Evacuation times

[Ashley Wood]

My client is installing a new 2 stage alarm system in his 4 floor building. There will be close on 800 persons in the building. He has asked me how long can people remain at their desks when the alarm is sounding intermittent i.e standby, before the system switches to full evacuate tone? This is to enable an orderly evacuation and to prevent congestion on the stairs. Am I correct in saying if the fire was on the 4th floor, for example, that floor and the one below would immediately go into full evacuation mode and the remaining floors would go on standby? If it was the 1st floor, would the ground and 2nd floor go on full evacuation and the others on standby? The escape stairs are all 1 hour rated.

[Pip]

My client is installing a new 2 stage alarm system in his 4 floor building. There will be close on 800 persons in the building. He has asked me how long can people remain at their desks when the alarm is sounding intermittent i.e standby, before the system switches to full evacuate tone? This is to enable an orderly evacuation and to prevent congestion on the stairs. Am I correct in saying if the fire was on the 4th floor, for example, that floor and the one below would immediately go into full evacuation mode and the remaining floors would go on standby? If it was the 1st floor, would the ground and 2nd floor go on full evacuation and the others on standby? The escape stairs are all 1 hour rated.

Quuick reply-may not be 100%:
a)max  recommended time 6 minutes
b)no, just the 4th floor (phased evac-fire floor and one above plus disabled  persons on all floors
c) just the first and second.
d)also stairs need to have lobby's/protected corridoor approach for phased evacuation, each floor needs to be a compartment floor(there is a fair chance in that size builsing they may not be.You will also need to calculate your stair capacity,although unless numbers are increasing,they may be okay as existing

[wee brian]

Fair summary - I'll go with that. Although "two stage" isnt a standard term. Phased evac usually involves evacuation progressively one or two floors at a time.

"Two Stage" is a term often used to describe a system where one floor goes on detection then the rest of the building evacuates simultaneousely.

[Ashley Wood]

Thank you. Where does it state 6 mins?

[wee brian]

BS 5839 Part 1 2002 -  Clause 19.2.2 e

This is the max investigation time recommended before the system goes into evacuate.

[AFD]

Phased evacuation is usually used in a building that was designed for that strategy, as in pips post above. The 6 minute delay on evacuation is usually used in buildings with a staff alarm system.  I think there are a few questions to ask in this case before going down either route !

[wee brian]

Yes - i think there are a few crossed wires here.

6 mins investigation - thats time of detection to the alarm going off.

After that you will iether evacuate the whole building or (if its a phased evac building) start a controlled evac of the building starting with those most a risk (one or two floors at a time).

The time between phases is not fixed and is usually decided by whoever is managing the evacuation (starts with the security staff and finishes with the fire brigade)

[saddlers]

Pip,
ADB2006 now recommends only those with limited mobility and the fire floor as the first phase, due to the issue of people being unable to escape from the fire storey, due to escapees from the above storey clogging up the enclosure (I think!!).

I know this is different from advice in other standards, but seems to be the latest guidance.

[Pip]

Pip,
ADB2006 now recommends only those with limited mobility and the fire floor as the first phase, due to the issue of people being unable to escape from the fire storey, due to escapees from the above storey clogging up the enclosure (I think!!).

I know this is different from advice in other standards, but seems to be the latest guidance.

yes-good spot-a removal of a few words from the previous ADB. Now we need a debate on which should be used-the new B. regs or the BS!

[Ashley Wood]

Thanks chaps for your help so far. Its good to know that I am not the only one who gets confused!