How Do I Work Safely with Compressed Gases? What are cylinders and fittings? Compressed gases are stored in heavy-walled metal cylinders designed, produced and tested for use with compressed gases.  Cylinders are made in a wide variety of sizes and shapes.  They range from small lecture bottles, often used for demonstration purposes, to large cylinders over 3 meters long.  Cylinders must comply with regulations of the Canadian Transport Commission (CTC).  CTC regulations require certain permanent markings on every cylinder: the specifications which the cylinder meets, the designed service pressure, a serial number, inspection codes, and identification of the cylinder maker or manufacturer.  Cylinders for liquefied gases are also marked with the empty (tare) weight.  These markings are normally stamped into the cylinder's shoulder or the top surface of its neck.  Pending Transport Canada Regulations will give specifications for cylinders and their selection for service under Canadian Standards Association standards B339 and B340. Cylinders are tested under hydrostatic water pressure when they are made.  Usually, cylinders must be retested every five or ten years.  The date of each test must be stamped on the cylinder.  Acetylene cylinders are not tested hydrostatically.  It is too difficult to remove the water from the porous filler.  Instead, they receive careful visual inspections. Cylinder Valves and Connections Compressed gas cylinders must be connected only to regulators and equipment designed for the gas in the cylinder.  Since connecting the wrong equipment can be dangerous, a number of different standard cylinder valve outlets are available for different classes of gas.  For example, these standard connections prevent the valve connection for a flammable gas from fitting the connections for an incompatible gas, such as an oxidizing gas.  The current Canadian Standards Association (CSA) Standard B96, "Compressed Gas Cylinder Valve Outlet and Inlet Connections," contains detailed descriptions of the permissible valves and fittings. Most compressed gas cylinders have valve caps or some other method of protecting the valve from damage during handling and transportation.  A dust cap may be placed over the valve outlet itself to help keep it clean. What are cylinder safety devices? Most cylinders have one or more safety-relief devices.  These devices can prevent rupture of the cylinder if internal pressure builds up to levels exceeding design limits.  Pressure can become dangerously high if a cylinder is exposed to fire or heat, including high storage temperatures. There are three types of safety-relief devices.  Each relieves excessive gas pressures in a different way: Safety- or Pressure-Relief Valves: These valves are usually a part of the cylinder.  They are normally held closed by a spring.  The force holding the valve closed is set according to the type of gas in the cylinder.  The valve opens if the cylinder pressure exceeds the set safety limit.  Gas is released until the cylinder pressure drops back to the safety limit.  The valve then closes and retains the remaining gas in the cylinder. Rupture Discs (also known as frangible or bursting discs): These discs are usually made from metal.  They burst or rupture at a certain pressure, releasing the gas in the cylinder.  The bursting pressure is designed so that the disc ruptures before the cylinder test pressure is reached.  These devices cannot be reclosed, so the entire contents of the cylinder are released. Fusible Plugs (also called fuse or melt plugs): Temperature, not pressure, activates fusible plugs.  These safety devices are used where heat could initiate an explosive chemical reaction.  A pressure-relief valve or rupture disc acts too slowly and too late to prevent rupture of the cylinder if an explosive reaction has already begun.  The fusible plug releases the gas before the hazardous reaction can begin.  Fusible plugs are made of metals that melt at low temperatures.  For example, acetylene cylinders have a fusible plug which melts at about 100°C (212°F).  This temperature is safely below the temperature at which hazardous polymerization may occur. Not all compressed gas cylinders have safety devices.  Some gases are so toxic that their release through a safety device would be hazardous.  Cylinders for these gases are built to withstand higher pressures than normal cylinders.  When these "toxic gas" cylinders are involved in a fire, the area must be evacuated. Why should I use substitution as a method of controlling exposure to compressed gases? Substitution can be the best way to avoid or reduce a hazard.  But it is not always easy or even possible to find a less hazardous substitute for a particular compressed gas used for a certain job.  