Smoke pressurisation and fire door seals

[Rocha]

I have recently visited a building where the main fire fighting stair and lobbies were installed with a smoke pressurisation system.  The fire doors to the lobbies from the main stair and to the tenants demise were not installed with intumescent strips or cold smoke seals.

Could this be a design feature for the smoke pressurisation system, or have the doors just been missed.

Rocha

[wee brian]

Leaving off the smoke seals is standard practice - If you did install them you wouldnt be able to open the doors.

Intumescent seals are a different issue - do remember that they are not always visible when installed.

[kurnal]

I guess this was an older building. Theres two different things here.

The test for fire doors was changed some years ago and a positive pressure was introduced into the furnace for the test to replicate what happens in a real fire. This made it essential for doors to have fire and smoke seals if they were to pass. So you will not find a modern  fire door set without smoke seals. Where buildings were erected using doors which passed the old test the chances are that their door sets would not pass the new  test but were ok under the old test method. Most fire brigades recommend upgrading all doors to fire and smoke seals. But it really is guesswork as to whether they are as good as a new door set. However common sense says they have got to be better with seals than without.

Pressurisation systems have been around a while and fan sizes were calculated based on leakage past the doors assuming a standard gap of 3mm. Smoke seals will reduce the leakage - that cant be a bad thing . But the pressurisation will be designed to cope without seals. As always it is vital that is seals are retro fitted that they are fitted well with good workmanship so that they do not make the doors stick partially open.

In these situations all doors should open in the direction of escape and I cant see why fitting seals should make it any  more difficult to open.

[Firewolf]

You have to be careful here.

As someone already pointed out above if you stick cold smoke seals on a door entering a pressurised staircase you may have trouble opening it.

Infact I recently dealt with a premises with that very same problem.

Initially on new systems cold smoke seals are fitted - but the whole system has been designed with that in mind - if you stick cold smoke seals into the scheme of an old pressurisation system you wil have problems.

So the answer is simple - old systems no cold smoke sals - newer systems will probably be designed to incorporate smoke seals on staircase fire doors.

[wee brian]

Sorry Kurnal but your a bit off track there mate.

Smoke seals are not always provided on fire doors and would not be necessary to pass a fire resistance test.

Intumescent seals are now usually necessary because of the change in testing to which you refer.

if the door opens in the direction of escape then the pressure (in the stairway) will hold the door closed.

Firewolf - you are probably more up to date than me, I think we are on yet another new design code - A BS EN and I am not familiar with the ins and outs of it.

[kurnal]

Thanks Wee B always happy to stand corrected.
Experience counts for more than anything in my book.

But I dont  really understand why there should be a problem though- any techies out there able to suggest what additional force in newtons  is needed to open a door with seals assuming 50 pascalls of air pressure acting on the surface?

[Martin Burford]

kurnal
Is that not the whole idea of not needing smoke seal facilities as the pressurisation inhibits smoke entering the staircase................or have I got it wrong ?  My old College notes seem to back up my statement.
Conqueror.

[kurnal]

Yes thats exactly right Conqueror. There should be no smoke leakage into the staircase because the positive pressure within the stair will drive the smoke out and away. Tried and tested. Its great. Do you remember standing in Industrial A staircase with the crib well alight and seeing the door open driving the smoke back? Happy days. Or maybe the memories of the bugs made a stronger impression.

The point was whether smoke seals should be provided nowadays when lets face it just about every doorset is tested and approved with them or whether they should still be omitted if the stair is pressurised. In the old days before seals became commonplace the pressurisation system was calculated expecting certain levels of leakage appropriate to a 3mm gap. I dont know, I am happy to be advised on this.

[wee brian]

Having seen these things tested - you really can't open the door!!!!

[Thebeardedyorkshireman]

I am a bit knac.... with metric units but I think a force of 100 Newtons would be required assuming the door was 2Msq.
As the door is hinged down one edge and the force is applied on the other, the calculation would be turning moments about a point which would reduce it to 50 Newtons at the finger plate. This may be complete garbage,but it looked fine when I scribbled down the calc on paper. Any advance?
Dave

[wee brian]

Part of the commisioning procedure is to check the force required to open doors - max 100N springs to mind (too lazy to look it up).

Remember 50pa is the minimum and I think this has to be achived when another door is left open (cant remember)

[Auntie LIn]

Just let me throw my three penn'orth in here.  

a) I agree with Wee B, that it's not necessary for fire doors to the modern standard to have smoke seals - and there are manufacturers testing, passing and selling without them.

b) If you've got a pressurised stair system you must have a 'leaky' doorset if the system is going to work.
You will also need a leaky room, otherwise the pressures will balance out in the two spaces and the smoke will come through.  (Leastways that's what I was always told).

c) The other issue you need to remember is AD M which is causing a huge amount of grief, particularly to door and hardware manufacturers.   I can't remember the exact figures but we're struggling to achieve the AD M figures when you take into account friction from hinges, force of closer etc before you even start on seals.

[kurnal]

I think its 20 newtons in ADM. But show me a fire door where this is possible!
100N on the other hand is very high.
 
Dave the calcs look impressive- you dont sell cars do you?

[wee brian]

Thanks Lin. a good summary of the issue.

The 100n in the pressurisation standard is a fair bit more than the 20n max for disabled access - another one of lifes little complications.

Worth including in a risk assessment if you have people with disabilities in a building with pressurised stairs?

[Thebeardedyorkshireman]

Kurnal
If our industry does not move away from 'cheepest price wins everytime' I may consider selling cars or fruit and veg!
ps  on point( b) If you have equal pressure on both sides of the door then there will be no differential to cause a flow of anything.
You would require a significant increase of smoke pressure to cause flow due to static pressure on t'other side. As pressure increases then static pressure will also increase due to equalibrium of forces. At this point you may get some smoke/air movement through the door gap but the amount would be directly proportional to the volume of the second room.
Dave