UK Water Mist Seminar 2016

The UK Water Mist Seminar 2016 was held in the lecture theatre at BRE, Watford, on Tuesday 8th March 2016. I was there, and so were 120 others, mostly from fire protection companies, insurance companies, consultants, building control and a few from fire brigades and academia.

The seminar was organised by the International Water Mist Association (IWMA), which has a specific agenda - to promote the use of water mist, so it is not surprising that the majority of things said from the stage during the day were very much in favour of water mist use, as an alternative to traditional sprinklers. The implication in a few presentations was that sprinklers are old technology, whereas water mist is the future of fire protection.

"How does water mist work?" was the title of the first presentation of the day, and in his opening remarks Erling Mengshoel, from Protect Systems in Norway, apologised to the academics in the room that his presentation wouldn't contain any equations or complicated theories. It didn't contain any significant science either, got the fire triangle wrong (he gave it as "Oxygen", "Fuel load" and "Temperature") and, unfortunately, set the tone for the rest of the day, in that none of the other presentations really got to grips with important questions like where, when and why water mist is better or more efficient at mitigating the effects of fire compared to traditional sprinklers.

To summarise, water mist is a water spray system which uses higher water pressure and different kinds of nozzles from traditional sprinklers, to produce (much) smaller water droplets. These water droplets interact with flames directly, quenching the burning in the gas phase, cooling the volume, and displacing air, effectively pushing the oxygen needed for combustion away from where the burning is happening. So water mist achieves its fire protection aims by cooling and dilution. Traditional sprinklers, on the other hand, achieve their aims by surface wetting - keeping the potential fuel around the fire cool and wet, so that fire spread and growth cannot occur.

Is water mist a kind of sprinkler system? The answer given in this seminar is no, it is not. It is an alternative and rival technology.

Bob Whitely from Tyco UK gave two presentations back-to-back on where water mist is used at the moment, and on the development of a British Standard for water mist, BS 8489, which should be published in the next few weeks. Where are we? Well, water mist is used on only about 3% of land based applications with an active fire protection system. I say "land based" as water mist has a much bigger market share in offshore and marine applications. The agenda of the day, however, was to promote water mist for onshore applications, and try to get engineers, designers, regulators & insurers to consider the possibility of water mist in the other 97% of the market.

Why a British Standard? Well, the answer to that question seems to be that we really want a European or ISO standard, but they are taking so long to develop that someone has to lead the field here, and it might as well be us. Another British Standard, BS 8458, which focuses on residential use of water mist, will also be along soon.

Bob Whitely painted a fairly bleak picture of the regulation and insurance industries with regard to water mist acceptance and approval. He basically said that there are not enough people working in these industries who actually understand fire safety engineering, and so there is a bias towards traditional sprinklers and away from 'novel' systems like water mist, simply because those with the authority to approve such systems are not equipped to make the decision. I noted that when the representative of the insurance industry (Gary Howe, from Zurich Insurance) took the stage an hour later, he did not attempt to rebut this opinion.

Gary Howe's presentation was interesting and frustrating in equal measure. His main point was that if you want to put in a water mist system as an alternative to sprinklers, you have to demonstrate that your system works in each different kind of occupancy in a building you are proposing to protect - in essence, he was saying that you might need to carry out multiple full scale fire tests to demonstrate your system, for use in a single building, if you want insurance approval. That is, use a performance based approach. However, he also made a big deal of the necessity for approved nozzles, approved pumps, approved pipework, etc. That is, a prescriptive approach. Basically if you want to get a water mist system approved you have to jump through many more hoops than if you propose a traditional sprinkler (which is all prescription and no performance-based approval required). You rarely have to demonstrate that a sprinkler will work, it is just assumed to do so.

The rest of the day was a mixture of case studies and presentations from water mist companies saying how great their product is. One presentation from BAFSA spoke about the lack of and need for proper qualifications and training for sprinkler engineers, but as the topic wasn't specifically on water mist, most of the audience seemed to dismiss the message.

The most important questions about water mist are those that were not asked or addressed. Specifically, when should water mist not be used? When are traditional sprinklers better? What are the situations where neither sprinklers or water mist are effective? And so on. I guess I wasn't expecting such questions to be addressing in this forum, but I think there really is a need for discussion and research into these questions.

Yes, water mist can be a great technology for fire protection, and yes, it could be used in many applications currently served by traditional sprinklers. There may even be financial and ecological savings along the way. We already know this. Understandably, the focus of this event was on persuading the building control and insurance industries to approve water mist in cases where it can and should be approved. But I think this agenda would actually be served better by research into and education explaining the territory where water mist reaches the limits of its capabilities.

