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 someone else’s.

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 requirements.

Markings

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 (e.g., 3AA).

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 test.

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- year retest.

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 173.115(b)

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 of combustion.

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 transportation, or 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 jpodojil@podojilconsulting.com. 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.