Residential Sprinklers in Compliance with ADB

[wee brian]

1 pump set and one 1000 litre tank between the lot?

That's what it says

[Jon Barrett]

The resilience and robustness of the system is proportional to the potential impact of a fire.

If a fire occurs in a clothing shop in a covered shopping centre then it is imperative that the sprinklers activate and contain the fire, otherwise hundreds of people could be injured/killed. Hence the requirement to meet the life safety requirements of 12845.

An apartment is fire compartmented from others around and perhaps there could be 6 people in an apartment - the failure of a sprinkler system has a much lower potential impact. Not much consolation for the people in the flat but that is how it works.

You also have to remember that the risk posed by a fire in an apartment is dependant on the type of fire (chip pan, christmas tree, cigarette etc), the time in occurs in the day (day/night) and the state of the occupants of the compartment (asleep, drunk etc.). Only a cetain percentage of fires will result in death.

For me a system designed to 9251 is appropriate for the potential impact. Remember ODPM's report found that for apartments over 30m sprinklers might be cost effective (emotive subject I know when you start putting a value on peoples lives). Sprinklers for apartments lower than 30m were not considered cost effective.

The ODPM report concluded that... 'The frequency of fire per accommodation unit increases with building height' - hence why they concluded that if sprinklers were installed in apartment buildings over 11 storeys then they might be cost effective.

It is a general rule of fire engineering that you only design for one fire.

[Jon Barrett]

Confirmation received from LPCB is that the sprinkler contractor CAN'T issue a LPCB certificate for a installation to 9251 in a building over 20m because it is a 'major departure'.

Confirmation received from BRE (FPA) that the interpretation of ADB as identified in first post is correct.

However, as Wee Brian has already commented, they go on to say... 'You do need to be carful where people are proposing "design freedoms" or trade offs on the back of the sprinklers being installed. I would suggest that in such cases the specification of the sprinklers may need to be higher than BS 9251 provides'.

How much higher? This is where it becomes subjective and there is no clear guidance available.

[kurnal]

It is a general rule of fire engineering that you only design for one fire.

Yes but that general rule is applied per building- not per street.
Surely flats are considered to be totally seperate occupancies?

If you have 180 flats protected by a single minimal source of water  you could have 179 flats with no protection at all for a considerable time  following the single fire.

[Jon Barrett]

A block of flats is a building and much smaller than a large shopping centre where the same rule is applied.

If you look at the incidence of fire you'll probably find you can cover a large area before buildings in the area would have coincidental fires (occuring independantly).

We looked at fire death stats for a 300 apartment block and according to the stats you would have one fire related death every 123 years.

[wee brian]

Kurnal, think about how often you have had a fire in your own street. I expect that the installer would fit a zone valve for each flat, or each floor in a big block so you wouldn't necessaritly loose protection to the whole block after one incident.

I think 9251 could do with a bit of tidying up now that its being used by regulators.

[kurnal]

I hope so too Wee Brian but am worried that someone may allow you to put in your small cistern to cover the lot because the rules dont specify otherwise.

Yes Jon but if the one fire in your shopping centre had the potential to put all the sprinklers out of commission there would be something very wrong with the installation. Especially if installed for life safety.

And the shopping centre has one centre management and one regime responsible for facilities management and repairs, whereas the flats may have 181 different persons responsible, 180 different installers fiddling with bits of the system some of which may be maintained, and 181 different insurance companies arguing with each other.

The ADB is a nightmare in this respect.

[Jon Barrett]

The ADB has introduced the nightmare because they've referred to a domestic standard (diagrams are for houses only) and applied it to residential when the resi aspects of the standard haven't been sufficiently detailed.

This is where you get different people interpreting it differently.

The general industry conscensus seems to be a monitored valve and flowswitch on each apartment block floor serving a number of apartments. So there would be no parts requiring maintainence in the apartments. Complete installation in the apartments as the initial installation.

In respect of loss of sprinkler protection to the apartments if they were shut down for a period, it has to be remembered that (as long as there's no significant design freedoms) then sprinklers to apartments over 30m are really an enhancement and not an essential element such as fire compartmentation.

If design freedom, in terms of extended escape distances and reducing fire resistance, then yes are more robust system would be required I believe.

A 'small cistern' to cover the lot is what is currently being done because the standards don't ask for any more and as long as there are no significant design freedoms adopted then I think that's fine.

You don't have to have any storage, it could just be fed off the mains if there was enough pressure in them. Again it goes back to it being an enhancement rather than an essential element of the fire strategy.

9251 sprinkler installations with a 80% success rate (hopefully much higher) is better than them not being installed at all.

[peanut]

The ODPM report concluded that... 'The frequency of fire per accommodation unit increases with building height' - hence why they concluded that if sprinklers were installed in apartment buildings over 11 storeys then they might be cost effective.

This conclusion was indeed in a nice yellow box, but there was no explanation of how the conclusion was reached.  There are clearly more fires in higher buildings, but a quick glance at the graph above this conclusion shows that the number of fires in 8+ storey buildings is approximately double the number in 4 storey buildings.  Not really suprising, as one would expect there to be twice as many flats in an 8 storey building as in a 4 storey building.

[wee brian]

Yup - but the cost of the sprinkler supply is shared out so it gets more cost effective.

Its also fair to say that things get a bit hairy in very tall buildings when tey are on fire so even if the numbers are a bit wayward the result is a sensible one.

[Jon Barrett]

If anyone's still following this thread...

