Compressed gases can be toxic, flammable, oxidizing, corrosive, and inert or they may possess combinations of these hazards. Besides their chemical hazards, compressed gases are rather pressurized. The amount of energy in a compressed gas cylinder makes it a potential rocket. It is of essential importance to handle and use compressed gas cylinders appropriately.
Following risks of hazards should be kept in mind while handling, working with storing compressed gases:
- Asphyxiation: This is the most important hazard associated with inert gases. These gases may easily leak into atmosphere and rapidly reduce the oxygen amount below minimum oxygen concentration for human breathing. Since they are colorless and odourless, it is hard to detect the leak. An equipment to monitor oxygen level should always be carried while working with inert gases in enclosed areas.
- Fire and Explosion: This is the most important hazard associated with flammable gases such as oxygen and oxidizers. Static electric or a heat source such as flame or a hot object can ignite flammable gases. Although oxygen or oxidizing agent does not burn, they start a combustion reaction with organic materials. The rate of this combustion reaction enhances as the amount of oxidizers in the reaction medium increase. In addition, non-flammable materials may also burn in an oxygen-enriched medium.
- Chemical Burns: Corrosive gases can chemically attack various materials, including fire-resistant clothing. They may rapidly destruct skin and eye tissue. Some gaseous substances that are normally non-corrosive may become extremely dangerous in the presence of moisture, even in a very small amount.
- Chemical Poisoning: This is the most important hazard associated with toxic gases. A short-time exposure to these gases may result in severe injuries of poisoning, even in very small concentrations. Symptoms of exposure may not be acute, delayed symptoms are more likely to be observed.
- High Pressure: Since the containers/cylinders of compressed gases are in high levels of pressure, they are potentially hazardous. A sudden release of pressurized gas, by means of propelling a cylinder or whipping a line, may cause several injuries.
- Cylinder Weight: A full size cylinder may weigh more than 58 kg. Manual movement of a cylinder, including dropping and dragging may cause injuries concerning back, spinal cord or muscles.
- Do not drop, drag or slide cylinders. Even for short distances a suitable hand truck or a chain-equipped-cart should be used and cylinders must be belted to secure the cylinder to the cart.
- Do not permit cylinders to strike each other violently. Cylinders are not intended to use as rollers to move other materials or equipment.
- Cylinder caps protect the valve on top of the cylinder from damage, therefore they should be kept on cylinder until it has been secured and the regulator has installed. Securing may be done against a wall or bench or by placing in a cylinder stand.
- Do not tamper with pressure relief devices in valves or cylinders.
- Only the wrenches or tools provided by the cylinder supplier should be used to remove a cylinder cap or to open a valve. Do not use a screwdriver or pliers.
- If the cylinder is not in use, keep the cylinder valve closed all the time.
- Place cylinders in a position that the cylinder valve is accessed easily.
- Compressed gases should only be used in well-ventilated areas. Toxic, flammable and corrosive gases should be kept in a hood or gas cabinet and be handled carefully. Containment systems should be proper to use and there should be only necessary amount of these products kept in the working area.
- A trap or a suitable check valve should be used upon discharging gas into a liquid to prevent liquid from escaping back into the cylinder or regulator.
- Label gas lines if more than one type of gas is in use. This is particularly important when the gas supply is not in the same room or area as the operation using the gases.
- Do not use the cylinder valve itself to control flow by adjusting the pressure.
Storage of Compressed Gas Cylinders
- Secure all cylinders against to a wall, bench or fixed support via a chain or strap placed 2/3 of the way up. As an alternative to straps, cylinder stands can be used.
- Keep the cylinders strapped individually.
- Full and empty cylinders should not be stored together.
- Store oxidizers and flammable gases in areas separately at least 6 m. by a non-combustible wall.
- Do not store cylinders close to heat sources including radiators. Protect cylinders from weather differences if you store cylinders outdoor and damp ground to prevent corrosion.
- Cylinders should not be subjected to temperatures higher than 51 °C. Never permit a flame to come in contact with any part of a compressed gas cylinder.
