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FIRE SERVICE AND GENERAL FIRE SAFETY TOPICS => Fire Safety => Topic started by: FSO on December 09, 2008, 10:14:09 AM
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Hi All
A little issue, I would like some opinions on please.
9999 would suggest that shops fall under the B3 risk profile (im sure its a matter of opinion there though).
The single direction travel distance for this risk profile is suggested at 16 metres. However in the CLG guide for Offices and shops, a medium risk shop is is the usual 18 metres.
If you have AFD (with an obvious advantage) and a ceiling between 3- 4 metres you can extend this distance to 19.3 according to 9999. Which are obviously huge enhancements on the assumption of having nothing at a medium risk shop in CLG guides.
This just does not seem to make sense to me. Conflicting guides yet again or am i just missing the point?
Your opinions would be welcomed.
J
Regards
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It will possibly be the fast fire growth rate that is not taken account of in CLG guidance.
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It was mentioned by the speakers on my 9999 course (one of which was on the 9999 board) that Table 5 - Examples of typical risk profiles should be removed as it causes confussion like this and is going to be looked into.
The example they used was that a bar is down as a B2 risk profile. Where does someone draw the line with a bar, is it a small village pub with very few combustibles (B1) or is it modern bar with curtained booths, candles and dancing girls (B3)? To label building types in examples could be dangerous.
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What happens in a shop when the alarm sounds? Customers ignore the alarm and carry on shopping till they are told what to do. Then they go to the tills and try and pay for what they have in their trolleys and argue about having to go and stand out in the cold before they can finish their shopping. Staff wonder whether to start ther evacuation or not and tend to stand around looking confused till someone on the non fire rated tannoy tells them what to do.
The travel distances all date back to the post war building studies and the old 0.8m/sec on the flat and 0.6m/sec on stairs and units of exit width and have been interpolated to the nth degree for the purposes of writing simple guidance for us practicioners. Meanwhile the fire loading in shops has changed beyond all recognition from the days of brown paper bags and horsehair.
Despite all this I could have safely made my way 100m in a dead end condition past the fire had I responded immediately the alarm sounded or smelt the smoke. I believe that in its attempt to give us positive tangible benefits of high ceilings and early detection the new guidance has become far too pernickity and definitive in terms of travel distance and percentage enhancements when all invariably comes apart in an emergency due to the human factors in the management of an emergency.
It could be very difficult to justify in court but I rely on whether my bottom twitches or not when auditing standards in premises.
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It will possibly be the fast fire growth rate that is not taken account of in CLG guidance.
Thats exactly my point. The suggested risk profile of any type of shop is B3.
This makes it a little difficult to justify that a shop is B2 when the information supplied about fire growth is very little.
If shops are that high risk, why would CLG guides suggest that even a 'medium' risk premises is 18 metres. Surely a meduim risk is between a B2/B3 (which convieniently is 18 metres) with no scope to calculate for this.
I feel the risk profiles are a little limited ::)
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What happens in a shop when the alarm sounds? Customers ignore the alarm and carry on shopping till they are told what to do. Then they go to the tills and try and pay for what they have in their trolleys and argue about having to go and stand out in the cold before they can finish their shopping. Staff wonder whether to start ther evacuation or not and tend to stand around looking confused till someone on the non fire rated tannoy tells them what to do.
The travel distances all date back to the post war building studies and the old 0.8m/sec on the flat and 0.6m/sec on stairs and units of exit width and have been interpolated to the nth degree for the purposes of writing simple guidance for us practicioners. Meanwhile the fire loading in shops has changed beyond all recognition from the days of brown paper bags and horsehair.
Despite all this I could have safely made my way 100m in a dead end condition past the fire had I responded immediately the alarm sounded or smelt the smoke. I believe that in its attempt to give us positive tangible benefits of high ceilings and early detection the new guidance has become far too pernickity and definitive in terms of travel distance and percentage enhancements when all invariably comes apart in an emergency due to the human factors in the management of an emergency.
