been claimed that the accidental failure rate for a sprinkler head is one in 16 million, so the possibility of damage being caused by one of the heads going off accidentally is very low. However, leaks from pipework are not included in these statistics, so concerns raised over the possibility of accidental damage to historic fabric have not been assuaged. Incidents involving water in heritage buildings from all sources are estimated to be nine times more common than fire incidents. SYSTEM DESIGN Generally the pipes used for water sprinkler systems have been made of durable steel or copper which are arguably the most reliable options when fitting them in historic buildings. A commonly used alternative is a durable type of rigid plastic, CPVC. However, there are some types of CPVC pipes in use that can be prone to catastrophic failure which makes them unsuitable for certain historic buildings, such as those with fine ornamental ceilings or historic collections. The failures can be caused by a number of situations that cause physical or chemical weaknesses, such as: • dropping the pipes during delivery • storing the pipes in sunlight • standing on the pipes before fitting or when in situ • spraying fly killer or hairspray on the pipes • having PVC electrical cables touching the pipe (illustrated above) • incorrect gluing of the joints – joints must be turned by 90 degrees when glued. This is particularly relevant when commissioning because the pressure testing is undertaken with water rather than air. There are two types of water fire suppression systems, automatic sprinklers and water mist. The British standard for sprinkler systems is BSEN 12845, but there are also Loss Prevention Council Rules and Technical Bulletins , which are authorised by the Fire Protection Association. This organisation acts on behalf of the insurance industry, so their rules should be followed if the requirement for sprinklers is insurance led. Water mist systems in domestic buildings are covered by BS 8458 while BS 8489 Part 1 sets out the design criteria for non-domestic buildings. However, unlike the sprinkler standard, BS 8489’s suitability for a particular fire risk is dependent on there being an acceptable test protocol. If there is no evidence of suitability for a particular application, then a specific protocol will have to be developed for the proposed use. There is a division between advocates of each type of system, with some insurance companies insisting on sprinkler protection in certain situations and being totally against water mist systems. There is no preference by contractors who fit these systems. The benefits of domestic water mist systems was confirmed in 2006 when Cheshire fire and rescue service compared the efficiency of a low pressure water mist system with a domestic sprinkler system in a pair of condemned semi-detached houses. At the time the Domestic Sprinkler Association claimed that water mist would not work if the windows or doors were open because the mist would escape from the room on fire. It was found that both systems were similarly effective, but in the fully ventilated room, when sprinklers operated, the expansion of the water into steam created a pressure that drove the smoke up the staircase. The water mist used less water, which equated to much less steam. The water mist also entrained smoke back toward the fire, which needed oxygen, rather than allowing it to spread up the staircase. This made escape down the staircase from the upper floor possible. Sprinkler systems in historic buildings should be designed with great care to fully respect the historic building fabric. This means that each system will have to be precisely engineered in order to be acceptable, both in terms of avoiding unnecessary damage to the fabric and also in terms of its appearance (illustrated top right). The reason for the fitting of a suppression system must be well understood, so that the protection afforded is as expected by the designer. A sympathetic approach to fitting modern technology to a historic building can be seen Lygon arms sprinklers in lieu of fire doors (Photos: Steve Emery unless otherwise stated) CPVC sprinkler pipe with PVC cables laid across it Simple sprinkler on copper pipe, Norway