Protectospray System - Mather and Platt
Common sense often dictates that when a fire involving a highly inflammable liquid or gas breaks out, the vapors should be permitted to burn at the point of escape until the flow of fuel can be stopped. Efforts to minimize fire damage and to reduce the risk of explosion are then concentrated on protecting adjacent equipment such as tanks, pipes supporting structures and valves by means of the cooling effect of water spray. This method avoids the danger of spreading the heavier-than-air explosive vapors which might collect in cellars, trenches and low places, thereby creating hazardous flash explosion conditions.
SYSTEM - The Protectospray system protects plant, structures and machinery against fires which may involve highly inflammable liquids, gases and solids, and renders them safe by the application of water in the most effective manner, in the correct quantity and at the right place. The equipment is permanently installed around the risk and, where practicable, installations should be automatically and manually controlled for immediate operation in the event of fire. Certain special installations are designed with only manual control but wherever possible the system is designed to respond automatically to the heat of a fire, with freedom from the human element.
PRINCIPLES - When a fire occurs Protectospray equipment applies water in finely divided droplets traveling at medium velocity and gives protection to tanks, structures and factory equipment by cooling, by controlled burning of inflammable liquids and by the dilution of explosive gases. Protection by cooling When the Protectospray system is brought into operation over a tank involved in a fire and containing an inflammable liquid or gas the protective film of water flows over the external surface of the exposed vessels and the supporting structure, to reduce the temperature and prevent a dangerous absorption of heat. To achieve this object under fire conditions and to ensure the efficient protection of plant, the rate of water application and the distribution of water from all sprayers protecting the risk require detailed study and design.
Protection by Controlled Burning - The rate of burning of an inflammable liquid depends upon the rate at which vapor is given off from the surface of the liquid, and the supply of air or oxygen to support combustion. Normally, when an inflammable liquid burns, the rate of vaporization increases until the fire reaches a maximum rate of burning; at this stage the surface of the liquid is boiling.
The Protectospray System can control these conditions in three ways; firstly, by directly cooling the surface of the liquid, thus reducing the rate of vaporization; secondly, by producing steam which dilutes the air and vapor feeding the fire; and thirdly, by introducing droplets into flame, thus cooling it and reducing the transfer of heat back to the liquid surface. Fires involving highly inflammable liquids can thus be controlled to a point where personnel can soon approach and extinguish the fire with little danger to themselves.
Protection by Dilution of Inflammable Gases - When highly inflammable gases leak from their containers to form a mixture with air, a critical mixture will form so that any source of ignition may cause an explosion or fire. If the Protectospray system is operated when a leakage has been detected and before fire has started, it produces air turbulence, which promotes quicker dilution of the gases by air and water vapor. Fire can often by prevented by employing this method to produce quickly a mixture which is too weak to burn. If fire did occur, then the Protectospray system could prevent a dangerous increase of pressure inside the containing vessels, and protect the supporting structure against failure caused by high temperature.