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FIRE SERVICE AND GENERAL FIRE SAFETY TOPICS => Fire related queries from non specialists => Topic started by: Tom Sutton on February 05, 2014, 02:58:06 PM
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What is the reasoning behind 60 minute fire resistant walls only requiring 30 minute doors in some blocks of flats.
A question I was asked and I cannot remember the answer which I am sure I have been told?
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Its all down to the internal layout of the flat. With most flats you walk through the front door into a small hall from which you can access all other rooms. In some flats you get a larger hall which is becomes more of a corridor leading to all the other rooms in the flat.
The internal doors within each flat that form those halls or "short corridors" should be fire rated. The main entrance door to the flat should be atleast 30 minutes f/r and in total the front entrance door and internal doors combined should give you around 60 minutes fire resistance.
Thats the theory...In reality of course we all know resisdents prop (or even in some cases remove internall doors)
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The other aspect is two flats side by side 30 min fire doors on both give a total of 1 hour, but the single separating wall needs to be 1 hour to provide the separation.
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Becoming more aware of developers in flat developments who want to put glazed elements between the flat and the communal corridor. These are required to give 60/60 integrity and insulation. They only want to put 60/30 in or in some cases 30 mins for both. Anybody have any views.
Sorry I should say opinions. I read it back and thought I can't put window and views in the same paragraph without getting childish responses ;D
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They only want to put 60/30 in or in some cases 30 mins for both. Anybody have any views.
Depends on the size of the development and whether the blocks / flats are sprinklered - if they're not sprinklered then anything less than 60 / 60 would be unacceptable in my opinion!
Low rise - quite a few proposals I've seen recently seem to favour 30 minutes compartmentation, AFD throughout, and simultaneous evacuation policy ! Me no likey ::)
Thats my view, er opinion, DD ;D
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If you check ADB vol 2 2013 Table B1 page 134 is states any door that separates the flat from common areas should be FD30s and and door that protects the hall/landing should be FD20 so you will not achieve the 60 minutes. If you check the 1972 regs E10 any door in a protected shaft need only be half the fire resistance of the shaft, minimum 30 minutes. So I believe this concept of the door being half the fire resistance of the enclosure has been around some time but I cannot find why.
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Hi Tom
Thats why I said it will give you around 60 mins as you say ADB asks for FD20 - in most cases FD30 doors were fitted internally from my experience as buildiers tended to buy FD30 on bulk for various reasons.
The theory is that a fire in, say the lounge, would have to burn through two doors (internal and flat entrance door) before it spread to the communal area, and then through another door to get into a neighbouring flat which is very unlikely to happen.
So no you don't truly get 60 mins F/R necessarily.
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ADB vol 2 2013 Table B1 2c page 134 it says doors in a compartment wall enclosing a protected staircase, requires half the fire resistance of the wall minimum FD 30s.
Again I ask the question why?
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ADB vol 2 2013 Table B1 2c page 134 it says doors in a compartment wall enclosing a protected staircase, requires half the fire resistance of the wall minimum FD 30s.
Again I ask the question why?
Whilst I don't think it the correct answer consider the fact that the fire service will attend and commence firefighting in about 10-15 minutes. To do this we open the door and enter the compartment, once we open the door doesn't really matter whether it is 30 or 60 minutes.
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Tom, this is not uncommon, for example I seem to recall that walls on the stairways of a firefighting shaft should be FR60 yet the doors only need to be FR30 and the walls of FF shaft lobbies should be FR120 and yet the doors only need to be FR60.
My understanding is that this is all about direct flame implingement.
Combustibles can easily be stored against the walls but not so against doors, otherwise the doors couldn't be opened/closed.
It makes perfect sense to me, but as alway I stand to be corrected. ;)
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My understanding was and still is that the compartmentation is to prevent the rapid spread of fire and to give the building some structural integrity in a fire. As the building height increases so does the fire resistance of the compartmentation. The degree of fire resistance can vary from 30 mins to 120 mins depending on the purpose group and building height.
As to the lesser fire resistance of doors in compartment walls I would think this has more to do with door technology and ease of use. A 1hr or greater door can be quite heavy.
I would suggest that the area of door openings in a compartment wall would be quite small percentage wise and a few 30 min doors in a 60 min wall would not generally result in a significant weakness in the building's compartmentation and would have little bearing on the structural integrity of the wall.
Just my thoughts.
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Thanks for your responses I am now ready to answer my enquirer.
