Section 11:
Compressed Gas Cylinders
OVERVIEW
Compressed gas cylinders are specifically designed to contain gases under pressure
and to safely dispense the gas through a control valve. This section provides
information about compressed gas cylinders and their associated hazards and safe
handling guidelines.
WHAT KINDS OF COMPRESSED GASES ARE
STORED IN CYLINDERS?
There are three major categories of compressed gases stored in cylinders: liquefied,
non-liquefied, and dissolved gases.
Liquefied Gases
Liquefied gases become liquids at normal
temperatures but at high pressures when they are
inside cylinders. They exist inside the cylinder in a
liquid-vapor balance or equilibrium. When the
cylinder is fully charged with liquefied gas and
unopened, it primarily contains liquid with the gas
vapors filling the space above the liquid. As the
liquid-gas is removed from the cylinder, liquid vaporizes inside the cylinder to replace it,
keeping the pressure inside the cylinder constant. This vaporization process can take
heat out of the surrounding environment, so sometimes a gas-cylinder can get very cold
to the touch, including frost forming the sides of the cylinder during high-humidity
weather, when a significant amount of gas is removed from the cylinder in a short period
of time. Anhydrous ammonia, chlorine, propane, nitrous oxide, and carbon dioxide are
examples of liquefied gases.
Non-Liquefied Gases / Cryogenic Liquids
Non-liquefied gases are also known as compressed, pressurized, or permanent gases.
These gases do not become liquid when they are compressed, unless they are exposed
to extremely low temperatures. Common examples of these are oxygen, nitrogen,
helium, and argon. Non-liquified gases that are made into liquid by super-chilling the
gas are called “cryogens” or “cryogenic liquids”. They are rarely used in shops, but are
often used in labs that have shop processes as part of lab / research activities.
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Dissolved Gases
Dissolved gases are dissolved in a volatile solvent in order to stabilize them. Acetylene
is the only common dissolved gas used on campus. It is an unstable chemical and can
explode at atmospheric pressure. Nevertheless, acetylene is routinely stored and used
safely in cylinders at high pressures (up to 250 psi at 21°C), because the cylinders are
filled with an inert, porous filler. The filler is saturated with acetone or another suitable
solvent. When acetylene gas is added to the cylinder, the gas dissolves in the filler,
resulting in a stable solution. As the gas is used, the pressure drops inside the cylinder
slightly causing more gas to come out of solution and be delivered to the gas piping
distribution system.
COMPRESSED GAS HAZARDS
Compressed gases present unique hazards. Depending on the particular gas, there is
a potential for simultaneous exposure to both mechanical and chemical hazards.
Mechanical hazards
All compressed gas cylinders are hazardous because of the high pressures (as high as
3500 psi.) inside the cylinders. Gas can be released deliberately by opening the cylinder
valve, or it can be released accidentally from a broken valve, leaking valve, or from a
damaged safety device. Even at relatively low pressure, gas can flow rapidly from an
open or leaking cylinder. The large amount of stored energy in the gas under pressure
inside the cylinder makes the cylinder a potential rocket or fragmentation bomb if the
cylinder and high-pressure valve on top of the cylinder is damaged in any way.
Exposing the cylinders to extreme temperatures or physically damaging them in any
way can pose serious threats to life and property. Cryogenic gas / liquid is extremely
cold and can cause “frost bite” or immediate sometimes irreparable tissue damage on
contact.
Chemical hazards
Gases stored in cylinders range from inert and harmless to toxic and explosive. The
range includes the following:






Flammable or combustible
Explosive
Corrosive
Toxic or poisonous
Inert
A combination of hazards
Flammable gases, such as acetylene, butane, ethylene,
hydrogen, methylamine, and vinyl chloride, can burn or explode
under certain conditions. A gas can ignite and burn at
temperatures between its lower flammable limit (LFL) and upper
flammable limit (UFL), called the “flammability range”. The flammability range of any gas
is widened in the presence of oxidizing gases such as air, oxygen or chlorine and by
higher temperatures or pressures.
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An ignition source must be present for a flammable gas to ignite.
There are many possible ignition sources in most workplaces,
including open flames, sparks, static electricity, electrical contactors
and hot surfaces.
