In 1984 the innovative Swedish concepts of 'offensive' water-fog applications were introduced to us by Mats Rosander and Krister Giselsson. Their approach revolutionised compartmental firefighting techniques and several fire authorities around the world have since approved this form of attack. In 1994 the UK Fire Research Station confirmed the principles involved were sound and the techniques were adopted a year later as national policy. That same year the U.S Navy adopted this style of fire attack on board ships and by 1998 firefighters in Australia were developing the techniques further still. Currently fire authorities in Holland, France, Germany, Spain, Italy and USA are seen to be exploring the most recent developments concerning 'new-wave' water-fog techniques. However, there are current and emerging trends throughout the UK fire service, in terms of compartment firefighting techniques, that may appear somewhat disturbing and may prompt some cause for concern.

When Rosander & Giselsson originally reported on the Swedish concepts they recommended a 'minimum' flow-rate of 100 litres per minute (LPM) for gaseous-phase cooling applications. The TA Fogfighter jet/spray branch that is commonly used by Swedish firefighters incorporates a flow-range of 100-300 LPM or 175-450 LPM. In the UK we have adapted the Swedish techniques in-line with our initial attack strategy which is based around 19mm (some brigades use 25mm) hosereel tubing supplied by high-pressure pumps. Where operated within the previously accepted range of 15-40 bars (pump pressure) the expected flows from the nozzle would be somewhere within the range of 85-230 LPM for 19mm bore and 250-400 for 25mm bore hoselines. These flows were considered generally acceptable for compartmental gas-cooling applications and routine fireground work including most one-room fires, car fires, rubbish fires etc although some Swedish FBT specialists, at the time, did voice their concerns over the lower flow-range being utilised by UK firefighters. However, as fire behaviour training has developed over the past five years in the UK and firefighters have become accustomed to the 20 Cu.metres of 'container' fire where they learn, practice and perfect the techniques of 'gaseous-phase-cooling', a realisation has dawned that the 'ideal' flow-rate for tackling a container 'burn' is around 40 LPM. It has been suggested that where flow-rates are utilised in excess of this 40 LPM the danger of steam-burns exists to nozzle operators. This has resulted in manufacturers offering 'low-flow' options for the hosereel branches and brigades are now seen to be equipping themselves with an initial 'attack' flow-range of 45-90 LPM on the hosereel system - This is dangerous and throws up major Health & Safety implications. It is not difficult to recognise that the average one room fire may be 3-4 times the size of a standard container training burn. Additionally, the fire loading of a furnished 'room' is far higher than will be found in the standard container, be it carbonaceous chip-board or gas fuelled. It is essential to remember that container systems are only simulators and they simulate igntions of fire gas layers, not class 'A' furnishings.

As an extinguishing medium water has a theoretical cooling capability of 2.6 MegWatts per litre per second although in the practical application of a 'real' fire it's capability is more likely to be around 0.84 MW per litre per second. To the firefighter this means that the nozzle in use has a maximum 'practical' cooling capability and reliable estimates may be derived -

50 lpm - 0.70MW

100 lpm - 1.40MW

150 lpm - 2.10MW

200 lpm - 2.80MW

300 lpm - 4.20MW

550 lpm - 7.70MW

800 lpm - 11.20MW

1000 lpm - 14.00MW

Sofa (2-seater) - 3.0MW

Sofa (3-seater) - 3.5MW

Upholstered Chair - 2.0MW

Rubbish Bin (small) - 300KW

Light Bulb - 100W

Xmas Tree - 0.7MW

Small Dresser - 1.8MW

Single Mattress - 1.0MW

Pine Bunk Beds - 4.5MW

5 Timber Pallets - 1.8MW

2 Panel Work Station - 1.8MW

3 Panel Work Station - 7.0MW

Kings Cross Fire - 15-25MW

Container Simulation - 1.5MW

It is generally accepted, as a 'rule of thumb' guide, that a fire of at least one MegaWatt HRR is required to achieve flashover. However, it has also been observed that flashover may occasionally be achieved with a HRR as low as 300KW and a recent US report!described a backdraft that had been modelled on trash bags emitting just 25KW HRR! It should further be noted that a HRR recorded from a hotel bedroom 'furniture' fire peaked from 2MW to 7MW when the timber wall linings became involved!

It now becomes apparent that flow-rates below 100 lpm are dangerously low and would not provide the firefighter with a safe and effective means of tackling anything more than the smallest of fires. I have spoken to firefighters who have occasionally struggled with the 40 lpm flow-rate in a container simulation and then just managed to control the 'burn' when opting for the higher flow-rate of 90 lpm. This would confirm the above estimates (table one) as realistically achievable flow-rates. (Remember - container burns are three-dimensional simulations producing burning gas layers - there is no major class 'A' fuel load). There have, in the past, been situations where fire authorities have been held vicariously liable for allowing firefighters to utilise low-flow rates in compartment fires where the risk of 'flashover' is existent (isn't that almost every compartment fire?).

A further 'cause for concern' in relation to flow-rates is emerging in terms of 'maximum' available flow for compartment firefighting. As UK fire brigades begin the modern transition from solid stream 'smooth-bore' branches to the more versatile combination fog nozzles a disturbing trend has seen several brigades (including the largest metropolitan brigade) reduce their maximum compartmental flow capability for hand held hoselines from 850 lpm (25mm nozzle @ 4 bars NP) to 450 lpm (combination nozzle @ 7 bars NP). This has been the result of several internal operational reviews of compartment fire-flow requirements and I have discussed this drastic 47% reduction in flow-rate with several fire officers who are of the opinion that 450 lpm is the highest flow needed for a single handline. It is worthy of note that such flow-rates fall way below the recommended minimums recognised by recent european standards commissions in France and Germany in relation to main-line firefighting nozzles. Let's take a close look at this 'maximum' flow-rate and assess it's practical capability on the fireground.

The 450 lpm combination nozzle is a versatile tool that will provide optimum flows normally at a factory pre-set of 7 bars nozzle inlet pressure although this can be lowered as an option. It can be seen, from table one, the 450 lpm nozzle may appear to handle most residential room and contents fires although it will certainly be on its limit if a set of pine bunk beds become fully involved! However, what happens if these 'furniture' fires spread to involve additional items? What if they achieve flashover in the room and involve everything including flammable wall linings? What if the fire spreads into the hallway or even involves two rooms? What if the fire's in a 'commercial' compartment with an increased fire load? What if it's involving the 3-panel work station in a modern office complex? Suddenly things look different and the critical flow rate (CFR) we normally try and achieve to counter such propagating fires is beyond the capability of the hoseline in our hands. Things can only get worse! What if the hoseline we are using is the 45mm line consisting of three 25m lengths - a standard run into an average to large property. The pump pressure required to deliver 450 lpm at the nozzle is 11 bars (on the level)! That's above the UK fire service routine test pressure for hose so let's reduce it to a workable 9 bars. You will now see our original 450 lpm at the nozzle has reduced drastically! If it's the bunk-bed fire we will either have to lay a second hoseline in support!of the initial attack line or the crew on the nozzle are in for a hard time and will take unneccessary punishment. The fire may even propagate in its transition from compartmental to structural as the firefighters attempt to play 'catch-up' inline with it's development.

As we adapt to new techniques and progress the gradual transition towards technologically advanced firefighting branches it is essential we recognise the true capability of our firefighting streams. If we fail to respect the demands placed on firefighters advancing decreasing interior hoseline capabilities against increasing fire loads then we may undermine their own capable limits also.