The wall between a flat and the common areas is a compartment walls and tested to BS 476 part 21 which includes stability as well as integrity, so it needs to remain stable as well as resist the passage of fire for the appointed time (60mins). Fire doors are non-load bearing and tested to BS 476 part 22 for integrity, I have chosen to ignore insulation because it is not relevant in this discussion.
Therefore compartment walls have remain stable and resist the passage of fire for the full 60 minutes and fire doors only have to resist the passage of fire. Because fire doors do not have to remain stable you can have two doors protecting the opening, one from the habitable rooms to the hall and then a second (front door) from the hall to the common areas a combination of 60 minutes.
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Tam, you are making it all too complicated and your explanation does not take into account flats with no internal fire doors.
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Point taken Colin what is the simple answer taking into account flats without internal fire doors?
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OK, here goes the reasons are as follows;
High periods of FR for Doors is difficult/expensive etc.
Doors are a small part of a wall, stuff isnt usually right in front of the door (or you couldn't open it).
Also, much better that the first component to fail is the door than some random part of the wall (better for firefighters)
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I wondered when you were going to tell them, Wee B. I was beginning to think you were ashamed of the answer, but then I remembered that civil servants are like I/O's who get it toally wwrong, they know no shame or emabarassment.
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It may be a simple answer Colin but I am still trying to work out the logic. Some compartment walls have to meet the full standard and any opening have be protected with fire shutters with fusible links.
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Yes, its not always 50% for doors.
I could come up with a plausible explanation given time. But I haven't got it right now.
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What a lot of reasons - all good but here is the simple one.
Suppose a building requires 60 mins FR between compartments and the floors are compartment floors. If the fire were to get from one floor to the one above via the staircase it would have to go through the fire door to the stairs, up the staircase then back through the fire door to the floor above. It would have to go through two fire doors (let alone traverse the theoretically 'sterile' staircase) so each only has to have half the fire resistance of the walls and ceiling.
This is why a fire door in a compartment wall that leads horizontally from one compartment to another has to have the full fire resistance of the wall - because there's only the one door.
If there are lobbies onto the staircase then this is a bonus, this is for means of escape and not for compartmentation. Remember that this issue is to do with restricting the spread of fire, not protecting means of escape.
Mike Buckley said this ages ago and no one seemed to notice.
Stu
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The point didn't go unnoticed but ADB states separation from a place in common use which is on the same floor and consequently the staircase is not involved.
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Tom,
I believe you are referring to flats so we can talk about them. ADB states that fire doors from a flat to a space in common use have to have a minimum of 30 mins FR (Table B1). It also states that walls separating flats from other parts of the building have to be 60 mins (Table A1). I think that is what you are referring to.
Well, the same argument holds for these horizontally accessed common spaces as for staircases. For a fire to get from one flat to another it would have to go through either a 60 minute wall or two 30 minute doors. Remember the 60 minute walls are not to protect the means of escape (although this is an important secondary effect) but to stop fire spread from one flat to another. The means of escape are protected by the 30 minute doors.
Stu
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I accept that Stu but why a 60 min wall if it was 30 mins it would achieve the same aims. I think wee brian's response 14 is likely to be the right answer like many decisions in fire safety based on arbitrary figures and little research.
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Tam!!!!! How could you suggest such a thing. Next you will tell me that the duty manager at the Empire Palace fire didnt really have a stop watch when he said that the audience took 2minutes 30 seconds to evacuate (back in 1911, when the Edinburgh Sheriff wanted to know the ASET-now tell me the Scots arent ahead of the game).
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Do bear in mind that fire resistance tests are not particulalry good replicas of real fire exposure. You can get a bit too academic with all this stuff.
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Wee Brian I fully agree and real fire exposure extends from the toast that catches fire that may attract a fine to a the major conflagrations that attract the media attention - not every new building is worth playing the RSET/ASET guessing game or modelling on a super computer therefore lines have been drawn in the sand that make some basic assumptions. Some of the figures have come from research, some are arbitrary standards plucked from the air - I'm quite glad that I don't have to advise people to get fire doors rated to 36 minutes and 27.6 seconds. What is important is that these standards are seen to work and are challenged when they are ineffective or become a burden.
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Nor is the standard for smoke control doors, Wee B.
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That's the thing with this subject. The more you know, the more you realise you don't know.
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The process of education means you start off knowing nothing about everything and finish off knowing everything about nothing.
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In London Fire Brigade, they know that they know everything about everything and know that what they dont know is not worth knowing, know wat I mean, guv, though its late, so I could have got that the wrong way round.