FR vs AFD

[Firewolf]

Heres a quick poser for you

Imagine a store cupboard under a staircase.

The cupboard is fire resisting and  it has a fire door leading into it fitted with cold smoke seals and intumescent strips.

There is no AFD in the cupboard.

In theory a fire could start inside the cupboard and effectively go unoticed until it has breached the door at some point nearing the 30 minutes FR of the fire door.

What I guess Im asking is this: Wherever we look to provide Fire Resistance in isolated spaces or little used rooms such as cupboards should we also be asking for AFD to give early warning of a fire starting within them?

And by that logic could we therefore state that FR or AFD isn't req'd because a fire in a cupboard without FR or AFd would breach the door very quickly and be spotted by someone!!

Its an argument someone threw at me earlier today and it has me stumped for I feel this is quite plausible in certain applications other than residential premises and high risk etc.

What are your thoughts on this?

[Mike Buckley]

Two factors to take into account. If the cupboard is fire resisting and with the seals, the most likely outcome is that the fire would self extinguish by using up the oxygen before it has a chance to breach the half hour door.

The other factor is the MOE. If the stair case is the sole MOE from the upper floors the case is different from where there are alternative MOE.

It would appear to me that it all falls back on the Risk Assessment. Take into account the materials stored in the cupboard, potential sources of ignition etc. then the severity of the result and base your actions on this. Decide what is "reasonably practicable".

I am afraid we are going to have to get used to the idea that there are no fixed answers under the new regime.

[Chris Houston]

My personal opinion is that it would depend on numerous factors, two being:

The presence of any possible ignition sources within the cupboard
My opinion on how well the fire resisting elements of the cupboard will remain maintained

And, yes, it will depend on the fire safety risk assessment.

[PhilB]

Good point Firewolf....for years we have been asking for stores in stairs to be enclosed in FR without detection it is pointless exercise. It matters not a jot Chris how well the the fire resisting elements will remain intact...without AFD you won't know that there's a problem until it's too late

[kurnal]

The question we should ask first is could a fire in the cupboard cut off the means of escape for people using the building. In many circumstances in commercial buildings the staircase may not need to be a protected route - if there is an alternative way out from the upper floors, if a fire could not affect both routes at the same time and if travel distances are reasonable there may not be a need for fire resistance or detection.

But if it needs to be a protected route it needs BOTH detection and FR. Then the detector will cause the alarm to be raised giving people time to pass the fire within the protection window  offered by the structure.

The Risk assessment will determine whether the route needs to be protected or not.

But assuming we come across the situation in the real world and if we decide we need a protected route then as Chris points out  our first thoughts should be to eliminate the risk- ignition sources and combustible materials. Sealing  up the cupboard may be a solution that eliminates the need for anything else. Depends on how much confidence we have on it being maintained.  If the stakes are high- eg sleeping risk - then its reasonable to provide AFD and FR - ie protected routes throughout and full AFD because of the potential consequences of the fire. Slow response, occupants asleep, possibly unfamiliar with the building etc.

[John Webb]

By coincidence I was looking at some past work I did at the Fire Research Station in the 1980s in response to another question in this forum. It was for the Home Office regarding the siting of detectors in corridors of hotels and other sleeping accomodation. We were asked to see if smoke detectors in the corridor could be relied on to give an alarm from a room accessed from the corridor, and the effect of different sorts of door on the speed with which the alarm was given.
We used ordinary domestic doors, FR doors without intumescent seals and FR doors with seals.
In summary:
Domestic doors always allowed enough smoke out to trigger a detector well before the corridor became impassable to people due to smoke or flame penetration.
FR Doors without seals - those with a poor fit gave a longer time to alarm from the start of the fire than a domestic door of any fit did. Well fitting FR doors could allow a 'plug' of smoke to build up in the corridor which rendered the corridor impassable often well before the alarm was raised by a corridor detector.
FR Doors with seals - poor fitting ones would allow smoke plugs to form, well-fitted ones often resulted in only cool, low-level smoke, undetectable and not hindering passage.
The conclusion was that if FR doors were to be fitted, a heat detector should be put in each room accessed from the corridor. It would not necessarily save the life of the room's occupant, but it would raise the alarm well before the corridor was rendered impassable. It would also be less susceptible to false alarms from any activity of the occupant.

