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NSW Fire Brigades - Australia - 3D Nozzle 'pulsing' Techniques
For most effective 'PULSE' cooling of fire gases in the overhead a nozzle setting of around 115 LPM at 7 bars NP is ideal. A spray pattern with finely divided water droplets will optimise the application.
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'We moved in on the fire....instantly the dense, hot smoke entered the stairwell from our door opening. The hose crew immediately commenced pulsing into the gases as they exited. The unit had been completely shut down with no windows open anywhere and the only exit for the smoke was the self vent in the window as noted on arrival and now the open door. I advanced in with the crew and the rescue crew pulled the door closed against our hose to restrict the opening. This was one of the blackest fires in my memory with ZERO visibility! All I could hear was the 'pulsing' of the hose crew in front and the vapourisation in the gases above as they advanced. With each pulse the immediate area cooled noticeably'......... Gas-Phase Cooling' - 'New-wave' techniques developed by Swedish fire engineers Krister Gisselson and Mats Rosander, using innovative 'bursts' of water-fog, to counter the hazards associated with flashover, backdraft and smoke-gas explosions. These techniques have been further developed by firefighters in the UK, USA, Spain, Germany and Australia and are now being adopted by fire authorities around the world.
The above sequence of pictures demonstrates a 'short' pulse of water-fog droplets - used to cool or inert dangerous fire gases in the overhead; knock-back a rollover; or extinguish gases burning off in small compartments. The 'pulsed' droplets are created by briefly 'cracking' the flow-control mechanism to enable the finely divided water droplets to suspend in the gas layers.
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The above sequence of pictures demonstrates how a longer 'pulse' can be used to penetrate a fire plume in larger compartments and reach fire gases further away from the operator. Note a narrower cone is used for this purpose. The intention is to suspend the water droplets directly into the fire gases as opposed to striking the heated wall linings and ceiling. Inevitably some water will reach surfaces but an application of fine droplets that evaporates mostly within the gases will lead to gas contraction and not steam expansion. CLICK HERE TO SEE HOW THIS OCCURS An application of water-fog that favours super-heated surfaces over three-dimensional gas suspension is termed an INDIRECT application. CLICK HERE TO SEE HOW THIS OCCURS The
term 'three-dimensional water-fog' is not to be confused with
that of 'indirect water-fog' and the associated applications of
either style are completely different. Quite simply, the 'indirect'
approach is where water is applied in a fine spray form onto the heated
surfaces of a fire involved compartment, or room, to create steam. This
massive expansion of steam creates a positive pressure within the room
and smothers the fire to extinction within seconds. However, the steam
will create a sudden rise in compartmental temperature and cause a major
problem for firefighters occupying the compartment. The
'three-dimensional' approach, when used as a firefighting tool, places
the water-fog directly into the heated fire gases and this, in turn,
cools the environment effectively.
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In 1994 Dr. Maarit Tuomisaari of the Fire Technology Laboratory of the Technical Research Centre of Finland (VTT) completed an extensive study evaluating the Suppression of Compartment Fires using a Small Amount of Water. This research had lasted four years and compared the effectiveness of combination spray nozzles in cooling fire gases in sweep, or intermittent pulsing, patterns as well as evaluating the sprays abilities at extinguishing fires. In 2000 a further research project was completed in Sweden at the request of the Stockholm Fire Brigade when Anders Handell, of Lund University, evaluated various firefighting fog/spray streams using computer aided technology and live-fire experience to compare the effectiveness of a wide range of nozzles in cooling the super-heated gaseous conditions that exist in the overhead of a fire-involved compartment. Both research projects were independent of each other but it is worthy of note that each study recommended exactly the same nozzle as being the most effective in gas-phase cooling and fire extinguishing applications!
This particular nozzle is used by London Fire Brigade and many other fire authorities throughout Europe to deal with impending flashover and backdraft conditions. As a result of this research the Stockholm Fire Brigade, established experts in 3D gaseous-phase cooling techniques, are initiating a replacement program to equip their brigade throughout with the recommended nozzle. MORE LINKS TO BE ADDED Last Update on 06 September 2006 Contact John McDONOUGH |
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FLASHOVER
& NOZZLE TECHNIQUES
John
McDonough
