Occupancy & exit widths

[Mar62]

Would like to ask opinions. I am currently working out occupancy figures for the 10th floor of a building in London (and struggling a bit due to the layout)!

1.  As far as I know, generally guidance says you should exclude the widest exit. One escape route from this floor goes through part of a kitchen (not brilliant). I would like to exclude this route instead as in my opinion this is the highest risk area. Is this acceptable?

2.  There are three routes from this floor. The kitchen exit, a similar exit on the other side of the floor and a central pressurised staircase. Both exits (not the central one) exit to open air, then along a suitable barriered walkway (trav distance 39m) to an entrance to an enclosed escape staircase. Would you say that the "place of safety" can be considered once exited from the building onto the walkway or would it be once in the enclosed staircase?

I would very much appreciate some advice from someone more experienced in this than me! Have done a few of these before but this seems to be a bit more complicated!!

[jokar]

At this level, I would assume that the doors to the staircases are lobbied and therefore there is no need to discount any of them. ( See vertical escape in B1 to ADB.  Not a good idea to go from a low risk area to a high risk area to escape.  Again in B1, Kitchen areas need a separate escape route.

If you have not got a copy of ADB then you can download it free form CLG.

A relative place of safety is ok if the whole of the route is FR.  The external route should be protected along its length by FR construction and non openable windows.  Also in B1.

I am quoting ADB as this building would have been built to that standard.

[Tom Sutton]

It sounds like the council tenement blocks of the 1960's which used a concept known as smoke dispersal favoured by council architects, not smoke containment favoured by the fire brigades. This concept considered once you were on the balcony you were in a place of comparative safety because it could not get smoke logged and providing you had alternative escape from the balcony. If it was travel in one direction all the doors and windows, opening onto the balcony had to be half hour.

[kurnal]

What is the building used for and when was it built?

[CivvyFSO]

At this level, I would assume that the doors to the staircases are lobbied and therefore there is no need to discount any of them.

So very wrong. You still discount on horizontal rules.

Imagine you are on the floor where the fire is. Does the lobby stop that exit being unavailable to you?

The lobby just means that you do not have to discount the staircase.

[CivvyFSO]

1.  As far as I know, generally guidance says you should exclude the widest exit. One escape route from this floor goes through part of a kitchen (not brilliant). I would like to exclude this route instead as in my opinion this is the highest risk area. Is this acceptable?

A simple no. You should always discount the widest. Regardless of the likelihood of fire, the worst case scenario when dealing with exit width is losing the widest exit. Now if you are saying that the kitchen is dangerous and a fire in there may rapidly get out of hand then I suggest you look at measures to minimise that risk.

2.  There are three routes from this floor. The kitchen exit, a similar exit on the other side of the floor and a central pressurised staircase. Both exits (not the central one) exit to open air, then along a suitable barriered walkway (trav distance 39m) to an entrance to an enclosed escape staircase. Would you say that the "place of safety" can be considered once exited from the building onto the walkway or would it be once in the enclosed staircase?

Remember you only need to measure travel distance to the closest exit. On this floor what is the furthest you can get away from the central pressurised stair?

[CivvyFSO]

Again in B1, Kitchen areas need a separate escape route.

Where does it say that in B1? I agree that we shouldn't be sending people through a kitchen, but to my knowledge there is no specific reference in ADB that says we can't.

[jokar]

Civvy, see clause 3.15, table 4 and Clause 4.20.

[Mar62]

Thanks all for your replys. The use of the building is multi tenanted office use. The 10th floor is used as a function area only. I believe it was originally built late 1800's early 1900's but has been massively refurbished. This is the same building I asked a while ago about hoses in offices which was massively debated! Central pressurised staircase (annual test recently done) serves all levels. The rest of the levels the staircase is enclosed by metal framed fire resistant glazing. The top of the staircase at 10th floor leads to a large landing with six lifts. From here you can go left or right to each side of the building to small and large function areas, rooms etc. From each of these sides of the building you can gain access to the final exits. The external walkway is indeed very external - open to the elements (and a great view!) I

CIVVYFSO: Thanks, I was looking at discounting the kitchen exit due to the highest risk scenario. Proper measures have been taken there, ANSUL system etc. All kitchen staff have been fire trained. The plans of the building are in the office and I'm not! I will get a measurement tomorrow for the furthest distance from the pressurised staircase.