- Cylinders should not be placed where they may become part of an electric circuit.
- Minimum number of cylinders should be kept in a laboratory in order to reduce the risk of fire and toxicity hazards.
- Cylinder should be properly and prominently labelled as to its contents.
- NEVER place acetylene cylinders on their side.
Using Compressed Gas Cylinders
SDSs, along with label information, of the gas being used should be carefully read prior to use. The cylinder valve outlet connections are intended to prevent incompatible gases from mixing. The outlet threads vary in diameter i.e., some are internal and some are external while some are right-handed and some are left-handed. Right-handed threads are generally used for fuel gases. Follow the steps below to set up and use the cylinder:
- Closed regulators should be attached to cylinders. Unless the regulator is completely closed, do not open a cylinder valve. Note that regulators are gas-specific; therefore they are easily attached to appropriate gas cylinders. Do not force the threads to attach a regulator to a cylinder. Do not force a regulator to attach if the inlet of it does not fit the outlet of cylinder. If the fit is poor, it indicates that the regulator is not intended for the gas cylinder being attached.
- Turning the delivery pressure by adjusting screw counter-clockwise until it turns freely prevents unintended gas flow into the regulator.
- Open the cylinder slowly until the inlet gauge on the regulator registers the cylinder pressure. The cylinder valve may be leaking if the pressure read is lower than expected.
- Turn the delivery pressure adjusting screw clockwise until the required delivery pressure is reached while the flow control valve at the regulator outlet is closed.
- Use a Snoop or soap solution to detect a leak. Instead of soap, a mixture of glycerine and water, such as Snoop, should be used to check the leaks at/below freezing temperature. Do not use an open flame to check the leak.
- Close the cylinder valve and release regulator pressure when you’re done with compressed gas containers.
Assembly of Equipment and Piping
- Threads should never be forced if they do not fit exactly.
- A Teflon tape or thread lubricant should be used for assembly. Use Teflon tape only for tapered pipe thread, they are not intended to use for straight lines or metal-to-metal contacts.
- Since copper hardens and cracks with repeated bending, do not bend copper tubing sharply.
- Inspect tubing frequently and replace when necessary.
- Since Tygon and plastic tubing may easily fail under pressure or thermal stress, they are not appropriate for most pressure work.
- Brands and types of tube fittings should be the same. Construction parts are usually not interchangeable; therefore do not mix different brands and types.
- Never use oil or lubricants on equipment used with oxygen.
- Never use copper piping for acetylene.
- Never use cast iron piping for chlorine.
Leaking usually takes place at the valve attached to cylinder and may usually arise from failed valve threads, valve stem, valve outlet, or pressure relief devices. Call LS/LSS in case if there’s a necessity to repair a leaking cylinder.
Following action can be taken if there’s no risk of serious exposure to lab users:
- Move the cylinder to an isolated, well-ventilated area (away from combustible materials especially if the cylinder contains a flammable or oxidizing gas).
- Contact LS/LSS.
- Evacuate the area and immediately contact security if there’s a large or uncontrollable leak takes place.
- When the cylinder is emptied, regulator should be removed and the cylinder cap must be replaced.
- Empty cylinder should be labelled and stored in an area designated to return to the supplier.
- Full and empty cylinders should not be stored together.
- A reverse flow may take place when an empty cylinder is connected to a pressurized system. Therefore, full and empty cylinders should not be connected to the same manifold.
- Empty cylinders should not be filled. Only the cylinder supplier is in charge to refill gases.
- Compressed gas cylinders should never be emptied to a pressure below 25 psi (172 KPa). The remaining contents may become contaminated with air.
- Lecture bottles should always be returned to the distributor or manufacturer promptly when no longer needed. Do not purchase lecture bottles that cannot be returned.
- Any possible source of ignition should be kept away from the cylinders.
- Store oxidizers and flammable gases in areas separately at least 6 meters by a non-combustible wall.
- All cylinders, lines and equipment used with flammable compressed gases should be bonded and grounded.
