Benchmark Guidance

[jokar]

If you can travel 18 metres in a dead end condition, regardless of your physical condition, with a 2 metre ceiling height, then if the ceiling height is 3 mteres then you can add a third to the travel distance and have a 27 metre dead end condition surely?  If I want to build a building and use 10 square metres as an occupancy factor for this office then I can, surely?  If I want 2 access rooms to my inner room as I only use the inner room occasionally and then someone is always in the outer access room then I can, surely?  If I run a Residential Care home for older residents and want a defend in place strategy where there is no audible alarm and only a staff alarm then I can surely?  Any comments?

[wee brian]

I think you're fishing, but why not.


Dead ends

Dead ends are are exception to the simple rule that one should be able to walk away from a fire.

Limiting the distance covers two factors - 1 - escape time and 2 awareness of the fire.

given that I have to travel towards the fire in order to esape I will need to do this efore the fire has got so big that I can't - This has little to do with ceiling height other than raising the ceiling may reduce the heat feedback from the smoke layer. If there is a relationship with ceiling height it wont be as simple as you suggest.

Factor No 2 is one we tend to forget - if I can actually see the fire that is threatening my escape route I can make a judgement about the hazard that it presents. I may decide to ignore fire engineering practice and move a bit qucker than 2m/sec! Fire alarms are all well and good but until I see smoke or my eybrows curling I will probably think its a false alarm. The further away from the fire I am the less likely I am to see it or appreciate what's happening. ceiling height wont help me here iether.

Having said all of this the 18m figure is an entirely abitrary number selected by a bunch of people sitting in a committee room (or maybe a pub) and so we shouldn't get too excited about a couple of metres here and there.

Inner rooms

Yes seams fair to me - need to think about the effectiveness of vision panels (put in a sensible place) or afd so that occupants of the inner inner room are aware (there it is again)

Res Care

Yes I dont see why not, but you will need to think the whole thing through from first principles.

[Ashley Wood]

Well put Wee Brian. I support what you have said.

[Tom Sutton]

jokar I will ignore your wind up, except, surely if an inner room has two access rooms it has alternative MOE then it is not an inner room.

[jokar]

No wind up, just a thread, to follow on from a number that have occurred over the last months about benchmark standards which some think are religious.  Comments on all will be helpful to us all.  The 2 access room scenario is that used in B1 where I suppose most FSO's would say 2 inner rooms and 1 access room.

[Big A]

Does DD 9999 include 'dead-ends'?

[jokar]

Yes, Sections 8.7.3.1 and 8.7.3.3.

[kurnal]

Jokar
No problem with any of these provided you can show that persons are not placed at risk as a result. And what is an acceptable level of risk? Thats where the benchmark comes in.
In some of your examples a qualitative analysis would be appropriate, in other cases a quantitative analysis would be more appropriate.   And maybe a mixture of the two in the dead end example.

Spent the day in a vey confined workplace very overcrowded density factors 0.5m per person with a ceiling height of 1.5 metres, doors locked by an electronic devices with no over ride, full of foamed plastics and with a plastic vessel  containing 55 litres of highly flammable liquid. But didn't feel uneasy about it.

[Chris Houston]

If you can travel 18 metres in a dead end condition, regardless of your physical condition, with a 2 metre ceiling height, then if the ceiling height is 3 mteres then you can add a third to the travel distance

Even assuming you mean "in a fire" I can't follow your logic that a person's ability to move over distances is directly connected to ceiling height.  Can you back this up with any research, facts or hypothesis?

I would suggest that our ability to move any specific distance (in a fire or otherwise) is goverened by many, many factors.

[PhilB]

Of course it is Chris but I am very surprised that you cannot see why ceiling height may be of considerable importance.

[dave bev]

unless of course they are very tall people walking upright to escape!

dave bev

[Chris Houston]

Of course it is Chris but I am very surprised that you cannot see why ceiling height may be of considerable importance.

Well, I'm more of a property protection person than a life safety, so don't be too surprised if my knowledge of this is issue is poorer than most.  I'm assuming that a high ceiling would enable smoke and gas to collect above the occupants, but surely you can't just keep raising the ceiling and escape distance otherwise we would have very high ceilings and very long escape distances....there must be more to it than that?

[jokar]

There is, it is all about people.  The same scenario could occur 27 metres and 3 metre ceining height and an FRA could reduce it due to the risk to the occupants.  Vunerable persons with disabilities or mothers/father with pushchairs.  There is also the missing bit about the width of the corridor.  This whole thread and lots of others discuss benchmark guidance in isolated bits,  What is needed of course, is joined up thinking, and all or none could/would fit.  That is the main difficulty with a fire certificate plan drawing, it assumes so much whereas an FRA is adaptable.  ( I know competent professional peope undertake joined up fire safety thinking and perhaps non professionals do not)