So what is the way forward with this. Do I just discount the central pressurised staircase from calculations?

Like i said earlier, I have done some simpler ones of these before, but this is a bit more complicated.

[CivvyFSO]

Jokar

3.15 is referring to escape from restaurants etc, not specifically kitchens. But if functions are held here then it is quite a valid point if people are drinking. Maybe I misunderstood your post that seemed to say that kitchens need a seperate escape route. (I hold my hands up at the reference to escape routes not passing through a kitchen in 3.15b though

4.20 is referring to discounting stairs. As I said, you still discount the door from horizontal rules as it could be blocked by a fire regardless of any lobby/pressurisation system that is designed to protect the stair.

[CivvyFSO]

Martin

I would like to suggest completely removing the exit route from through the kitchen. There is nothing that particularly says you have to, but the idea of people escaping through a room with hot fat, greasy floors, knives etc is not ideal. At the end of the day though, this is what risk assessments are all about, this may turn into more of a H&S issue, but the RRO does also state " the event of danger, it must be possible for persons to evacuate the premises as quickly and as safely as possible"

Some management regime/procedures where kitchen staff quickly attempt to make the kitchen safe to pass through (i.e. pans moved away from the edge etc)  in the event of a fire may make the route a bit safer.

If you can make the kitchen passable then just simply discount the largest exit on the floor as ADB suggests.

[Mr. P]

CivvyFSO, you beat me to that re kitchen.  I would discount kitchen and assess the capacity and exits and come up with new numbers of person limits within the function area.  Probably it would not affect their max numbers too much.

[Mar62]

Thanks again for your replys guys.

CivvyFSO: As requested, the furthest away you can get from the central pressurised staircase is approx 32m.

Although when using the kitchen route you do not pass directly through the cooking area you do pass through the kitchen "demise" as it were. When i visited there were food trolleys reducing the width, cloths hung over the crash bar, bag containing overalls in front of the doors etc - you get the picture! These issues are being dealt with separately. This is part of the reason I wanted to discount this route. The reason this has all come about is that somewhere (when under FPA) the FRS quoted max figure of 145, but its not on F cert. Recently they had a function and the building manager found out they had nearly 500 up there!! Yes he blew his top! They are going to be applying for a license as they havent had one before? So obviously the FRS will be involved in that anyway wont they?
I can scan in a plan of the floor tomorrow morning and PM it to you if you want to take further look? Unfortunately my Co' doesnt have that technology!

So to recap on comments. Discount the kitchen route. Assess the floor area for numbers of persons. Then work out the number of people that can safely use the two remaining routes - the press' staircase and the external route.

[CivvyFSO]

Since 32m is the furthest you can get away from the central staircase then I wouldn't worry too much about the other travel distances/routes to protected stairs. There is the 45 degree rule to consider though.

I didn't make myself too clear above; What I was suggesting is completely remove the kitchen route, THEN discount the widest remaining exit, then look at your occupancy figure you can fit through the remaining exit width. Unfortunately it seems you would be down to one door, so the occupancy would not be particularly good. Especially if the place can actually hold 500.

From the sounds of it the kitchen could be made passable, but this would be down to the ongoing future management of it. If this is possible, then another whole exit door would make a big impact on the occupancy figure. If you are doing a risk assessment here then I would document any measures required in the kitchen very well and make the RP well aware of the potential repercussions should they fail to maintain that standard.

FRS's involvement with licensing applications may be minimal depending on the FRS involved. The consultation could simply be "Do a risk assessment and act on the findings, CLG guidance can be found at.... blah blah blah..."

[Mar62]

Ah ok Civvy - misread yr comment re kitchen! Thanks for all of that. As you suggest, the kitchen route COULD be made passable with better management. Time to get the calculator out then!!

Thanks