It was suggested earlier in this thread that 'domestic' standard could be used for flats over 30m rather than 'residential standard'. This was on the basis, as defined in BS9251, that as long as any individual room doesn't exceed 40m2 then the system only needs to be designed for the activation of 2 heads (rather than 4 heads if it was a residential application).

This is where the issue becomes a little grey...

A domestic occupancy is defined as an 'individual dwelling house, individul flats, maisonettes...'.

A residential occupancy is defined as an 'occupancy for multiple occupation not exceeding 20m in height... such as apartments'.

The definition of 'domestic' doesn't make reference to height, I think on the basis that it is for low-rise flats/maisonettes not those over 30m.

If you have a residential block that requires sprinklers because it is higher than 30m (as required by ADB) then I would suggest you should be applying the residential (i.e. for apartments) rather than the domestic specificaiton (i.e. design for 4 sprinklers not 2) as it falls more closely into that category.

Another issue that requires clear clarification by the authorities to avoid diverse views and debate!

[wee brian]

I still take the view that flats are domestic. Given that ADB tells you to ignore the 20m limit on scope.

I can see how you have come to a different conlclusion and iether of us could be right!  perhaps the BS could be tydied up a bit to deal with this.

[kurnal]

Absolutely agree with that Jon. Keep bangin the drum!

[slubberdegullion]

'You do need to be carful where people are proposing "design freedoms" or trade offs on the back of the sprinklers being installed. I would suggest that in such cases the specification of the sprinklers may need to be higher than BS 9251 provides'.

How much higher? This is where it becomes subjective and there is no clear guidance available.

Any "design freedoms" must be decided upon after full analysis of the effects of the compensating feature and of the effects of omitting whatever is being omitted.  It's a balancing act and cannot be entered into lightly.

For example, there have been cases where recessed sprinkler heads have breached compartmentation in buildings.  That is, the sprinkler system will operate for 10 or 30 minutes, but after that time it leaves a hole in what would otherwise be a line of fire resistance (the plasterboard ceiling).  If the required level of fire resistance in the building is longer than 30 minutes (or 10 minutes!) then there is the potential for a breach.  This is hardly what the designers anticipated and it illustrates how rigorous analysis is required.

It's also fair to say that things get a bit hairy in very tall buildings when they are on fire

The residential standard has to be the one for flats.  The ten minute domestic standard is for houses where everyone is likely to be out in ten minutes (if they're going to get out).  Flats are different.  If you are comparing an individual flat to an individual house, then yes the same principle applies, everyone, if they are going to get out, should be out in ten minutes.  But there is the added complication of the rest of the building.  Ok, if the compartmentation is up to scratch then there should be no reason why anyone else should even find out about the fire, let alone evacuate, but maybe the compartmentation isn't always as good as we'd like to think it is.  To come up with a particular solution for a particular building we're back to the balancing act.

perhaps the BS could be tidied up a bit to deal with this

There are many areas where the BS does not give complete answers, but application of sound reasoning when interpreting the principles being strived for should provide best solutions.

But ADB also states that ‘Sprinklers only need be provided in individual flats’.
Therefore corridors and common areas are unsprinklered.

What is the point of sprinklering an area where there will never be any fire load?

1. Flowswitches and audible alarms
For resi it states that... 'alarm arrangements should be in accordance with the authority having jurisdiction'
We should discuss and agree with the relevant authorities applicable to the project

The fire service may find it useful to have an indication outside a flat that the sprinklers are going off inside, but maybe it would be undesirable to raise the alarm for other residents. Maybe it would be desirable.  It depends.  So that's where the AHJ can have their say and tie the sprinkler arrangements in with the more general fire strategy for the building.

Stu

[Jon Barrett]

Thanks for your comments Stu.

It's very helpful to flag up the issue of looking at what you're reducing when considering trade-offs.

Sprinklers have been introduced in ADB with no (or very little) trade-offs. Therefore I can see how people are looking to install the bare minimum because the requirement is an extra-over in some ways.

The ADB requirements have been introduced to protect life in the immediate vicinity of the fire, within the compartment.

As soon as you start looking at 'design freedoms' then you're in a different ball park and this is where your comments are extremely relevant - a common one is the extending of escape distances and eliminating fire rated enclosure of the entrance hallway in apartments - I guess though that even in that case it could be argues that 10 minutes (technically) would be adequate as they are reductions in the immediate vicinity of the fire and do not reduce down apartment to apartment separation. Although the resilience of the system needs to be considered - dual pumps and tanks etc.

However, I agree with you that resi standard SHOULD be applied to flats and I think that is what the BS is inferring.

The difference in domestic to resi standard is quite significant - 4 sprinks rather than 2 and 30 mins rather than 10 - that equates to a comparision of 820 litres to 5020 litres! Obviously the resi standard installation has a greater capacity to deal with a larger fire.

This difference can have quite a significant difference in installation cost - pipe sizes etc.

You stated that... 'There are many areas where the BS does not give complete answers, but application of sound reasoning when interpreting the principles being strived for should provide best solutions' - Unfortunately BS9251 falls woefully short of coming near the level of standard that is normally expected when we look at sprinkler installations (i.e. 5306:pt2). It is so open to interpretation, as this thread goes to prove.

Sprinklering corridors - this is a carry over from the LPC rules. Sprinkler contractors have suggested that this needs to be done to protect the sprinkler main (as is required by LPC rules). I agree with you, these are not required as the ADB states.

It just goes to prove how confusing the whole situation is when professional people can have views at opposite ends of the spectrum!

I'll be dropping a letter to the IFE Journal - be interesting to see the comments.