occupancy levels in churches

[alfi]

Hi there,

how would occupancy levels be calulated in churches?, would you base it on table C1?

[John Webb]

The maximum capacity can be calculated from ADB. But if you are working on a Fire Risk Assessment then it would be practicable to look at the attendence over a year or so. Or even the number of people that can be seated could be used as a sensible guide.

The majority of churches will not be full all the time, but baptisms, weddings and funerals are likely to increase numbers above the average and will often bring in people unfamilier with the building. It is these infrequent occassions which the church needs to be prepared for in terms of extra stewards, sidespeople etc.

Those churches in industrial buildings, converted cinemas and the like may need another approach dependent on the building construction, age etc.

The IFE Heritage Special Interest Group is working on a new Guidence document; I was away and missed the meeting last month so I'm uncertain how its progressing, not having caught up with the paperwork yet!

Hope the above is of help.

[kurnal]

I agree with John but we always have to remember that the average attendance does not give the full picture and for some festivals, popular funerals and weddings- in these cases there will be a peak attendance based on the available area for standing and the number of seats/ prayer mats.  In extreme cases it may be necessary to assess the standing areas at 3 persons per sq m. I would then consider what is a reasonable evacuation time based on the RSET/ASET approach. Yes this extreme attendance is unusual but its best to have your strategy and plan for such events in the back pocket ready to go. For a mosque there are special problems as you cannot calculate exit flows in the conventional way due to the congestion caused by persons looking for their shoes, and family members seeking each other in different parts of the building.

[Phoenix]

I agree with the above generally.  I usually imagine the church at a very busy time - maybe a popular wedding or funeral - count the seating spaces (try to imagine how many could squeeze onto those pews) then assess the total area of the spaces where people can reasonably be expected to stand and allow 2 (maybe 3 as kurnal says) people per sq m.  Add the choir and other bods up the front.  And there's your number. 

Also I ask the minister what he reckons is the maximum number - very important.

But then, unless the ceiling is very low, I allow leeway on ADB figures because of ceiling height.  (The ADB exit width figures are rarely appropriate in churches.)  Now, of course, you can formalise this 'leeway' by referring to tables in BS9999.  Don't forget to take 25% off t.d.s if they've been boozing! 

Stu

   

[alfi]

Thanks guys

[alfi]

What is RSET/ASET and how does that work Kurnal?,

[CivvyFSO]

Sorry for butting in, but I might as well save Kurnals typing finger...

It is; Required Safe Evacuation Time (i.e. How much time you actually need to get all the people out of the place)

measured against:

Available Safe Evacuation Time (i.e. The amount of time that is available before conditions are no good for escape)

We need the available time (ASET) to be quite a bit more than the required time (RSET), because if it is the other way round people are still in the building when conditions within the building will stop them getting any further. (i.e. Dead)

[alfi]

Thanks for that!,  is this software or hard calulations?, sorry for sounding thick but I like to understand how these things work, could you give a quick example of how it would be used?

Thanks hugely

[nearlythere]

Should we not just count bums on available seats at 1 per 1/2M and aisles maintained clear just like any concert hall with a fixed seating arrangement? High ceilings to allow mitigation if exit numbers and widths lacking.

[John Webb]

Increasing numbers of churches are getting rid of the 'fixed' seating - ie pews - and going for greater flexibility by using chairs. My own church is going down this route early next year for a number of reasons, including easier incorporation of those in wheelchairs or with young children in prams etc into the main part of the congregation, different seating arrangement for services or for when concerts or drama takes place. We shall have a number of chairs with and without arms for general use, and a quantity of folding chairs kept on a trolley for the larger and better attended services.

I'm already trying to work out how the FRA needs to be rewritten for these changed circumstances!

[Phoenix]

Increasing numbers of churches are getting rid of the 'fixed' seating - ie pews - and going for greater flexibility by using chairs. My own church is going down this route early next year for a number of reasons, including easier incorporation of those in wheelchairs or with young children in prams etc into the main part of the congregation, different seating arrangement for services or for when concerts or drama takes place. We shall have a number of chairs with and without arms for general use, and a quantity of folding chairs kept on a trolley for the larger and better attended services.

I'm already trying to work out how the FRA needs to be rewritten for these changed circumstances!

John,

I would recommend that you look at the guidance available regarding interlocking of seats within rows, and the possible interlocking of rows.

Stu

[CivvyFSO]

Thanks for that!,  is this software or hard calulations?, sorry for sounding thick but I like to understand how these things work, could you give a quick example of how it would be used?

Thanks hugely

It can be both, and it is also behind the variations that come with BS9999.

Kurnal might be able to explain in plain English from experience and common sense that conditions in the church will easily allow a 4 minute evacuation. Stu, might look at what fire loading is in the church, the speed of fire growth, smoke produced, any ventilation supplied, the volume of the room and the height and give a load of calculations based on these various details.

There is also software that can be used. Some spreadsheets are used that simply do the calcs for you, and then there is CFD. Even when the software is being used you still need a good idea of what is going on and what 'should' happen.

An example of how it could be calculated is as follows: (Keeping as basic as possible)

An uncontrolled fire is particularly hard to deal with so we will try restrict the fire...
Restrict the fire by creating fuel islands with enough space inbetween them to stop any ignition by radiated heat...
So we will have X megawatts (max output, calculated on fuel load/type and area) islands where it can be expected that the fire will not go from island to island...
A X MW fire of a specific perimeter will create a specific amount of smoke depending on the height of rise of the smoke...
This smoke is either going to fill the room eventually, or if there is a suitable amount of ventilation it might reach a height where the smoke produced is equal to the smoke being removed, and reach an equilibrium.
At some point this smoke may be of a temperature and at a height where it will incapacitate persons that are trying to escape.
We want everyone out well before this happens.

Simples.

[John Webb]

John,
I would recommend that you look at the guidance available regarding interlocking of seats within rows, and the possible interlocking of rows.

Stu

Thanks Stu - I am aware of such guidence. But when the whole point of changing to chairs is so that wheelchairs, prams and the like can be added to or inserted within rows so that families can sit together rather than the disabled or very young being limited to set-aside areas, it adds a considerable new dimension to the whole!

Hopefully the IFE guidence under preparation will help on this important factor.

[Phoenix]

John,

Just another thought about your free standing chairs, do make sure you have good normal and emergency lighting covering the seating area.  In an evacuation, the chairs are prone to being pushed out of alignment and people may need reasonable light to be able to negotiate the slalom created.

Civvy,

A brilliantly concise precis.

Tony,

Civvy summed it all up nicely there but, for practical purposes, you'd be best making sure you're familiar with the techniques employed in BS9999 and sticking to those.

Stu

[alfi]

The main reason i ask chaps is I heard London Fire authority  sucessfully prosecuted a church for 20K because of occupancy levels, anyone know if ther is any tructh in this and why such a big fine?