So I would suggest that if you cannot control what is put away in the cupboard, fit it with an FR door and put a heat detector in it.

[kurnal]

John
Please correct me if I am wrong ( again) but I thought the reason that  heat detectors were specified for rooms following your research ( and I do remember that very well at the time and some excellent mock ups to demonstrate your findings) was because then many people smoked and there was a need to control unwanted signals? We were not interested then in protecting the occupant of the room- we were simply wanting to focus on raising the alarm before the means of escape was jeopardised?

So I would have thought that a smoke detector would have given an earlier response to a fire in the cupboard- and thus enhance everybodies safety.

[John Webb]

I suggested a heat detector for the cupboard location as they are cheaper than smoke detectors and less likely to give any false alarm through dust and the like - if, for example, the cupboard is used for housing cleaning equipment. Also potentially more robust and therefore more likely to resist any bump from whatever is being stored. And in a small cupboard I would expect a heat detector to give an alarm quite quickly because the heat would build up faster than in a large room. Just a bit of pragmatism on my part as far as Firewolf's scenario goes.

What about Para 5.29 of AD 'B' which says that a protected stairway "needs to be free of potential sources of fire"? A cupboard with FR construction is allowed but only if it is not the only staircase to the building. Can Firewolf enlighten us as to whether this is the case or not?

[Chris Houston]

My experience (of working in the fire alarm industry) is that the price between a point heat detector and a point smoke detectors did not vary by more than £1 in terms of cost.

[wee brian]

This discussion is based on the assumption that smopke from a fire in the cupboard won't find its way into the stairwell.

Even a well fitted door with smoke seals will leak enough smoke to trigger a smoke alarm well before it becomes a threat to anybody.

so don't worry about it.

[PhilB]

Wee Brian...the smoke will find its way into the stair but it may have lost it's bouyancy...I think it was B.K.Ghosh that provided evidence of this in his research.....but I'm sure someone can elaborate.

[John Webb]

The work on doors and corridors mentioned in my post #6 above also involved Mr Ghosh. It is possible he wrote something about the work after the Home Office considered our results, but I have nothing in my records - I'd been moved onto work on fire-fighting foams by then.

But I confirm that a well-fitted* FR door, with or without seals, will not usually allow bouyant smoke through until the later stages of a fire. In the corridor this resulted in the formation of a 'plug' of cool smoke which blocked the corridor but did not move towards a detector in the corridor.

How this would translate into a vertical stairwell I am not certain, but if there was only a detector at the top of the stairwell I suspect we could end up with cool smoke filling the bottom of the stairwell and no detection. And could an understair cupboard contain sufficient fuel to eventually breach an FR door? Where would the air for combustion get in?

I continue to think that the best solution is to put a detector in the cupboard. This will give an early alarm before there is any loss of visibility in the stairwell.

*Well-fitted means a 1mm gap around the door between the door frame and door edge. Door stops firm against the corridor side of the door, the door opening into the room. Doors with a 3mm gap but fitted with seals behaved rather like the 1mm gapped doors without seals.

[wee brian]

I'm aware of the work you are talking about. obviously a detector in the cupboard is ideal but i don't think its necessary.

[John Webb]

Well, I did query in my last post about the ability of a cupboard's contents to sustain a fire  for any length of time. If the risk assessment shows that the nature of the contents is such that it is unlikely a fire would start and be sustained, then relying on the FR door would be OK with me.

[Firewolf]

Thanks for your replies so far its been a very big help.