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Cryogenic (Primary Hazard: Cold Burns)
Some gases having very low boiling points are stored as liquids
in insulated vacuum-jacketed dewars or insulated pressurized cylinders.
Contact with these liquids causes "cryogenic
burns" due to the freezing of skin tissue by the rapidly evaporating
liquid. Also, the liquid produces a large volume of gas
upon vaporizing. In inadequately ventilated areas, except for
oxygen, this may decrease the oxygen content below that necessary
to sustain life. Adequate ventilation, monitoring
of the oxygen content of confined areas, and the use of protective
clothing minimize these hazards. (EXAMPLES: LIQUID ARGON, NITROGEN,
OXYGEN)
Flammable (Primary Hazard: Fire and Explosion)
Flammable gas as defined by the DOT is "any compressed gas that
either forms a flammable mixture with air at a concentration of
less than 13% (by volume) or his aflammable range in air wider
than 12%, regardless of the lower explosive limit (LEL)." Flammable
gases, when mixed with air, oxygen, or other oxidants, bum or
explode upon ignition depending upon the degree of confinement.
Pyrophoric gases like silane require no ignition source and will
ignite in air, increasing the severity of the flammability hazard.
Each flammable gas has a gasin-air concentration range within
which limits the gas may be ignited. Flammable ranges are expressed
in terms of air at ambient temperature and atmospheric pressure.
A change in temperature, pressure, or oxidant concentration may
vary the flammable range.
Mixtures above and below the flammable range do
not ignite. As a precaution in handling flammables, care must
be taken to eliminate all possible sources of ignition through
the proper design of facilities, installation of approved electrical
systems, and the restriction of smoking and open flame. An explosimeter
should be used to determine the existence of a flammable mixture
in areas of suspected leakage. (EXAMPLES: BUTANE, HYDROGEN, SILANE)
Oxidant (Primary Hazard: Fire)
A number of gases, although nonflammable, may initiate and support
combustion. Materials that burn in air bum more vigorously, or
even explosively, in oxygen and certain other oxidants. All
possible sources of ignition must be eliminated when handling
oxidants. Oxidants must not be stored with combustible materials.
Oil, grease, or other readily combustible substances must not
come in contact with cylinders or equipment used in oxidant service.
In many cases, oxidant materials may also be corrosive and/or
toxic. (EXAMPLES: OXYGEN, BROMINE TRIFLUORIDE)
Corrosive (Primary Hazard: Chemical Sums)
Corrosives are those products that chemically react with and
deteriorate materials with which they come in contact, such as
metals, fabrics, and human tissue. Some gases, although not corrosive
in their anhydrous form, become corrosive in the presence of water
or moisture in the air. Special care must be
taken when selecting the proper construction materials for equipment
in which conro- sives are handled. Gases that do not cause
deterioration but induce inflammation of human tissue are irritants.
Inflammation of the tissue may occur after immediate, prolonged,
or repeated contact with the irritant. Protective clothing and
equipment must be used to minimize expo- sure to corrosive or
irritating materials. (EXAMPLES: SILICON TETRACHLORIDE,
HYDROGEN FLUORIDE)
Toxic (Primary Hazard: Chemical Poisoning)
Toxic materials are those substances that
may cause injuries or death when inhaled, ingested, or adsorbed
on the skin. The degree of toxicity and the effects vary
with the compound. Gases such as carbon monoxide are especially
dangerous because as a colorless, odorless product, they do not
provide adequate warning of their presence. Also, some products
that are nontoxic in themselves may react with certain chemicals
or decompose at elevated temperatures to produce toxic materials.
Adequate ventilation, protective clothing, and suitable breathing
equipment must be used to minimize exposure. (EXAMPLES: ARSINE,
PHOSPHINE, FLUORINE)
Inert (Primary Hazard: Asphyxiation)
Inert products can, if released in confined areas,
displace the oxygen content of the air below that level which
is nec- essary to sustain life. OSHA sets a minimum concentration
of 19.5% oxygen for any work area. Asphyxiation is the hazard
most commonly associated with inert, gaseous products. Adequate
ventilation and monitoring of confined areas for the oxygen content
of the atmosphere are the best ways to minimize this hazard. (EXAMPLES:
HELIUM, KRYPTON, CARBON DIOXIDE, NITROGEN)
High Pressure (Primary Hazard: Serious Injury)
Gases are compressed to pressures up to 6,000 psig. A sudden release
of pressure may cause injury to personnel and damage to equipment
by propelling a cylinder or whipping a line. Factors that must
be considered when choosing construction materials and designing
gashandling systems are the temperature, the pressure of the gas,
and the possibility of pressure buildup in the system.
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