Water mist systems

[Phoenix]

I went to a seminar the other day, at the FIA, about water mist systems.  I expect a few of you were there (it was free). I thought it was good.  The people from the industry presented an open and revealing picture of the state of the 'art'.  They were excellent.

Interesting things to come out of it were as follows (some of these may be my surmissions (good luck spell-checking that word), see if you can guess which, but does it matter?):

1. The industry states that there are two sorts of systems, those that suppress fire and those that extinguish fire.  When considering a living room, to extinguish a fire there would need to be heads just about everywhere (under tables, under chairs, behind settees, etc), which is not practical, so the best we can hope for is suppression.

2. Suppression is just what it says and water mist systems have a poor record of extinguishing fires that are shielded from the mist in some way.

3. If fires are not extinguished, but merely suppressed, then the production of toxic gases may continue and the space containing the fire may not be as safe for means of escape as would be an enclosed hallway or staircase enclosure.

4. The acceptance criteria in the draft for development accept a temperature of 95 degrees C at 1.6m above the floor, so clearly this has not been developed with the idea of tenability in mind.

5. Only a complete idiot would suggest that a water mist system can compensate for the lack of an enclosed means of escape (e.g. inner bedrooms in a flat layout).

6.  Domestic sprinkler systems claim no more effectiveness at extinguishing fires than water mist systems, so can the same conclusion be held for domestic sprinkler systems (this is of particular significance in Scotland).

Has anyone any thoughts on this matter?  Does my argument fall down at any particular step above?  I'm open to all opinions on this.

Stu

[BLEVE]

must be a subtle argument

[wee brian]

It depends on the fire.

Comparing fire suppresion with protected enclosures is a futile exercise. They do different things in different ways.

[Phoenix]

Comparing fire suppresion with protected enclosures is a futile exercise. They do different things in different ways.

Yet some people compensate for the lack of one by using the other.  That implies that these people think they do the same thing.

[wee brian]

Maybe a bit unfair.

Are you happy to extend travel distances with a voice alarm system?

Or maybe protected lobbies for AFD?

etc

[Phoenix]

I would suggest that travel distance limitations and voice alarm installations both achieve the same thing.  The objective of both is to get people away from the area of danger in a period of time that is short enough so that they are not threatened by the fire.  Limiting travel distance can achieve this and so too can installing a voice alarm system.  Therefore, the application of one can off-set a slackening off of the other.  Same for protected lobbies and AFD.  etc.

I'm not arguing with you though, I agree absolutely with your first post. 

What interests me is that the Scottish Technical Handbook along with many English (and probably Welsh and N. Irish ("other countries are available")) organisations are happy to accept escape routes protected by suppression systems instead of by enclosure when there has been no clear presentation of conclusive evidence that it is safe to do so.   Or has there?

Stu

[AnthonyB]

I was reading in one of the fire journals of a recent independent practical study in offices comparing a traditional sprinkler system with three different, purpose designed for the risk, mist systems (one low & two high pressure).

Unless the fire was directly under a mist head with no obstructions the mist systems all failed miserably to control the fire and combustion products (unlike the traditional sprinkler system).

It's all very well on paper or simulation saying that they will work if practical tests show the opposite!

[Golden]

I carried out some tests on a fire fighting water mist type system when in the LFB - the tool operated at 300 bar and could cut a hole in a wall to get at a fire and was very impressive but had limitations and they are the same as described above. You had to apply the mist directly into the hot gases to be really effective plus if the fire managed to get a hold and had a decent air supply then the mist was quickly overcome, I don't know how the fixed water mist systems would overcome this problem as there must be some limit to the supply at higher pressure or its simply a sprinkler system? My conclusion for water mist still remains that it is absolutely brilliant for suppressing a fire if you can apply early and in the right spot - you won't extinguish a fire with mist - there are too many unknowns to rely on it for life safety.

[fitter]

In response to Phoenix's first post, particularly point No.5, I would just like to offer an opinion on the inner room situations. In the UK, or parts of it at least, we seem to have this view that inner room sleeping arrangements must never be accepted. Surely you have to consider the circumstances. In my home for example, I would have absolutely no worries about sleeping in an inner room because of the way I live and run my life. I dont smoke, I am particularly careful about home fire routines etc and do not consider the risk to be excessive to the point that it should not be considered. If I were to have an inner room sleeping area I would also ensure that a smoke detector was fitted to the access room.
Now in other situations to accept inner room sleeping arrangements would be asking for problems.
A lot of housing codes outside of the UK seem to accept inner room sleeping and they do not seem to have excessive fire death rates.
Think about the sleeping arrangements that will be taking place with visitors to homes over the Christmas period for example. Will there be many visitors sleeping on camp beds or similar in dining rooms off lounges etc. I would think probably a lot.
As I said, just an opinion.

[Fishy]

As Stu said, you can design these sytems in two ways - to suppress or extinguish.  In some ways, those systems designed for suppression are the most robust, in fire safety terms, because you're not reliant upon them putting the fire out - their purpose is to keep it small until safe egress is completed or some form of intervention occurs.  Nothing wrong with suppression - sprinklers are designed to suppress, not extinguish.

[CivvyFSO]

Surely you have to consider the circumstances. In my home for example, I would have absolutely no worries about sleeping in an inner room because of the way I live and run my life. I dont smoke, I am particularly careful about home fire routines etc and do not consider the risk to be excessive to the point that it should not be considered. If I were to have an inner room sleeping area I would also ensure that a smoke detector was fitted to the access room.

No, as admirable as it may be, such individual behaviour or circumstances are out of the scope of what can be considered at design stage. The building has to be safe for a large percentage of the population. If you are involved with the design of something like a shopping centre or some other commercial premises you can often make allowances for management, knowing that the legislation is there which should control the behaviour of such bodies, with the possiblity of enforcing suitable behaviour/practices. In the residential sector it needs to be as safe as is reasonable with limited 'management' on behalf of the potential occupier. You can make no such allowances in the residential side of things, apart from in resi-care etc, but in the likes of resi-care, due to the occupancy involved, I would suggest that it would be even more difficult to prove safety in such a premises.

On a separate note: If they are unable to prove tenability in the MOE then IMO they should apply for a relaxation on B1 on the basis that the persons may be trapped, but can stay in the bedroom in relative safety. (If that can also be proven) However, I doubt that the SoS would approve that.

[Northern Uproar]

Was told this week that a water mist system installed in the malls (open at each end) of a shopping centre would improve the fire safety, as they would reduce the effects of fire in a retail unit that is not covered by the system. When I questioned this, it was suggested that I didn't appreciate the subtle differences between water mist and sprinklers.

[CivvyFSO]

I would respectfully suggest that they maybe don't know their ar*e from their elbow.

[Northern Uproar]

Should have done but it was more of a    but the whole 'shielded fire' claims seem to have mutated into 'will drag the mist from outside the room of  fire origin by magic'

[kurnal]

Who was it that was making such claims?
The architect or the supplier of the mist system or A N Other?