Controlling Magnesium Fires by Cellulose Flake Blanketing and Subsequent Water Mist Cooling

Abstract

A novel technique was developed to fight magnesium fires of different sizes and vigour. In essence, cellulose flakes, as they are used as blow-in insulation material, are modified with inorganic salts. The salts constitute 30 wt% of the mix and are intimately mixed into the flakes. Sodium borate and magnesium sulfate were found to be particularly effective. These salt-laden flakes are transported to a burning magnesium spot by an optimized blow-in machine (dilute phase conveying). From a distance of between 3 and 10 m, the flakes are directed at the magnesium fire. What seems to be counterintuitive works effectively and efficiently: The flakes take a few seconds to completely cover the entire metal fire. Then, the fire ceases for a short period of time, due to oxygen deficiency under the "blanket". It is at that point in time that a water mist can be directed at the covered, burning metal heap. The water will soak the upper flakes and then, heated by the lower-lying metal, start evaporating, while the fire is deprived of oxygen and is made to cool down. The water mist attack can be carried out for an extended period of time. The mixture with 15% of sodium borate was found to work best, by yielding the most stable crust. The novel process allows to control a medium to large-scale magnesium fire within less than one minute, with substantially lower danger potential for fire fighters than in current practice.