Speak to the chemical supplier to find out if safer substitutes are available.  For example, in some cases, methylacetylene-propadiene (MAPP) gas, propylene, propane or mixtures of liquefied petroleum gas can be substituted for acetylene as fuel gases for cutting, welding and brazing.  These gases are more stable and can be stored in normal cylinders.  Their flammable limits are much narrower than those of acetylene (e.g., 3.4 to 10.8 percent for MAPP versus 2.5 to 82 percent for acetylene), so they represent a reduced fire hazard. Obtain MSDSs for all possible substitutes.  Find out about all of the hazards (health, fire, corrosivity, chemical reactivity) of these materials before making any changes. Sometimes, process changes or modifications can reduce a material's hazards.  For example, many cylinders of the same gas may be used in different areas of a workplace.  Installing fixed pipelines connected to a central gas supply in a safe area can often reduce the hazard.  It can also reduce the need for many sets of portable equipment supplied through flexible hoses.  Similarly, ordering cylinders equipped with flow limiting restrictors can minimize the hazards of a sudden failure of a process gas line. Choose the least hazardous material and process that can do the job effectively and safely.  Then learn how to work safely with them. Why is proper ventilation important? Well-designed and well-maintained ventilation systems remove gases from the workplace and reduce their hazards. The amount and type of ventilation needed depends on such things as the type of job, the kind and amount of materials used, and the size and layout of the work area. Assess the specific ways your workplace stores, handles, uses and disposes of its compressed gases.  An assessment can reveal if existing ventilation controls and other hazard control methods are adequate.  Some workplaces may need a complete system of hoods and ducts to provide acceptable ventilation.  Others may require a single, well-placed exhaust fan.  Storage facilities for particularly hazardous materials such as chlorine, may require an additional emergency ventilation system, or continuous monitoring with appropriate alarms.  Other workplaces using small amounts of inert gases may require no special ventilation system. Make sure ventilation systems are designed and built so that they do not result in an unintended hazard.  Ensure that hoods, ducts, air cleaners and fan are made from materials compatible with the gas used.  Systems may require explosion-proof and corrosion-resistant equipment.  Separate ventilation systems may be needed for some compressed gases to keep them away from systems exhausting incompatible substances. How do I store compressed gas cylinders? Store compressed gas cylinders in compliance with the occupational health and safety regulations and fire and building codes applying to your workplace.  These laws may specify the permissible kinds of storage areas and the construction of these storage areas.  They may also specify the kinds and amounts of different gases that can be stored in each safe storage area. What should I do when I receive cylinders? Inspect all incoming cylinders before storing to ensure they are undamaged and properly labelled.  Do not accept delivery of defective cylinders.  Be sure they are not giving off odours, visible fumes or hissing sounds.  Check that the cylinder was last tested within the required time (usually five years).  Also check that the cylinder labels are intact and that they match other identifying markings on the cylinder.  Do not rely on cylinder colour to identify the gas.  Different suppliers may use different colours for cylinders of the same gas.  In addition, colours appear different under artificial lights and some people are colour blind. Call compressed gases by the name on the supplier label.  This reduces confusion, promotes recognition of the hazards involved and precautions to take, and can prevent accidental use of the wrong gas.  If oxygen is called "air," someone who wants air to run a tool may use oxygen with possible serious results.  Leave the valve cap securely in place until the cylinder is to be used.  Inspect the cylinder valve by looking through the ports in the valve cap.  Do not accept dirty, rusted or otherwise damaged valves and fixtures. How do I transport or move cylinders? Always transport cylinders with valve caps or other valve protection in place.  Pulling cylinders by their valve caps, rolling them on their sides or dragging or sliding them can cause damage.  Rolling cylinders on their bottom edge ("milk churning") may be acceptable for short distances.  Never lift cylinders with magnets or chain or wire rope slings.  Transport cylinders on specially built hand carts or trolleys or other devices designed for this.  