Nozzles for the fire safety industry

Fire extinguishing key spray challenge - Fine droplets

The finer the droplets are in a spray the quicker they will evaporate or boil.  The evaporation of water in a spray helps to displace oxygen and so not only does it remove heat from the fire, it also helps starve the fire of oxygen.  So fine sprays have many advantages when combating fire, but it needs to be remembered that fine sprays also have far less impact than ones composed of heavier droplets.  This means that very fine mists might not penetrate into a fire to deliver cooling.

Furthermore, the process of atomising sprays uses up energy and (in direct pressure nozzles) this comes from the potential energy of the fluid being sprayed.  Generally speaking this means that flow rates will be lower (for any given pressure) if the nozzle is producing fine droplets.  This limitation of flow rate often means that the very finest droplets simply do not deliver enough fluid to fight fires.

In theory this problem could be overcome by using air atomising nozzles.  These nozzles break up the fluid by using compressed air.  This means that none of the potential energy of the fluid is used up in the atomisation process.  So theoretically a very fine spray could be delivered at a high flow rate.  In practice, however, even high flow rate air atomisers cannot deliver enough fluid for fire extinguishing systems.  The amount of compressed air needed to break up the fluid from a larger flow rate nozzle would actually be prohibitively high, making such a system impractical. 

The best nozzles for producing very fine droplets for fire extinguishing applications are our various ranges of misting nozzles. These are energy efficient nozzles and whilst limited in overall flow rate, are suitable for many fire extinguishing applications.   In particular they are the nozzle of choice for halon replacement/misting fire suppression systems.

Droplet size mix

As mentioned above the fine droplets in a spray provide the most cooling power per unit volume of fluid but heavier droplets are able to penetrate further.  As a fire will automatically set up potentially strong thermal air currents some spray penetrative power is required.  A nozzle like the TF or N series spirals will give relatively fine atomisation for cooling power but also some larger droplets for penetration.  This makes them ideal for many fire extinguishing applications.