Height of wet risers

[BB]

Just trying find out what the correct height is for wet risers in commercial buildings. I have always quoted 60m, however I have been informed by a colleague that the height has now been reduced to 50m. He is not sure where that information has come from.

I've had a look at BS6306 but not sure if I'm looking in the right place. If anybody has the correct information and an electronic copy of the relevent document it would be greatly received.

Many thanks  BB

[nearlythere]

Just trying find out what the correct height is for wet risers in commercial buildings. I have always quoted 60m, however I have been informed by a colleague that the height has now been reduced to 50m. He is not sure where that information has come from.

I've had a look at BS6306 but not sure if I'm looking in the right place. If anybody has the correct information and an electronic copy of the relevent document it would be greatly received.

Many thanks  BB

BS9999?
Fire mains should be installed in buildings where any floor is higher than 18 m above ground level. Where there are no floors higher than 50 m above ground level, wet or dry fire mains may be installed.
Where there are floors higher than 50 m above fire-fighting access level, wet fire mains are necessary owing to the pressures required to provide adequate water supplies at the landing valves at upper floors and also to ensure that water is immediately available at all floor levels.

[JC100]

Approved Doc B states (15.6) - Wet fire mains should be provided in buildings with a floor at more than 50m above fire and rescue sevice vehicle access level. In lower buildings where fire mains are provided, either wet or dry mains are suitable.

The standard that covers this is BS9990:2006 Non-automatic fire-fighting systems in buildings.

[BB]

Many thanks nearlythere did not think of looking in BS9999.

Thanks also to smokescreen for referencing ADB

[wee brian]

It changed because somebody discovered gravity.

Turns out that the all singing all dancing compartment firefighting techniques now used by our good freinds in red lorries requires water!

In fact it requires water at the right flow and pressure.

A 60m dry riser wasnt up to the job - Gravity - doh!!!! (pressure at the bottom would be too high)

Hence the change. The research report is online if you want to read all about it.

[Midland Retty]

It relates to current firefighting tactics, and in particular the water pressue at which "fog nozzles / branches"  can provide sufficient volume for effective gas cooling.

Water pressure at the branch should be around 5 bar minimum (if I remember correctly without going over my notes )

[kurnal]

Whereas the optimum pressure for the old standard class A branch with a 12.5mm nozzle was about 2.5 Bar (half inch and 35 psi in your money Thomas).

So the reduction in height by 10 m gives them another bar to play with. Allow 0.1 Bar pressure loss per metre head we can pump into the main at 10 Bar, lose 5 bar due to head and still have about 5 Bar to play with.

And if this is piffle dont hesitate to tell me. Memory aint what it was.

[Tom Sutton]

BB  to make up for my sins I found an advert for a company called Celsius Fire that mentions the 50M maximum height for dry risers if you contact them they may be able to advise you where the information comes from. http://www.celsiusfire.co.uk/dry-wet-risers-supply-install.htm

[wee brian]

http://www.communities.gov.uk/documents/fire/pdf/381216.pdf

http://www.communities.gov.uk/documents/fire/pdf/381219.pdf

These two reports cover the issue. These are what brought about the change.

[Tom Sutton]

BB It looks like the answer to your question is BS 9990: 2006 Code of Practise for non automatic fire fighting systems in building. I do not have copy but need to go to the local reference library to confirm it but FRS Circular 71/2006 is pretty clear. Check out http://www.communities.gov.uk/documents/fire/pdf/154175.pdf

NT gave us the answer but one digit was incorrect 

[Mike Buckley]

Wonderful, I remember in my day the magic 10 bar pressure was there as it was about the maximum pressure we expected the hose to take without bursting. If the pump operator exceeded this, with a bit of help from the branch being shut off, there would be a large bang and a new water feature between the pump and the dry riser inlet.

To get a reasonable jet at the branch we usually called for 4 bars pressure, which given friction loss etc. would be less at the branch but still a good jet hence the 60 m.

OK I was using the old rubber lined canvas hose, hose scrub, rubber acid, drying towers ramble ramble.

[wee brian]

I think the hoses and branches need to be the right spec too.

The choise was, up the pressure and get some better hoses. or install wet risers in several thousand buildings.

Tough choice....

[Tom Sutton]

The choise was, up the pressure and get some better hoses. or install wet risers in several thousand buildings.

Tough choice....

I suspect you are not EX Fire Service and had to lug up hose six floors and the time this takes while the fire is getting out of control. I see this as the reason and not having to purchase hose with higher working pressures.

[CivvyFSO]

I think the hoses and branches need to be the right spec too.

The choise was, up the pressure and get some better hoses. or install wet risers in several thousand buildings.

Tough choice....

And how exactly do they up the pressure? Ah, simple... Fit new pumps to all fire service pump vehicles, then throw the old hoses away and purchase new ones that can handle the increase in pressure. All at the taxpayers expense and the council tax payers expense.

Or do they put the cost in the hands of the people who want to build these tall buildings in the first place? The very same people who will be making the profit from the building.

TW, your argument seems a little misplaced. In the circumstances where the 10m will make a difference there will be a firefighting lift, and if it is out of commission you still have to carry the hose up regardless of whether it is a wet/dry riser. Unless you mean that the newer hose might be heavier due to an increased strength requirement, and as such in ALL jobs it would become another increase in the burden, which might be worth clarifying.

[kurnal]

Wee B was right in his earlier posting and we mustn't lose sight of the fact when falling out with each other.

Firefighting techniques changed to reduce the risk of backdraft to firefighters on entering a fire compartment. The new techniques require higher pressure at the branch.
There is a maximum safe working pressure for the pumps and hose systems and these are fairly common throughout the UK fire service. Ideally for safety the working pressure should be about 2/3 of the test pressure. It doesn't really matter if this 2/3 is exceeded when necessary but this should not be the norm. It is a slight risk but perhaps a lesser one compared to sending crews in without adequate cover.
This point will always be arguable for existing buildings, new builds cater for this by placing a lower limit of 50m for dry risers, therefore making the developer pay, and, as Civvy points out, this is how it should be.