All transport devices should have some way of securing cylinders to prevent them from falling. What should I know about the compressed gas storage area? Store compressed gas cylinders separately, away from processing and handling areas, and from incompatible materials.  Separate storage can minimize personal injury and damage in case of fires, spills or leaks.  Many compressed gases can undergo dangerous reactions if they come in contact with incompatible materials (gases, liquids or solids), so store them apart from each other.  For example, store oxidizing gases at least 6 metres (20 feet) away from fuel gases or other combustible materials, or separate them with an approved fire wall.  Check the reactivity information and storage requirements sections of the MSDS for details about which materials are incompatible with a particular compressed gas.  The National Fire Code addresses requirements for segregation of different gases in storage. If compressed gas cylinders are stored outside, use a well-drained, securely fenced area.  Keep them on a raised concrete pad or non-combustible rack.  Protect cylinders from the weather and do not allow them to stand directly on wet soil as this can cause corrosion. Indoor storage areas must have walls, floors and fittings made of suitable materials.  For example, use non-combustible building materials in storage areas for oxidizing gas and corrosion-resistant materials in storage areas for corrosive gas.  Make sure floors are level and protect cylinders from dampness.  Avoid overcrowding in storage areas or storing cylinders in out-of-the-way locations. Always chain or securely restrain cylinders in an upright position to a wall, rack or other solid structure wherever they are stored, handled or used.  Securing each cylinder individually is best.  Stacking of groups of cylinders together offers some protection, but if this is done improperly, the entire group or individual cylinders could fall. Store compressed gas cylinders in areas which are: well-ventilated and dry fire-resistant and supplied with suitable firefighting equipment including sprinklers, where appropriate away from electrical circuits and ignition sources such as sparks, flames or hot surfaces accessible at all times, but away from elevators, staircases or main traffic routes where cylinders may be dangerous obstacles labelled with suitable warning signs Always store full cylinders separately from empty cylinders. What should I know about compressed gas storage temperatures? Store compressed gas cylinders in dry, cool areas, out of direct sunlight and away from steam pipes, boilers or other heat sources. Follow the gas supplier's recommendations for storage and use temperatures.  To prevent excessive pressure buildup, never expose cylinders to temperatures above 52°C (125°F).  Do not subject them to temperatures below -29°C (-20°F), unless they are designed for this.  Cylinders that become frozen to a surface can be freed by using warm water (less than 52°C).  Never apply direct heat to a cylinder. What are some general precautions about compressed gas storage? At all times: Allow only trained, authorized people into storage areas. Keep the amount of compressed gases in storage as small as possible. Inspect storage areas regularly for any deficiencies such as damaged or leaking cylinders and poor housekeeping. Correct all deficiencies as soon as possible. What should I know about using and discharging compressed gas cylinders? General precautions When moving cylinders, securely fasten them to a suitable cylinder transporting device.  At the site, chain or otherwise secure the cylinder in place.  Remove the valve cap only after the cylinder has been safely installed then check the cylinder valve and fixture.  Remove any dirt or rust.  Grit, dirt, oil or dirty water can cause gas leaks if they get into the cylinder valve or gas connection. Never open a damaged valve.  Contact your gas supplier for advice. There are four standard types of cylinder valve outlets to prevent interchanges of gas handling equipment between incompatible gases.  Use only the proper equipment for discharging a particular gas from its cylinder.  Never use homemade adaptors or force connections between the cylinder valve outlet and gas handling equipment. Whether a compressed gas is a liquefied, non-liquefied or dissolved gas, the gas supplier can give the best advice on the most suitable gas discharge equipment and the safest way to use it for a specific job. In general, do not lubricate any cylinder valves, fittings, or regulator threads, or apply jointing compounds and tape.  Use only lubricants and sealants recommended by the gas supplier. Cylinders stored in cold areas may have frozen valves.  