FireNet Community
FIRE SERVICE AND GENERAL FIRE SAFETY TOPICS => Fire Safety => Topic started by: Tom Sutton on August 04, 2010, 10:56:59 PM
-
I received the following enquiry today regarding seating in a church hall any observations.
1) Is ordinary polypropylene sufficiently fire safe or do we need to go for the fire retardant version? Data sheets I have seen suggest that polypropylene in itself is self-extinguishing in small scale, but does to a limited extent burn when continually forced by external flame. The building is heated by fan powered sealed combustion gas heaters (Vulcana).
2) Most of the time the chairs are used in small random quantities with the remainder stacked (in groups of 5 - the new ones may be 1 or 2 higher) but for Church services and some meetings they are used in rows of usually 5 but sometimes 6 either side of a central aisle. The bulk of the chairs are plain, but to aid impaired mobility people chairs with arms are interspersed, usually one per row, amongst them. Linking of the ordinary chairs to the armed chairs is impractical because the armed chairs are larger. How critical would linking be deemed to be under these circumstances, particularly since it is impractical to fix them in position? Normal capacity is about 90, but can be 130, of which 15 are chairs with arms. There are two well separated exits available.
-
Heat release rate of 2000 Kw for 5-6 stacked pp chairs, other problems due to smoke, obscuration and loose chairs being displaced hindering evacuation.
Check your PM
-
I think the key phrase you have used Tom is "sufficiently fire safe".
In your case would the chairs be exposed to fire in it's early stages, or at all, to be a risk to the occupiers? What are the chances of a fire starting?
Fire retardant is not fire proof and the chairs will burn but would they be of any significent benefit over polypropylene with regards to risk to persons, in your situation?
Your main issue I think is the linking of chairs which if not done could be a bigger risk to occupiers than the combustibility of polypropylene chairs and then what type of persons are you dealing with?
If your fire risk in the room is low would there be a mad scramble for the exits? (In your case)
-
Fire resistant polymers are normally found in seating which is in confined areas, aeroplanes, trains etc.
If there are suitable control measures for ignition sources and the chairs are in a kirk with the required available fire exits then they should be suitable for use.
Would need to review the type of alarm system to ensure you have no inner areas where an external fire could develop and trap individuals.
Hope this is of some assistance.
-
Just to confirm what has gone ahead.
We are primarily interested in the early fire growth rate and its potential to inhibit means of escape.
If the chairs are laid out in rows in the hall, how significant is their contribution going to be to the initial growth of a fire that starts in material around or beneath them? Not very, I would suggest. Firstly, the fire loading presented by the chairs is very spread out and secondly, even if one or two chairs do become involved in the fire early in its development, this is not likely to occur before all the occupants have left the hall - assuming exits are ok [the more people in the hall, the earlier the fire will be spotted].
If the chairs are stacked within the hall then they present a much more significant fire loading. But, even so, are they likely to be a major contributor to the fire growth during the evacuation stage? The fire will be noticed early, again, and if the exits are adequate then people will be able to evacuate in good time before the chairs start to contribute to fire development.
Care and judgement may be required in both the above cases, as there are often inner rooms or upper levels where people may be and which have questionable means for giving early warning of fire as well as means of escape that may rely on the main hall remaining tenable.
If the chairs are stacked in a separate room to where all the people are (a store or back room) then the fire may have time to develop to a stage where the chairs contribute significantly to the fire growth before the fire becomes noticed. But in this case the chairs are in a separate space and the means of escape for the occupants of the hall should be safe for sufficient time to evacuate.
If BLEVE's figure of 2000kW is right for 5 or 6 chairs then a hundred or so chairs is quite a fire load! There could ultimately be a lot of damage to the property due to the fire loading.
