Almost 200 years ago, a spring pole cable drilling rig was developed in an effort to bring oil to the surface of the earth and, in 1897, the first oil well drilled from a wharf over water was completed in Summerland, California. Drillers moved from wharfs to platforms over water in 1911 and have continued to explore the world’s waters in the pursuit of oil. In 1979, oil wells were drilled in water 1,000ft (305 metres) deep and in 2001, a well was drilled at a depth of 9,687ft (2,953 metres).
Offshore drilling rigs and the offshore production facilities used to process oil have special fire protection requirements. These facilities are basically small stand- alone cities in the ocean. Power for the facilities is generated with turbine and diesel engine-powered electrical generators. Seawater is converted to fresh water for drinking and bathing. The workers are housed in living quarters that can be compared with multi-story hotels. Food is prepared in cafeterias for the staff, and waste treatment plants process much of the waste. Oil is brought to the earth’s surface and processed for shipment via tanker or pipeline.
Almost every portion of the platform requires some form of fire protection. Many of the spaces found on offshore oil drilling and production facilities can be protected with water mist systems. Water mist systems have tremendous fire suppression and extinguishing capabilities whether the area protected contains flammable liquids or ordinary combustibles. System testing protocols developed by the International Maritime Organization (IMO) have set the standard for water mist design requirements. Coupled with the National Fire Protection Association (NFPA) 750 Standard on Water Mist Fire Protection, these global guidelines set the benchmark for fire protection engineering companies to use when designing water mist systems.
Water mist systems provide suppression and extinguishment of fires through the use of three primary mechanisms:
- cooling;
- oxygen depletion (inerting); and
- radiant heat blocking.
Water is the most basic fire extinguishing agent known to man and has tremendous cooling properties. Water converted to steam is a very efficient fire extinguishing agent. Since one unit of high pressure water mist creates 1,700 units of steam, it does not take a large quantity of water mist to create large quantities of steam. The generation of steam from the mist water droplets depletes the oxygen on the flame front and the fire is extinguished. The mist system also cools the fuel to prevent the fire from reflashing and water mist blocks radiant heat to objects not involved with the fire.
High pressure water mist systems can produce 8,000 droplets of water from a unit of water required to produce a single droplet from a conventional sprinkler head. The large number of small water droplets result in a vaporisation rate of 400 to one compared with a conventional sprinkler head. Obviously, a high pressure water mist system provides the more efficient use of water in the extinguishment and suppression of fires.
Historically, the first area of offshore facilities to be protected with water mist was the power generation modules. The turbines and diesel drivers for the generators are essential to the operation of the facilities and a fire can create catastrophic results. Water mist systems provide excellent fire extinguishment in the power generation modules and require very little valuable deck space. Modular systems are typically provided for the power modules with a 10-minute water mist discharge being the norm. A typical turbine module requires only 150 litres of water for a 10-minute period. High pressure water mist is delivered through small diameter, 12mm and 16mm, stainless steel tubing to four nozzles. The water is transformed into water particles approximately 100 microns in diameter, creating a high pressure water fog in the protected space. Fires are quickly extinguished and the system can quickly be placed back in service by simply refilling the three water storage cylinders and replacing the 50 litre nitrogen cylinder. No equipment has to go inshore for service and the down time is minimal.
Water mist systems have been tested by numerous agencies to prove that the mist will not harm turbines or diesel engines due to thermal shock. With the price of a new turbine being millions of dollars, preventing damage to the turbine is a major consideration when a fire protection system is selected.
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Health & Safety
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