SAFETY SOLUTIONS: Safe Handling of Compressed Gas Cylinders
I was recently teaching an OSHA “Train the Trainer”
course at the OSHA Training Institute, when I asked
the many safety professionals who were attending the
class, “Can anyone tell me what the markings on top of the
compressed gas cylinder represent?” Can you believe it,
not one of them knew the answer. Do you know the
answer to that question? If not; let’s take a look at this
very important safety information, it may save your life or
Every industrial manufacturing, construction and technical
school environment has compressed gas cylinders.
These cylinders, if not treated properly, can be like time
bombs ready to explode if they are not handled correctly.
The transportation of high pressure cylinders is regulated
by many governments throughout the world. Various
levels of testing are generally required by the governing
authority for the country in which it is to be transported.
In the United States, this authority is the United States
Department of Transportation (DOT). For Canada, this
authority is Transport Canada (TC).
Cylinders may have additional requirements placed on
design and or performance from independent testing
agencies such as Underwriter’s Laboratory (UL). Each
manufacturer of high pressure cylinders is required to
have independent quality agent that will inspect the product
for quality and safety.
During the manufacturing process, vital information is
usually stamped or permanently marked on the cylinder.
This information usually includes the type of cylinder,
the working or service pressure, the serial number,
date of manufacture, the manufacture’s registered code
and sometimes the test pressure. Other information
may also be stamped depending on the regulation
The following information was furnished from Airgas.
Specialty gas cylinders are stamped with markings
designed to indicate ownership, specifications, pressure
ratings and other important data. Airgas also utilizes a
bar code label for product identification and tracking.
1. Cylinder Specification
DOT—Department of Transportation (previously ICC –
Interstate Commerce Commission), which is the regulatory
body that governs the use of cylinders.
Specification of the cylinder type of material of construction
Service or working pressure in pounds per square inch
(e.g., 2,265 psig).
2. Cylinder Serial Number
3. Date of Manufacture
This date (month-year) also indicates the original hydrostatic
4. Neck Ring Identification
The cylinder neck ring displays the name of the original
owner of the cylinder.
5. Retest Markings
The format for a retest marking is: Month – Facility –
Year – Plus Rating – Star Stamp.
The + symbol (Plus Rating) indicates that the cylinder
qualifies for 10% overfill.
The H symbol (Star Stamp) indicates that the cylinder
meets the requirements for 10-year retest, instead of a 5-
6. Bar Code Label
The bar code label provides a unique cylinder identifier
and is used by computer systems to track cylinders
throughout the fill process. As an optional service, we have
the capability of tracking cylinders to and from customers.
7. Cylinder Manufacturer’s Inspection Marking
8. Cylinder Tare (Empty) Weight
This value may be preceded by the letters TW. D.O.T. Classifications
Your compressed gas cylinders will have one or more of
the hazardous materials placards shown below. The United
States Department of Transportation (US DOT) in Title 49
Section 173 of the United States Code of Federal
Regulations (49 CFR 173) requires the use of hazardous
materials placards when shipping compressed gases. These
hazardous materials placards are intended to indicate the
general hazards associated with the contents of the gas in
the cylinder. For complete hazardous material information,
refer to the Material Data Safety Sheet (MSDS).
Division 2.1 Flammable Gas 173.115(a)
454 kg (1001 lbs) of any material which
is a gas at 20°C (68°F) or less and 101.3
kPa (14.7 psi) of pressure (a material
which has a boiling point of 20°C (68°F)
or less at 101.3 kPa (14.7 psi)) which-
1. is ignitable at 101.3 kPa (14.7 psi)
when in a mixture of 13 percent or
less by volume with air; or
2. has a flammable range at 101.3 kPa (14.7 psi) with air
of at least 12 percent regardless of the lower limit.
Division 2.2 Non-flammable, Non-poisonus Gas
This division includes compressed gas,
liquefied gas, pressurized cryogenic gas,
compressed gas in solution, asphyxiant
gas and oxidizing gas. A non-flammable,
nonpoisonous compressed gas (Division
2.2) means any material (or mixture)
which-1. exerts in the packaging an absolute pressure of 280
kPa (40.6 psia) or greater at 20°C (68°F), and
2. does not meet the definition of Division 2.1 or 2.3.
Division 2.2 Oxygen
This is an optional placard to the 2.2
Non-flammable Gas placard for compressed
Oxygen in either the gas or liquid
state. Oxygen is considered a nonflammable
because it in and of itself
does not burn. It is, however, required
for combustion to take place. High concentrations
of oxygen greatly increases the rate and intensity
2.3 Poison Gas 173.115(b)
Gas poisonous by inhalation means a
material which is a gas at 20°C or less
and a pressure of 101.3 kPa (a material
which has a boiling point of 20°C or less
at 101.3kPa (14.7 psi)) and which:
1. is known to be so toxic to humans as
to pose a hazard to health during
2. in the absence of adequate data on human toxicity, is
presumed to be toxic to humans because when tested
on laboratory animals it has an LC50 value of not more
than 5000 ml/m3. See 49CFR 173.116(a) for assignment
of Hazard Zones A, B, C or D. LC50 values for values
for mixtures may be determined using the formula
in 49CFR 173.133(b)(1)(i)
Because the contents are under pressure and are sometimes
hazardous, there are special safety regulations for
handling bottled gases. These include chaining bottles to
prevent falling and breaking, proper ventilation to prevent
injury or death in case of leaks and signage to indicate the
potential hazards. Installing and replacing gas cylinders
should be done by trained personnel.
In a fire, the pressure in a gas cylinder rises in direct
proportion to its temperature. If the internal pressure
exceeds the mechanical limitations of the cylinder and
there are no means to safely vent the pressurized gas to
the atmosphere, the vessel will fail mechanically. If the vessel
contents are ignitable, this event may result in a "fireball".
If the cylinder's contents are liquid but become a gas
at ambient conditions, this is commonly referred to as a
Boiling Liquid Expanding Vapor Explosion (BLEVE).
In addition to the guidance in the OSHA regulations,
Compressed Gas Association (CGA) pamphlets determine
requirements for handling, storing, and using compressed
gases in cylinders, portable tanks, rail tankcars and motor
vehicle cargo tanks. They also identify how to install and
maintain required pressure relief valves on these containers.
The in-plant handling, storage and utilization of all compressed
gases in cylinders, portable tanks, rail tankcars
and motor vehicle cargo tanks shall be in accordance with
CGA Pamphlet P-1.
Compressed gas cylinders, portable tanks, and cargo
tanks shall have pressure relief devices installed and maintained
in accordance with CGA Pamphlets S-1.1 and S-1.2
I hope this information will help you identify these sleeping
giants. There is a little poem “A Sleeping Giant” on our
website for you to read to your employees when they are
handling compressed gas cylinders. This poem has been
around for as long as I have been in the safety field.
If you need more information on this subject or are
interested in OSHA safety training, please contact me at
firstname.lastname@example.org. My special thanks to
Arigas and the Compressed Gas Association for allowing
the use of some of their materials.
For more information, click on the author biography at the top of the page.