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The publication of a new watermist standard should give a boost to this type of system. But Alan Cox warns that insufficient care with design and installation can be potentially disastrous.
There has been a great deal of publicity given to watermist fire systems recently and while some manufacturers would have you believe that you can use them virtually anywhere, a great deal of caution needs to be exercised if you are thinking of installing such a system.
I was involved a few years ago in the installation of a system to cover a number of large generators. While I was sceptical about some of the claims made by the manufacturers, the insurers were recommending its installation.
I visited a number of companies that had installed similar systems to protect their generators and was surprised that no one had actually carried out a discharge test to see if the systems lived up to the manufacturer’s claims. However, it was decided to go ahead with the installation – which consisted of five individual systems protecting each generator in a large generator hall – based on information that had been provided to us by the companies involved.
The systems were installed by an authorised company in accordance with the design manual. When it came to system commissioning, I asked the contractors how they normally commissioned such systems. They replied that they used a cigarette lighter to activate the detectors and then checked that all the valves worked correctly. I was not happy with this procedure so I suggested a test involving setting fire to some oily rags in a bucket.
The generator was sheeted up and the bucket placed adjacent to the injector pump to simulate a fuel fire. The contents were ignited and the detectors detected the fire and initiated the system. But what happened next was very surprising. The watermist discharged correctly but did not extinguish the fire – in fact it appeared to make the fire worse, which then had to be extinguished manually.
The ‘post-mortem’ by the installers concluded that because the air conditioning was left running, this had influenced the way that the system performed. So it was decided to carry out another test with the air conditioning turned off. I should state at this point that the air conditioning would have needed to be operational if the generators were running, as if a fire occurred in one generator it was reasonable to assume that it was under emergency conditions and that other generators in the hall would still be running.
Another test was carried out and again it failed to extinguish the fire. What was remarkable was that when the air conditioning was running, the water mist was contained in an envelope around the generator, but without it, the water mist filled the whole room and it was difficult to see anything except the fire burning away. Clearly there was a major problem and the contractors agreed to seek help from the manufacturer’s agent.
Wrong type of fire!
The advice from the manufacturer’s agent was to make some changes to the discharge heads and to change the type of fire. Yes, they informed me that we had used the wrong type of fire and the system had failed because the fire was in the bucket and the mist could not get into it. This was somewhat of a surprise to me, but as I didn’t have a lot of previous experience about these systems, I went along with the explanation and agreed to an open tray fire, which they said would not be a problem for the system. Two more tests were carried out under similar conditions to the first ones, but with the same result. The only difference was that because we were using a tray fire we ended up with a very large fire that was quite difficult to extinguish manually! By this time I thought the system would never work correctly. I was on the point of instructing the contractors to remove the systems but the manufacturer’s agent asked me for one more chance, and said that they would build a mock-up of the generators and carry out further tests.
This test showed that while it was designed in accordance with the manufacturer’s design manual, the discharge piping needed to be doubled in size in order to deliver enough water to extinguish the test fire. The modifications were made and the system was finally able to extinguish the fire.
While it would be nice to think that this was the end of the story, there was another surprise in store. Some time later I was speaking to the manufacturer of the system and he asked me why we had not installed any more of the systems. When I told him what happened he was very surprised, as he new nothing of our troubles. I took him to look at the system and he said: “It’s not installed correctly and you haven’t got sufficient discharge heads, and it’s not really the best system for this type of risk.” So Some more modifications were then made to bring the system up to standard.
I am now confident the system will work in the heat of battle, so to speak, but I often think about the number of systems that have been installed and not tested, and are just sitting there with the owners of the premises thinking that they are well protected. And I bet the contractors or manufacturer’s agent didn’t go around and tell people about this experience!
Alan Cox is a fire and safety consultant and previously held senior fire safety posts in the public and private sectors.
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The publication of a new watermist standard should give a boost to this type of system. But Alan Cox warns that insufficient care with design and installation can be potentially disastrous.
There has been a great deal of publicity given to watermist fire systems recently and while some manufacturers would have you believe that you can use them virtually anywhere, a great deal of caution needs to be exercised if you are thinking of installing such a system.
I was involved a few years ago in the installation of a system to cover a number of large generators. While I was sceptical about some of the claims made by the manufacturers, the insurers were recommending its installation.
I visited a number of companies that had installed similar systems to protect their generators and was surprised that no one had actually carried out a discharge test to see if the systems lived up to the manufacturer’s claims. However, it was decided to go ahead with the installation – which consisted of five individual systems protecting each generator in a large generator hall – based on information that had been provided to us by the companies involved.
The systems were installed by an authorised company in accordance with the design manual. When it came to system commissioning, I asked the contractors how they normally commissioned such systems. They replied that they used a cigarette lighter to activate the detectors and then checked that all the valves worked correctly. I was not happy with this procedure so I suggested a test involving setting fire to some oily rags in a bucket.
The generator was sheeted up and the bucket placed adjacent to the injector pump to simulate a fuel fire. The contents were ignited and the detectors detected the fire and initiated the system. But what happened next was very surprising. The watermist discharged correctly but did not extinguish the fire — in fact it appeared to make the fire worse, which then had to be extinguished manually.
The ‘post-mortem’ by the installers concluded that because the air conditioning was left running, this had influenced the way that the system performed. So it was decided to carry out another test with the air conditioning turned off. I should state at this point that the air conditioning would have needed to be operational if the generators were running, as if a fire occurred in one generator it was reasonable to assume that it was under emergency conditions and that other generators in the hall would still be running.
Another test was carried out and again it failed to extinguish the fire. What was remarkable was that when the air conditioning was running, the water mist was contained in an envelope around the generator, but without it, the water mist filled the whole room and it was difficult to see anything except the fire burning away. Clearly there was a major problem and the contractors agreed to seek help from the manufacturer’s agent.
Wrong type of fire!
The advice from the manufacturer’s agent was to make some changes to the discharge heads and to change the type of fire. Yes, they informed me that we had used the wrong type of fire and the system had failed because the fire was in the bucket and the mist could not get into it. This was somewhat of a surprise to me, but as I didn’t have a lot of previous experience about these systems, I went along with the explanation and agreed to an open tray fire, which they said would not be a problem for the system. Two more tests were carried out under similar conditions to the first ones, but with the same result. The only difference was that because we were using a tray fire we ended up with a very large fire that was quite difficult to extinguish manually! By this time I thought the system would never work correctly. I was on the point of instructing the contractors to remove the systems but the manufacturer’s agent asked me for one more chance, and said that they would build a mock-up of the generators and carry out further tests.
This test showed that while it was designed in accordance with the manufacturer’s design manual, the discharge piping needed to be doubled in size in order to deliver enough water to extinguish the test fire. The modifications were made and the system was finally able to extinguish the fire.
While it would be nice to think that this was the end of the story, there was another surprise in store. Some time later I was speaking to the manufacturer of the system and he asked me why we had not installed any more of the systems. When I told him what happened he was very surprised, as he new nothing of our troubles. I took him to look at the system and he said: "It’s not installed correctly and you haven’t got sufficient discharge heads, and it’s not really the best system for this type of risk." So Some more modifications were then made to bring the system up to standard.
I am now confident the system will work in the heat of battle, so to speak, but I often think about the number of systems that have been installed and not tested, and are just sitting there with the owners of the premises thinking that they are well protected. And I bet the contractors or manufacturer’s agent didn’t go around and tell people about this experience!
Alan Cox is a fire and safety consultant and previously held senior fire safety posts in the public and private sectors.