Flash-back can occur with flammable gases. Most flammable gases
are heavier than air. If a cylinder leaks in a poorly ventilated area,
these gases can settle and collect in sewers, pits, trenches, basements or other low
areas. The gas trail can spread far from the cylinder. If the gas trail contacts an ignition
source, the fire produced can flash back to the cylinder igniting any flammables along its
path, and potentially causing an explosion at the source tank.
Some pure compressed gases are chemically unstable. If exposed to slight
temperature or pressure increases, or mechanical shock, they can readily undergo
certain types of chemical reactions such as polymerization or decomposition. These
reactions may be violent, resulting in fire or explosion.
Some compressed gases are corrosive. They can burn and
destroy body tissues on contact. Corrosive gases can also attack
and corrode metals. Common corrosive gases include ammonia,
hydrogen chloride, chlorine, and methylamine.
Many compressed gases are toxic or very toxic. Health
problems can result from exposure depending on the specific gas,
its concentration, length of exposure, and the route of exposure
(that is, inhalation, eye, or skin contact).
Even though inert gases, such as argon, helium, and nitrogen,
are not toxic and do not burn or explode, they can cause injury or
death if present in high concentrations. Large quantities can
displace enough air to reduce oxygen levels. If oxygen levels are
below 16% in the atmosphere (normal levels is 20%), people
entering the area can lose consciousness or die from
asphyxiation. Low oxygen levels can be a problem in poorly
ventilated areas, such as confined spaces.
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WHO CAN HANDLE GAS CYLINDERS?
You must be trained before handling compressed gas cylinders. Training must include
how to read and interpret the cylinder label and the Safety Data Sheet (SDS) for the gas
in the cylinder. You also need to understand the hazards that cylinders present and how
to handle, transport, and dispose of cylinders. If you are required to use PPE, you must
be provided with it and trained in its use and wear.
Hardcopies of SDS for all compressed gases that you handle must be kept in your shop
for easy access.
HOW DO I KNOW WHAT IS IN A COMPRESSED
GAS CYLINDER?
“Read the label….” The contents of all compressed gas
cylinders must be clearly identified. The manufacturer or
shipper must label or tag each cylinder with the name of
its contents.
Do not accept any compressed gas cylinder without
an identifying label or tag. If the labeling on a cylinder
becomes unclear or a tag is defaced to the point where
the contents cannot be identified, mark the cylinder as
“contents unknown” and return directly to the shipper or
manufacturer. If you discover unlabeled cylinders
already on your campus, contact your EH&S department
for further guidance on how to handle / dispose of them.
Never rely on the color of the cylinder for identification. Color coding is not reliable,
because cylinder colors may vary with the supplier. Additionally, the cap labels have
little value because caps are interchangeable.
What other identifying information is required?
Rooms with compressed gases must have a prominent and
conspicuous “Compressed Gas” sign as well as a National Fire
Protection Association (NFPA) fire diamond posted at the entry
of the room with the hazard class and the name of the gases
stored.
All gas lines leading from a compressed gas supply should be
clearly labeled to identify the gas, the shop or area served, and
the relevant emergency telephone numbers.
It is recommended that cylinders be tagged to indicate the
status using with a perforated three-in-one tag. The tags are
available on request from your campus EH&S department.
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GAS CYLINDER SAFE HANDLING PROCEDURES
Safe Handling Procedures are necessary for handling compressed gases in cylinders.
In addition, procedures must include the gas-handling regulators or valves used to
control the gas flow, and the piping used to confine the gases during flow.
Basic Safe Handling Procedures
Users and installers must know the type of gas contained in cylinders before installation
and use. An inventory must be kept of all gas cylinders used and stored in your shop.
The inventory must be kept in the shop’s SDS binder.
The cylinder must be returned to the supplier if its content is not identified, if the
hydrostatic test date is past due, or if it is damaged.
Never modify, tamper with, paint, deface, obstruct, remove, or repair any part of the
cylinder, including the pressure relief device, the container valve, or the valve protection
device. This can turn a cylinder into a potential rocket or fragmentation bomb and result
in serious injury. Never strike an electric arc on the cylinder. This can cause an
explosion and fire.
