Firstly, let me give a little back ground as to the project I was involved in. It may or may not fit this scenario but it is worthy of some debate and consideration.
The project involved a large listed building in the historic heart of Edinburgh. I do not wish to mention the client other than to say it was a major Scottish bank and this was its head quarters building.
The problem was that the building was a rambling building with many floors and mezzanines that had been added over the years, as result the means of escape had become a bit of a shambles. Whilst there were other escape stairs, these were not accessible to a large % of the staff within the building (including the board of directors)! The only escape route for the people within this part of the building was down a single stairs, down four floors (or up if you were in the basement) and out into a large reception lobby. A lot of the office areas off the stairway had no doors let alone fire rated doors! The inspecting authority were rightly concerned by this and insisted that as part of the building refurbishment a solution must be found. They wanted the stair way to be enclosed, but this would have upset the conservationists and the architect. In the end the solution that was agreed was to fit fire doors to all offices and corridors opening onto the escape stairs and to protect the escape stairs with a high pressure water mist system. The system selected was Fogtec but there are others that would have been acceptable for the task. I advised that the system should be controlled by smoke detectors rather than by heat activated glass bulbs, but this was not taken up. There were several reasons why the fire authorities accepted this solution.
1) The ability for the system to remove a large quantity of large smoke particles i. e smoke washing and to keep the escape stairs free of smoke.
2) The rapid temperature reduction that you see when these systems operate.
3) The ability to suppress and control, and in some instances extinguish a fire within the large lobby area.
In general it was seen by the fire service as an escape stair protection solution and to extend survivability to escapees.
From an engineering point of view there were many reasons for this system to be chosen, including;
a) Low water consumption compared to a sprinkler system.
b) Smaller water storage capacity required.
c) Small bore stainless steel pipework.
d) Ease of installation within an architecturally sensitive building.
The final solution was a pump system producing 120 lpm at 100bar pressure, wet pipe, fast acting bulb actuated nozzles and a 1000 ltr break tank toped up from the towns mains via a 45mm feed pipe at 6bar. Each nozzle produced 12 lpm of water mist with droplet sizes of between 60-100 micron, the K-Factor was 1.2
Now, moving onto the questions concerning approvals. There is NO BS for these systems, there is no LPCB approval for these systems. The reason for this is that the LPCB do not have a test written for HPWM systems and the BS do not have any interest! However, there are approvals available but all a risk specific i.e FM, VdS, IMO, Lloyds. Primarily these systems grew up in the shipping and offshore business and as mentioned before, the testing requirements for these applications are very stringent. From these tests organisations such as Factory Mutual (FM) developed there test standards and approvals. For example IMO A800 which covers all accommodation & public areas on board a ship is the basis of the FM light and ordinary hazard approvals.
I have worked with these types of systems now for many years and can say that they are not a 'one size fits all' solution. For example any deep seated fire would not be controlled by a high pressure water mist system in the traditional sense, but install a detection system to activate the system rather than using glass bulbs, and the system works very well indeed. These systems are not new, in there present form they have been available since 1990, but infact were around 100 yrs ago!
The sprinkler companies are concerned that there traditional market may be at threat and as such often mislead people regarding what these systems can and cannot do. However, they have seen the writing on the wall and are them selves now offering HPWM systems. If you were to compare a sprinkler and a HPWM system on price, lets say for a supermarket, sprinklers would be in the region of 25% cheaper. This is due to the fact that HPWM systems use 316 stainless steel!
For cases where it is not practical to install sprinklers due to water supply problems, space restrictions, architectural constraints etc, these systems are worth a look at. A word of caution, and this is where an LPCB accreditation would be useful (but one does not exists), whilst some companies profess to being 'water mist specialists' this is often not the case. This is even the case for the large fire protection companies. My experience is that there are one or two very good small companies out there that specialise in these systems and often do the installation work, etc. for the big boys!