Use only warm water to thaw the valve or bring the cylinder into a warm area and allow it to thaw at room temperature. Use only recommended keys or handwheels to open valves.  Never use longer keys or modify keys to increase their leverage.  Avoid using even the correct key if it is badly worn.  Do not use pipe wrenches or similar tools on handwheels.  Any of these practices could easily damage the valve seat or spindle. Always open valves on all gas discharge equipment slowly.  Rapid opening of valves results in rapid compression of the gas in the high-pressure passages leading to the seats.  The rapid compression can lead to temperatures high enough to burn out the regulator and valve seats.  Many accidents involving oxidizing gases result from burned out regulator and valve seats, usually caused by opening valves too quickly. Do not use excessive force when opening cylinder valves--use no more than three quarters of a turn if possible.  If a problem develops, the valve can then be closed quickly.  Leave keys on cylinders when valves are open so the valve can be closed quickly in an emergency.  Some cylinder valves, such as oxygen valves, have double seating.  These valves should be fully opened, otherwise they may leak. Do not use excessive force when opening or closing a cylinder valve.  When closing, turn it just enough to stop the gas flow completely.  Never force the valve shut. Close cylinder valves when the cylinder is not actually in use.  Do not stop the gas flow from a cylinder by just backing off on the regulator.  Regulators can develop seat leaks, allowing pressure to build up in equipment attached to the regulator.  Also if the cylinder valve is left open, foreign matter can enter the cylinder if the cylinder pressure drops lower than the pressure in attached equipment.  Close the cylinder valve first and then close the regulator. Liquefied Gases Manual valves are normally used on cylinders containing liquefied gases.  Special liquid flow regulators are also available.  If it is necessary to remove liquid as well as gas from a cylinder, discuss this with the gas supplier before ordering.  Some liquefied gas cylinders have eductor tubes which allow the liquid to be withdrawn from the cylinder.  The supplier can provide suitable cylinders and special instructions. Do not remove gas rapidly.  The pressure in the cylinder could drop below the required level.  If this happens, or if rapid gas removal is needed, follow the gas supplier's advice. Non-Liquefied and Dissolved Gases Use automatic pressure regulators to reduce gas pressure from the high levels in the cylinder to safe levels for a particular job. There are two basic types of automatic pressure regulators: single-stage, and double- or two-stage.  Generally, two-stage regulators deliver a more constant pressure under more precise conditions than single-stage regulators.  Sometimes, manual flow controls are used on non-liquefied gases.  Fine flow control can be obtained, but an operator must be present at all times.  Manual flow controls do not automatically adjust to pressure buildups in blocked systems. What are some guidelines for safe handling and use? Use the smallest practical cylinder size for a particular job.  Do not keep cylinders longer than the supplier recommends.  Compressed gas cylinders are mainly shipping containers.  They are built to be as light as possible while remaining safe and durable.  Do not drop cylinders or otherwise allow them to strike each other.  Rough handling, including using cylinders as hammers or as rollers to move equipment, can seriously damage them. Do not strike an electric arc on a cylinder.  Arc burns can make the metal brittle and weaken the cylinder. Never tamper with cylinders in any way.  Do not repaint them, change markings or identification, or interfere with valve threads or safety devices. Apart from the fact that it is illegal, it can be dangerous for non-specialists to refill cylinders or to change their contents.  Explosions, cylinder contamination or corrosion can result. What should I know about equipment associated with compressed gases? All equipment used with compressed gases must be clean, properly designed and maintained, and made from materials compatible with the gas used.  For example, acetylene forms explosive compounds in contact with copper, silver and mercury or their alloys, including bronze or brass containing more than 65 percent copper.  Ammonia attacks brass and can react with mercury to form an explosive compound.  Do not use mercury pressure gauges in ammonia systems. In general, avoid pressurizing ordinary glass equipment.  Use specially designed glass equipment and protective devices.  Where cylinders are connected to a manifold or header, make sure specialists properly design and install the system.  