Compressed gases expose users to both chemical and physical hazards. Gases contained within cylinders can be toxic, flammable, oxidizing, corrosive, inert, or a combination of these hazards. Because the pressurized chemical is released in gaseous form, a leak from the cylinder, regulator, or any part of the system used to deliver the gas can quickly contaminate a large area. Therefore, it is necessary to be familiar with the chemical hazards of the gas and possibility of asphyxiation. In addition to the chemical hazards, there are hazards from the gas pressure and the physical weight of the cylinder. A gas cylinder falling over can break chemical containers and crush feet. The cylinder can itself become a dangerous propelled object if its valve is broken off. Appropriate care in the handling and storage of compressed gas cylinders is essential and information is provided below.
Airgas is currently the gas cylinder vendor on campus. If you have any questions or concerns regarding gas cylinders, please contact the Airgas University Specialist, Tyler McKenzie, at firstname.lastname@example.org or the Division of Research Safety.
Gases that corrode material or tissue with which they come in contact, or do so in the presence of water, are classified as corrosive.
A gas at normal atmospheric temperature and pressure that can be ignited and burned when mixed with the proper proportions of air, oxygen, or other oxidizers is considered flammable. Changes in temperature, pressure, or oxidant concentration may cause the flammability range to vary considerably.
Gases that do not react with other materials at standard temperature and pressure are classified as inert. They are colorless, odorless, nonflammable, and nontoxic. The primary hazards of these gases are the high pressure and potential for asphyxiation. These gases are often stored at pressures exceeding 2,000 psi. They can displace the amount of oxygen necessary to support life when released in a confined place. Use of adequate ventilation and monitoring the oxygen content in confined places will minimize the danger of asphyxiation.
Gases that do not burn but will support combustion are classified as oxidants.
Gases that may produce lethal or other harmful effects on humans are classified as toxic. The degree of toxicity and the effects will vary depending on the gas. The Safety Data Sheet should be consulted to determine the toxicity.
SDS (safety data sheets) for compressed gases can be found on the Airgas website http://www.airgas.com/sds-search. If you are having trouble locating a SDS, contact Airgas.
There are two types of gas cylinders used on campus.
Disposable Lecture Bottle
The Division of Research Safety encourages all researchers to rent refillable gas cylinders.
Small Refillable Gas Cylinder
Most gas vendors are able to provide a complete line of small quantity gases for rent in refillable, returnable cylinders which are generally about 20 inches long and 4 inches in diameter. These refillable, returnable cylinders are as portable as lecture bottles and almost always cost less than the same product delivered in a lecture bottle. The cylinders contain more product than lecture bottles and may be returned to the gas vendor for free even if they are not empty.
The amount of hazardous compressed gases permitted within a laboratory work area is regulated by NFPA 45 as outlined in the table below.
Health Hazard 3 or 4 (NFPA)
Amount allowed per 500 ft2
Number of cylinders allowed per 500 ft2
3 cylinders (9"x51" cylinder)
3 cylinders (9"x51" cylinder)
Amount of gas allowed per ft2 of lab space
In addition to the maximum quantities listed in the table above, the number of lecture bottle cylinders is limited to 25.
A regulator allows the high pressure in a gas cylinder to be reduced to a manageable and usable pressure. A regulator controls delivery pressure and should not be used for flow control. Chose a regulator with an appropriate delivery-pressure range for the application. The maximum should be at least twice as high as the desired pressure.
Regulators can be single-stage or two-stage. You cannot tell the difference between a single and two-stage regulator by the number of gauges it has. A single-stage pressure regulator is used when inlet pressure does not vary greatly or when readjusting the inlet pressures does not cause a problem with the experiment/application. As the pressure inside the cylinder drops, the outlet pressure increases due to the lack of pressure to raise the poppet. The pressure adjustment handle will need to be regularly adjusted to maintain a constant outlet pressure.A two-stage pressure regulator is used with gas cylinders to deliver a constant pressure of gas without constant minor adjustments of the pressure adjustment handle when the pressure inside the cylinder changes. The first stage of this regulator decreases the inlet pressure to a preset pressure. The second stage then reduces this pressure to the desired delivery pressure.