As for fixing the chairs, this is usually advisable. You do not want people ploughing through the lines of chairs to get to the exits, you want people to follow the rows so that everyone has the best routes to the exits. A factor that can affect the need for interlinking the chairs is the provision of normal and emergency lighting. If the audience may be plunged into darkness or semi-darkness then the need for interlinking of chairs is greater. If there will always be bags of light available then the need for interlinking diminishes.
Finally, Cullenloon, are you in Cullen? I am.
Stu
-
The chairs should be fixed together and should really be fixed to the floor. People should be well on their way prior to the chairs hitting the 2,000kW mark, but not if people are falling all over their chairs and each other in order to get out.
CLG guidance explains the general requirements: http://www.communities.gov.uk/documents/fire/pdf/144821.pdf (p60)
'Impractical' doesn't really wash in this scenario, it is probably more in the region of "can't be bothered to change what has always gone on". (I am rather cynical though) Some slight alterations might be required regarding the bigger chairs, but nothing that would take a huge amount of imagination to work through.
-
The likelihood of a fire starting and spreading in chairs set out is pretty low; it is when they are stacked that the problem may arise, as Peterborough Cathedral found out several years ago. But as I know well most churches/church halls always have storage problems and one can only insist that storage takes place off escape routes. (I once found 24 PP chairs stacked at the bottom of a fire escape staircase when inspecting a church hall!)
Re linking - I have no hard and fast rules about this. As I understand it, chair-linking came about as a result of church/village halls and the like being used for film shows or drama, where people were sitting in the dark or near-dark, and particularly with early films there was the risk of a sudden fire. But in a church or hall that is in daylight or lit and where the 'fire alarm' is likely to be a firm request to leave the building by the church leader, there should be no sudden 'rush for the exits' which might lead to chairs being upset. Many churches are changing to chairs to allow those in wheelchairs and those with young children in buggies and the like to sit where they like as part of the congregation, so chairs need to be unlinked easily to allow for rearrangement to accomodate these - again the risk assessment needs to take this mix into account and to assist any decision about linking.
-
Additional to above, there is virtually no possibility of fixing such chairs to a floor as CivvyFSO would like - church halls are used for a wide variety of purposes - my own church hall is used by Martial Arts, dance classes and a pre-school amongst other things and any obstruction/hole in the flooring for fixing chairs would cause considerable difficulties.
-
Thanks guys, quite a lot to digest. ???
NT nothing to do with me I am simple trying to answer an enquiry emailed to me and if I need any clarification I will get back to him.
-
Check your PM
Nothing in my messages. ???
-
Links to stacked chair heat release rates and loose chairs in evacuation study :)
http://www.hugedrive.com/published/WG/show.php?q=SElMVFNGSUxFUw==-a2a4f402
-
Thanks BLEVE and the rest of you guys. I think the conclusions in the report confirmed what most of us thought about linking the chairs.
The Peterborough Cathedral incident http://www.buildingconservation.com/articles/peterborough/peterborough.htm (http://www.buildingconservation.com/articles/peterborough/peterborough.htm) and the graph highlighted the importance of storage (Stacking of chairs) also security needs to be given much consideration.
Finally IMO the fire resistance if polypropylene is irrelevant in the early stages of a fire (evacuation Stage) but should be considered with regards to property protection in the later stages of a fire.
-
BLEVE - thanks for the link to the Swedish work - most interesting. Shame it wasn't stackable chairs with the manufacturer's links - that might have been quite revealing as well.
We're currently using our church hall for services with PP chairs in slightly curved rows of between 4 and 6 chairs per row, unlinked, but with a 1m spacing between rows, a 2m central aisle and 1 to 2m side aisles. We've not had any problem with chairs being disturbed. When we return to the church proper - under renovation at the moment - we will have around 100 wood chairs of (non-stackable) construction rather than the former fixed pews and around 50 steel-framed stacking chairs for when additional seating is required. It will be interesting to observe the way all these are used for a couple of weeks before a major rewrite of our fire risk assessment......
-
The generous dimensions between rows and access/egress would make all the difference wrt chair scattering etc.
