Smoke shaft in 1960's tower block

[Drew]

Just before we all settle into the weekend I would like to run this one by the forum-


A 24 storey tower block constructed in the late 1960's is to be fully refurbished next year.The building consists of a single staircase with doors at each level leading into a lobby with another door separating the lobby from the 4 flats.There are two lifts (not fire fighting) and every other floor has a dry riser outlet point.
The tenants are being rehoused at present but there are 23 flats out of 96 that are still occupied spread throughout the building. Some of these flats are privately owned so my inital plan of moving everyone down to the lower floors is a non starter. The floors 4-14 are empty and will not be reused now.

There is a smoke shaft with manually operated steel doors which has a large fan housing in the roof space and a chimmney section out to the roof. First question is what operates the fans once the doors are opened? (I've not seen one of these before!) The fans in the housing no longer work and the drive belts are hanging off.
Second question-My initial thoughts were either to remove the fans and perminantly open up the smokeshaft doors on each level / or only the levels where the flats are occupied, so therefore any smoke in the building will be drawn out via the shaft. Would this be acceptable in your opinions or as the fans are part of the fire fighting equipment they must be maintained and the fans/motors replaced?

Also would it be deemed acceptable for floors 4-14 to be sealed at the staircase entry level with the appropriate fire resiting materials and the lift to these floors disabled?

I look forward to your comments

many thanks in advance

Drew

[spanner]

In my opinion, if the original design was to have a fan at the top of the shaft then it will be required to provide the correct amount of extract. So I would suggest that it requires maintenance. As for operating the motor, I take it there is a control unit for the fan somewhere. It could either be operated by a fireman’s key switch or the manual doors may have switches fitted to operate the fan when door is opened.

I know it was a slightly more modern building (2004) but what was fitted there was a smoke shaft with doors on each level, but each door had a door opening unit which was held closed using a magnetic lock connected to the fire system. In the event of a fire on the floor, the door would open smoke would be extracted by a vacuum caused by outside air passing over the top of the shaft.

Where about are the premises? PM me.

[jayjay]

I would be very carfull of considering natutral ventilation as apposed to the installed fan extraction.

The effects of the prevailing winds can have considerable impact on natural ventilation and a detailed study may be required.

As with all ventilation the need for adequate inlet air must be assessed.

I can not put my hands on it at the moment but I am sure there is a BRE deocument on smoke ventilation in high rise flats.

[rn976]

Could be BRE 390 "wind around tall buildings "?

regards 

[kurnal]

What size is the shaft? Is it the recommended 1.4 sq m for natural ventilation?
How far above the surrounding roof and the top most ceiling is the outlet of the shaft?
What arrangements would you put in place on the floors to keep the smoke in the shaft and prevent it spilling out into floors above the fire in varying weather conditions and temperatures? You would need Automatic Opening vents.

It sounds to me like the best course of action may be to reinstate the original equipment and without it the original fire strategy for the building is fatally flawed.

[CivvyFSO]

Smoke shafts protecting fire fighting shafts: their performance and design. 2002

Project Report 79204

?

This is where BRE looked into the effectiveness of natural shafts as opposed to openable windows, and it is where the BRE shaft comes from.

[CivvyFSO]

perminantly open up the smokeshaft doors on each level / or only the levels where the flats are occupied, so therefore any smoke in the building will be drawn out via the shaft.

If this is what I think you mean, then this would mean that any smoke/heat entering the lobby can make it into the lobby on any of the floors above it. This would not be good.

[Drew]

Thanks for your responses so far- It seems that the obvious solution is that the fans are there for a very good reason and therefore should be maintained . would it therefore be deemed that the fire service would be the ones who would be operating the doors to vent smoke on the floor of the fire as the tenants would probably 'stay put'. I cound not see a micoswitch on the doors or any firemans switch but I am going back to the site next week to inspect further.

[spanner]

I would expect that the fire service would open the doors for the smoke shaft. Hopefully when you return to site there should be a control panel for the fans, fingers crossed you trace what activates the fans. Good luck.

[Drew]

An update on the above mentioned posts is that there is indeed a firemans drop key switch in the ground floor lobby - this was dicovered after much searching behind a notice board! The centrifugal fans will now be tested and put back in use,

 Thanks to everyone's input on this matter

Drew

[wee brian]

This raises an interesting point.

Why reinstate the 1960s design. It might well be a nonsense. There's been a lot of development since then and a better solution may be available.

This is obviousely a complex example but consider a simple one.

You do an FRA on a 1960s block that is designed using smoke dispersal. The long corridor has a permanent vent at each end. However, some bright spark has blocked the vents up (cos it's chilly).

Do you

a) get the vents opened up, so the original design is restored; or

b) find a solution that might actually work

c) install an all singing all dancing mechanical system that costs billions

d) stick some more fire doors in the corridor and stick with good old containment

answers on a postcard....

[kurnal]

I am with you Wee Brian but the bottom line is that very often the easiest thing to do is to re-instate the old vents provided for the dispersal of smoke.

Yes containment may be an option especially on some of those with extended corridors to the full 60m but there a limit to the numbers of doors you can put in a CP3 dead end corridor in lieu of the permanent vent when someones filled it in with a piece of double glazing and pvc.

Can we say that the old smoke dispersal methods dont work? If we go down that path we are saying that here are thousands of tower blocks that will not function as the designer and authorities thought they would.  If we are saying that then either they  all need fixing or if there isn't really a problem then none of them do.

Of course the original posting was over mechanical vents to the staircase lobby and so much more significant than the horizontal component in the larger blocks or the short dead end sections of corridor.

[wee brian]

ICan we say that the old smoke dispersal methods dont work? If we go down that path we are saying that here are thousands of tower blocks that will not function as the designer and authorities thought they would.  If we are saying that then either they  all need fixing or if there isn't really a problem then none of them do.

My point exactly. When FRS tested dispersal, full scale, they concluded you would need wind speeds in excess of Mach 2! or thereabouts.  It seems daft to reinstate something that doesnt work. But what do you do instead.

I've no idea, just wondered what other thought.

[Tom Sutton]

Surely that was about natural ventilation this is mechanical ventilation of a sort.

[wee brian]

I'm being hypothetical. Although how do we know what design criteria were used for a mech system designed in the 1960s?