Fan Temperature Rating

[GB]

I am looking to utilise a smoke extraction fan (post sprinkler opertion) within domestic premises. Does anyone know what BS would cover that and what the temperature rating of the fan would need to be?

[Gasmeter]

Sorry GB, I've asked around but nobody knows of a relevant standard.

[kurnal]

Its an unusual query GB. Domestic sprinklers are usually the ultimate safety solution in themselves- is there a reason why we would need a fan as well ? Is this for life safety?
For post sprinkler operation there should be no specific temperature rating- cos the fire will be out. The sprinklers in most cases will operate at 68C so provided the fan can stand this plus a safety margin - say 100C I guess  you should be well in. Fire rating for fans is  only usually an issue where ventilation system is the fire safety solution for life safety to maintain tenable conditions during peoples escape from the occupied space.

[GB]

I have conducted extensive modelling with sprinklers that show that tenanbility is not maintained in relation to visibility requirements under PD7974. The fan therefore is required to respond to the issue where inner room situations occur.

I agree that high temps are not required due to post sprinkler operation but was trying to relate to a standard or guidance in order to convince local BCO's or FSO's. As you know sometimes common sense isn't something that people use!!

[wee brian]

Blimey - how much smoke do you need to move to clear an inner room. I doubt this is practical.

There is usually a fair bit of mixing before the smoke gets to the fan which is why 300/400 deg fans are usually used. With domestic geometries the fan will be so close to the fire that the smoke will be up to 700 degs plus! I dont think you can get one that works at those temps.

[GB]

I am assuming that the compartment temp will not reach these high temperatures due to the presence of the sprinklers (which I suppose is the theory behind their inclusion). If the fan was operating in islolation then I agree that these temperatures may be reached only if the oxygen availbility would support this level of combustion.

As I mentioned I am looking at a domestic environment, with reasonable ventilation prior to the fire, domestic sprinklers with the usual rating and the fan to remove the smoke once the sprinkler has activated - therefore tempertures should not reach +700C in any isolated position irrespective of mixing.

[kurnal]

GB
I am surprised that visibility is used as a tenability issue in a domestic property, where there is no requirement for escape lighting in any of the building codes, outside the common areas? The worst case would be a fire at night- darkness will surely be a bigger factor than smoke obscuration of exit signs or even the exit routes? If I recall correctly, I think  it is the visibility of the exit signs ( of which there will be none) that determine the tenability levels specified in 7974? Please correct me if I am wrong.

For individual rooms in hotels or private dwellings the justification for there being no escape lighting was that persons can be trusted to know and remember the layout and hazards within their own domain.

And besides I think the fire Authority and Building control are more likely to be sympathetic to a logical argument based on common sense that they can understand, than impressive calculations that they cannot understand. I should take the argument down to their level of understanding. (I used to be a simple fire enforcement officer myself- and actually it was always the simple questions that floored the so called experts!)

[GB]

Thanks for that Kurnal.

I am dealing with a BCO and FA who at the moment are preventing a large housing project from progressing due to this very issue. I agree that 'impressive calculations' are meaningless if the arguement falls down. I was also a 'simple fire officer' to use your words therefore am sympathetic to all involved in such negotiations where hopefully the common goal is obtained rather than who simply wins the arguement.

Is it suggested therefore that 7974 details tenability limits for non-domestic properties rather than domestic. Is there a qualifying statement to say that limits are not applicable in certain circumstances? Are there seperate tenability limits set for domestic properties - if so where are they?

I ask these questions out of a quest to learn rather than a notion of appearing to have an answer. Post's like these alas don't always generate the true tone of a question and can be misinterpreted. Apologies if this has been the case in this instance.

[kurnal]

GB
I only have an early consultation draft of 7974 I am sorry to say. But I will take a look tomorrow to see what it says about scope. My comments were based on the answers I was given on this subject when last at Moreton 4 years ago , and rely on my rather dodgy memory.
Have you looked at the ODPM study into the effectiveness of residential sprinklers carried out as part of the building regs review a couple of years ago? I remember Tony Bird and Ian Gough giving presentations on the subject relating to HMOs.

In any case I am baffled how anybody could predict smoke/ visibility/ tenabiity with any meaningful accuracy for a sprinkler controlled  domestic fire in any case. Too many variables for me! Are we planning for a cooking/ furnishings/ tv set fire? The sprinkler will operate an audible alarm so the expected time to detection should be short?

