Required flow rate

[chris7]

Hi all,

I remember that the Americans have a rough and simple formla for calculating the approximate required flow rate needed based on  a given area or volume on fire. Can't remember the formula . Sure someone will help me out, if there is a UK formula all the better as it will save me converting. Many thanks.

Chris

[kurnal]

Is this for the application of water or foam?

[Kaiser]

I was always told

50 litres of finished foam, per square metre per minute for a minimum of 20 minutes.  Always ensure that you have enough foam concentrate available to maintain the foam blanket before commencing foam application.

[kurnal]

If its foam a gallon per square foot per minute standard application rate for standard non polar fuels. Or Kaisers rule for you modernised  metricated people. Funny how they never metricated time thank goodness else I would be 5000 metriyears old.

[chris7]

For the application of water.

[John Webb]

From memory of reading the American fire journals before I retired, the American Fire Departments set great store in 'SOPs' - Standard Operating Procedures. It was very clear from reading accounts of American fires that their main domestic fire was very distinctly different from the UK experience. In particular the majority of American homes seem to be timber frame/timber clad structures in which fire spread is considerably more rapid than in the British brick/block-built houses. The American practice, as I recall, therefore tends to be to pull out a hose of at least 45mm diameter and nozzle flowing at least 200gpm at virtually every structural fire they attend. Obviously the bigger the floor area, or if it is a two-storey house, the more water is likely to be needed, hence their rough and simple formula.

This contrasts with the British approach generally with the hose-reels unless there is clear evidence that a larger quantity of water is needed immediately because the fire has developed beyond hosereel control. I cannot recall having ever seen recommended application rates for water application ever laid down in a UK publication, and this is a clear contrast with the American approach.

Hope this helps.

PS - Sorry, I cannot recall the details of the American formula but I think it likely to be one 200gpm jet per 'X' sq feet of floor area.

[chris7]

In reply to Kaiser, I was referring to water not foam but as you mention it I remember 4-10 litres of finished foam per square metre or 12 litres as recommended by the Americans. Minimum of 1 hour and a second application of half the ammount for a further half hour. The American recommendation of 12 litres seems better as it will cover loss due to wind, misdirection, initial breakdown and run off. This is for low expansion foam.


Good point from John_s.webb , seems right that it is a SOP adopted by our colonial friends, and that thier construction and therefore tactics will vary.

[Paul Grimwood]

Metric Formula based on 120 fire study in London

Area x 4 = litres/min, or

Area x 6 = litres/min where ceiling or compartment boundaries (not natural openings) breached by fire

Area of fire involvement in square metres

Critical (minimum) flow-rate A x 2 = LPM (will lead to 50% of compartment fires being suppressed in the decay stages)

Formula is only valid for fire-involvement between 50-600 sq.metres in structures with up to 3m high ceilings

www.euro-firefighter.com

[chris7]

Thanks PaulG. This is the formula I was after.

[kurnal]

Is this based on Jet, spray or fog and does it matter?

Is the formula likely to be any practical use on the fireground due to its limittions and the fact that you have only the equipment you carry and the pressure and flow can only be coarsely calculated and controlled?
And irrespecive of the area of the fire the most important tactic is to surround the fire?

[Paul Grimwood]

No problem Chris - really great to talk with you again after so many years!

Kurnal - good questions! I would suggest that the formula is extremely practical, tried and tested on the fireground over several years. It is of use in pre-planning and at fires as it is easy to apply. The lower end of the formula (50m2) suggests that a 5-roomed flat fire (65sq.m) fully involved will require a practical minimum flow-rate of 65 x 4 = 260LPM to handle this amount of fire during the growth or steady state stages of development. If, however, the fire has breached the structural elements (for example its in the walls or ceiling); OR if exterior winds are intensifying the burn-rate, then 65 x 6 = 390LPM is your minimum flow-rate. (Note this formula is based on mid-range fire loading (office/residential etc) in structures with 2.3 mere high ceilings).

Note that the 'average' flow-rate used on a layflat attack line in the UK is 280LPM. Obviously greater flows are achievable but as most brigades (89%) under-pump their hose-lines this is the typical 'average' flowed.

Also note, a one-room fire can rapidly develop to involve all five rooms in the flat in less than sixty seconds! So how long will it take to get another line in if a single hose-reel is flowing on the fire (120LPM).

The primary objective is to control the fire; the secondary objective is to suppress the fire; the surrounding of a fire comes next. If exterior exposures are your primary concern then suppression or protection are primary considerations prior to 'surrounding' a fire.

Yes the formula is only a general fire-flow formula. It applies to the flow-rate whatever stream pattern or suppression (water) technique is used. If you go into the differences between fog/spray/straight stream, then the calculations become complex and unsuited to fireground use.

Hope this helps. Try some pre-planning and then practice it at real fires.

www.euro-firefighter.com

[kurnal]

Note that the 'average' flow-rate used on a layflat attack line in the UK is 280LPM. Obviously greater flows are achievable but as most brigades (89%) under-pump their hose-lines this is the typical 'average' flowed.

Also note, a one-room fire can rapidly develop to involve all five rooms in the flat in less than sixty seconds! So how long will it take to get another line in if a single hose-reel is flowing on the fire (120LPM).

Thanks Paul. Sadly my firefighting days are over but always interested to hear of new approaches and ideas.