What PPE is required?
Steel-toed, sip-resistant shoes and gloves are required when transporting cylinders.
Eye-protection, face shields, and protective aprons may be required depending on the
gas in the cylinder.
When are regulators and caps required?
Regulators and caps are always required. Never move a gas
cylinder from its storage rack without closing the cylinder valve,
removing the regulator and then securely attaching the cap to the top
of the cylinder to protect the valve and stem. Never use a cylinder
without attaching the correct pressure regulator for the pressure of the
cylinder and the type of gas inside the cylinder. After attaching the
regulator, turn the adjusting screw of the regulator fully counterclockwise to see that it is released before opening the cylinder valve. Turn valves and
regulators slowly and deliberately and never permit the gas to enter the regulator
suddenly.
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Before using a cylinder, slowly “crack” the valve to clear dust or dirt. Always stand to
the side of the regulator gauge glass when opening the valve and make sure that the
opening is not pointed toward
anyone. The face of the
pressure gage could explode,
so never stand in front of the
pressure gage when adding
pressure to the piping system.
Additional precautions must be
taken with toxic or flammable
gas cylinders. Ask your
Supervisor if you are
unfamiliar with safe-handling
and the plumbing of any gas
delivery system or gas
cylinders.
If there is a leak between the cylinder and regulator, always close the cylinder-valve
before attempting to tighten the union nut.
Regulators must be removed from the cylinders when not in use and replaced
with caps. Never force the regulator or cap when removing or replacing them. In
addition, the cap should only be hand tightened.
How do I handle leaking cylinders?
If you discover a leaking cylinder, first evaluate the size of the leak and hazards of the
gas. For minor leaks, immediately evacuate the room or area. If it is safe to do so, wear
the appropriate PPE to protect yourself from the hazards present and type of gas, and
move the cylinder to a safe place such as a fume hood. Immediately contact both the
Environment Health & Safety department and the cylinder vendor to inform them of the
leaking cylinder.
If you find a major and uncontrollable leak, immediately evacuate the room or area. Call
911 and initiate the emergency response procedures outlined in your emergency
response plan or chemical release procedures.
STORAGE OF COMPRESSED GAS CYLINDERS
Chaining
Compressed gas cylinders must be
double chained to a stable structure,
such as a wall. Install one chain one
third from the bottom of the cylinder and
a second chain one third from the top of
the cylinder. Do not use straps,
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bungee cords or bench clamps for securing cylinders. Use storage racks and
devices that are not made from flammable or combustible materials and are securely
attached to the structure of the building. Do not rely on sheet-rock anchors to hold a
cylinder storage rack. Use concrete anchors into the floor or lag-bolts into wood wall
studs to secure cylinder racks.
A maximum of three cylinders may be clustered together. Secure cylinders of equal
sizes together to avoid chaining problems.
How do I store cylinders that contain different types of gases?
You must store oxygen, or oxidizing gas,
cylinders at least 20 feet away from fuelgas cylinders or combustible materials
(especially oil or grease). If this is not
possible, you can separate them by a
noncombustible barrier that is at least
five feet high with a fire resistance rating
of least one-half hour. The barrier must
be at least 18 inches above the tallest
cylinder. Some shops have affixed fivefoot sheet metal partitions between
cylinders to meet regulations.
Additional Storage
Requirements
As a general rule, never store cylinders on transportation carts. The only exception
to this rule involves the use of welding cylinders (oxygen and fuel cylinders). When used
for portable service or for intermittent use, welding cylinders may remain on carts
designed for this purpose.
Always store cylinders in upright positions on their base unless they are
designed for use in a horizontal position. If used horizontally, they must be secured
horizontally.
TRANSPORTING CYLINDERS
Unless cylinders are secured on a special cart, remove
the regulators, close the valves, and replace with the
protective valve caps before moving them. Do not lift the
cylinder by the protective valve caps. Transport
cylinders weighing more than 40 pounds on a cart and
secure them with a chain.