I wouldn't mind betting that if you took your case to a determination on the basis of sprinklers providing sufficient compensation you would win. And whilst we all want a safe standard perhaps an approved inspector may take a realistic view.

I guess you are looking at providing bedrooms that are inner rooms?

[wee brian]

Visibility is a limit that has widely been used for domestic properties. The BRE study into the effectiveness of Res sprinks identified this as a key problem with using them as an compensatory feature. (I think they used 2 or 3m)

Based on the results from that work the hotest gas temps were around the 200 deg c mark. A 300 fan sounds like the right spec.

[wee brian]

As for determinations - if you look at the cases that have been through before, I think you would struggle to win without the sums to back it up.

[DF]

Kurnal,

Based on my understanding of the BRE / ODPM study on the effectiveness of residential sprinklers as well as comments made at the launch of the ADB consultation documents, I would be very suprised if a determination of sprinklers, on there own, providing suitable compensation for an inner room situation and / or the lack of a protected escape route would be successful.

Also I am a bit concerned that you have assumed that the BCO who is not agreeing to this solution is Local Authority (being unreasonable in your eyes?) and that an AI would probably rubber stamp this as yet unproven solution.

Hopefully both LABC and AIs will base there decisions on the same information and in the vast majority of cases come up with the same correct decision. If this is not the case then clearly the current Building Control regime is not functioning as it should (and I have to say that this unfortunately may be the real world situation).

Regards
Dave.

[kurnal]

Guilty as charged DF! Get a bit excited sometimes.
The trouble with trying to find the right answer through these forums is that none of us can clearly see the problem.  I fully agree that the only acceptable solution is the safe solution. And have no axe to grind with most Local Authority BCOs  ( but most of the good ones I used to work with have gone into private practice).

But there are a number of jobsworths around and I percieved that this may be the case in this situation. I imagined sitting round a table with a BCO who would rubber stamp my plan with a traditional layout, rising butt hinges etc fully understanding thet virtually nobody closes doors in their flat so everybody effectively sleeps in an inner room, but if I create an inner bedroom and use the same travel distances  and then  provide a compensating feature such as sprinklers its not acceptable.  

Then the jobsworth asks me to provide calculations to prove tenability due to visibility. If the occupant is in the inner  bedroom room the chances are its night time and dark. There is never any requirement for escape lighing in  a private dwelling. So why is visibility an appropriate measure of tenability in this case? Smoke levels, toxicity,  temperature, I could understand. But are they predictable in any case in this environment?  

Personally I would prefer an inner room with sprinklers to a traditional layout without. And I think the principles of prevention would point us  towards active rather than passive measures as a means of controlling risk if there is a choice. As long as they are maintained of course.

One final point- the sprinkler solution would do far more than just protect the occupants of the unit involved. By controlling a fire and arresting its development they also protect all other persons in the building.

[DF]

Cheers Kurnal,

Still plenty of good LABC BCOs around, but like in any walk of life there are good ones and bad ones, just the same as with Fire Consultants, FPOs and AIs etc.

I have a few worries with this type of layout.
What if the occupier has children in another bedroom? I've had the arguement put to me that you would be safe to stay in the inner room especially if it is provided with 30 min FR. However if I had children in another room I'm sure I wouldn't sit tight and hope for the best. I would rather that I could get to them via the protected corridor or in the worse case my 6 year old had the chance of walking down a protected corridor rather than through a smoke filled room.

I've also had the arguement that there will be little inlet air in the sprinklered fire situation as temperatures not be high enough to shatter the windows and hence a smaller fire - this seemed to overlook that in summer every window may be open - the nice patio doors these flats tend to have may provide close to 4m2 on their own!

I understand the issue of doors being wedged open, but being responsible, even if the doors in my house are open during the day I close them at night.
In reality, if people living in the existing housing stock closed their doors at night and fitted smoke alarms  this would have a far more dramatic effect on reducing fire casualties than controlling new builds to the nth degree. It seems that DCLG may be realising this in the ADB consultation with regards to the need for self closing devices on fire doors within dwellings - educate people to shut doors whether fire doors or not, as a shut door will be of great benefit where as a wedged open fire door obviously isn't. Get this message accross to as wide an audience as possible and this would make a big difference.

I am not anti sprinkler in any way and in fact recommend there use as often as I can, but think we all need to be careful to ensure their use and any subsequent reduction of other fire safety measures is appropriate. They can provide huge benefits but they are not the answer to all problems.