Oxygen Cylinder Safety

Gaseous oxygen (GOX) is packaged, transported, and used in compressed gas cylinders by many industries throughout the world. This portable, versatile packaging of oxygen is used for breathing gas (medical, aircraft, scuba diving, etc.), combustion (cutting, welding, etc.), and other applications like laboratory-scale experimentation in the power, metal refining and chemical processing industries.

All compressed gas cylinders should be used with caution due to their high-pressure contents, which can quickly turn a cylinder into a rocket if dropped, shearing off the isolation valve (Google “Myth Busters Air Cylinder Rocket”). For more information about general pressure-related hazards of compressed gas cylinders, there are many useful resources available from trade associations like the Compressed Gas Association (CGA) and regulatory agencies like OSHA. GOX cylinders present a unique hazard, however: the risk of fire. They require special handling and operating practices that differ from any other compressed gas.

 “Many people don’t realize that oxygen cylinders require unique safety measures. A welder, for instance, may have two compressed gas cylinders side-by-side, oxygen and acetylene, but each must be handled and operated very differently.”

Elliot Forsyth, WHA Engineer

GOX cylinders are typically fitted with a stand-alone cylinder valve or a valve integrated pressure regulator (VIPR). Stand-alone cylinder valves are designed to be connected to a stand-alone regulator or a manifold and require special handling (as outlined below). VIPRs require less special handling because the cylinder valve and regulator are combined in one device but users must follow manufacturer instructions and particularly avoid contaminating the ports of the VIPR, especially the fill port.

Regardless of application, all oxygen cylinder users should know best practices associated with safe use. At WHA we believe in educating people with the “why” behind the “what,” so users can better understand (and remember) how to safely handle and operate compressed oxygen in cylinders and associated systems.

In this article, our engineers have outlined several best practices that are taught in every WHA oxygen safety course.

Oxygen Safety Fundamentals

Oxygen hazards can seem mysterious, and proper handling methods are not always intuitive. The best way to remember oxygen safety practices is to recall the “fire triangle” illustration that many of us learned about in science class. The fire triangle has three sides which, at the most basic level, remind us there are three factors that all must be present for a fire to occur: oxidizer, fuel, and ignition.

In a compressed oxygen cylinder, pure oxygen gas is the oxidizer, not the fuel – it is not a flammable gas and will not ignite or burn by itself. Instead, oxygen works to make materials (fuels) more flammable and easier to ignite. It is one of three primary elements required for a fire to occur.

Oxygen makes up almost 21% of our atmosphere, which is not necessarily a high concentration, but sufficient to enable many materials to ignite and burn in the presence of an energy or heat source. Of course, there are also many materials will not easily burn under normal atmospheric conditions.

However, as oxygen pressures and concentrations increase, nearly all materials will ignite and burn more easily than they do in air! Even the stainless steel components of a regulator can ignite and burn with the ample oxidizer provided within a compressed oxygen cylinder.

The basic philosophy behind oxygen safety, therefore, is to reduce risk by limiting potential ignition and/or fuel sources in the given oxygen environment. Common oxygen hazards include:

1. Contaminants like oils and greases (hydrocarbon-based): These may seem harmless in ambient air, but they become extremely dangerous fuels in the presence of oxygen.
2. Small particle contaminants: Metal shavings and other small debris can accelerate and ignite upon impact in compressed oxygen, providing both the fuel and the ignition source to start a fire.
3. Fast pressurization: Certain valve styles (ball valves and cylinder valves, for example) open quickly and can rapidly pressurize systems with compressed oxygen, creating sufficient heat to ignite certain materials and cause a fire.

Finally, the safe use of oxygen also includes concepts such as reducing fire consequence by minimizing personnel exposure (i.e. standing to the side of a valve while opening) and limiting the kindling chain of potential fuels that could propagate a small ignition into a large fire.

Best Practices for Handling and Using Compressed Oxygen Cylinders with Cylinder Valves

1. Inspect Your Equipment

Always assess your equipment before using an oxygen cylinder. Only use oxygen cylinders:

1. If experienced and properly trained
2. If wearing approved personal protective equipment (PPE) including safety glasses
3. After identifying the product from cylinder label
4. After ensuring no oils or greases on hands, gloves, or equipment

2. Clear Cylinder Valve

Inspecting and “clearing” or purging the cylinder valve is a critical first step when using any oxygen cylinder to avoid ingesting potential contaminants from the cylinder valve into your regulator or downstream system.

