Dry rising mains

[xan]

I would value your views on this:
Proposal to convert an old water tower into flats (it is a tall and skinny building).
Main staircase to entrance of topmost flat entrance door is 17.5m high (Just below the 18m threshold requirement for a FF shaft.).
However it is over the 11m threshold which I believe (I admit I am not sure-guidance in ADB/BS9999 is a bit vague,but does appear to be so in the old BS5588-5 table 4 )requires  a dry riser.
The uppermost flat has an additional 3 internal stories,uppermost floor at 26.5m.However the furthest point from fire service access to furthest point in flat is approx 48m (only just over 45m threshold).Because of limited space,they are finding it difficult to install a riser,and have proposed a Residential sprinkler system,mains fed.
Should they be able to provide a sprinkler system (and there are water supply requirements to be overcome yet), would you accept sprinklers in lieu of the dry mains,despite the height that equipment will have to be carried upstairs by FF,even though the actual distance is just over 45m?There does not appear to be any relaxations given for the provision of sprinklers (Sprinklers would  be compulsory at 30m)
thanks,Xan

[wee brian]

Sounds fair enough to me.

[kurnal]

You can only do what you can to make an existing structure fit the guides,  the stumbling block may be convincing that the fire authority that the provision of sprinklers (that have been proven in tests to suppress rather than extinguish a fire- especially a shielded fire) will control a fire sufficiently such that they do not need to carry as much equipment up those stairs. The mains supply to the sprinklers will give confidence in this respect- much better than a tank supply that will run out after 10 minutes.

The 45m bit helps because with sprinklers a hosereel is more than likely to be their weapon of choice- its lighter, easier to manouvre, better knock down, quicker to get to work, more controllable, better protection for firefighters etc.  Can you reach all areas from the appliance parking position within 60m- the standard hosereel length?

Now just be  sure that mains pressure will give you the necessary 0.5 Bar at the highest sprinkler and the necessary flow (allow for 200l/min forget the 168 l/min in BS9251) I bet you will need a pump.If you have a problem with water pressure you could look at water mist.

[Phoenix]

What you are proposing sounds, as presented, perfectly reasonable.  Kurnal explains the fire fighting logistical arguments well.

You might struggle with the mains supply.  You will need over 3 bar at the main sprinkler valve and this may not be supported by the normal mains supply (24/7 requirement).  The water suppliers may be reluctant to allow a pump to boost your supply as this reduces pressure in the main and can lead to contamination of the water supply through leaky mains.  You will only find out what is feasible by approaching the water supplier.

You mention a "residential" sprinkler system.  Be clear of what you want, "residential" is different to "domestic."  A "residential" system has a much higher requirement for the water supply than a "domestic" system.  You probably want a "domestic" system which requires, as kurnal states, ten minutes of water supply.  Also, if it is a "domestic" system you're after, then the flow requirements (at the 3+ bar that is required at the control valve) will actually be much less than the 200l/min kurnal suggests - his figure is for a "residential" system - the actual requirement is likely to be around half of that.  If a tank is required for the supply then you are likely to need a tank of between one and two cubic metres.  This can be located anywhere in the building but you will also need a pump.  The pump has some demands for its electrical supply but these are not too demanding.

As kurnal states, your biggest issue is not going to be in the technology, but in the act of putting a convincing argument to building control and the fire service.  Kurnal's comments about fire-fighting give you an idea of how to put your argument together.  You should bear in mind, if you go for the domestic system, that the system will only last ten minutes and if the building is located somewhere where the fire service will take 20 minutes to get to the building then the ten minute supply is unlikely to seem like an attractive option for them.  If, however, they are likely to get an appliance there within ten minutes then they might be happy that they will be faced with a smaller fire when they attend.

As for water mist, there's no BS and the NFPA standard won't really give you precise guidance on the design of the required system.  Remember that you are intending to install the system as a life safety compensatory feature.  The NFPA life safety system requires 30 minutes supply and this is infrequently proposed in this country.  You may find it hard to present a rigorous argument to building control and the fire service if you propose water mist as compensation for the lack of internal fire fighting facilities.

Stu

 
 

[kurnal]

Thanks Stu yes I was getting my domestic sprinkler standard mixed up round the residential standard. The domestic standard provides for two heads to operate for 10 minutes. The residential system provides for up to 4 heads to operate for 30 minutes.

