be formed when cylinders containing residual combustible gases such as hydrogen, propane, or acetylene are charged with air or oxygen. The reverse of this procedure is equally hazardous. Cylinders used for aviators’ breathing oxygen, dry nitrogen, dry argon, dry helium, or dry air that are found to have open valves and/or a positive internal pressure of less than 25 psi (gauge) should be tagged “Dry Before Refilling.” When operating the compressed air servicing trailers, (gaseous oxygen or nitrogen) the following precautions should be observed: 1. Only qualified operators should operate the trailers while charging. Complete familiarity with the trailer is a basic prerequisite for safe operation. 2. The servicing hose end and installation connection fitting should be thoroughly inspected prior to servicing and any foreign matter removed. 3. Never charge an installation without the proper fusible safety plug and blowout disc in the trailer charging system. 4. Always know the pressure existing in the system to be filled and the pressure in all cylinders to be used in the cascading process before starting charging operations. 5. A malfunctioning pressure regulator should be disconnected from the line by closing its associated shut-off valve. The trailer can then be operated with the remaining pressure regulator. 6. The charging hose should never be stretched tightly to reach a connection. Position the trailer so that the servicing hose is not under tension while charging. 7. Always open all valves slowly. The dangers of rapid cascade charging must be avoided. Compressed air should never be blown towards anyone, used for cleaning of personal clothing, or as a means of cooling off a person. SAFETY PRECAUTIONS FOR EJECTION SEATS AND EXPLOSIVE DEVICES Learning Objective: Identify the importance of the ejection seat check-out program. Ejection seats have several inherently dangerous features that are a definite hazard to uninformed and/or careless personnel. Con- sequently, whenever the aircraft is on the ground, all safety pins must be installed and not removed until the aircraft is ready for flight. Caution must be observed at all times during maintenance of and around the seats to avoid injury and equip- ment damage by explosive devices of the seat. Safety precautions and correct procedures cannot be overemphasized. Keep all cartridges away from live circuits. Under no circumstances should any person reach within or enter an enclosure for the purpose of servicing or adjusting equipment without the immediate presence or assistance of another person capable of rendering aid. When removing cartridges for inspections or for safety reasons, they must be marked for identification so they can be reinstalled in the same device from which they were removed. Under no circumstances should an unmarked or unidentified cartridge be installed in any cartridge- actuated device. Cartridges should be handled as little as practicable to minimize risk of fire, explosion, and damage from accidental causes. All safety devices must be kept in good order and used only as designated. Cartridges must be stored where they will not be exposed to direct rays of the sun, and they must be protected from extremely high temperatures. When in containers, they must be stored in a cool, dry place where they can be readily inspected. The seat must always be disarmed before removal from the aircraft because firing of the seat may occur. While handling percussion-fired cartridges, you must exercise extreme caution not to drop cartridges because they can fire upon impact. The following general precautions should always be kept in mind. 1. Ejection seats must be treated with the same respect as a loaded gun. 2. Always consider an ejection seat system as loaded and armed. 3. Before you enter a cockpit, know where the ejection seat safety pins are located, and make certain of their installation. 4. Only authorized personnel may work on, remove, or install ejection seats and components, and only in authorized areas. EJECTION SEAT CHECK-OUTS The modern, high-performance aircraft used by todays Navy place extreme demands on emergency escape systems. These systems contain highly explosive devices that are designed for one- time use only. Actuation of these devices could 1-7