It could be very difficult to justify in court but I rely on whether my bottom twitches or not when auditing standards in premises.
Totally agree with you Kurnal.
In this case I am trying to apply 9999 to a small post office/newsagent with slightly extended travel distances where AFD in a basement would have a good advantage.
The bottom twitch is always a reliable method ;D
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[This makes it a little difficult to justify that a shop is B2 when the information supplied about fire growth is very little.
Look in BS7974, fast fire growth is standard for any shop. Also look in the average shop and you have to appreciate why this is the case. It could be that certain shops could be risk assessed down a group depending on the contents, but the design stage is generally looking at a shell, or allowing for future use. i.e. You might have a shop selling ceramics that would certain not have a fast fire growth, but by allowing a medium growth rate and all the dimensions particular to that, you limit the future use of the shop.
Sprinklers quite obviously knock this fire growth down, hence the switch to medium growth which tallys with the "2" part of the rating.
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What happens in a shop when the alarm sounds? Customers ignore the alarm and carry on shopping till they are told what to do. Then they go to the tills and try and pay for what they have in their trolleys and argue about having to go and stand out in the cold before they can finish their shopping. Staff wonder whether to start ther evacuation or not and tend to stand around looking confused till someone on the non fire rated tannoy tells them what to do.
The travel distances all date back to the post war building studies and the old 0.8m/sec on the flat and 0.6m/sec on stairs and units of exit width and have been interpolated to the nth degree for the purposes of writing simple guidance for us practicioners. Meanwhile the fire loading in shops has changed beyond all recognition from the days of brown paper bags and horsehair.
Despite all this I could have safely made my way 100m in a dead end condition past the fire had I responded immediately the alarm sounded or smelt the smoke. I believe that in its attempt to give us positive tangible benefits of high ceilings and early detection the new guidance has become far too pernickity and definitive in terms of travel distance and percentage enhancements when all invariably comes apart in an emergency due to the human factors in the management of an emergency.
It could be very difficult to justify in court but I rely on whether my bottom twitches or not when auditing standards in premises.
Totally agree with you Kurnal.
In this case I am trying to apply 9999 to a small post office/newsagent with slightly extended travel distances where AFD in a basement would have a good advantage.
The bottom twitch is always a reliable method ;D
FSO. Why would you not consider a small post office a place where persons would be familiar with their surroundings and attract an A2 or even an A1 profile.
Scenario. - Small post office with one way in and as such one way out. Exit door obvious from any point in public area. Travel distance within guidelines. Open floor area.
Would you not consider that a stranger walking into the public area would be immediately familiar with his surroundings in such a short time period?
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In this case I am trying to apply 9999 to a small post office/newsagent with slightly extended travel distances where AFD in a basement would have a good advantage.
Just being awkward for a second...
Why are you as an FSO trying to apply 9999? The document should be used in its entirety, (i.e. assumed management levels etc) not just looking at certain sections to justify extended travel.
IF the basement is not seperated from the ground floor (not knowing if any of the small premises guidance fits) then really the detection in a basement would only really compensate for the lack of fire resistance, not for the travel distance. Look at the ground floor as a risk on its own. Detection in an open plan ground floor is of no benefit in a shop as the fire would be visible before detection picks it up anyway.
Also a typical newsagents is stacked to the roof with nicely packaged combustible content (papers, crisps, newspapers, magazines) which would IMO warrant the fast fire growth rating.
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In this case I am trying to apply 9999 to a small post office/newsagent with slightly extended travel distances where AFD in a basement would have a good advantage.
Just being awkward for a second...
Why are you as an FSO trying to apply 9999? The document should be used in its entirety, (i.e. assumed management levels etc) not just looking at certain sections to justify extended travel.
IF the basement is not seperated from the ground floor (not knowing if any of the small premises guidance fits) then really the detection in a basement would only really compensate for the lack of fire resistance, not for the travel distance. Look at the ground floor as a risk on its own. Detection in an open plan ground floor is of no benefit in a shop as the fire would be visible before detection picks it up anyway.