A two-stage pressure regulator is used with gas cylinders to deliver a constant pressure of gas without constant minor adjustments of the pressure adjustment handle when the pressure inside the cylinder changes. The first stage of this regulator decreases the inlet pressure to a preset pressure. The second stage then reduces this pressure to the desired delivery pressure.
Different gases and cylinder sizes have different requirements for regulators. The cylinder connection can be male or female and be composed of different materials. A CGA number printed on the gas cylinder and the regulator is used to find the correct match. Below are a few examples of different connectors and their CGA numbers.
For flammable gases, a left-handed thread is used. This is often indicated by a notch or line on the adaptor.
The diaphram within the regulator can be made from different materials. Depending on the gas used, some materials are preferred or even required. Two common materials include elastomers (e.g., neoprene) and stainless steel. The diaphrams made of elastomers can introduce contaminates to the system as they can absorb moisture or contaminates from the air. To maintain purity it is recommended to use a stainless steel diaphram whenever possible.
Regulators do not last forever. Depending on the type of gas and frequency of use, regulators can become compromised. Contact Airgas to determine if the regulator you are using is safe.
Never use a connection adapater to mount the wrong regulator on a cylinder. The CGA connections must match between the cylinder outlet valve and the regulator. The CGA connection depends on the type of gas and also the size of the cylinder. Modifying connections can lead to a serious risk using the cylinder.
Teflon tape should not be used on the CGA connection. This can cause leaks and contamination of the regulator. The CGA connection is designed to be metal on metal and no additional materials are needed to improve the seal. Do not lubricate fittings. Lubricants can react with certain gases or introduce impurities to the system that can damage connections and the regulator. Carefully inspect the CGA connection for damage before using the gas. If there is any damage, contact the gas vendor.
Consult with the gas supply company for questions about the correct type of regulator and materials for the gas being used.
In addition to the above guidelines, the following measures should be taken when handling flammable gases:
In addition to the general guidelines, the following measures should be taken when handling toxic gases:
Gas detection is not required if the gas has physiological warning properties below the permissible exposure limit (PEL). The table at the end of the document marks highly toxic and toxic gases with “HT” or “T”, respectively.
Gas Cabinet for Toxic Gas
In addition to the general guidelines, the following measures should be taken when handling oxidizing gases:
In addition to the general guidelines, the following measures should be taken when handling corrosive gases:
In addition to the general guidelines, the following measures should be taken when handling pyrophoric gases:
Gas Cabinets for Pyrophoric Gases
All gas cylinders that are empty or partly full that will no longer be used must be disposed of properly.
Rented cylinders must be returned to the vendor. Contact the vendor or campus unit that supplied the cylinder and arrange a pickup according to the rental plan.
Lecture bottles and disposable gas cylinders must be managed as potentially hazardous waste, as they are purchased outright. Examples of disposable gas cylinders are cylinders of propane, butane, helium, or calibration gases. Indicate on the non-refillable gas cylinder whether it is empty or still contains product above one atmosphere of pressure, and dispose of the cylinder through DRS.
Flammable Limits in Air (Vol. %) (1)
2.5 - 82
5.1 - 78
2.0 - 12
1.6 - 8.4
1.6 - 10
12.5 - 74
0.8 – 98
4.1 - 98.8
2.8 - 14.4
3.0 - 12.5
2.7 - 36
3 - 100
4.0 - 75
1.8 – 8.4
1.8 - 9.6
5.0 - 15.0
8.1 - 17.4
4.9 - 20.7
1.6 – 99
2.1 - 9.5
2.0 – 11.1
1.5 – 98
2.0 – 11.6
3.6 - 33
Other information about compressed gas safety can be obtained from the Division of Research Safety at 217-333-2755 or e-mail to email@example.com.