Smoke control in common corridoors (flats)

[xan]

I am having a daft moment -I understand that the main reason for AOV in corridoors/lobbies is to protect the staircase,but for some reason I also thought it was also to give protection to the route from the flat door to the staircase,but that doesn't fit according to ADB diagram 8 (b),so is the only reason to protect the lobby,or am I missing something?What is concerning me is that,you can't 'dash' across more than 4.5m through an unventilated lobby in a single staircase building (diagram 9a),but seems ok to be able to go through an unventilated corridoor(up to 30m in length) and in theory,may have to 'dash' up to 15m through smoke to get to the vented lobby.

[kurnal]

The changes to ADB were based on the following report (extracts only in this link)

http://www.bre.co.uk/filelibrary/pdf/rpts/partb/Smoke_Ventilation.pdf

The report acknowledges what you say about smokelogging of unventilated corridors. Not all the findings of the BRE report appear to have been incorporated in the updated ADB.

If there is a choice of routes is there a need for a "Dash" by residents? Would the ventilated lobby help maintain access to the scene by firefighters who could then assist the evacuation of occupiers if necessary?

[Tom Sutton]

How about this,   IMO the ventilated lobby is to protect the staircase by providing inlet air so when the door to the staircase is opened it allows the smoke to rise to the head of the staircase and be expelled consequently keeping the staircase clear. Before the stair case door is opened the vent on the fire floor will act as an outlet reducing the speed of build up of smoke thus increasing the travel distance. Over to you mister starter?

[kurnal]

I disagree Tom, my understanding is that the ventilated lobby is to ensure that the pressure in the lobby is negative compared to that in the stair thus keeping the staircase clear. Without a ventilated lobby the pressure in the lobby is likely to be higher than int he stair thus forcing smoke into the staircase.

[Tom Sutton]

I agree and bow to your superior knowledge K as there is most likely to be an inlet vent at the base of the staircase to create the stack effect. But what about the second statement regarding the travel distance of 4.5m if there is no ventilation and 7.5 if there is. I see them as accepted travel distances for one way travel and the 30m for alternative MOE. The difference between 4.5 and 7.5 being as I suggested in the second statement.

[xan]

The changes to ADB were based on the following report (extracts only in this link)

http://www.bre.co.uk/filelibrary/pdf/rpts/partb/Smoke_Ventilation.pdf

The report acknowledges what you say about smokelogging of unventilated corridors. Not all the findings of the BRE report appear to have been incorporated in the updated ADB.

If there is a choice of routes is there a need for a "Dash" by residents? Would the ventilated lobby help maintain access to the scene by firefighters who could then assist the evacuation of occupiers if necessary?

Yes,I don't disagree-ADB does only say that the ventilation is to maintain the stairs free of smoke,and the BRE report suggests that conditions in the lobby/corridoor may not be tenable-therefore that raises the possibility of FF evacuating residents from non fire affected flats on the fire floor through those conditions-which raises more questions!


it could be that the 'dash to safety' is a red herring on my part -but It is mentioned in BRE report (BD2410-annexe A) where it  is discussing the maintenance of conditions suitable for  MOE,and suggests that a 'visibility distance' of up to 10m may be reasonable,but usually only when occupants are familiar with their surroundings or where evacuation is in the context of 'Dash to safety'.In the concluding remarks it suggests that,where no there is no smoke ventilation measures*,there is early evacuation of the fire floor-*but it is not clear whether this is referring to just the 'corridoor', or the building as a whole.I can't quite understand the reasoning on why you can only go up to 4.5m through a smokey unventilated lobby,but 15m or more in a similar smoke filled corridoor (or is there some argument that there is an assumption that the amount of smoke released from the fire compartment is the same,and the corridoor (volume) being much bigger,will therefore have more diluted smoke and therefore less of a hazard?) ???Also I note that you can travel up to 7.5m in an unventilated corridoor where there is only single direction,which may support that previous argument?

[William 29]

In my view the ventilation of the stair is also there to reduce the heat and smoke that may penetrate the staircase or landing and thereby helping to reduce the attack on other flats fire doors plus make conditions in the staircase more tenable for persons choosing to escape and for fire fighters to gain access and make an attack on the fire.

[Midland Retty]

Diagram 8 is very confusing.

Compare 8a with 8b and then go andlook at diagram 7 - they all contradict one another!

[xan]

Diagram 8 is very confusing.

Compare 8a with 8b and then go andlook at diagram 7 - they all contradict one another!

please divulge-they all show ventilated corridoor or lobby approach to the stairs.

[CivvyFSO]

I also disagree about any contradiction. They are solutions for two different scenarios, a single stair, and more than one stair. The level of protection offered to the stairs is essentially the same, with the main difference being the unvented stretch of corridor that is being discussed.

There is a slightly different door layout adjacent to the stair, (2 doors immediately next to the stair) in the single stair 7.5 version) but when you consider that in the solution with more than one stair, the persons in the longer corridor have access to a different stair, the door provision is suitable. The persons in the dead end have their stair protected from a fire in the unvented section, and the persons in the unvented section have the choice of two, so they can afford to lose access to one of them.

[wee brian]

The ADB 2006 approach is to generate a pressure difference so that smoke tends not to flow into the stair. It wasnt really viable to clear the smoke from the corridor, so a travel distance/containment approach was adopted. Essentially, The distances used are unchanged as the research only looked at smoke control.

I cant see any contradictions either.

[Tom Sutton]

MF I also do you see a contradiction. The way I see it they are separate issues, protecting the staircase is one issue and travel distance the other.

I think they considered there was a need to protect staircases using a ventilated lobby in blocks of flats with the exception of small single stair building which didn’t require protecting providing you reduced the travel distance to 4.5m. If however if you did provide a ventilated lobby you could extend the TD to 7.5.

They then considered what the travel distance should be and decided a travel distance of 7.5m for escape in one direction and 30m for escape in more than one direction with or without ventilation. I do accept there are additional benefits when ventilation is provided, which are useful but not the principle aim.

As to where they get the TD,s from that has been discussed many times on this forum.

[Midland Retty]

Yes apologies it's me - I didn't study the diagrams properly. Dunce cap for me!

If you look at Diagram 8b the 30 metre unventilated corridor is segregated by three sets of doors to protect the staircases.

In 8a you have only have two sets of doors protecting the staircases in this is why the corridor is shown as hatched and needs to be ventilated.

That is for the protection of the staircase rather than residents. Where you have two or more directions of travel ADB permits a greater corridor length because in theory you should be able to turn your back on fire and safely reach an alternative escape route.

But I agree with you Tom that in the real world sometimes travel distances seem a little arbitrary