Gas and Engineering
Linde Gas Division
Safety Instructions
4
02.02
Oxygen enrichment
4. Hazards
enrichment
1. Preliminary remarks
These safety instructions are
recommendations on how to work
under safe conditions when oxygen
enrichment has to be expected.
They do not replace but complete
mandatory safey regulations.
2. Composition
atmosphere
of
It is unnecessary to take into
account other gases which are
present only in small quantities.
oxygen
3. Properties of oxygen
Oxygen is not flammable but
supports combustion. Although at
ambient temperature it is 11%
heavier than air there is no
dissociation of air with subsequent
accumulation of oxygen on the
ground.
Oxygen in the liquid state has a
very low temperature (-183°C at
atmospheric pressure). This low
temperature can rapidly cause
”cold burns” and make certain
materials brittle. (See also Safety
Instructions 1 Handling of cryogenic
liquid gases).
The atmospheric gases are nontoxic, but alterations in their relative
concentrations – expecially that of
oxygen – have an effect upon the
life and combustion processes. In
addition, as these changes cannot
be detected by human senses, they
may cause even well-informed
persons to come into dangerous
situations. If the composition of the
breathing air is liable to change it is
absolutely necessary to know the
concentration (measure!).
to
Oxygen
enrichment
of
the
atmosphere, even by a few
percent, considerably increases the
risk of fire. Materials which do not
burn in air, including fireproofing
materials, may burn vigorously or
even spontaneously in enriched air.
ambient
The
approximate
volumetric
composition of air is as follows:
21% by vol.
Oxygen O2
Nitrogen N2
78% by vol.
Argon
Ar
1% by vol.
due
The flames are much hotter and
are propagated at great speed.
Ignition, speed, violence and extent
of this reaction depend on:
• concentration, temperature and
pressure of the reacting
substances,
• ignition energy and type of
ignition.
Persons who have been exposed
to an oxygen enriched atmosphere
must ventilate their clothes very
thoroughly, since oxygen saturates
the clothes. Lighting of a cigarette
for instance can cause ignition of
the clothes.
Breathing of pure oxygen or highly
enriched air has, as a rule, no
adverse
effects
on
human
organism.
Oils and grease are particulary
hazardous in the presence of
oxygen as they can ignite
spontaneously and burn with
explosive violence. They must
never be used to lubricate oxygen
or
enriched
air
equipment.
Equipment contaminated with oil
and grease shall be cleaned
immediately
using
suitable
solvants.
Liquid oxygen leaking onto grounds
such as asphalt or wood can cause
an explosion.
5. Causes of oxygen enrichment
and its prevention
Leakage of oxygen should always
be avioded especially in closed or
inadequately ventilated rooms, at
least leakage quantity should be
kept to a minimum.
Some of the most important causes
of enrichment and precautions for
its prevention are listed below:
Newly assembled equipment for
oxygen
service
should
be
thoroughly leak checked. Periodic
retests are recommended. All
equipment, for instance welding
and cutting nozzles and hose
connections, should be properly
fitted. All maintenance and repair
work should be carried our by
experienced and fully skilled
personnel.
It is important for reasons of
precention of enrichment during
welding, cutting, etc. to select the
correct nozzles and pressures. In
addtion, many processes where
oxygen is used, e.g. gouging, flame
cutting, flame desurfacing, oxygen
lancing,
etc.,
involve
a
technological excess of oxygen.
Therefore, adequate ventilation of
the working space must be ensured
to avoid oxygen enrichment.
When the work is over, the valves
on welding or cutting torches and
the cylinder valve or oxygen supply
stop valve shall be turned off in
order to avoid possible oxygen
leakage in the time between the
end of one working period and the
beginning of the next.
Apart from the technologically
implied oxygen enrichment of air,
the following misuses of oxygen are
particularly dangerous and must be
strictly forbidden:
• driving pneumatic tools
• inflating vehicle tyres, rubber
boats, etc.
• cooling or freshening the air in
confined spaces
• cooling the person
• dusting benches, machinery
and clothing
• starting i.c. engines
• spray-painting
• etc.
Oxygen shall only be used if it
cannot be replaced by another gas.
Even a small amount of liquid
oxygen can lead to the formation of
a
large
amount
of
gas.
Consequently, liquid spillage can
rapidly cause significant oxygen
enrichment.
In the gaseous state cryogenic
oxygen is considerably heavier
than air. Areas where spillage of
cryogenic liquid oxygen may be
expected must not include drain
inlets without liquid seal, open
cellar windows or other entries of
deep level rooms, drains, etc.
because oxygen might accumulate
in these areas.
Vessels and equipment for storage
and filling of liquid oxygen shall be
designed for this purpose and
thoroughly
inspected
and
maintained.
When cryogenic liquid gases are
used having a lower boiling point
than oxyen such as nitrogen or air,
atmospheric
oxygen
can
condensate e.g. on uninsulated
piping (see Safety Instructions 1
Handling of cryogenic liquid gases).
Oxygen enrichment must be
expected in the vicinity of this
uninsulated piping.
Oxygen can be released in
appreciable
quantities
when
absorbents
(e.g.
silica
gel,
molecular sieves are warmed).
Linde AG, Linde Gas Division, Seitnerstraße 70, 82049 Höllriegelskreuth, Germany, Tel. +49/89/7446-0
8474/3 02.02
Adequate
ventilation
oxygen enrichment.
prevents
6. Environment protection
Oxygen is a natural constituent of
the air and makes up 21% of the
atmospher. When oxygen is
released into the atmosphere there
is no pollution. Inadvertent spillage
of liquid oxygen does not lead to
contamination of the ground,
because cryogenic liquid oxygen
vaporises. Temporary local soil
freezing
does
not
involve
permanent damage to the ground.
7. Conclusion
Safe handling of oxygen is only
posible if personnel are aware of its
specific properties and know how to
use them. Inappropriate use of
oxygen can lead to accidents.
However, oxygen has neither good
nor bad properties. What matters is
the knowledge how to use these
properties in the right way.
Our Application experts tell you
how.
Linde AG, Linde Gas Division, Seitnerstraße 70, 82049 Höllriegelskreuth, Germany, Tel. +49/89/7446-0
8474/3 02.02