Also a typical newsagents is stacked to the roof with nicely packaged combustible content (papers, crisps, newspapers, magazines) which would IMO warrant the fast fire growth rating.
Yes I am aware of that.
FYI, This is not an FSO job :)
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In this case I am trying to apply 9999 to a small post office/newsagent with slightly extended travel distances where AFD in a basement would have a good advantage.
Just being awkward for a second...
Why are you as an FSO trying to apply 9999? The document should be used in its entirety, (i.e. assumed management levels etc) not just looking at certain sections to justify extended travel.
IF the basement is not seperated from the ground floor (not knowing if any of the small premises guidance fits) then really the detection in a basement would only really compensate for the lack of fire resistance, not for the travel distance. Look at the ground floor as a risk on its own. Detection in an open plan ground floor is of no benefit in a shop as the fire would be visible before detection picks it up anyway.
Also a typical newsagents is stacked to the roof with nicely packaged combustible content (papers, crisps, newspapers, magazines) which would IMO warrant the fast fire growth rating.
Yes I am aware of that.
FYI, This is not an FSO job :)
Detection within the open area is of little use to the shop occupants, I fully agree. But it is very relevant for the HMO above the shop. There is lack of FR where detection is relevant.
Anyhow, I was after opinions on 9999 only...thank you.
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It's interesting that a few of us are comparing 9999 with the CLG guidance, ADB etc as if they are definitive and irrefutable standards.
They are just educated guesses like anything else. 9999 is by no means perfect but there was some analysis done to produce all of these tables. Something of an innovation.
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Detection within the open area is of little use to the shop occupants, I fully agree. But it is very relevant for the HMO above the shop. There is lack of FR where detection is relevant.
Anyhow, I was after opinions on 9999 only...thank you.
Improving conditions for people in the HMO has little relevance for travel distance in the shop then?
My opinion on 9999 is simply that the fire growth rate of 3, or 'fast' is suitable. Nearlythere had a good point regarding immediate familiarisation but looking at pre-movement times from BS7974 the unfamiliar group tend to have slightly longer pre-movement times (Thresher vid shows the problems), which could account for keeping it at B3. Sorry for dragging 7974 into it again, but I am sure that this type of thing was taken account of 'behind the scenes' in the development of BS9999 and the specific figures they came up with.
The guides are going to differ, as 9999 tries to take more account of the variations within certain groups and premises.
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I realise what follows is off theme but I am trying to get to grips with DD 9999 which I hope is close enough to BS 9999 not to make any major difference.
I progressed fairly well until I reached width of doors and I am having difficulty understanding how you calculate the width of a door using the table 13 “Door widths when minimum fire protection measures are provided”. Could any person explain it and show me an example either on or off line?
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It could be very difficult to justify in court but I rely on whether my bottom twitches or not when auditing standards in premises.
You just ruined my dinner. That'll teach me to read firenet while eating.
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I realise what follows is off theme but I am trying to get to grips with DD 9999 which I hope is close enough to BS 9999 not to make any major difference.
I progressed fairly well until I reached width of doors and I am having difficulty understanding how you calculate the width of a door using the table 13 “Door widths when minimum fire protection measures are provided”. Could any person explain it and show me an example either on or off line?
Take profile A1 and a big square room that can hold 500 people.
3.1mm x 500 people = 1550
You need at least 1550mm of exit width.
But due to the normal discounting rules you will need 2 lots of 1550mm.
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TW, I understand it as; minimum exit door width for exit point, plus additional width per person over that for the said door width allowance. ie 1100mm door width allows 183 persons (risk profile B3), then add 6mm per person additional to that.
Note 4 below Figure 13 page 83 basically says this too.
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I realise what follows is off theme but I am trying to get to grips with DD 9999 which I hope is close enough to BS 9999 not to make any major difference.
I progressed fairly well until I reached width of doors and I am having difficulty understanding how you calculate the width of a door using the table 13 “Door widths when minimum fire protection measures are provided”. Could any person explain it and show me an example either on or off line?
Take profile A1 and a big square room that can hold 500 people.
