Compressed gas cylinders are everywhere, but their use entails a high level of responsibility.
Compressed gas cylinders are the most common way research laboratories obtain and use bulk gas. Special cylinder designs and handling practices ensure safety. All images: Airgas
Gas is an indispensable component of a successful laboratory, and the ubiquitous gas cylinder is a common sight at research facilities across the spectrum of technology, from the RNA laboratory to the solar cell fabrication plant.
The average compressed gas cylinder is about four feet tall, weighs 34 kg, and holds a certain concentration of gas pressurized to 2,000 to 2,600 psi. Although designed to be portable, rugged, convenient, and safe, they are one of the most significant safety hazards in the laboratory. The obvious risk is rupture, and tanks that have been impacted or have not been properly maintained can cause serious injury. The gases stored are typically either toxic or flammable. In some cases, they are pyrophoric (spontaneously combustible above 57 C) or cryogenic. Finally, simply handling the tanks themselves can cause injury.
Gas is generally stored in tanks either within the laboratory or at a centralized location on site, such as a trailer. Compressed gases are subject to strict regulations governing storage and use, but the presence of poisonous process gas and flammable gases such as hydrogen require that a facility’s personnel must be attentive and knowledgeable.
Regulation of compressed gas falls under the jurisdiction of several bodies, most notably the Occupational Safety and Health Administration (OSHA) and the U.S. Department of Transportation, which regulates how gases can be delivered to sites. OSHA recommendations are administered by the Compressed Gas Association (CGA), which has published a series of guidelines and bulletins that recommend proper practices. The overarching general guidelines are contained with OSHA CFR 29 1910.101 and handling recommendations are distributed in the CGA's Pamphlet P-1-1965.
Faithful adherence to these guidelines can mean the difference between flawless operation and disaster, but in the experience of some gas supply companies, the presence of extensive guidelines can't always guarantee safe operation. Over time, gas companies increasingly have looked to training programs and outreach to help workers establish safer gas handling practices. And laboratory executives also realize that training for use of compressed gas is a constant process.
While OSHA itself offers training related to compressed gas cylinder handling, safety training is a service component of all the major compressed gas suppliers, including Airgas, Matheson, Proton Onsite, Air Liquide America, and others, and offer the best avenue to safe research facility operation.
Best practices for handling compressed gas
According to Bob Davis, vice president of environmental sustainability at Airgas, Ann Arbor, Mich., almost all accidents involving compressed gases result from not following established methods for the safe handling and transportation of compressed gas cylinders. Davis began his career tending to discarded or waste gas cylinders, cutting them apart, cleaning them out, and scrapping them. As a result, he has a deep experience with the safety issues involved with compressed gas.
"The biggest no-no I see in gas usage is transportation," says Davis. "Users throw [a cylinder] in the back seat of their vehicle without securing it. Between that and letting it fall, those are the most hazardous things I see."
The weight and bulk of gas cylinders pose potential hazards during handling. Cylinders must be secured while at rest or in motion.
For a long period of time, says Davis, falling cylinders was not deemed a leading risk for handling cylinder gas. The pressurized gas itself was seen as the true danger. But figures generated by OSHA studies on injuries caused by use of compressed gas cylinders, he says, showed that cylinder falls were a leading factor in worker injury claims. In response, training programs conducted by Airgas stress the importance of securing cylinders. Davis now believes the tendency for cylinders to fall over generates the most common hazard for customers; these injuries are incurred as the result of a user's reaction to a tipping cylinder.
"When a cylinder is falling, they try to catch it, often bending a different way than they are used to in the effort. This can cause an injury whether they catch it or not," says Davis.
Contusions and leg fractures are the most common injuries, usually breaks in the toes, feet, tibia, and fibula bones. The second-most common injuries are sprains, strains, and spinal cord injuries in the lower lumbar spine. Herniated or bulged discs are common. Other handling missteps can occur. Pulling the cylinder cap to move a cylinder sometimes results in a cap projected toward the worker's face. Broken teeth are a common result. In these cases, prevention is as simple as leaving the cylinder in place until it needs to be changed out, or using a cylinder cart if the containers must be moved. In any case, the cylinder should be secure.
"First of all, it's got to be strapped. You of course want to separate oxidizers from flammable gases, but the main thing is that they are securely fastened," he says.
Although Davis is now helping customers improve their environmental impact through wise use of compressed gas, he has written extensively about the risks of storing gas, and in his many years of experience with Airgas has encountered a number of unexpected "do's" and "dont's".
