An even more important consideration when picking a fire protection system is personnel safety. Water mist systems do not create a safety problem for personnel. Breathing the water mist will not cause harm to people within the protected space, which is a real advantage over other fire protection systems utilising carbon dioxide. For many years, carbon dioxide systems have been used for turbines and power generation equipment. Personnel within a space protected with a carbon dioxide system can be fatally injured if they fail to exit the space before the system discharge.
Cleaning up after a water mist discharge is also very simple. A 10-minute water mist discharge in a power module will usually result in a residual water depth of less than a quarter of an inch (6mm) on floor surfaces. Unlike many gaseous extinguishing agents, the water mist discharge has no impact on the environment. With no ozone depletion level or atmospheric life, water mist systems provide a green alternative for fire protection needs.
Figure 1
While self-contained or modular water mist systems are typically used for power generation modules, pump-based systems can provide mist coverage for the entire offshore facility. In the past, several different types of systems have been used for various areas of the offshore facility. Living quarters were protected with conventional sprinklers. Cafeteria cooking areas have been protected with dry chemical or wet chemical extinguishing systems. Production areas, pump rooms and machinery spaces have been protected with clean agent, deluge or foam systems. Flammable liquid storage spaces have been protected with dry chemical or clean agent systems. Now, all of these areas can be protected by a single pump-based water mist system.
A pump-based system can utilise electric motors or diesel engines to drive the positive displacement high pressure pumps. The pumps generate pressures up to 2,900 pounds per square inch (psi) (200 bar) and the flow volumes can be provided to meet the needs of the largest hazard. Stainless steel tubing is routed to each of the protected spaces and section valves are located strategically to sectionalise the facility. The mist can be delivered through open nozzles in a local application or total flooding deluge method, or with heat-activated fusible water mist spray nozzles.
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