Fire Loading on Balconys within Atrium

[Fairway123]

Hi All,

One of our premises has a very large atrium running down the middle of it with a office wings on either side. At upper levels there are bridges that connect the 2 wings on each floor. The staff would like to hold an event and use the bridges for serving drinks etc, they've also enquired about putting some plants on the bridges to improve the d?cor.

I've reviewed the HTM guidance which mentions loading on balconies, but doesn't provide guidance on safe fire load levels. I'm aware of the requirements for fire loads on the base - but I can't find any guidance as to assessing how to advise on the safe use in terms of fire and the impact on the atriums performance during a fire?

The fire strategy for the building states that the bridges aren't included in calculations for egress, and we would be able to comfortably maintain a safe walkway to allow egress to either wing in the event of an evacuation.

Can anyone advise me on how best to approach this problem? Is it a no no, or with sensible precautions can some fire load be allowed on the bridges?

Thanks

Colin

[Fishy]

I hate working on Atrium designs.  Any form of construction that generates 22 different diagrams showing 'Exemplar' configurations in Annex C of BS 9999 is apt to make my head swim!

I must confess that I don't know the HTMs but if you can get hold of BS 9999 then have a look at Annex B & C & see whether it gives you a clue as to your particular configuration.  In concept, if you've got a configuration that allows an open atrium (which I guess it must be, if it has bridges), and which allows either uncontrolled or limited fire load on the atrium base then intuitively I can't see what difference the fact that some of the fire load is on the bridges would cause, provided that the total fire load is less than that in B.8.1 of the standard?  Big caveat, of course, is that BS 9999 might not be entirely appropriate for Category 'D' occupancies, but it might provide some guidance?

[Phoenix]

Hi Colin,

You should have a fire risk assessment carried out for the event. 

The means of escape may be fine but there may be other issues.  If you're using the HTM documents then I guess it's a healthcare building.  This will have it's own issues and BS9999 may not give a full answer.

[Fairway123]

Thanks for the responses, Fishy - I thought about applying the guidance about a controlled fire load but was after something specific for the balconies. I can't see how there will be too much difference in the fire load at the base or higher up. There is extract at the top of the atrium. Thanks for this.

Phoenix - Thanks will cover off the event with a risk assessment, I think I can apply the BS9999 guidance in a fairly straightforward fashion. I used the HTM guidance as it was the only guidance that included anything specific to balconies within atria, the building itself is an office block.

[col10]

Use ADB if you can.  It is much simpler.  ADB sends you off to atrium guidance if compartment floors are penetrated, but if they are not compartment floors then you may be able to use ADB and follow the ADB guidance for open spatial planning.

[Jim Scott]

I have to agree with Phoenix on this one.

Atriums can be complex beasts and there are clearly limitations to the advice that can be provided without looking at the premises.

[Phoenix]

Colin,

A couple of points. 

If you are the fire risk assessor but are not sure of how the atrium is meant to work then I would seek specialist advice. 
As Colin Cox has stated, you could use ADB, and it sounds from the information you provide in the original post that this could be appropriate, or
You might be able to use ADB but adapt it using the standard methodology for accepting escape routes within 4.5m of a void edge, or
You could follow the flow charts in BS9999 (do not use the HTM guidance), or
You could make it up as you go along use fire engineering first principles.

You indicate that you know that the means of escape is ok without any reliance on the bridges so all you have to do is keep routes from the bridges to the office accommodation clear in both directions. 

You have the fire startegy for the building and if this states that a fire loading is acceptable in the base of the atrium then you can be pretty confident that a fire loading on one of the bridges will also be acceptable provided that it is a reasonably small fire loading (see further comments below).

The building might have been designed not to have fire or smoke in the atrium in which case there might be inadequate detection in the atrium, the HVAC system might not shut down quickly or extensively enough to prevent smoke being carried into all parts of the building, the atrium might smoke log (the ventilation in there is probably for smoke clearance only, is probably at high level only and is probably no more than about 10% of the floor area of the base of the atrium and so will not be effective at maintaining any clear layer below the smoke layer) which could lead to smoke spread through the building and which could produce a disproportionate amount of smoke damage for even a relatively small fire. 

Is the building designed for simultaneous evacuation?  It might have phased evacuation if the atrium is enclosed in FR.  If it is phased, when is the atrium evacuated?  First phase?  Or does it vary from level to level?

If the atrium is surrounded by at least smoke retarding construction then you can be more confident about the means of escape.

Is fire fighting access suitable for fires on the bridges in the atrium?

Sometimes, in atria, it is assumed that the elements of structure and construction in and around the atrium (e.g. steel members, glass roofs, glass walls) will be subjected to smoke at a lowered temperature because of the fact that any fire will be well below those elements of structutre and construction, and smoke will have cooled by the time it ascends to those elements.  You may be stepping outside of this safety net if you allow fire loads at higher levels in the atrium.  You might be able to check this from the fire strategy.

You will have to do a specific FRA for the event if the building is not being used in a way that fits into the general pattern of use which has been assumed under the prevailing FRA.  Also, you might want to consider some general health and safety points.  For example, we don't like display stands next to voids in shopping malls as things can drop off them over the edge.  Perhaps a H&S RA is also required.  Neither of these RAs need be prohibitively time consuming or restrictive.

[Fairway123]

Hi All,

Thanks very much for the comments. I am H&S by trade (if you can call it a trade), but find myself being drawn towards fire safety. Knowing my limits, I often defer to a fire consultant - but if I'm to learn (in time) , I feel it best to try to and get my head around the issues first.

This is a great resource and thanks so again for the help.

Fairway123

[wee brian]

Withe the Atrium you need to understand how its being treated in the strategy - partuclalry if there's a smoke control system.

I think there are maybe three potential situations

1 - theres some sort of smoke control system in place - in which case you need to see the design and see what it says about fire loading on the baclonies.

2 - there's no smoke control system on the basis of theire being no fire loading in the atrium - if this is the case then you'd need to rethink the entire strategy.

3 - there's no smoke control system because it just doesn't need one. In which case the only issues are normal means of escape issues.

[colin todd]

Brian, are some of these spellings typos or some strange lingo you picked up in your American holiday, which I, the British taxpayer helped fund.

[wee brian]

Drunk on the joy of being back in dear old England.

I'm grateful to you and all the other taxpayers, whithout whom I would have to get a proper job.