Evacuation times

[Bert]

Is there any specific guidance on acceptable evacuation times for buildings?
I’ve always worked on a basis of four minutes for buildings operating under simultaneous evacuation protocols, and three minutes per floor for buildings operating under phased evacuation protocols.
I’m sure that I read this somewhere many years ago but can’t remember where.

[Firewolf]

Hi Bert

Evacuation times are governed by several factors, but as a general rule most guides state that you should reach a place of comparitive safety (i.e; protected route) or ultimate safety within the following times:-

Class A Building 3.0 mins
Class B Building 2.5 mins
Class C Building 2.0 mins

Phased evacuation is more complex however.

Again you must take into account building construction. Obviously in phased evacuation the floor where the fire has originated and the floor above should be evacuated immediately with the other floors evacuated as and when nessecary.

As a general rule I'd tend to apply exactly the same times as those given above for normal evacuation - that is to say that upon hearing the "evacuation alarm" occupants of that floor should reach a place of comparitive safety or ultimate safety in say three minutes (if it were a class A building).

The total evacuation time - ie time it takes for people to evacuate once they are in a protected route is not stated to the best of my knowledge in any fire safety guide.

I would suggest that the total time to evacuate should not exceed anywhere near the time offered by the level of fire resistance.


Hope this helps

[jokar]

Bert,  Firewolf is correct with the times ha has stated but assessment of risk is also a factor.  Vunerable people have an effect on distance and time for evacuation as do extremely fit people.  The times are guidelines and can be up or down dependent on how an assessor have viewed and reviewed the circumstance in any one premises.

[wee brian]

The times you are referring to are design evac times they are not real time.

If you can evacuate a 50 storey building in 2.5 minutes then I am a chinaman! (I am not) (I havent got anything against them iether - its just a turn of phrase)

[Firewolf]

Aha! Wee Brian if you notice I did state that the e times relate to reaching point of comparitive safety not necessarily ultimate safety - so in a high rise block it would be 2.5 mins to reach a protected staircase for example.

But yep will agree that the times should be risk assessed too and Jokar quite rightly pointed out the need to consider the less abled in the evactuation procedure.

[Mike Buckley]

Where do you get these escape times from? I have looked in both the RROs for Offices & Shops and Factories & Warehouses as well as Approved Document B and there are no evacuation times laid down in any of these. They all use travel distances.

As the RRO replaces previous fire legisaltion are these times relevant?

[Firewolf]

Hi Mike

You are right - latest guidance does not talk about time factors.

Therefore as you suggest it does beg the question as to whether these are relevant these days.

I believe that the times originated from a fire at a London Theatre in Victorian times where a fire occurred and everyone was evacuated to the sound of the national anthem - it took the people approx three minutes.(?)

[jokar]

The figures appeared in Post war Building Studies No 29 and are repeated in the Yellow Guide for Entertainments.  There relevance to todays risk based society is whatever you wish it to be.

[kurnal]

The latest guidance does not talk about time factors - but time is more relevant than ever.
But the old days of one size fits all are gone forever. In a simple building I for one will still use the old guidance as a benchmark. If its not possible to reach a place of safety or relative safety within the old time frames I will look more closely at the risk assessment process. Bit like the filter principle in the Manual Handling Regs?

Time is  more important than ever - the available time to evacuate the building before the fire grows or smoke spreads to cut off escape from the building. And the new guidance doesnt specify prescriptive guidance because we know that the available time for evacuation depends not only on the building but what we put in it, and how we manage and maintain it.

[PhilB]

Kurnal has hit the nail on the head. Time to EVAC before time to untenability is what its all about. Historic events such as the Empire Threatre Fire in Edinburgh 1911 are the basis for 2.5 min evac time. For an alert disciplined occupancy longer to EVAC is cleary acceptable. We also need to consider ceiling heights, wall linings etc. etc.....hence the need for competent assessors and auditors.

[Mr. P]

What is the terminal velocity for a china man jumping off the 50th storey (Wee B's commnet on evac times)?

If he jumped with a lesser velocity, could he survive?

Come to think of it, what is the EN for the Light er side of comedy?

Appologies on a postage stamp...

[wee brian]

It depends if he has his arms out or not but its about 120mph.

Of course it's not the speed that's terminal but the collision with the ground!

This is, actually, quite an important issue for building managers. They are expected to carry out fire drills from time to time but there is no "usefull" guidelines for them to establish how long it should take.

[Mike Buckley]

I agree about the relevance to building managers. Time is a definite and understandable measure for evacuation of a building and official guidelines would help.

The time from when the alarm sounds to when everyone has reached a place of safety (ultimate or comparative) must give a good measure of the adequacy of the escape routes. It will also save a lot of arguement, it is difficult to argue with a stopwatch!

[Mr. P]

When we talk of protected routes as an interim place of safety, what does anyone consider on things like cable conduit/ducting? There is some pretty large stuff used now particularly where asthetics are concerned.  Where it passes through walls etc.  does anyone actually pull it apart to check fire/smoke stopping?  Mainly I am thinking of the large plastic squarish stuff.