1. First REMOVE PROTECTIVE CAP just prior to cylinder use. (Always keep the protective cap in place when not in use.) Remove any plastic wrapping and ensure no loose pieces remain in the valve outlet.
2. Visually INSPECT cylinder valve outlet for debris (If contaminated, DO NOT OPEN cylinder valve. Instead, RETURN to vendor.)
3. STAND to the side of the cylinder, point valve away from personnel and equipment.
4. BRIEFLY OPEN valve for an instant to clear potential debris.
5. CLOSE valve. (Do not over-torque cylinder valve upon closing.)
6. RE-INSPECT cylinder valve outlet for debris. (If contaminated, DO NOT use cylinder valve. Instead, RETURN to vendor.)

3. Assemble Components

In the United States, most compressed oxygen cylinders utilize a special connection called a CGA-540 fitting.

1. Always visually INSPECT the CGA-540 fitting before assembling any oxygen component to cylinder valve, including regulators, flexible hoses, “pigtail” tubing, or other equipment. (DO NOT use components if contaminated with debris.)
2. WHA recommends that the inlet be fitted with a SINTERED ELEMENT FILTER to protect the regulator from debris.
3. Securely CONNECT the fitting to the cylinder valve outlet.
4. ENSURE the regulator is fully reduced (i.e. closed).

4. System Start-Up

System start-up is one of the most critical steps in using an oxygen cylinder due to the risk of compression heating ignition, which can occur if high-pressure oxygen rapidly pressurizes in compatible downstream components. Chances are that you’ll never experience an oxygen fire, but these good practices reduce the risk.

“One of the most important things we teach about proper handling of oxygen cylinders is related to operation of the cylinder valve. Always remember to open SLOWLY but open FULLY.”

Elliot Forsyth, WHA Engineer

It’s important to note that oxygen cylinder valves have different construction and application from oxygen regulators. Cylinder valves are designed only for “isolation” purposes. As such, they should be operated either completely open or closed. Never partially-open an oxygen valve and leave it to “throttle” or control flow. Although it’s extremely rare, this improper operation can lead to ignition of the plastic valve seat.

1. STAND to one side and not in front or behind regulator when opening cylinder valve.
   

   

2. Although there is a low probability of fire, STAY OUT of potential fire path when opening cylinder valve (see illustration).
3. SLOWLY OPEN cylinder valve. (If audible leaks occur, CLOSE valve immediately.)
   1. To open most oxygen cylinder valve designs, “backseat” the stem on the packing (open all the way), then back ¼-turn. This helps keep the valve from sticking (and possibly appearing to be closed to other users).
   2. To close, don’t overload (over-tighten) the plastic valve seat. This can cause excessive wear and damage the valve seat, limiting durability and, more importantly, creating flammable plastic fibers inside the component. A good “rule of thumb” is to stop applying torque when the valve “feels” closed.
4. INSPECT gauge to ensure adequate pressure. (DO NOT use cylinders below 25-100 psi (170-700 kPa).)
5. DO NOT approach regulator or gauge until above steps have been performed.
6. Perform LEAK CHECK with compatible fluids on all required fittings. (If leaks occur, CLOSE cylinder valve, vent pressure, repair leaks.)
7. If no leaks, INCREASE (i.e. open) regulator to initiate flow.

5. System Shut-Down

Compressed gas cylinders, including oxygen cylinders, should never be emptied completely. Eliminating a positive pressure inside a cylinder can allow contaminants to enter the cylinder and endanger future users. Most suppliers recommend keeping pressures above 25-100 psig at all times.

1. CLOSE cylinder valve when work is complete.
2. VENT regulator to ambient pressure.
3. FULLY REDUCE (i.e. close) regulator.
4. If cylinder is empty (<25-100 psig):
   1. DISCONNECT CGA 540 fitting.
   2. REPLACE dust cap/plug (if present on flex hose).
   3. REPLACE protective cylinder cap.
   4. LABEL the cylinder “EMPTY”.
   5. STORE empty cylinders separately from full cylinders.
   6. RETURN cylinders promptly to supplier.

Concluding Remarks

It bears reminding that ALL users of oxygen cylinders should have a basic understanding of oxygen fire hazards and be trained in their proper use.

For end-users, WHA’s engineers have developed Level 2: O2 Practice, a training course that focuses on oxygen system operations and maintenance, including safe use of oxygen cylinders. This course is conveniently available for clients on-site, via live webinar, or as an interactive e-training module. Best practices are also reinforced in every comprehensive upper-level WHA oxygen safety course.