Use effective flashback arrestors on acetylene and other flammable gas systems. Always follow the correct procedures for assembling and disassembling compressed gas equipment.  Check that all the connections are clean and do not leak.  Check for leaks, using the gas suppliers recommended method, after assembling and before starting to use equipment.  Never use old clips or twisted wire for hose connections.  If a hose works loose and flails around, serious injury could result.  Poor hose connections are a common cause of accidents. Acetylene under pressure can explode.  Never use acetylene outside of the cylinder at pressures over 103 kPa (15 psig) unless you take special precautions.  If an acetylene cylinder has been accidentally left on its side, set it upright for at least an hour before use.  Otherwise, it will emit a burst of solvent instead of gas when the valve is opened. Corrosive gases can "freeze" the valve stem, making it hard to open the valve.  This results from the gas corroding the valve metal.  Minimize "freezing" by rotating the valve stem at least once a day while the cylinder is in use.  Also, flush the regulator or manual control valve with dry nitrogen or dry air as soon as possible after use. Are there special precautions for oxidizing gases? Special cleaning procedures (equivalent to oxygen service) are required for all equipment to be used with oxidizing gases.  There are several ways to do this.  Contact your gas supplier for the best methods for specific systems. Do not oil or grease any equipment that may contact oxidizing gases.  Keep greasy hands, rags and gloves away from any part of the cylinder and fittings.  Normal body oils are usually not hazardous, although it is a good practice never to touch any surface that may contact an oxidizing gas.  Use lubricants and connection or joint sealants recommended by the gas supplier. Only use oxygen for its intended purpose.  Never use it to purge pipelines or to provide ventilation.  Freshening the air with oxygen may make people more comfortable, but it also enriches the oxygen content in the area which can quickly create a major fire hazard.  Serious accidents have occurred when oxygen was used to run tools designed for compressed air.  High oxygen pressure can cause the lubricant in the tool to explode. Can I use compressed gases in confined spaces? Always comply with applicable occupational health and safety laws when working in a confined space.  When using compressed gases, including inert gases, in a confined space, be sure to check that all equipment connections are leak-tight.  Remove cylinders or connected equipment that are not in use from confined spaces, even during short breaks.  Check the air for oxygen levels (high and low).  Also check for any possible toxic, corrosive or flammable gases before entering confined spaces and during prolonged work periods.  Never work alone. How do I handle and store "empty" cylinders? Non-Liquefied and Dissolved Gases The amount of material remaining in a non-liquefied or dissolved gas (acetylene) cylinder is directly proportional to the cylinder pressure gauge reading.  As the gas is used, the reading on the cylinder pressure gauge drops.  When the cylinder pressure gauge reads zero, the cylinder is not really empty.  The cylinder still contains gas at atmospheric pressure.  Keep a slight positive pressure in the cylinder.  Consider it "empty" when the cylinder pressure gauge reads about 172 kPa (25 psig) or when the cylinder will not deliver at least 172 kPa to the outlet pressure gauge. Liquefied Gases The pressure in liquefied gas cylinders remains constant at a given temperature as long as any liquid remains in the cylinder.  The only way to know how much material remains in a liquefied gas cylinder is to weigh the cylinder.  The empty (tare) weight of the cylinder is stamped on its neck or valve stem.  Record the net weight of the cylinder contents on a card attached to it.  As with non-liquefied and dissolved gases, never empty the cylinder completely.  Keep a small amount of material in the cylinder to maintain a slight positive pressure. What are general precautions for "empty" cylinders? Keeping a positive pressure in an "empty" compressed gas cylinder helps to prevent back flow or suck back.  This back flow is the drawing-back into the cylinder of contaminants or moist air from a higher pressure system or the atmosphere. Keep the valves on all "empty" cylinders closed.  This practice maintains a positive pressure in them.  "Empty" cylinders with open valves can "breathe".  Temperature increases or drops in atmospheric pressure can force gas out of the open valve of an empty cylinder.  This release could result in hazardous conditions depending on the gas and how much is forced out.  Temperature drops or increases in atmospheric pressure can cause air to be drawn in through the open valve.  