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 vender on campus. If you have any questions or concerns regarding gas cylinders, please contact the Airgas University Specialist, Brent Hart, 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. Oxidizing gases can react violently with organic chemicals or material.
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 or the supplier of the gas.
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.
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.
Small Refillable Gas Cylinder
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.
Caps used for valve protection should be kept on the cylinder except when the cylinder is in use. A cylinder's cap should be screwed on tightly.
If a cylinder or valve is noticeably corroded, the gas vendor should be contacted for instructions. Any other damage that might impair the integrity of the cylinder should be called to the attention of the gas vendor before the cylinder is returned.
Transferring compressed gases from one commercial cylinder to another is not permitted.
Do not use compressed gas cylinders for any purpose other than for transporting and supplying gas.
Never tamper with, repair, or alter cylinders, regulators, or any pressure-relief devices. Return defective cylinders to the gas vendor immediately.
Do not attempt to remove a stuck cylinder cap by using a lever in the cap ports. The lever may accidentally open the valve when the cap turns.
Do not place cylinders where they might become part of an electric circuit or allow them to come into contact with an electrically energized system.
Use pressure regulators that are equipped with pressure relief devices.
Users must be properly trained in using gas cylinders by someone with experience.
If a gas cabinet is used, label the outside of the cabinet with the contents.
Label all piping that contains gases. NFPA 55 identifies the following points as requiring markings:
At each critical process control valve
At wall, floor, or ceiling penetrations
At each change of direction
At a minimum of every 20 ft. or fraction thereof throughout the piping run.
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 pressure 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.
Single Stage Regulator 
Two-Stage Regulator 
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 diaphragm 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 diaphragms 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 diaphragm 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. Airgas has guidance for regulator maintenance.
Never use a connection adapter 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 at on the CGA connection. This can cause leaks, connection to fail, or contamination of the regulator. The CGA connection is designed so 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 Airgas.
If you notice one of the pressure gauges not working, remove it from service. Likely the gauge has been blown by an over-pressurization event causing the bourdon tube to be compromised. It is necessary to investigate how the regulator was damaged in order to prevent future incidents.
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:
Cylinders containing flammable gases (empty or full) should be separated from cylinders containing oxidizing gases by a minimum distance of 20 feet or by a barrier at least 5 feet high that has a fire-resistance rating of at least one-half hour; e.g., a concrete block wall.
Storage of flammable gases in a ventilated, fire resistant enclosure is recommended (e.g., an approved gas cabinet or chemical fume hood). If this is not possible, flammable gas cylinders should be stored in a well-ventilated space.
The quantity of flammable gases in a laboratory should be kept to a minimum. A maximum of three full-size cylinders of flammable gas are permitted in one laboratory (500 ft2).
The use of flow restrictors or surge protectors on flammable gas cylinders is recommended to prevent a sudden large flow of gas in case of a rupture or other unexpected release.
There may be circumstances where using a pure flammable gas may pose unacceptable risks. Under these circumstances, it may be necessary to use the flammable gas in a mixture with an inert gas to lower the flammability of the gas (e.g., 1% hydrogen in 99% argon). If in doubt, contact the Division of Research Safety.
Flashback arrestors stop flashbacks, reverse flow of gases, and hose burn backs. It is important to uses these especially when using the flammable gas as a torch.
In addition to the general guidelines, the following measures should be taken when handling toxic gases:
Toxic and highly toxic gases categorized by Airgas and NFPA must be stored in a ventilated gas cabinet, exhausted enclosure, or gas room (NFPA 55 188.8.131.52). NFPA defines toxic gases and highly toxic gases to have an LC50 greater than 200 ppm and less than or equal to 2000 ppm, and an LC50 less than or equal to 200 ppm, respectively. This information can be found in the Safety Data Sheet for the gas.
The quantity of toxic gas in a laboratory should be kept to a minimum.
Flow restrictors are required on most toxic gas cylinders.