When you say tha most brigades under pump their hose lines do you mean that operationally they deliver water at less than the optimum  pressure or the nozzle in use?

Interested also in your comment about the one room fire in a flat developing to involve all rooms in less than 60 seconds. I would be interested in any evidence for this- I spend a lot of my time designing fire safety measures for flats! I presume you mean once the fire in the room of origin has developed to fully involve the room  to or near  flashover  ( which can be 4-30 minutes dependng on loads of other factors) then it it a small step to total involvement of the flat if someone does the wrong thing or the door to the room fails. We fit at least a 20 minute door ito all rooms but without self closers these days.

I haven't looked at the website yet but  all honesty my reaction to your formula  is that it has value as an educational and pre planning tool for crews  to inform the decision over hosereel / 45mm / 64mm hose for different scenarios but little practical use on the fireground where for water supplies the old formula of allowing for 300l/m per 45mm hose line and 600l/m for 64mm hose has stood the test of time and is ultimately simplisitic and easy to apply.

[Paul Grimwood]

Under-pumping hose-lines - Yes, UK brigades are generally operating without guidance or a clear understanding of hose and nozzle requirements. There was a national transition during the late 1980s-1990s towards combination nozzles of US design. These demand much higher nozzle pressures than the deflector type spray nozzles we used prior to this period. Currently, brigades are seen to pump ineffective pressures to these nozzles and often fail to meet the manufacturer's minimum performance criteria. Some brigades still teach recruits to start pumping at 3 bars nozzle pressure! That is an old adage from the days of yore!

To adequately pump 'some' of the automatic nozzles you need at least 10 bars at the pump. If the same nozzle is 15 floors up then you cannot meet safe pumping pressures to fully flow these nozzles.

There is also an issue in the belief that the 1990s Swedish nozzle tactics mean you need less water at the nozzle now to achieve the same effect. Some national officers and CFBT instructors truly believe that 40LPM will put out a room fire! That may be so within the confines of a training container where there is virtually no fire load but in a 'real' room fire that is most certainly not the case.

There have been several instances of rapid fire spread in flats following the initial flashover in the room of origin. I have seen this many times and researched the reasons why. Of course if all the doors are closed in a flat this will not occur so quickly. You can wonder about interior fire protection in poor social conditions because self closers rarely work or doors are propped open; poor maintenance; batteries removed or depleted in smoke detectors etc. I can attest to a recent fire that killed two firefighters in Hertfordshire where a one room fire developed beyond the room of origin to involve the entire flat within 60 seconds following original room flashover.

There have been many other instances of rapid fire development in commercial structures once the fire breaches the ceiling space where fire stopping is sometimes not what it should be.

The formula is more useful in the pre-planning stages as you rightly suggest. Even so, I have used it with good effect at large building fires to estimate flow needs and calculate the resources and staffing that is needed on-scene to deal with a developing fire. It is an easy calculation in the head, even at 3am!

We should be able to easily get 500LPM from 45mm and 750LPM from 65mm lines.

Hope things are going well in retirement ;-)

[kurnal]

It is an easy calculation in the head, even at 3am!

Hope things are going well in retirement ;-)

Thats probably why I am retired. My head stopped working at that time of day many years ago.

I know what you mean in terms of the modern branches- as equipment officer I bought the akron turbojet for my brigade in  1980 but must  hold my hand up to never providing effective training at the time.

I accept what you say on the volume of water needed for effective attack on a developed room fire. Interesting also to look at the BRE evaluation of residential sprinklers which would operate earlier in a fire and work on the first head  delivering 60l/min and two heads about 100l/min.

And even more interesting to look at water mist installations such as those used on ships which use minimal volumes of water at high pressure and have been shown to extinguish or control fairly significant fires under the IMO test scenarios. Of course these attacks are initiated automatically on heat sensors long before the  fire is developed to flashover phase.
But what strikes me about this is that as  fire growth is exponential -  typically following t2 curve, the requirement for water must also  follow the same curve if we were to apply just the minimal, optimum amount.

Of course this is taking things too far - because we can only use the equipment we have got on the truck.

[Paul Grimwood]

In 1980 you were an innovator and the Turbojet is an excellent nozzle. These days I think we seem to have have lost the plot in establishing how much water is needed to deal with a fire. I repeatedly hear of hose stream reviews and assessments by health & safety officers, national fire officers and established leaders who are leading the way in how we flow our lines. They make incredible statements! 'It looks like a good stream'! Without realizing that the intention of many modern nozzles are to automatically trade flow for reach. How can anyone possibly suggest a stream is adequate if it 'looks' good! How about testing the flow content and then matching that with fire loading! The trouble is, these 'experts' haven't got  the practical experience in assessing a firefighting stream!

I agree that early detection and low flow-rates will deal with an incipient fire and also that water-mist systems can suppress a lot of fire with a tiny amount of water. I was a project engineer on the development of such a system and saw first hand what these systems can do. However, they rely more on oxygen depletion that they do on fire gas cooling so we would need to think our approach to operational firefighting. Actually, the Cobra system reportedly achieved similar effects in a large room fire test. I can imagine this as may offer potential for dealing with fires in some larger structures that are too dangerous to approach because of visibility and access to the fire, although the practicalities may be restricted in dimensions.