Fire separation

[colin todd]

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.

[Tom Sutton]

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.

[wee brian]

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.

[Phoenix]

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

[Tom Sutton]

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.

[Phoenix]

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

[Tom Sutton]

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.

[colin todd]

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).

[wee brian]

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.

[Golden]

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.

[colin todd]

Nor is the standard for smoke control doors, Wee B.

[wee brian]

That's the thing with this subject. The more you know, the more you realise you don't know.

[Mike Buckley]

The process of education means you start off knowing nothing about everything and finish off knowing everything about nothing.

[colin todd]

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.