and clearly, when called, require immediate investigation. BETWEEN 25,000 AND 30,000 FEET.— Between 25,000 and 30,000 feet, collapse, unconsciousnes, and death quickly follow interruption of the oxygen supply. Mask leakage at these altitudes may cause a degree of hypoxia that, although not noticed during flight, can produce considerable fatigue and have serious cumulative effects. ABOVE 30,000 FEET.— Above 30,000 feet, unconsciousness and death strike rapidly and often without warning. At such altitudes, it is imperative that all oxygen equipment be functioning correctly and that each breath be taken through a properly fitted oxygen mask. Above a pressure altitude of 35,000 feet, pressure breathing oxygen equipment is required. GASEOUS OXYGEN SYSTEMS Learning Objective: Identify safety pre- cautions, components, typical systems, and maintenance procedures for gaseous oxygen systems. Gaseous oxygen systems are used primarily in large, multiplace aircraft where space and weight limitations are less important items and the systems are used only periodically. HANDLING/SAFETY PRECAUTIONS The pressure in gaseous oxygen supply cylinders should not be allowed to fall below 50 psi. If the pressure falls much below this value, moisture is likely to accumulate in the cylinder and could be introduced into the oxygen system of the aircraft, causing component malfunction. All oxygen under pressure is potentially very dangerous if handled carelessly. Personnel servicing or maintaining oxygen systems and components must be meticulously careful about preventing grease, oil, hydraulic fluid, or similar hydrocarbons as well as other contamination from coming in contact with lines, hoses, fittings, and equipment as this contact presents a fire and explosion hazard. If, because of hydraulic leaks or some other unpreventable malfunction, components of the oxygen system do become externally con- taminated, they should be cleaned using only 4-4 approved oxygen system cleaning compounds. While some MIMs specify the use of a variety of cleaning compounds, the preferred compound is oxygen system cleaning compound conforming to Military Specification MIL-C-8638 or ultra clean solvent cleaning compound (type I, trichlorotri- fluoroethane) conforming to Military Specifica- tion MIL-C-81302B. The following safety precautions should be adhered to: l Under no circumstances should a non- approved cleaning compound be used on any oxygen lines, fittings, or components. . When handling oxygen cylinders, the valve protection cap should always be in place. Before removing the cap and opening the valve, ensure that the cylinder is firmly supported. A broken valve may cause a pressurized cylinder to be propelled like a rocket. . Do NOT use oxygen in systems intended for other gases or as a substitute for compressed air. . Cylinders being stored for use on gaseous oxygen servicing trailers or any other use must always be properly secured. Do not handle cylinders or any other oxygen equipment with greasy hands, gloves, or other greasy materials. The storage area should be located so that oil or grease from other equipment cannot be accidentally splashed or spilled on the cylinders. Additional safety precautions may be found in the publications technical manual NAVAIROSH Requirements for the Shore Establishment, NAVAIR A1-NAOSH-SAF-000/ P-5100; Aviators Breathing Oxygen (ABO) Surveillance Program Laboratory Manual and Field Guide, A6-332A0-GYD-000; Aviation-Crew System, Oxygen Equipment, NAVAIR 13-1-6.4. SYSTEM COMPONENTS Basically, all gaseous oxygen systems consist of the following: 1. 2. 3. Containers (cylinders) for storing the oxygen supply Tubing to route the oxygen from the main supply to the user(s) Various valves for directing the oxygen through the proper tubing