If I had the time and it was not considered by some as being clever, I would calculate and compare PolyP vs Timber chair HRR, RHF, Tig and Tg.
Subject to the results of the above comparison, I would imagine that 100 timber chairs result in a lesser fire load than 100 PP chairs. Howver, 100 Aluminium chairs would be better again, although there may be an increased hazard over chair collapse/failure rate taking into account continual use and the relevant Youngs Modulus.
-
Some interesting points regarding this evacuation experiment.
Participants were aware of the nature of the experiment and as such could have behaved in a manner to help achieve the desired result. These were students from the Fire Protection Engineering programme who would have known what the experiment was trying to demonstrate and mostly would have played the game.
Reminds me of my practical promotion exam when the crew would intentionally make mistakes so that I had something to pick them up on.
One comment was “Unfortunately I did not notice any difference at all between the experiments.” Why unfortunately? Did it not happen for him?
The experiment does not give consideration to the degree of risk from fire people believe they are escaping from. Low fire risk - less urgency & less panic.
-
Agree totally,
It would have been better to have at least used different groups of students from different reas of the campus for each experiment.
I supoose that given todays litigious climate it would have been difficult to have carried out the study unanounced for fear of injury.
Common sense tells me that given reduced spacing between rows, reduced egress widths and given the required visual cues e.g. smoke initiating some degree of evacuation and flame initiating a greater and more urgent rate of evacuation, it would be expected that a number of chairswould become displaced.
-
More displaced chairs yes but to a level so as to be a significant and unacceptable risk????
-
That depends on the number, location of chairs displaced,number of occupants taking part in the evac, number of MOE provided and strength of cue to initiate evac action.
Maybe the potential to model this but would offfer the opinion that direct experiment is the way to go.
I would also agree and offer the opinion that given reduced row length and generous access/egress dimension, then I would not have thought the number of displaced chairs would prevent complete evacuation until conditions became untenable.
-
If I had the time and it was not considered by some as being clever, I would calculate and compare PolyP vs Timber chair HRR, RHF, Tig and Tg.
I would be interested in seeing the results of this please Bleve. Having seen PolpyP baking trays and pallets burning I am concerned about this from a property protection, firefighter safety and environmental protection viewpoint.
-
Will give a go as soon as get a chance
-
From calculations, as we expected, it seems that the PP chair is the greater fire risk.
Interesting to note that if timber seats are positioned at a distance in excess of 0.35 metres then fire spread from timber seat to timber seat is not an issue as the piloted heat flux value cannot be achieved.
Also of apparent interest is the case whereby the PP seating material combusts and falls to the floor resulting in a viscous pool. Where a number of stacked seats are involved in fire, this may result in an additional volume of PP at the floor surface/pool resulting in an increased heat flux.
For anyone interested, the results are posted at
http://www.hugedrive.com/published/WG/show.php?q=SElMVFNGSUxFUw==-392debf5
-
Thanks Bleve. Thats an interesting comparison. I wonder how easily they are ignited?
-
BLEVE on your first graph regarding PP it showed no significant rise in temp for about ten minutes then a rapid rise. To me this indicates it took 10 mins to get started but then the temp rose rapidly evolving a great deal of heat. Also when they are stacked they pose the greatest danger, would you agree.
-
Tom
It would seem that the stacked chairs result in a pool of greater surface area and heat release.
If we take the ignition temperature listed for the PP seats then piloted ignition is calculated as 7.6 kW/m2
If we consider the advised critical heat flux for ignition without pilot 20 kW/m2, we then require some 769 kelvin in order to initiate combustion of the first seat in the stack.
-
Mr or Ms arsonist would need only 125 ml Ethanol and a match to initiate combustion,
This results in a HRR of 44 kW and RHF of 25 kW/m2 at source
-
Of course they could always use a church candle,
21 mm dia candle provides heat flux of 65 kW/m2 at 50 mm above flame.
-
DOH ???