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Sticks and stones
For three decades now, Williams Fire & Hazard Control has been adapting its fire extinguishing systems and tactics to the varying fire dynamics being experienced by the oil and petrochemical industries. Speaking at the International Liquid Terminals Association (ILTA) trade show in Houston this past June, the company’s Dwight Williams concentrated on the emerging threats posed by the storage of ethanol fuels and other polar solvents.
Ethanol fires do not respond to traditional foam products. Instead, Williams has developed a specific foam – ThunderStorm AR-AFFF – and new tactics to best deliver this foam to a fire. The tactics are always based on a fundamental understanding of foam chemistry and the behavioural characteristics of the fire.
Dwight commented: “When considering the variables for a foam attack on a storage tank fire, several factors are often overlooked in the industry.” In particular, he said, a foam blanket may have to travel some distance over a burning fuel surface, and firefighters need to be aware that additional foam will be required for post-extinguishment vapour suppression.
Conditions after a full surface fire is extinguished are not unlike a sunken roof scenario, Dwight explained. There may be a need to re-apply a fresh foam blanket several times while moving the product out of the affected tank simply to suppress vapour or undesirable emissions.
How to do it
Williams Fire & Hazard Control’s patented FootPrint technology uses several different methods to extinguish a fire. When combating a fire in a petroleum storage tank firefighters deploy a react line immediately after flame collapse.
There will be two react lines standing by on either side of the tank aiming at the side of the tank nearest the firefighters. The react lines are needed as the foam will dehydrate and may become an obstacle between the FootPrint of foam and the inner wall. On some fuels this may be the last area of the surface to extinguish, and often the hardest.
Williams Fire & Hazard Control found that when tackling a fire in a 200-foot diameter tank, the point furthest from the foam line will have to be extinguished first, otherwise the rest of the fire cannot be dealt with successfully. The company found that on crude oil, heavy fuels and heated products a technique called ‘teasing’ proved very effective as a means of gaining control and effectively achieving extinguishment. “This technique may cause some product to expel out of the tank,” warned Dwight. “This methodology is designed to control the reaction of the product and enhance extinguishment. It is important and recommended to have experienced personnel directing this attack.”
When teasing the fire, the nozzle of the hose should be raised and the pattern should be adjusted between a straight stream and power cone (30° angle) feathered stream. The nozzle is then swept across the surface aggressively from outside to outside of the tank allowing the surface to ‘cut-up’ and cool down. The method cuts up the hot crude oil allowing the foam blanket to go on top, otherwise it will spit it right back, increasing risk.
When tackling ethanol fires it is important not to tease the surface of the product. Dwight explained that no foam has yet been invented that allows the user to apply it straight on to the heart of the liquid - the firefighter must always move it in from the tank wall. This is always the case with ethanol fires. When aiming the foam at the wall of the tank it will create a swell that circulates around the inside of the tank, distributing foam in a whirlpool-like motion. The foam must be applied in this fashion throughout the process of extinguishing the fire as the flames will be extinguished from the outside in.
Giving advice on what to do when a fire breaks out, Dwight informed delegates that they should only cool down the tanks surrounding the tank on fire. It is imperative that the operator does not cool down the problem tank until it is ready to be put out otherwise it will curl inwards and can tear, creating a bigger and more dangerous situation.
“If you don’t have water, you better have insurance” stated Dwight. “Equipment that has been successful on traditional hydrocarbon fires is just as effective on polar solvents when the applications are understood, and correct methodology is exercised.”