3.1mm x 500 people = 1550
You need at least 1550mm of exit width.
But due to the normal discounting rules you will need 2 lots of 1550mm.
I hindsight my last line is sort of wrong... After discounting the largest exit you need 1550mm of exit width left. And as Mr P points out, this is subject to the normal minimum widths. In this example 3 suitably placed 850 doors cover it, as if you discount one you are left with 1700mm of width left. 1700/3.1 allows 548 people through for that risk profile.
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I am a little puzzled as to the example given in note 4 page 83, which says 850 divided by 4.4 ( from table 13), is this a typo error? as I cant see any mention in table 13 of 4.4 at all.( or is it me getting it wrong) I see a 4.1 for risk profile B2.
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Brilliant! Good job Christmas is coming. Sell ourselves to be pulled as crackers, make a nice little earner by giving them the RA prior to pulling us... we may go spludge, bang or other wise, scream loudly, heres some ear defenders that'll be a nice £2.60 thank-you , cheap at twice the price!!!!
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I am a little puzzled as to the example given in note 4 page 83, which says 850 divided by 4.4 ( from table 13), is this a typo error? as I cant see any mention in table 13 of 4.4 at all.( or is it me getting it wrong) I see a 4.1 for risk profile B2.
You are quite right, it is clearly an error.
850/4.1mm per person gives 207 people per door. Discount one door of the three 850mm doors, you have 2 times exit width appropriate for 207 people giving 414 people.
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Thanks guys, but it looks like I have a problem, in DD9999 B3 indicates 7mm/person not six and there is no notes below Table 13. I do have the 4.4 for B2 Ricardo spoke of but I am afraid it’s a case of saving up my pennies and getting BS 9999 before continuing with this project. :'(
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The DD is very different from the BS.
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Now I have had time to digest I can now see my calculations were correct despite the erroneous examples shown in DD9999 but what I could not get my head around was the numbers of people a 750mm door could accommodate, seemed so high, I felt I must have made a mistake. For example using previous guides a 750mm door could accommodate between 80 and 120 person depending on the risk category. Using DD9999 a 750mm door could now accommodate between 81 and 241 persons with acceptably an increased number of risk categories.
I now realise that WB but how long do we have to wait for BS 9999 to sort out the mistakes and typos, I do not want to pay twice for the same document?
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BS9999 16.5.6 (e) has the following formula for the calculation of the minimum permissible width of a final exit where flows merge from a staircase and a ground floor storey exit into a ground floor lobby.The formula previously appeared in ADB.
W= [(N/2.5)+(60S)]/80
where N= the number of persons served by the ground floor storey exit, S = stair width in metres and W=the width of the final exit in metres.
To me this formula appears to undermine the risk based approach of 9999 where we design the means of escape using risk profiles. Surely the 2.5 in the fomula is simply determining the flow rate in persons per minute based on a "Normal risk" evacuation time of 2.5 minutes- ie the 5mm per person derived and extrapolated from the post war building studies. This seems to undermine the general risk based approach- or am I missing something?
Have just been using the document for a new building where I had been using table 13 which I think should read 4.4mm per person not the 4.1 stated in the table for B2 risk profile?? )
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Prof
On one of the other threads on 9999 I quoted errors in the BS as given to me by the main author
davo
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Hi kurnal
The formula you quoted can be boiled down to three quarters of the width of the stairs plus 5mm per person for all those coming from the ground floor.
You are right that this is anomalous within the context of 9999 because a different width per person is probably applicable. It's not perfect, this 9999. But it's a best guess for the time being (just as are all other fire safety numbers). You'll find a similar anomaly in the section on shopping mall exit widths, they're still basing mall exits on 5mm per person.
At least these little quirks are erring on the side of safety. Also, they are simple (increased accuracy would bring increased complexity).
Another thing to note about the formula you quoted. Even if only 50 people are joining the flow from the ground floor you still apply the 5mm per person and that doesn't seem to sit right with the fact that you cannot use 5mm per person for less than 220 people. But the formula does make sense because those few people that are joining the flow from the ground floor are joining a larger flow from the upper storeys which, hopefully, takes the total above 220.
