The High velocity Water Spray System has been developed for the extinguishments of oil fines, and it introduces an entirely new principle in fire extinguishments. It is employed to bring about a fundamental change in the nature of the inflammable liquid, which is converted temporarily into an emulsion which cannot burn.
A special type of nozzle, termed a projector, is employed, discharging a cone of water in the form of evenly distributed broken streams of high velocity and high momentum. The rapid movement of the broken streams of water is suddenly arrested at the oil surface and the impact causes the oil to be broken up into tiny globules to form an emulsion with the water. In this manner, almost immediately the water from the projector strikes the burning oil-in-water emulsion is formed which cannot burn.
In addition, the dispersion of the oil in minute globules in the water gives almost instantaneous cooling and thus, together with the extinguishments of the fire, there is simultaneous cessation of the formation of oil vapour.
When an emulsion formed by the "High Velocity Water Spray" system is allowed to rest for a considerable period of time, the oil and water will separate. Such an emulsion is said to be unstable. It must be realized, however, that most emulsions formed by the "High Velocity Water Spray" system, although not stable (or permanent), remain emulsions for a sufficient length of time to prevent recurrence of ignition after the water discharge has ceased.
With the "High Velocity Water Spray" System, fires of all light mineral spirits such as petrol, paraffin, benzene and white spirit can be extinguished, but whereas the emulsions formed with the heavier oils persist for sometime, those formed with the light spirits are transient.
For this reason, complete extinguishments of the light mineral spirit cannot be assured unless the whole of the burning surface is brought under simultaneous bombardment from the projectors. It will be appreciated that such a state of affairs is not always possible, for even with the ideal design of protection the fire may be preceded by an explosion causing disarrangement of the plant and some shielding of the burning liquids. On this account the "High Velocity Water Spray" system can only be put forward in such cases after a full enquiry into all the circumstances.
