Controlling Metal Fires through Cellulose Flake Blanketing Followed by Water Spray Cooling

Abstract

The traditional methods of fighting metal fires are not always safe for firefighters. The sand and salts that are thrown onto the fire to suffocate the flames can lead to splashes of molten metal, putting the firefighters and the surroundings at risk. A novel process is described where magnesium fires are brought under control using a simple two-step process. First, coated cellulose flakes, which contain approx. 30% inorganic salts, are blown onto the fire from a distance of several meters. Due to its low bulk density, the material settles smoothly on the fire and immediately covers the flames for several seconds. Before the hot metal can break through this cover, a fine water spray is applied to the fire. The water spray wets the top layer of the cellulose flakes, which will begin to char from the bottom. The water evaporates from within the cellulose flake layer and withdraws heat. It was observed that no hydrogen is formed and that this technique can safely control fires. It is judged that 90 kg of flakes could safely bring a pile of 75 kg of burning Mg flakes under control. By using a pneumatic conveying unit for the flakes, firefighters can effectively and efficiently cover the flames from a safe distance. This novel method could be recommended to firefighters in industrial magnesium processing plants, as well as local firefighters in the vicinity of such plants.

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

“…A water jet would have "blown off" the charred cellulose cover and immediately have led to a spread of the molten metal and its reignition, with oxyhydrogen explosion. The mixture of the salts in the cellulose flakes had been optimized in lab trials [8,9], and was confirmed in a field trial with up to 75 kg of burning magnesium. The amount of flakes there was needed to control magnesium fires of different sizes -see Figure 1 below.…”