Why do you think B2 in Table 13 should be 4.4?
Davo, is this one of the errors you spoke of?
Stu
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What happens in a shop when the alarm sounds? Customers ignore the alarm and carry on shopping till they are told what to do. Then they go to the tills and try and pay for what they have in their trolleys and argue about having to go and stand out in the cold before they can finish their shopping. Staff wonder whether to start ther evacuation or not and tend to stand around looking confused till someone on the non fire rated tannoy tells them what to do.
very true...I was in a supermarket the other day when the fire alarm sounded...it was like the muppets 'pigs in space'...every one looking skywards wondering what the noise was...all those old enough to remember the Woolworths fire in Manchester will know that human behaviour doesn't always do what it says on the evacuation tin
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Phoenix
General Interest Jan 28 2009, sorry can't do the technical stuff :-X
davo
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Is this the one you are talking about http://www.kingfell.com/~forum/index.php?topic=4019.msg42354#new
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Thanks Guys,
What table 13 says is:
"Table 13 Door widths when minimum fire protection measures are provided
Risk profile Minimum door width per person (mm)
A1 3.3
A2 3.6
A3 4.6
A4 Not applicable
B1 3.6
B2 4.1
B3 6.0
etc..."
What note 4 on page 83 of 9999 says is:
"NOTE 4 The total number of persons that two or more available exits can accommodate is found by adding the maximum number of persons for each exit width. For example, three exits each 850 mm wide, in a building with a B2 risk profile, will accommodate 386 persons. This is calculated by:
• 850 divided by 4.4 (from Table 13) = 193;
• discount one exit;
• 2 × 193 = 386 persons [not the 579 persons who could be accommodated through a single exit 2 550 mm (i.e. 3 × 850 mm)
wide]."
Now, everyone can see that B2 in the table says 4.1mm and the note says 4.4mm
Ok, so this is a typo, but how is it corrected? Like this:
"two 100% official typos for you to amend:
page 83 17.6.1 Note 4
850 should be divided by 4.6 rather than 4.4...."
Where does 4.6mm come from?!
Ok, here's another thing. That whole note 4 (quoted above) is a dog's dinner anyway. It is a redundant note that was put in for spurious reasons:
Many years ago designers had a habit of adding together all the individual exit widths to produce one aggregated width, they then subtracted the largest exit and then divided the result by 5mm to come up with an occupancy figure. For reasons that are a little complicated to explain this method gives correct results provided that all exits are at least 1100mm wide. If any exits are below this width then what is being done is that the 5mm per person is being applied to doors below 1100mm which (according to ADB) should not be done.
In an effort to stop this happening ADB introduced paragraph 3.22:
"3.22 The total number of persons which two or more available exits (after discounting) can accommodate is found by adding the maximum number of persons that can be accommodated by each exit width. For example, 3 exits each 850mm wide will accommodate 3 x 110 = 330 persons (not the 510 persons accommodated by a single exit 2550mm wide)."
That makes sense within the context of ADB's table 4. But in 9999, where "x"mm per person is applied down to the minimum exit width possible, this statement is meaningless and redundant. In effect, all note 4 says is to repeat that the largest exit should be discounted. In light of the confusion it generates, I would recommend ignoring note 4.
Stu
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Phoenix
The 4.6 came from David Smith, Chair of the BSI Committee FSH14
davo
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Thanks Davo,
So, irrespective of what note 4 says do we take it that table 13 should have 4.6mm against B2?
Seeing that this is currently being applied to scores of bars and clubs around the country I'd have thought that it was quite an urgent thing to publish a correction.
Stu
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Why do you think B2 in Table 13 should be 4.4?
Davo, is this one of the errors you spoke of?
Stu
Just because 4.4 is used in the worked example but now from what Davo says even that is wrong. Still it sat better for me taking into account the risk involved. rather than 4.1.
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it sat better for me taking into account the risk involved.
Agreed.