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SECTION 2F: Compressed Gases
Compressed gases can be toxic, flammable, oxidizing, corrosive, inert,
or some  combination
of these hazards. In addition to the chemical hazards, the amount of energy
resulting from the compression of the gas makes a compressed gas cylinder
a potential rocket. Appropriate care in the handling and storage of compressed
gas cylinders is essential. Following are general recommendations.
- Know and Understand Gas Properties: Know
and understand the properties, uses, and safety precautions before
using any gas or gas mixture. Consult Material Safety Data Sheets
(MSDSs) for safety information on the gases that you will be using.
- Check Equipment: Leak test lines and
equipment before they are used. Lines and equipment should be designed
and maintained to handle full cylinder pressure. Materials of construction
should be compatible with the gases being used.
- When in Doubt, Contact Environmental Health
& Safety: If you are unfamiliar with the hazards associated
with a particular gas or unsure of the correct handling and storage
procedures, call Environmental Health & Safety at 8-5294.
Primary Hazards (top)
The following is an overview of the primary hazards to be avoided when
handling and storing compressed gases.
- Asphyxiation: Simple
asphyxiation is the primary hazard associated with inert gases. Because
inert gases are colorless and odorless, they can escape into the atmosphere
undetected and quickly reduce the concentration of oxygen below the
level necessary to support life. The use of oxygen monitoring equipment
is strongly recommended for enclosed areas where inert gases are being
used.
- Fire and Explosion: Fire and explosion
are the primary hazards associated with flammable gases, oxygen, and
other oxidizing gases. Flammable gases can be ignited by static electricity
or by a heat source, such as a flame or a hot object. Oxygen and other
oxidizing gases do not burn, but will support combustion of flammable
materials. Increasing the concentration of an oxidizer accelerates
the rate of combustion. Materials that are nonflammable under normal
conditions may burn in an oxygen-enriched atmosphere.
- Chemical Burns: Corrosive gases can
chemically attack various materials, including fire-resistant clothing.
Some gases are not corrosive in their pure form, but can become extremely
destructive if a small amount of moisture is added. Corrosive gases
can cause rapid destruction of skin tissue.
- Chemical Poisoning: Chemical poisoning
is the primary hazard of toxic gases. Even in very
small concentrations, brief exposure to these gases can result in
serious poisoning injuries. Symptoms of exposure may be delayed.
- High Pressure: All compressed gases are potentially hazardous because of the high pressure stored inside the cylinder. A sudden release of pressure can cause injuries by propelling a cylinder or flailing an air hose.
- Improper Handling of Cylinders: Compressed
gas cylinders are heavy and awkward to handle. Improper handling of
cylinders could result in sprains, strains, falls, bruises, and broken
bones. Other hazards such as fire, explosion, chemical burns, poisoning,
and cold burns could occur if gases accidentally escape from the cylinder
due to mishandling.
Handling, Storage, and Use of Gases (top)
Only persons familiar with the hazards should handle compressed gas
cylinders. All cylinder movement should be done with material handling
equipment. Always secure the cylinders when in storage or use. Safety
glasses, work gloves, and appropriate work shoes should be worn.
Compressed gas cylinders should not be subjected to any mechanical
shock that could cause damage to their valves or pressure relief devices.
Cylinders should not be dropped, dragged, slid, or used as rollers for
moving material or other equipment. Use cylinder carts to transport
cylinders.
Cylinder caps perform two functions. First,
they protect the valve on the top of the cylinder from damage if it
is knocked over. Second, if gas is accidentally released through the
valve, the cap will vent the gas out of both sides, minimizing the likelihood
that the cylinder will topple. Cylinder caps should not be removed until
the cylinder is secured in place and ready for use.
Cylinder Storage Precautions
Several precautions should be taken during storage of compressed gas
cylinders. Full and empty cylinders should be stored separately. Cylinders
should be stored upright and secured at all times. Oxidizers and flammable
gases must be stored in areas separated by at least 20 feet or by a
noncombustible wall.
All cylinders should either have a cylinder cap in place or be attached
to a regulator. Do not store cylinders with nothing protecting the neck.
Do not store acetylene cylinders on their
side. If an acetylene cylinder has tipped over or was stored on its
side, carefully place the cylinder upright and do not use until the
liquid has settled to the bottom. The rule of thumb is not to use the
cylinder for as many minutes as the cylinder was on its side, up to
24 hours.
Cylinders should not be stored near radiators or other heat sources.
If storage is outdoors, protect cylinders against weather extremes and
damp ground to prevent rusting.
Things to Keep Away from Cylinders
Several precautions should be taken to prevent the release of high-pressure
gases, fire, and explosion. Compressed gas cylinders should not be
exposed
to sparks, flames, or temperatures above 125°F. Cylinders should
not be places where they could come into contact with any electrical
apparatus or circuits.
Smoking and open flames should not be permitted in areas used for storage
of oxygen or flammable gas cylinders. Never
permit oil, grease, or other combustible substances to come into contact
with oxygen or other oxidizing gas cylinders, valves, and systems.
Returning Cylinders
When returning an empty cylinder, close the valve before shipment,
leaving 25 psig of residual pressure in the cylinder. Replace the valve
cap and any valve outlet caps or plugs originally shipped with the cylinder.
If repair is needed on a cylinder or its valve, be sure to mark it and
return it to the supplier.
Lecture bottles should always be returned
to the distributor or manufacturer promptly when no longer needed. Since
many distributors and manufacturers do not take back lecture bottles,
always check before purchasing the cylinder and opt for returnable or
refillable cylinders. See the EHS web page (www.princeton.edu/~ehs/lecturebottles.html)
for a list of distributors that offer returnable or refillable cylinders
Highly Toxic Gases (top)
Highly toxic gases, such as arsine, diborane, fluorine, hydrogen cyanide,
phosgene, and silane, can pose a significant health risk in the event
of a leak. Use of these materials requires written approval by the Principal
Investigator or supervisor.
The following additional precautions must be taken:
- Use and store in a specially ventilated gas cabinet or fume hood.
- Use coaxial (double walled) tubing with nitrogen between the walls
for feed lines operating above atmospheric pressure.
- Regulators should be equipped with an automatic shut-off to turn
off gas supply in the event of sudden loss of pressure in the supply
line.
- An alarm system should be installed to check for leaks in routinely
used gases with poor warning properties. The alarm level must be set
at or lower than the permissible exposure limit of the substance.
- Self-contained breathing apparatus (SCBA) may be appropriate for
changing cylinders of highly toxic gases. Use of an SCBA requires
enrollment in the Respiratory Protection Program and annual training
and fit-testing.
Handling Leaking Cylinders (top)
Most leaks occur at the valve in the top of the cylinder and may involve
the valve threads, valve stem, valve outlet, or pressure relief devices.
Lab personnel should not attempt to repair leaking cylinders.
Where action can be taken without serious exposure to lab personnel,
move the cylinder to an isolated, well-ventilated area (away from combustible
materials if the cylinder contains a flammable or oxidizing gas) and
contact Public
Safety.
Whenever a large or uncontrollable leak occurs, evacuate the area and
immediately contact Public
Safety.
 Section
2e Section
2g
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