Always handle cylinders with care. Cylinders must never be dragged, pushed, or pulled
across the floor. Never drop a cylinder, or permit cylinders to strike each other violently
when moving. Never roll cylinders along the edge of the base while tilting it to move it
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from one location to another. It’s easy to have them get-away from you and fall on the
floor. Load cylinders onto transport carts to allow as little movement as possible and
secure them to prevent violent contact or upsetting.
DISPOSAL
When cylinders are empty or no longer needed, you must dispose of them. Empty
cylinders must be marked “Empty” and stored apart from other cylinders. Whenever
possible, return empty cylinders to the supplier. If the supplier is unknown, dispose of
the cylinder as hazardous chemical waste by completing an on-line hazardous waste
tag for the cylinders and bring them to the designated EH&S hazardous waste pick up
location.
Never discard pressurized cylinders in the normal trash!
[REY - PLEASE REDO THIS TABLE FOR MORE CLEAR / BETTER GRAPHICS BUT
THE CONTENTS IS OK AS IS. THANK YOU, JIM G.]
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SECTION 11 QUIZ –
COMPRESSED GAS CYLINDERS
1. True or False?
It is safe to conduct minor repairs on the valves of a cylinder containing “harmless”
gases.
2. If you find a compressed gas cylinder that is unlabeled, you should:
a. Guess what the gas is based on the color of the cylinder.
b. Mark “Contents Unknown” and immediately return it to the supplier. If supplier
is unknown, call your EH&S department.
c. Attach a regulator and test the gas.
d. Leave it alone and wait for someone else to deal with it.
3. True or False?
Cylinders should never be rolled or dragged.
4. If the regulator on an oxygen cylinder is difficult to thread, you should:
a. Oil the threads.
b. Use a crescent wrench to tighten it.
c. Return the cylinder or regulator to the supplier.
d. Repair the threads.
5. Cylinders containing flammable gases should never be stored near:
a. Spark-producing activities (grinding, welding, etc.)
b. Pilot lights
c. Static electricity
d. Oxidizers
e. All of the above
6. True or False
I have a cylinder in my shop that I’m not using. It’s chained up correctly, therefore I
don’t need the cylinder cap on the top of the cylinder.
7. True or False
It’s OK to store propane cylinders and ammonia gas cylinders in the same storage
rack.
8. Bonus Question………True or False
It’s OK to close-up the vent-valves tight on very cold cryogenic gas-liquid such as
liquid nitrogen, liquid helium, liquid oxygen as long as they are stored in rolling
dewars.
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September, 2012
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Table of Contents
Answers:
1. False – All gasses in cylinders are under extreme pressure. Never tamper with the cylinder or valve.
2. b - If the label is worn or missing, mark the cylinder “contents unknown” and return it to the manufacturer or
supplier.
3. True – Never roll or drag a cylinder. Cylinders can become rockets or bombs if physically damaged by rolling or
dragging.
4. c – Oxygen creates rapid combustion and can make some materials burn that would not burn in normal air. Oil
can add fuel to a potential fire. Never tighten any regulator more than “hand tight.” Never try to repair a cylinder.
Always return defective cylinders to the manufacturer or supplier.
5. e – Never store flammable gasses in areas that have open flames, oxidizers, sparks or extreme heat.
6. False – Always put the cylinder cap on a cylinder when it is in storage, even if it’s empty and you’re not using it.
7. False – Propane is flammable and ammonia gas is an oxidizer. Never store flammable gas cylinders and
oxidizers next to each other.
8. False – Cryogenic (very cold) liquid gases are kept as a liquid at atmospheric pressure by them being extremely
cold. Rolling and hand-carried dewars are insulated storage vessels designed to keep the extremely cold liquid
gas in a safe manner for shop and lab use. Because the gas is kept as a liquid not by high pressure but by low
temperature, the liquid is constantly boiling off and turning into gas. Every dewar has a vent valve designed to
allow the gas boiling off the liquid inside to vent to atmosphere. If you encounter a dewar, you’ll likely hear the
boiling gas escaping through the vent valve. Depending upon the type of gas, the vented gas may need to
exhausted into a fume hood, or piped to a place away from personnel. In any event, dewars are not designed to
build-up pressure inside the dewar and must constantly vent to atmosphere to maintain safety. Ask your
supervisor for training and information about safely handling cryogenic liquid gases.
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