For example, oily hands or gloves can spell disaster when moving oxidizers. These can react violently with oil or grease if it comes in direct contact with the cylinder valve. Securing the protective valve cap is extremely important. If a cap is unable to protect the valve during a fall, the cylinder could become an unguided missile.
Storage in a fire-resistant area that is dry, well-ventilated, and less than 52 C is common knowledge, but also mandatory is storage at least 20 feet from electrical sources including switches, outlets, and even extension cords.
Training sessions from Airgas also include guidance on how to inspect the cylinders themselves. A customer must never assume the tank is foolproof. As per OSHA's 1910.101 standard, the receiver must, says Davis, inspect the tank, looking for burn marks, dents, or corrosion and that the valve is properly attached. Another key responsibility is to check the purchase order and ensure that the facility is not receiving cylinders that contain incorrect contents.
CGA offers additional guidelines that are likely to be part of any gas supply company's training. An empty tank, for example, is never truly empty. It still contains gas at atmospheric pressure, or about 15 psi, and depending on the size of cylinder this can mean a substantial amount of potentially toxic gas.
Another recommendation is the importance of avoiding zero gas. Below about 250 psig, cylinders run the risk of becoming contaminated. Gas companies can deal with this issue by cleaning tanks, but keeping existing cylinders free of potential contamination issues helps guarantee the integrity of the cylinder supply.
Finally, the use of adaptors is frowned upon; cylinders should be used only with compatible regulators. Regulators have been carefully designed so as to be relatively foolproof, but plenty of best practices exist.
"Regulators are pretty good. Even if they are sheared off, the tank keeps its integrity," says Davis, "they are sealed to the cylinder and won't burst. Plus, these days the hole is drilled down at a slight angle so they don't take off like a rocket. Instead it will typically spin in a circle."
Ruptures can occer if certain precautions are not followed. Most major gas suppliers and the Compressed Gas Association publish handling guides and offer safety training for laboratory employees.
Most valve outlet connections are designed with metal-to-metal seals. Washers should only be used if indicated. Leak testing is performed prior to delivery, but in the event of leaks, workers must refrain from quick fixes to prevent leaks. The use of Teflon tape, for example, is not good because it may become powdered and catch on the regulator poppet, causing sudden full pressure release. Even crossing threads is a safety hazard because brass particles can interfere with gas flow.
Safety improvements beyond best practices
Gas release, then, is a constant concern for research facilities. In the event of a breach in a gas cylinder, solutions like gas cabinets, gas bunkers, and scrubbers are often employed to reduce the immediate danger of an explosion from a flammable carrier gas.
But other factors have also made the laboratory a safer place to use compressed gas. An unanticipated improvement has been the reduction in concentration of some hazardous and volatile gases, such as hydrogen. The cause for this change is two-fold.
First, government regulations have tightened on concentration levels. Second, laboratory instruments, such as chromatographs, have become both more efficient in the use of gas and more accurate.
"They've gone down significantly. They've gotten a lot more accurate and lot smaller in terms of concentrations," says Davis. "A tenth of a part per million is now commonplace." Asphyxiation risks still exist, but because concentrations are far lower the risks in the event of a ruptured tank are certainly lessened.
Long experience with compressed gas has produced a secure and safe system for transport and use. Containers themselves are steel. Regulators are sometimes brass, sometimes stainless steel depending on the application. They are hydrotested every five years, which involves submerging the tank and applying high pressure to the cylinder walls. This is a required test, but companies like Airgas also examine tanks electronically through X-ray imaging, looking for hidden faults or damage.
The proliferation of analytical instrumentation has meant a steadily rising demand in the use of compressed gas, says Davis. For some industries, bulk is crucial.
"Any industry that is using a significant number of sensors is going to be doing some stack testing. And any type of emissions source has to account for calibrating their instruments," says Davis.
"Because of the requirement of calibration, you have to challenge the instrument to meet that. The only way to do it is with a known concentration of gas."
Alternative gas delivery solutions, such as onsite gas generation from sources Proton Onsite (Wallingford, Ct.) are an avenue that customers can take to mitigate risks. But even with onsite generation, training is required to ensure that gas supplies are safely and responsibly handled. And often a facility will still require the use of delivered gas.
"Onsite gas is a trade-off," says Davis. Portable gas cylinders have an element of risk involved with their use, and safety depends on the integrity of the equipment. But, he says, "if you are producing gas onsite, you run into problems with mechanical issues, or with pumps." Carbon monoxide emission is also an added risk. Plus, depending on the type of gas being generated, there are heightened risks. Nitrogen is less problematic than hydrogen, for example.