concentrations of oxygen quickly. Many materials such
Q7-13.
High-pressure copper or aluminum alloy
as cloth, wood, grease, oil, paint, or tar will burn
tubing can withstand what amount of
violently when saturated with oxygen, provided an
pressure?
ignition source is supplied. A static electric discharge
Q7-14.
What is the purpose of oxygen check valves?
or spark can serve as an igniter. Once an
oxygen-enriched fire is started, it is virtually
LIQUID OXYGEN (LOX)
impossible to extinguish until the oxygen supply is cut
SYSTEMS
off.
LEARNING OBJECTIVE: Identify safety
An added danger exists if a combustible material is
precautions, components, installation and
saturated with oxygen at low temperatures. Many
testing of components, and operating proce-
materials, especially hydrocarbons, tar, etc., will burn
dures for liquid oxygen (LOX) systems.
with explosive violence when saturated or subjected to
very mild shock or impact.
Liquid oxygen, commonly referred to as LOX, is
normally obtained by a combined cooling and
Extreme care must be taken not to splash or spill
pressurization process. When the temperature of
LOX on clothing. When LOX comes in contact with
gaseous oxygen is lowered to 182F under 720 psi
cloth, an ideal and deadly situation for a fire exists--a
pressure, it will begin to form into a liquid. When the
fire that cannot be put out.
temperature is lowered to 297F, it will remain a liquid
LOX by itself will not burn, but mixing with the
under normal atmospheric pressure.
smallest amount of almost any material will cause the
Once converted into a liquid, oxygen will remain in
liquid to boil and splash violently, making combustion
its liquid state as long as the temperature is maintained
possible. If splashed out of a container, LOX will break
below 297F. The liquid has an expansion ratio of
into many parts upon contact with the floor/deck. It
about 862 to 1, which means that one volume of LOX
must be poured slowly from one container to another to
will expand about 862 times when converted to a gas at
avoid splashing, and to allow the gaining receptacle to
atmospheric pressure. Thus, 1 liter of LOX produces
cool sufficiently without thermal breakage.
about 862 liters of gaseous oxygen.
NEVER seal or cap the vent port of a liquid oxygen
SAFETY PRECAUTIONS
system, because liquid oxygen at atmospheric pressure
will generate up to 12,000 pounds of pressure if
As already mentioned, the main dangers of LOX
allowed to evaporate in a sealed container or system
are the extremely low temperature of the liquid, its
that has no relief provisions.
expansion ratio, and its support of violent combustion.
Access to oxygen supply/storage areas should be
The liquid is nontoxic, but will freeze (burn) the skin
limited only to personnel familiar with proper handling
severely upon contact.
procedures. The area should be adequately ventilated
Use extreme caution not to touch implements
and free of any materials that could present a fire
containing LOX unless gloves are worn. Without
hazard. All pressure-type containers, plumbing, and
gloves, bare skin would immediately stick and freeze to
pressure-relief devices should conform to the
the metal surface.
applicable maintenance manual and be kept in good
repair. The vents on LOX containers are designed to
Personnel who could be exposed to accidental
have a sufficient flow capacity to carry away any
spillage of LOX must wear a face shield, coveralls,
oxygen that may boil off in case of accidental loss of
gloves, and oxygen safety shoes to prevent skin and
insulation. Do NOT cap such vents or cause the
vision damage. Open gloves, low-cut shoes, trousers
opening to be restricted in any way.
with cuffs, and similar improper clothing that can form
pockets capable of holding a quantity of LOX present a
The pressure relief assembly in LOX system
severe hazard. All personnel handling LOX must wear
storage cylinders consists of a reseatable relief valve
the protective clothing specified in the protective
and rupture disc in parallel. The assembly is designed
clothing section of NAVAIR 13-1-6.4.
so that the relief valve relieves first, with the rupture
A greater danger than freezing is the
disc acting as a safety backup in the event the relief
combustion-supporting potential of oxygen. When
valve malfunctions or its relieving capacity is
LOX is used, it is possible to build up high
exceeded.
7-10