The Science of Suppression FIRESEAT symposium

On November 9th, 2011 the students from the International Masters of Science in Fire Safety Engineering (IMFSE) studying in Edinburgh University were invited to attend the 5th FIRESEAT symposium "The Science of Suppression". During this conference, attended by ~85 people, we saw eight different speakers from varying parts of the world discussing topics focus around fire suppression.

The first speaker we had the privilege of seeing was Ronald Alpert. As the Alpert Correlations were among the topics covered in our Fire Dynamics course, we were all excited to hear him speak. Alpert explained how he designed his correlations and revisited them with new experiments. He eagerly stressed his excitement for someone to advance his correlations past the current level in which they are.

The next speaker was Yibing Xin of FM Global. Sprinkler technology was the topic discussed. FM Global is working on being able to affectively model how sprinkler systems work during suppression. By doing so, they are creating a new modeling tool, FireFOAM. This would be a very useful tool because of the expensive costs of having full-scale burns. We recognize the challenges faced in order to create a program such as this, although there is no doubt that it would be a great use to the Fire Protection Community.

Andre Marshall form the University of Maryland was the third speaker of FireSeat. The research Marshall is conducting also focuses around sprinklers. In contrast to Yibing, his research involves quantitatively breaking down the spray pattern of a sprinkler head and analyzing it. The techniques being used by Marshall are nothing short of impressive.

FireSeat at this point made a turn toward the use of water mist sprinkler systems. Louise Jackman of LPCB discussed some research she was conducting. This involved using mist systems in different setting with different variables. All we could conclude from this was that mist systems are temperamental, in which the system requires just the right variables to effectively work.

The next speaker was Stefan Kratzmeir of IFAB. He discussed his research involving the use of water mist systems in tunnels, hiting mist could be effective in mitigating a fire. Our concern with this topic was the interaction between the mist and the ventilation. We felt this concern was not addressed.

The next research area discussed was the use of cryogenic suppression, presented by MichaelDelichatsios of the University of Ulster. He explained the used of cryogenic material (mainly liquid nitrogen) to extinguish pool fires and wood crib fires. Although the method was effective, the delivering of the agent to the seat of the fire seems to remain the issue in which water and foam systems still have over such a suppression agent.

Suppression in tunnels again arose with the next speaker, Elizabeth Blanchard. Her modelling results of fire suppression inside a medium size tunnel seemed to be more accurate than previous studies. But the question already began to loom among our students concerning the interaction between the mist delivered and ventilation. Our concern was again not addressed, despite the effectiveness of the mist system to mitigate fire and enhance visibility, we felt more research should be performed to address the issue.

The final speaker of the 2011 FireSeat was Stefano Chiti of COWI. This research involved using hypoxic air for fire suppression and prevention. This would basically displace oxygen in the combustion process making combustion slow or near impossible to occur. This is a good research area, especially since Halon is no longer being used. We can see the use of this being great as long as it is ensured not to effect human life.

FireSeat was a great experience. It showed suppression research has many different areas that will improve the suppression actions of the Fire Protection Community in the future.

by Joshua Reichert and Oriol Rios, 2011 IMFSE students

Water mist in tunnels - First hand experience

What follows are some personal reflections on my attendance at the SOLIT2 project workshop in Gijon, Spain, on 22nd & 23rd June 2011. But first, some context.

As might be expected for somebody who has worked in Fire Safety research for over a decade, I have seen quite a few experimental fires. We regularly fire test things in our lab and I've seen plenty of fires with heat release rates in the range of 300-500 kW. I have also seen fires in our lab as big as 700-800 kW and have seen the reactions of people to fires on this scale. They generally start backing away slowly and start feeling uncomfortable, both with the level of radiant heat they start experiencing and the 'what would happen if...' thoughts that start going through their minds.

Those fires are the limit of what our lab can handle (we can go transiently to 1000 kW - that is, 1 MW - but we rarely go that big). For various reasons, I've also been witness to some larger fire tests in the burn hall at BRE, for example, I've seen a pool fire that was a little over 2 MW and a solid plastic fire that was also about 2 MW. I've stood a few metres away from such fires and know what the radiant heat feels like. 2 MW is a big fire. When we did the Dalmarnock Fire Tests a few years ago, the peak heat release rate (for an entire living room / home office on fire) was around about 5 MW. 5 MW is a big fire.

But when we start talking about design fires for tunnels, we start hearing numbers like 30 MW or 100 MW and its hard to grasp just how big a fire that means.

So when I got the opportunity to witness an alleged '100 MW pool fire' in the San Pedro de Anes test tunnel, well, how could I refuse?

The SOLIT2 workshop was held in a nice hotel in Gijon, Spain, and featured not one but two visits to the nearby TST test tunnel to witness fire tests with water mist. These were allegedly not demonstration tests, but were part of the SOLIT2 test programme, investigating the abilities of a water mist suppression system to mitigate the effects of a fire in a tunnel.

