Dry chemical extinguishers have long been attractive because they are less than half the price of Halon and Halon alternative units. A visit to our local Home Depot store and a quick survey on the web found prices for 5B:C and larger dry chem extinguishers in the $35 to $70 range. However, the FAA specifically recommends against using them in aircraft in AC 20-42D. “In general, dry chemicals are not recommended for hand extinguishers for internal aircraft use, due to the potential for corrosion damage to electronic equipment, the possibility of visual obscuration if the agent were discharged into the flight deck area, and the cleanup problems from their use.”
