Ultra Surefire has undertaken a major project at Stirling Castle, historic seat of the Scottish monarchy, involving a unique application for a bespoke low pressure water mist fire protection system.
Dating back to the early 12th century, Stirling Castle stands at a spectacular strategic location high on a volcanic rock near the site of the Battle of Bannockburn, where Robert the Bruce defeated the English forces in 1314. James V’s Royal Palace in the castle is acknowledged as the finest Renaissance building in Scotland. Historic Scotland is responsible for the upkeep of the building and for ensuring a high level of protection against fire risk.
Because the fabric of the building is primarily constructed from stone and heavy timber, fire loading was not considered a major problem. However, while the fire hazard to the building itself was classed as light, the danger of damage to the historic fabric and losing priceless historic artefacts was a major focus of concern.
Among the best known of these treasures are the so-called Stirling Heads. Dating from around 1540, there are a total of 34 surviving of these oak medallions or roundels, measuring about a metre across, depicting kings, queens, courtiers, heroes and imps.
It was crucial that, while the fire system employed had to be fast and effective, it could not be allowed to inflict water damage on the historic fabric or new, furniture and fittings in the Palace. This indicated that a water mist system would be the best option.
Benefits of Water Mist Protection
Water mist technology offers both High and Low Pressure systems, each of which can demonstrate performance benefits over conventional sprinkler systems. These include:
- Minimised water and smoke damage: Water mist systems minimise collateral damage from water discharge which, as mentioned in the case of Stirling Castle, was of critical importance. Smoke damage is also reduced, particularly with High Pressure Water Mist (HPWM) systems, because of smoke particles binding to the minute water particles. Smoke damage can be particularly destructive and water mist acts swiftly in ensuring that smoke is washed down to floor level and that acid in the smoke is neutralised.
- Downsized pipework: HPWM and Low Pressure Water Mist (LPWM) systems use smaller and lighter pipework than conventional sprinklers, a difference in diameter of approximately 30mm to 100mm. This means that the system can be more easily concealed in historic buildings like Stirling Castle. The systems are also much easier to install and maintain.
- Reduced storage: About one third or less water storage space is required for LPWM and HPWM systems than that required for sprinklers. This was an important consideration for the Stirling project.
- Low water usage: HPWM systems use about 10% of the volume of water required by conventional systems and LPWM about 30%. This has an environmental benefit as well as reducing water damage.
- Energy Saving: Lower flow rates and smaller pumps mean lower power rates, about one third of those required for water sprinklers. This in turn means a reduction in the carbon footprint of the building.
- High pressure: Both HPWM and LPWM offer high pressure performance. While conventional water sprinklers are normally 1.5 to 2 bar (1 bar = 14.7 psi), LPWM offers up to 12 bar and HPWM over 35 bar but typically 120 to 200 bar.
High Road or Low Road
Ultra Surefire, which has worked extensively in historic buildings including Blenheim Palace, was one of four companies tendering for the Stirling Castle project. Peter Kemp, the company’s Managing Director, explained that Ultra Surefire had come out to lead the field by designing an LPWM system that exhibited HPWM characteristics. “Through a unique configuration, we were able to reproduce the low water usage and narrow discreet pipework associated with high pressure water mist in a low pressure system, which meant significant cost benefits for the project,” he said.
This pioneering solution was one of the main reasons that Ultra Surefire was awarded the fire protection contract against stiff opposition. They now joined the strong team established to work for Historic Scotland on the Stirling Project. Morris & Spottiswood had been appointed as main contractors and Arthur MacKay as electrical contractors. Stewart Kidd of the Cambridge based Loss Prevention Consultancy was consultant on the project and is also currently producing a fascinating case history about it for future publication.
Innovation With Discretion
The project within the Palace involved the Royal Lodgings, including the King’s and Queen’s bedchambers, the upper level, attic level and the vault level, which houses the tank for the system. This measures 3m long by 1m high and holds 4 cubic metres of water from the Castle water supply to provide up to 30 minutes of projection.
There is also access to the tank from a valve outside the building. This is for the use of the Fire Brigade in case they are unable to enter because of a need to keep that area free for evacuation. Another failsafe in the system is the ability to source power from two electricity boards, so that if one supply goes down the other can continue to be used.
The water for the fire suppression has to travel up a riser pipe to the top of the building, since the fabric of the building could not be interfered with by penetrating the walls. From the attic, pipes were dropped through the floor so that only nozzles were exposed. In the Royal Lodgings and King’s and Queen’s bedrooms, the system pipework was run within the oak ceiling coffers. At every point, no installation could be accepted that in any way compromised the aesthetic and historic character of the Castle. This made project management particularly challenging and absorbing for all concerned.
The Stirling fire protection system is particularly remarkable for providing the best of both worlds between high and low pressure. This is because the water coming out of the riser pipe, coming up from the basement tank via flexible hose, is split to travel through loops of smaller pipes between 15mm and 20mm in diameter. This replicates high pressure characteristics in a low pressure system.
For a historic building like Stirling the system is ideal. To cover a room 15m by 9m, a conventional water sprinkler would require 12 nozzles, whereas a water mist system can spray up to 25 square metres with a single nozzle. Sprinklers will use 5 litres of water per square metre per minute, while water mist can provide the same level of fire suppression with just 1.6 litres per minute.
As well as these benefits, the type of protection provided by a water mist system is also better for this type of fire protection project. “Water mist will protect rooms from wall to wall,” explained Peter Kemp. “The mist comes out horizontally, protecting the painted ceilings from fire rising upwards. Also, surfaces are wetted but not soaked, which minimises any damage to paintings and tapestries on the walls.”
“The Stirling Castle project has shown once again how water mist systems provide an ideal method of protecting historic buildings and their valuable artefacts by rapidly suppressing the fire while avoiding the water damage associated with conventional sprinkler systems,” he said.