Air could cause a serious contamination and corrosion problem inside the cylinder.  When a compressed gas cylinder is "empty," handle it as though it is full since it does contain gas. Always: Close the cylinder valve before removing the gas discharge equipment. Clearly mark or label the cylinder "empty" or "MT." Place the cylinder in a storage area separate from that used for full cylinders. Keep incompatible materials away from the cylinder. Notify the gas supplier if the cylinder or any part of it is damaged or defective, contaminated, or may have been exposed to a possibly hazardous condition such as a fire or electric arc. Take care when scrapping unserviceable cylinders.  Before scrapping, first destroy the cylinder as a pressure vessel.  Contact the gas supplier for advice on disposing of unserviceable cylinders. What are some good housekeeping rules for working with compressed gas cylinders? Maintain good housekeeping at all times in the workplace: Never hang clothes or equipment over a compressed gas cylinder.* Never use oxygen or even compressed air to remove dust from clothing or equipment. Promptly remove combustible wastes including wood, paper or rags, from the work area. Properly and promptly dispose of "empty" or unlabelled cylinders. *Note: Hanging things over a cylinder makes it harder to operate the valve.  In addition, clothing may become saturated with a hazardous gas.  Clothing saturated with either an oxidizing gas or flammable gas will catch on fire easily and burn intensely.  Hang clothes that are even partly saturated with an oxidizing gas or fuel gas in a well-ventilated area for at least 15 minutes to remove trapped gas. Why is personal cleanliness important? Personal cleanliness helps protect people working with hazardous materials: Wash hands before eating, drinking, smoking or going to the toilet. Remove contaminated clothing since it may be a severe fire or health hazard. Do not wear or carry items contaminated with oxidizing or flammable gases into areas having ignition sources or where smoking is allowed. Store food and tobacco products in uncontaminated areas. Clean yourself thoroughly at the end of the workday. Why is equipment maintenance important? Regular workplace inspections can help to spot situations where compressed gases are stored, handled, or used in potentially hazardous ways. Regular inspection of equipment can provide a warning of potential hazards: Examine regulators, pressure relief valves and cylinder connections. Ensure that cylinders are free of corrosion, leakage, pitting, dents or gouges. Regular equipment maintenance can prevent hazardous conditions in the workplace. Ensure that maintenance personnel: Know the possible hazards of the materials they may encounter and any special procedures and precautions before they begin to work. Carry out repairs to equipment properly, using equipment suitable for the contents of the compressed gas cylinder. Avoid forcing connections, using homemade adaptors or tampering with cylinders in any way. Comply with applicable regulations and contact the gas supplier for advice. What should I know about Personal Protective Equipment? If other methods, such as engineering controls, are not available or effective in controlling exposure to compressed gases, wear suitable personal protective equipment (PPE).  Choosing the right PPE for a particular job is essential.  Material Safety Data Sheets (MSDSs) should provide general guidance.  Also obtain help from someone who knows how to evaluate the hazards of the job and how to select the proper PPE. Avoid Skin Contact When using gases that are harmful by skin contact, wear protective gloves, aprons or other clothing depending on the risk of skin contact.  Choose clothing made of materials that resist penetration or damage by the chemical.  The MSDS should recommend appropriate materials.  If it does not, contact the gas supplier for specific information. Protect Your Eyes and Face Always wear eye protection when working with compressed gases.  Avoid ordinary safety glasses.  Use chemical safety goggles instead.  In some cases, you should also wear a faceshield to protect your face.  The current CSA Standard Z94.3, "Industrial Eye and Face Protectors," provides advice on selection and use of eye and face protectors. Avoid Breathing Harmful Gases If respirators must be used for breathing protection, there should be a written respiratory protection program to follow.  The current CSA Standard Z94.4, "Selection, Care, and Use of Respirators," gives guidance for developing a program.  Follow all legal requirements for respirator use and approvals.  These may vary between jurisdictions in Canada. Sorbents in air-purifying respirator cartridges and canisters must be compatible with the chemical they are supposed to protect against.  