A very significant difference if you are relying on stored water from a tank. But if able to use the towns mains- (and there is a national protocol allegedly the whole of the Water Industry is signed up to though it appears a bit patchy) then a residential sprinkler system over the domestic may be one to keep up your sleeve and could sway the argument ( but pipes need to be a lot bigger of course)

Stu is also right about the reluctance of many brigades to accept water mist- there are high and low pressure systems. There are only International Maritime Organisation standards to work to as far as I am aware but to me if you are on a ship in the middle of the ocean and you have a fire any help will be a long time coming. If the IMO is prepared to rely on water mist for ships its good enough for me.

[CivvyFSO]

Since it seems to comply with ADB without a riser, I think the FRS will be thrilled with a sprinkler system.

[kurnal]

Nice one civvy! well spotted.

looking in a bit more detail xan am a bit puzzled by this comment:

However it is over the 11m threshold which I believe (I admit I am not sure-guidance in ADB/BS9999 is a bit vague,but does appear to be so in the old BS5588-5 table 4 )requires  a dry riser.

There isnt a table 4 in the old 5588 part 5?  

The 11 m threshold for small single staircase buildings in ADB is in respect of means of escape, and of course assumes a normal storey height and flats on each storey. It allows a single means of escape.  I guess in a water tower there will be very little accommodation opening into the staircase at the lower levels? Is the dry riser an appropriate compensation for this means of escape issue? Or would you be better to focus the integrity of the means of escape? To this end para 36.2.2.1 on page 51 of BS5588 part 1 gave advice on dealing with small sngle stair flats over 11m in height.
 

[CivvyFSO]

Table 4 in BS5588-5 does suggest that shafts with unvented lobbies but no mains should be supplied in buildings between 11m and 18m.

ADB does say that where fire fighting shafts are provided they should be generally designed in accordance with BS5588-5, but the recommendations in ADB would not have a ff-shaft in the circumstances given here, so I see no reason to reference any part of BS5588-5.

FWIW, BS9999 follows the same lines of BS5588-5, so if you are designing to BS9999 then you might be stuck with it.

I believe the 11m limit was created in relation to the size of the FRS ladders, and IIRC it goes right back to the fire grading of buildings. (i.e 40ft[?] ladder pitched against a wall.)

[kurnal]

Thanks Civvy just found out I have been looking at an outdated version of the outdated standard part 5.  

[CivvyFSO]

It is nice to know that it happens even to you, Kurnal.

The uppermost flat has an additional 3 internal stories,uppermost floor at 26.5m. However the furthest point from fire service access to furthest point in flat is approx 48m

Kinda sneaked that one in there. A floor at 26.5m? You should be supplying a lift, never mind a riser.

You could raise the argument that the lift could only go to the floor at 17.5m anyway, I would point out that ADB makes reference to "Buildings with a floor at more than 18m above fire and rescue service vehicle access level..." which this building clearly has. (I would also suspect that the reason for the topmost flat being 3 storeys high is simply to try get around the 18m threshold anyway, but then again, I am quite a cynical person.)

I would like to see plans where the 45m hose criterion can be reached on a floor 26.5m above access level, taking into account that Mr. Pythagoras tells us there is at least 37.5m worth of steps. I am not saying it is impossible, just 'unlikely'.

I have no sympathy with any constraints on geometry whatsoever. It is an old water tower. If it is not suited for building flats that conform to current standards then don't build flats there.

All that being said, a residential sprinkler system (As Stu's comments) might compensate quite well but the whole B5 package needs looking at carefully and needs discussing with the appropriate FRS properly.

[Mr. P]

I believe the 11m limit was created in relation to the size of the FRS ladders, and IIRC it goes right back to the fire grading of buildings. (i.e 40ft[?] ladder pitched against a wall.)

Civvy, quite right! All about the 'size' of your equipment!!! Do you rmember the wheeled escape? 

[nearlythere]

I believe the 11m limit was created in relation to the size of the FRS ladders, and IIRC it goes right back to the fire grading of buildings. (i.e 40ft[?] ladder pitched against a wall.)

Civvy, quite right! All about the 'size' of your equipment!!! Do you rmember the wheeled escape? 

Gosh, the old wheeled escape by george. A he-man's ladder but a little awkward when you needed to get into a roof space from a bathroom. 

[CivvyFSO]

I am not old enough to remember them Mr. P. I hear hook ladders were the tool of the brave though.

[nearlythere]

I am not old enough to remember them Mr. P. I hear hook ladders were the tool of the brave though.

The "brave" bit was getting on to the roof of the tower.

[Midland Retty]

ah yes, hook ladders and wheeled escapes - back from the days when men were men, women were grateful, and sheep were afraid!!!

(Any complaints about the suitability of this post should be addressed to Firenet Admin)