Aircraft systems and LOX converters should be serviced in accordance with the appropriate maintenance instructions manual (MIM). Only LOX conforming to MIL-0-2710, type II, may be used in aircraft LOX systems. The fire-fighting agents listed below are prohibited from use in conjunction with LOX-enriched fires.

1. Soda-acid extinguishers

2. Mechanical (liquid) foam

3. Methyl bromide

4. Carbon tetrachloride

CONTAMINATION CONTROL Learning Objective: Recognize contamina-tion control procedures for oxygen equip-ment to include detection, purging, and purging equipment.

The importance of using uncontaminated LOX in aircraft systems cannot be overstressed. Because of this, the Navy has established-the Aviators Breathing Oxygen (ABO) Quality Evaluation Program (A6-332AO-GYD-000). For additional information on contamination control, oxygen sampling, and oxygen system purging, refer to that program.

DETECTION

LOX contamination is detected by means of an odor test, sampling, and analysis. Only the odor test will be discussed in this manual because all other tests and analysis must be performed in a laboratory. An odor test will be performed on LOX trailers after the first filling of the day, or each 6 days when the trailer is not in service. Aircraft LOX systems require an odor test to be performed as soon as possible after an aircraft accident/ incident or a report of in-flight odors by pilots or aircrew. The sample taken after an accident/ incident must be sent to a test site for analysis with details of the incident, including history of the supply source of the LOX.

Odor Test

The odor test is performed by pouring 200 milliliters (6.8 oz) of the sample into a clean 400 milliliter (13.8 oz) beaker or similar container after covering the bottom of the beaker with clean, dry filter paper or other absorbent paper. A watch glass cover or some other means of partially cover-ing the top of the beaker will be provided as the 200 milliliters evaporates to dryness. This will prevent atmospheric constituents from being absorbed by the exposed liquid. The liquid is permitted to evaporate to dryness and warm up to approximately room temperature in an area free from air currents or extraneous odors. When the liquid has completely evaporated, the watch glass is removed, and the beaker contents smelled at frequent intervals until the accumulated frost on the outside of the beaker has completely melted. Odors will be most prevalent when the beaker has warmed to nearly room temperature. If odors are present, the LOX container or system will be purged in accordance with existing directives.

Sampling

Sampling and analysis of LOX is required at any time contamination is suspected. Contamina-tion of oxygen used in aircraft can cause many problems, from fire hazards to death of the crew member using the oxygen system. The most dangerous contaminate is hydrocarbons. The presence of hydrocarbons in LOX constitutes a potential fire and explosive hazard as well as causing psychological and physiological dangers to aircrews. Physiologically, the effects may be uneasiness, apprehension, or possible panic resulting from detection of odor. Psychologically, the effects may be nausea, illness, intoxication, or possibly asphyxia. Acetylene is the most hazardous hydrocarbon contaminate because it is highly insoluble in LOX, changing into a solid at extremely low concentrations. Once in its solid form, it can be readily triggered into ignition, and since it is chemically unstable, it can decompose under certain conditions and become its own source of ignition. The presence of acetylene in LOX has caused several major LOX generating plant explosions. Inert solids are small contaminates that do not react with oxygen to create a fire or explosion, such as rust, dust, and fibers. They may cause mechanical malfunctions or failures by plugging filters, lines, or valves. Other contaminates commonly found in oxygen are water vapor, carbon dioxide, nitrous oxide, and halogenated compounds.