For example, oxidizable sorbents, such as activated charcoal, may not be acceptable if high concentrations of oxidizing gases are present.  A hazardous reaction might occur.  Keep in mind that air-purifying respirators do not protect against oxygen-deficient environments. Know and be familiar with the right PPE for use in emergencies as well as during normal operations. Wear the PPE needed for doing a particular job.  It cannot provide protection if it is not worn. What should I do in an emergency? Act fast in emergencies such as chemical fires or gas cylinder leaks. Evacuate the area at once if you are not trained to handle the problem or if it is clearly beyond your control. Alert other people in the area to the emergency. Call the fire department immediately. Report the problem to the people responsible for handling emergencies where you work. Obtain first aid and remove all contaminated clothes if you have been exposed to harmful chemicals. Note: All major compressed gas suppliers have emergency response teams.  These teams can be activated by calling the telephone number that is usually printed on the shipping documents and MSDSs. Locate emergency eyewash stations and safety showers wherever accidental exposure to gases that can damage skin or eyes is possible. Only specially trained and properly equipped people should handle emergencies.  Nobody else should go near the area until it is safe. Planning, training and practicing for emergencies help people to know what they must do. The MSDSs for the gases used are a starting point for drawing up an emergency plan.  MSDSs have specific sections on spill and leak procedures, first aid instructions, and fire and explosion hazards.  If the directions in each MSDS section are not clear or seem incomplete, contact the gas supplier or manufacturer for help.  Many other sources can also help develop emergency plans.  Local fire departments can assist with fire emergency plans and training.  Occupational health and safety and environmental enforcement agencies, provincial safety associations, CGA Canada (the Canadian division of the Compressed Gas Association Inc.), St. John Ambulance, insurance carriers, professional societies in occupational health and safety, labour unions, some colleges and universities, and CCOHS can supply useful information.  Specialized private consultants are also available. What are basic safe practices when working with compressed gases? Following these basic general safe practices will help protect you from the hazards of compressed gases: Read the MSDSs and labels for all of the materials you work with. Know all of the hazards (fire/explosion, health, chemical reactivity, corrosivity, pressure) of the materials you work with. Know which of the materials you work with are compressed gases and check the label, not the cylinder colour, to identify the gas. Store compressed gas cylinders in cool, dry, well-ventilated areas, away from incompatible materials and ignition sources.  Ensure that the storage temperature does not exceed 52°C (125°F). Store, handle and use compressed gas cylinders securely fastened in place in the upright position.  Never roll, drag, or drop cylinders or permit them to strike each other.   Move cylinders in handcarts or other devices designed for moving cylinders. Leave the cylinder valve protection cap in place until the cylinder is secured and ready for use. Discharge compressed gases safely using devices, such as pressure regulators, approved for the particular gas. Never force connections or use homemade adaptors. Ensure that equipment is compatible with cylinder pressure and contents. Carefully check all cylinder-to-equipment connections before use and periodically during use, to be sure they are tight, clean, in good condition and not leaking. Carefully open all valves, slowly, pointed away from you and others, using the proper tools. Close all valves when cylinders are not in use. Never tamper with safety devices in cylinders, valves or equipment. Do not allow flames to contact cylinders and do not strike an electric arc on cylinders. Always use cylinders in cool well-ventilated areas. Handle "empty" cylinders safely: leave a slight positive pressure in them, close cylinder valves, disassemble equipment properly, replace cylinder valve protection caps, mark cylinders "empty" or "MT," and store them separately from full cylinders. Wear the proper personal protective equipment for each of the jobs you do. Know how to handle emergencies such as fires, leaks or personal injury. Follow the health and safety rules that apply to your job. Prevention & Control of Hazards What are the pressure hazards associated with compressed gas cylinders? All compressed gases are hazardous because of the high pressures inside the cylinders.  