Ensure that pressure-relief devices vent directly to a laboratory exhaust system.
Gas detection systems may be required in laboratories using toxic gases:
Gas Cabinet for Toxic Gas
In addition to the general guidelines, the following measures should be taken when handling oxidizing gases:
Do not permit oil or grease to come in contact with compressed oxidizing gases; explosions could occur. Regulators and tubing used with oxidizing gases undergo a special cleaning by the manufacturer and are dedicated for the specific type of gas. Keep the regulator in a clean place (e.g. a zip-lock bag) when not in use and make sure it does not come into contact with any organic material.
Cylinders containing oxygen or other oxidizing gases (empty or full) should be separated from cylinders containing flammable gases by a minimum distance of 20 feet or by a barrier at least 5 feet high and having a fire-resistance rating of at least one-half hour (e.g., a concrete block wall).
Do not store oxidizing gases near flammable solvents, combustible materials, or near unprotected electrical connections, heat sources, or sources of ignition.
Corrosive gases categorized by Airgas and NFPA must be stored in a ventilated gas cabinet, exhausted enclosure, or gas room (NFPA 55 184.108.40.206).
Cylinders containing corrosive chemicals should be checked periodically to ensure that the valve has not corroded. If a cylinder or valve is noticeably corroded, contact the gas vendor for instructions.
Be cautious if flow does not immediately start when a valve is opened slightly. There could be a plug in the valve, and if the valve is opened more, the plug could clear suddenly with unexpected excessive flow.
Remove regulators after each use and flush with air or nitrogen to reduce regulator corrosion.
Pyrophoric gases have an autoignition temperature below 130 ºF (54.4 ºC).
In addition to the general guidelines, the following measures should be taken when handling pyrophoric gases:
Pyrophoric gases must be used only in spaces that have sprinkler systems.
Cylinders must be stored in continuously ventilated and fire suppressive gas cabinets.
Gas plumbing must have a leak detector.
Plumbing of the inboard/outboard style is recommended.
Flame resistant lab coats must be worn when using pyrophoric gases.
Gas Cabinets for Pyrophoric Gases
Flammable Limits in Air (Vol. %)
Storage in gas cabinet required
R = recommended; Y = yes; N = no
Oxidizer, Toxic, Corrosive
Flammable, Toxic, Corrosive
Oxidizer, Toxic, Corrosive
R = recommended; Y = yes; N = no
Note: The gases in the table are considered in their pure form. Mixed gases may have differing requirements.
All gas cylinders that are empty or partially full and 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.
Incidents involving compressed gases can be very dangerous. Like most incidents involving chemicals, the hazards of the gas, location, and scale all play a role in the severity of the incident.
In some situations, a small leak can easily be addressed by shutting the main valve to the cylinder tightly. If you suspect the leak is occurring due to damaged plumbing, shut off the main valve at the cylinder and begin diagnostics on the rest of your system. This response should only be if the leak is not causing an atmosphere that is dangerous for the person to enter.
Damaged to either the cylinder valve or gas system can sometimes cause larger leaks that are hazardous to a person entering the area in order to close the valve or isolate the problem. In this case, evacuate the area and call 911. Inert gases can fall into this category, especially in spaces with poor ventilation, because there is a risk of asphyxiation.
During any scale emergency, it is important to be able to identify the gas and access the shut off (e.g., cylinder valve). If the gas is not easily identified (label is facing away from the user or cylinder is inside a cabinet) it is important to create a secondary sign to indicate the gas in the cylinder. There must not be any obstructions between the responder and the ability to shut the valve. For example, if the cylinder is within a gas cabinet, the cabinet should be labeled on the outside and no lab equipment can block the cabinet doors from opening completely.
If you ever suspect a gas cylinder is damaged. Remove it from service and contact Airgas or the cylinder’s vendor immediately.
Matheson Gas Guide to Regulators https://www.mathesongas.com/pdfs/litCenter/SpecGas&EquipmentBrochures/Guide%20to%20Regulators.pdf