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1st Rule of Lab Safety
Haz-Waste No-No
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Updated June 2002
General Safety
Section 2.4 - Compressed Gas Safety
Since gas cylinders are tall and narrow,
they shall be secured at all times to prevent tipping . Cylinders may be attached to a
bench top, individually to the wall, placed in a holding cage, or have a non-tip base
attached.
When new cylinders are received, they should
be inspected. During this inspection, one should insure the proper cap is securely in
place and the cylinder is not leaking. Cylinders shall have clear labels indicating the
type of gas contained. If the cylinders are acceptable, they shall be stored in a proper
location. If a leaking cylinder is discovered, move it to a safe place (if it is safe to
do so) and inform Environmental Health & Safety Dept. You should also call the vendor
as soon as possible. Under no circumstances should any attempt be made to repair a
cylinder or valve.
Cylinders
containing flammable gases such as hydrogen or acetylene shall not be stored in close
proximity to open flames, areas where electrical sparks are generated, or where other
sources of ignition may be present. Cylinders containing acetylene shall never be stored
on their side. An open flame shall never be used to detect leaks of flammable gases.
Hydrogen flame is invisible, so "feel" for heat. All cylinders containing
flammable gases should be stored in a well-ventilated area.
Oxygen cylinders, full or empty, shall not
be stored in the same vicinity as flammable gases. The proper storage for oxygen cylinders
requires that a minimum of 50 feet be maintained between flammable gas cylinders and
oxygen cylinders or the storage areas be separated, at a minimum, by a fire wall five feet
high with a fire rating of 0.5 hours. Greasy and oily materials shall never be stored
around oxygen; nor should oil or grease be applied to fittings.
Standard cylinder-valve outlet connections
have been devised by the Compressed Gas Association (CGA) to prevent mixing of
incompatible gases. The outlet threads used vary in diameter; some are internal, some are
external; some are right-handed, some are left-handed. In general, right-handed threads
are used for non-fuel and water-pumped gases, while left-handed threads are used for fuel
and oil-pump gases. To minimize undesirable connections, only CGA standard combinations of
valves and fittings should be used in compressed gas installations; the assembly of
miscellaneous parts should be avoided. The threads on cylinder valves, regulators and
other fittings should be examined to ensure they correspond and are undamaged.
Cylinders should be placed with the valve accessible at all times. The main cylinder valve
should be closed as soon as it is no longer necessary that it be open (i.e., it should
never be left open when the equipment is unattended or not operating). This is necessary
not only for safety when the cylinder is under pressure, but also to prevent the corrosion
and contamination resulting from diffusion of air and moisture into the cylinder after it
has been emptied.
Cylinders are equipped with either a hand wheel or stem valve. For cylinders equipped with
a stem valve, the valve spindle key should remain on the stem while the cylinder is in
service. Only wrenches or tools provided by the cylinder supplier should be used to open
or close a valve. At no time should pliers be used to open a cylinder valve. Some valves
may require washers; this should be checked before the regulator is fitted. Cylinder
valves should be opened slowly. Oxygen cylinder valves should be opened all the way.
When opening the valve on a cylinder containing an irritating or toxic gas, the user
should position the cylinder with the valve pointing away from them and warn those working
nearby.
Regulators are gas specific and not
necessarily interchangeable. Always make sure that the regulator and valve fittings are
compatible. If there is any question as to the suitability of a regulator for a particular
gas, check with Environmental Health Services or call your vendor for advice. After the
regulator is attached, the cylinder valve should be opened just enough to indicate
pressure on the regulator gauge (no more than one full turn) and all the connections
checked with a soap solution for leaks. Never use oil or grease on the
regulator of a cylinder valve.
Piping material shall be compatible with the
gas being supplied. Copper piping shall not be used for acetylene, nor plastic piping for
any portion of a high pressure system. Do not use cast iron pipe for chlorine; do not
conceal distribution lines where a high concentration of a leaking hazardous gas can build
up and cause an accident. Distribution lines and their outlets should be clearly labeled
as to the type of gas contained. Piping systems should be inspected for leaks on a regular
basis. Special attention should be given to fittings as well as possible cracks that may
have developed.
A cylinder should never be emptied to a
pressure lower than 172 kPa (25 psi/in2) (the residual contents may become contaminated if
the valve is left open). When work involving a compressed gas is completed, the cylinder
must be turned off, and if possible, the lines bled. When the cylinder needs to be removed
or is empty (see above), all valves shall be closed, the system bled, and the regulator
removed. The valve cap shall be replaced, the cylinder clearly marked as
"empty," and returned to a storage area for pickup by the supplier. Empty and
full cylinders should be stored in separate areas.
Where the possibility of flow reversal
exists, the cylinder discharge lines should be equipped with approved check valves to
prevent inadvertent contamination of cylinders connected to a closed system. "Sucking
back" is particularly troublesome where gases are used as reactants in a closed
system. A cylinder in such a system should be shut off and removed from the system when
the pressure remaining in the cylinder is at least 172 kPa (25 psi/in2). If there is a
possibility that the container has been contaminated, it should be so labeled and returned
to the supplier.
Liquid bulk
cylinders may be used in laboratories where a high volume of gas is needed. These
cylinders usually have a number of valves on the top of the cylinder. All valves should be
clearly marked as to their function. These cylinders will also vent their contents when a
preset internal pressure is reached, therefore, they should be stored or placed in service
where there is adequate ventilation. If a liquid fraction is removed from a cylinder,
proper hand and eye protection must be worn and the liquid collected in a Dewar flask.
Always use safety glasses (preferably a face
shield) when handling and using compressed gases, especially when connecting and
disconnecting compressed gas regulators and lines.
All compressed gas cylinders, including
lecture-size cylinders, shall be returned to the supplier when empty or no longer
in use.
C. Transportation
of Cylinders
The cylinders that contain compressed gases
are primarily shipping containers and should not be subjected to rough handling or abuse.
Such misuse can seriously weaken the cylinder and render it unfit for further use or
transform it into a rocket having sufficient thrust to drive it through masonry walls.
To protect the valve during transportation,
the cover cap should be screwed on hand tight and remain on until the cylinder is in place
and ready for use.
Cylinders should never be rolled or dragged.
When moving large cylinders, they should be
strapped to a properly designed wheeled cart to ensure stability.
Only one cylinder should be handled (moved)
at a time.
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Cryogenic
Liquids
