Fire extinguisher CO types have the test information stamped on the cylinder, all other types get a sticker on the back of the cylinder. Once dry, the units are recharged. Unlike the UK, the US does not rebuild extinguishers and replace valves at specific intervals unless parts are found to be defective, with the exception of halon. Halon types are often given new o-rings and valve stems at every internal maintenance to minimize any leakage potential. OEM equipment must be used for replacement parts for the extinguisher to maintain its UL rating. If parts are unavailable, replacement is recommended, keep in mind
Fire extinguisher applications. Most class D extinguishers will have a special low-velocity nozzle or discharge wand to gently apply the agent in large volumes to avoid disrupting any finely divided burning materials. Agents are also available in bulk and can be applied with a scoop or shovel. Several modern "ball" or grenade-style extinguishers are available on the market. The modern version of the ball is a hard foam shell, wrapped in fuses that lead to a small black powder charge within. The ball bursts shortly after contact with flame, dispersing a cloud of ABC dry chemical powder which extinguishes the fire. The