Air-Pressurized Water Extinguishers
APW stands for "air-pressurized water." APWs are large, silver extinguishers which are filled about two-thirds of the way with ordinary tap water, then pressurized with normal air. In essence, an APW is just a giant squirt gun.
APWs stand about 2 feet tall and weigh approximately 25 pounds when full. They are designed for Class A (wood, paper, cloth) fires only.
POINTS TO REMEMBER ABOUT WATER EXTINGUISHERS
Water is a good conductor, and there is some concern for electrocution if you were to use water to extinguish an electrical fire. Electrical equipment, including computers, must be unplugged and/or de-energized before using a water extinguisher on it.
APWs extinguish fire by taking away the "heat" element of the fire triangle.