The workshop started at the hotel on Wednesday 22nd June 2011. The first presentation, by Stefan Kratzmeir of IFAB, gave the context of the SOLIT2 project - the aim is to develop and test water mist technology to either:

1. Achieve the same same level of safety in a tunnel with a water mist system at a reduced cost compared to other common tunnel safety systems (i.e. by installing water mist, you can 'trade-off' and reduce the specifications of other safety systems, such as structural fire protection, or ventilation systems, etc.), or
2. Achieve a greater level of safety in a tunnel with a water mist system at the same cost as would be spent on other systems (i.e. still trading off systems).

So it was clear from the outset, the objective of this project was to reduce costs without increasing risk. But enough on the presentations, we were rapidly shipped off to the test site to witness a large pool fire test.

The fire was not 100 MW as advertised. It was probably about 50-60 MW, which is still [insert adjective or expletive of your choice] big! The 700 l of diesel fuel was distributed across 7 large rectangular fuel pans (each at least 2 m.sq). Once lit, the fire grew rapidly in severity (as pool fires do) and soon we (the observers, standing about 45m upstream of the fire) found ourselves looking up at a layer of smoke billowing across the ceiling above us. This is the dreaded phenomenon of 'backlayering' - even though there was a longitudinal flow of about 2 m/s, it wasn't sufficient to drive the smoke away from us.

It became clear that this hadn't been an intentional part of the demonstration. Some of the Fogtec and IFAB people started looking worried. But the water mist system (spanning a stretch of 50m of tunnel straddling the fire location) was started about 90 s after ignition (I think the intention had been to start it after 60 s) and soon the backlayering began to shrink back and ultimately vanish into the mist.

What rapidly became clear was that the water mist was not extinguishing the fire. It was hard to tell from an observer's point of view, but it appeared that the water mist was also not suppressing the fire, at least, not using the dictionary definition of suppressing (which involves concepts like halting growth and reducing size). The fire appeared to burn at about the same level of severity while the water mist operated. However, what the mist achieved was a reduction in backlayering, possibly due to a reduction in smoke production, or possibly due to a reduction in the buoyancy of the smoke. The mist also provided thermal protection for the tunnel structure and (had there been anyone there) from the people in the vicinity of the fire.

After the pool fire test we were returned to the hotel for an odd lunch of nibbles and finger food and an afternoon of fairly uninteresting presentations (in which the same point was made over and over again - you can trade off other systems against water mist. OK. I get it). Apologies to the speakers, if they're reading this, it wasn't that they were all boring, it was just that I'd heard most of it before, and there was a lot of repetition.

Day 2 of the workshop featured another presentation on the findings of the SOLIT2 project and then another coach trip to the test tunnel. This time, the fire test was to involve a 'simulated truckload' - that is, lots and lots of wooden pallets, arranged in the basic shape of a HGV trailer, covered by a tarpaulin and held in place by a steel frame. The fire was lit, the fire was allowed to grow for about 4 minutes, and the water mist system was activated.

Once again, the mist did not extinguish the fire. Indeed, the fire grew from about 3-5 MW at the point of activation of the mist to about 20-25 MW while the mist was active. But in this test, we (the observers) got the chance to put on waterproofs and approach the fire location.

Here's where the context above comes in. I know what it feels like to stand about 2 m away from a 1-2 MW fire. I now know what it feels like to stand about 2 m away from a 15 MW fire (the size when I approached the fire) in water mist. It feels more or less the same. That is, the radiant heat from a 15 MW fire is attenuated by the mist to such a degree that its similar to the heat flux from a fire a tenth of the size without mist.

And I also know just how wet you get in water mist.

And how good the visibility was. That surprised me. Standing beside the wall on one side of the tunnel, I could clearly see the way-finding lights on the opposite wall. In other words, visibility was still of the order of 10 m.

After about half an hour of burning, the fire brigade were sent in to extinguish the fire. This they could do easily. After this we saw another demonstration of a portable mist system on a burning car (in the open air) and were returned to the hotel for another odd lunch of nibbles and a final summing up session.

So I now have first hand experience of what water mist systems can do for fires in tunnels. They can block heat and reduce smoke production / backlayering.

I have published quite a lot on the subject of the limitations of water mist in the past. Has this experience changed my mind? Well, yes and no.

Yes, in that I now consider heat release rate to be a largely irrelevant parameter when assessing the life safety situation in a tunnel with an active water mist system.

No, in that the workshop still has not addressed some of my other questions, the primary one being 'are water mists systems better than conventional sprinkler systems for fires in tunnels?'

But I've got more to think about and more research to do. This won't be the last thing I publish on the subject of water mists.