Highly Toxic Gases
Highly toxic gases possess serious hazard and risk of health in case of a leak. Following additional precautions must be taken upon working with or handling the highly toxic gases:
- Highly toxic gases should be stored and used only in well-ventilated gas cabinet or in a fume hood.
- Use coaxial (double-walled) tubing with nitrogen between the walls for feed lines operating above atmospheric pressure.
- To avoid sudden loss of pressure in the supply line, regulators should be equipped with an automatic shut-off to turn off gas supply.
- For a routine check for leaks, an alarm system with proper warning properties should be installed and the alarm level should be set to a level lower than or equal to permissible exposure limits of the gas.
- To install or change highly toxic gases, a self-contained breathing apparatus (SCBA) may be necessary.
- Label the storage and use area as “Designated area for highly toxic gases”.
Gases Requiring Special Handling
The following gases present special hazards either due to their toxicity or physical properties.
Pressurized acetylene is highly flammable and may undergo spontaneous combustion upon contact with air at pressure levels higher than 15 psig. If released to air in a confined area, acetylene may cause asphyxiation. Acetylene cylinders contain acetone, because acetylene is shock-sensitive and rapidly explode above 30 psi. Since acetone and binders may be dislodged, acetylene cylinders should never be placed on their sides. This may result in a polymerization reaction inside and acetone may also be released into regulator.
In case of skin contact: Skin effects are not likely to occur. An irritation may take place when in contact with liquid acetylene upon repeated exposures. Affected area(s) should be washed with soap and warm water. One should seek medical attention if irritation develops.
In case of eye contact: Since acetylene is gaseous at room temperature, this effect is not a likely route of exposure. Contact of liquid acetylene with the eyes may cause temporary irritation. In this case, eyes should be flushed with water for at least 15 minutes. Medical attention may be asked if needed.
In case of inhalation: Acetylene causes asphyxiation and at high concentrations it may cause anaesthetic effects. Victims should be assisted to an uncontaminated area with fresh air.
In case of ingestion: Since acetylene is gaseous at room temperature, this effect is not a likely route of exposure.
Shipment of acetylene is carried out in a cylinder packed with a porous material and a solvent such as acetone. When the valve of a charged acetylene cylinder is opened, the acetylene comes out of solution and passes out in the gaseous form. Inspection of fuse plugs in the top and bottom of an acetylene cylinder to detect the solvent loss is of utmost importance whenever handled. Any ignition source should be kept away from storage area. Move the cylinder to an open space and keep away from risk sources if leaking takes place due to incorrect handling or other occurrences. In this case, the cylinder should also be labelled as “Leaking Flammable Gas”.
Acetylene cylinders should never be placed on their side. Place the cylinder upright carefully if acetylene cylinder has tipped over was stored on its side and do not use until the liquid has settled to bottom. The rule of thumb is not to use the cylinder for as many minutes as the cylinder was horizontally placed, up to 24 hours.
Acetylene cylinders should be returned to the compressed gas distributor when emptied or no longer used.
Oxygen is a strong oxidizer and rapidly accelerates spontaneous combustion of many organics. Since there’s a risk of dangerous explosion upon contact high-pressure oxygen with oil, oxygen cylinders should be handled very carefully. Oil or grease should never be used on connections to an oxygen cylinder or gas line carrying oxygen. Oxygen should be stored separately from all flammable materials because it is incompatible with them.
Oxygen gas intended for laboratory use is non-toxic. On the other hand, liquid oxygen is cryogenic and may cause tissue damage when exposed with skin.
Oil, greases and other readily combustible substances should never be allowed to come in contact with any part of oxygen containers; cylinders, valves, regulators, and fittings. Since pneumatic equipment usually contains flammable lubricants, oxygen should not be used as a substitute for compressed air in pneumatic equipment. There’s a risk of explosion upon contact of liquid oxygen with many organic substances.
A distance of 6 meters or a non-combustible wall with a fire endurance of at least 1 hour must be maintained between an oxygen cylinder and flammable gases or any combustible material.
When emptied or are no longer in use, oxygen cylinders should be returned to the compressed gas distributor.