BS9999 and exit widths again

[CivvyFSO]

If it is of any consolation, one of the people who helped with the 9999 document also worked on the part of PD7974 that came up with "walking time = unimpeded walking speed x distance" So basically the slower you walk, the quicker you get there. I don't expect miracles from these people.

[Hightower]

Chaps (esses)

Having read BS9999 and DCLG guides about exit widths I am trying to apply the information to older buildings and the real world - so to speak.

My query is that the DCLG guides state that exit widths should be no less than 750mm wide and BS9999 says 800mm.  OK, great, so modern buildings are likely to be somewhere in the ball park of these dimenisons and so the guidance is easy to apply, but what about older buildings that have doors as narrow as 600mm, is there any guidance out there that states what capacity ratios are recommended for these?
Please don't say widen the door because in most cases this is not practicable.  I know risk assessment will come into it, but are there any values that can be applied for these minimal door widths?

[Davo]

Hightower

Logic would say interpolate down
However, Doc B p 37 says you can't do this.....


davo

ps some clue of expected numbers would help

[CivvyFSO]

Davo, there is no point interpolating down to be honest. The reason ADB states that there should be no interpolating is covering the difference beween the 1050 mm door and the door widths below that. As mentioned before, until the door is capable of taking 2 people side by side there is almost no difference in how many people will flow through it.

1 Minimum exit width has historically been approx 525mm. (Based on 21" IIRC, some guidance rounded it down to 525, some essentially rounded up to 550) Therefore I would say that, depending on the occupancy, a door of 600 is still simply single file walking, at a flow of 40 persons per minute, assuming the good ol' 2.5min evac you are still looking at 100 people through the door. (Unless it is a door out of a club for 'the unusually hefty' or something) If it is the only escape route then I would usually default to the standard 60 regardless of width. It is, as you say, one for the risk assessment simply due to the deviation from standard guidance. An impromptu fire drill would prove the safety (or otherwise) quite easily.

[nearlythere]

It is, as you say, one for the risk assessment simply due to the deviation from standard guidance.

It must have complied with a standard at one time. Generally, humans have not changed in size within the last 30 - 40 years, except those propping up the banter bar, and most people appreciate it can be physically impossible to apply new door width standards to existing buildings particularily when for thousands of years the standard size was 760ish mm.