SCIENTIFIC RESEARCHES

MSB report (ENG) – Practical & operational use of cobra

Dielectric test of cutting extinguisher, SP (ENG)

J Gsell (ENG) – Fire suppression capabilities of water mist

GMFRS – Steaming effects on human being

The cobra project (Swe) – Method development to create

safe & efficient interventions

Spray characterization of the cutting extinguisher, SP

Cutting extinguishing concept –practical & operational use

MSB & SP have conducted scientific studies based on almost 10 years usage of cobra and hundreds of interventions. Findings; cobra efficiently cool fire gases and stop fires and inerts fire gases also when temperature is lowcobra enables quicker start of actionTactical choices have been increased when combining cobra, thermal camera and PPVHigh quality education and training enhances the usage and advantages of cobraDamage to property and negative consequences for environment decreased significantly with the cobra-conceptUsage of cobra has improved health and safety aspects for fire fightersSome interventions are described, also multiple use of cobras

DIELECTRICAL TEST

FIRE SUPPRESSION CAPABILITY

Master thesis by Julien Gsell, University of UlsterNumber of burning tests - inerting effects also when compartment was ventilatedDroplet diameter 0,1 mm has a lifetime of 0,2 sec @ 400 degrees C and fall 30 mm before being vaporized. A droplet with diameter 1 mm and corresponding values give a lifetime of 230 sec and falling distance of 680 m!Mie-theory said increased atomization to 0,001-0,01 mm gives higher volumetric absorption efficiency

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GMFRS / FPA

Extensive testing done to establish if there will be any steaming effect of vaporized waterTotally 20 burningsConclusion; increased survivability when cobra is used!(Report is not public yet)

Steaming effect is sometimes an open issue, so information from GMFRS is valuable.

THE cobra PROJECTA two years project with following participating organizationSödertörn FRS FRS SYDStaffanstorp & Lomma FRSMSB & Health and Safety ExecutiveCold Cut Systems

A purpose was to develop tactics, methods and to exchange experience between the organizations.

Is it possible to perform interventions in a safer way by using cobra?Will usage of cobra increase the efficiency to quickly interrupt the fire?

Efficient fire fighting

Results when cobra was used in an initial stage

76% Huge impact to interrupt the fire

43% Very large effect for safer firefighting

62% Very large effect to reduce or eliminate water damages

55% Very large effect to reduce negative impact on the environment

ALL INTERVENTIONS

Diversity of usage

Detached houses

33%

Apartment blocks14%

Public buildings12%

Private buildings10%

Industries10%

Containers7%

Attached houses5%

Garage5%

Farms3%

Under ground.1%

THE cobra PROJECT

Some conclusions from the project:

The cobra cools fire gases in an very effective wayUsage of PPV facilitates when cobra is used as you can control fire gases before you start to ventilateWith a cobra you can also reach hidden fires which are normally very difficult to tacklecobra improve safety fire fightersWater damages and contaminated water were significantly reducedcobra were used, with very good result, in a diversity of different type of fires

SPRAY CHARACTERIZATION A project done by SP and Cold Cut Systems

Spray from cobra is characterized by very small droplets! Cooling, interting and radiation absorption becomes more effective with these small droplets compared to system with larger droplets.

Compared systems Attack and Diffuser fog spears and Fog nozzles connected to enhanced low pressure systems (i.e. 40 bar at pump)

Brief spray theory (atomization)D ≈ We crit ≈ 20 ∙ 73 ∙ 10-3 ≈ 25 micron pair * v2 1.2 ∙ 2202

100 bars pressure gives approx 2,5 times larger droplets

Drop size distribution Drop size distribution

Efficient fire fighting

Large drops means that extinguishing efficiency is dramatically reduced and water/environmental damages rapidly increases.

The cobra produces a very narrow distribution of extremely fine droplets. 5 times higher energy absorption rate than other water misting systems!

Efficient fire fighting

cobra distanced10= 70 micron 10 m -> 7 m/sd32= 170 micron 15 m -> 5 m/s

Attack fog spear distanced10=160 micron 4 m -> 1 m/sd32= 900 micronOff center & additive even smaller dropletsd10 arithmetic, the average of all diametersd32 Sauter mean, the ratio of volume to surface area for the entire spray

Efficient fire fighting

The high pressure, resulting in a high speed and high flow, creates a high momentum spray that pushes the water mist long distances into an enclosure fire, making it possible to act on fires distant from lance despite the small droplets

This also have additional benefit in certain circumstances of entraining vitiated/contaminated air into the fire by the turbulence created

High speed gives large exchange of heat

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