Gas can be released deliberately by opening the cylinder valve, or accidentally from a broken or leaking valve or from a safety device.  Even at a relatively low pressure, gas can flow rapidly from an open or leaking cylinder. There have been many cases in which damaged cylinders have become uncontrolled rockets or pinwheels and have caused severe injury and damage.  This danger has happened when unsecured, uncapped cylinders were knocked over causing the cylinder valve to break and high pressure gas to escape rapidly.  Most cylinder valves are designed to break at a point with an opening of about 0.75 cm (0.3 inches).  This design limits the rate of gas release and reduces cylinder velocity.  This limit may prevent larger, heavier cylinders from "rocketing" although smaller or lighter cylinders might take off. Poorly controlled release of compressed gas in chemical reaction systems can cause vessels to burst, create leaks in equipment or hoses, or produce runaway reactions. What are the fire and explosion hazards associated with compressed gases? Flammable Gases Flammable gases, such as acetylene, butane, ethylene, hydrogen, methylamine and vinyl chloride, can burn or explode under certain conditions: Gas Concentration within the Flammable Range: The concentration of the gas in air (or in contact with an oxidizing gas) must be between its lower flammable limit (LFL) and upper flammable limit (UFL) [sometimes called the lower and upper explosive limits (LEL and UEL)].  For example, the LFL of hydrogen gas in air is 4 percent and its UFL is 75 percent (at atmospheric pressure and temperature).  This means that hydrogen can be ignited when its concentration in the air is between 4 and 75 percent.  A concentration of hydrogen below 4 percent is too "lean" to burn.  Hydrogen gas levels above 75 percent are too "rich" to burn. The flammable range of a gas includes all of its concentrations in air between the LFL and UFL.  The flammable range of any gas is widened in the presence of oxidizing gases such as oxygen or chlorine and by higher temperatures or pressures.  For example, the flammable range of hydrogen in oxygen gas is 4 to 85 percent and the flammable range of hydrogen in chlorine gas is 4.1 to 89 percent. Ignition Source: For a flammable gas within its flammable limits in air (or oxidizing gas) to ignite, an ignition source must be present.  There are many possible ignition sources in most workplaces including open flames, sparks and hot surfaces. The auto-ignition (or ignition) temperature of a gas is the minimum temperature at which the gas self-ignites without any obvious ignition sources.  Some gases have very low auto-ignition temperatures.  For example, phosphine's auto-ignition temperature of 100°C (212°F) is low enough that it could be ignited by a steam pipe or a lit light bulb.  Some compressed gases, such as silane and diborane, are pyrophoric - they can ignite spontaneously in air. Flash-back can occur with flammable gases.  Many flammable compressed gases are heavier than air.  If a cylinder leaks in a poorly ventilated area, these gases can settle and collect in sewers, pits, trenches, basements or other low areas.  The gas trail can spread far from the cylinder.  If the gas trail contacts an ignition source, the fire produced can flash back to the cylinder. Oxidizing Gases Oxidizing gases include any gases containing oxygen at higher than atmospheric concentrations (above 23-25 percent), nitrogen oxides, and halogen gases such as chlorine and fluorine.  These gases can react rapidly and violently with combustible materials such as the following: organic (carbon-containing) substances such as most flammable gases, flammable and combustible liquids, oils, greases, many plastics and fabrics finely-divided metals other oxidizable substances such as hydrazine, hydrogen, hydrides, sulphur or sulphur compounds, silicon and ammonia or ammonia compounds. Fires or explosions can result. The normal oxygen content in air is 21 percent.  At slightly higher oxygen concentrations, for example 25 percent, combustible materials, including clothing fabrics, ignite more easily and burn much faster.  Fires in atmospheres enriched with oxidizing gases are very hard to extinguish and can spread rapidly. Dangerously Reactive Gases Some pure compressed gases are chemically unstable.  If exposed to slight temperature or pressure increases, or mechanical shock, they can readily undergo certain types of chemical reactions such as polymerization or decomposition.  These reactions may become violent, resulting in fire or explosion.  Some dangerously reactive gases have other chemicals, called inhibitors, added to prevent these hazardous reactions. Common dangerously reactive gases are acetylene, 1,3-butadiene, methyl acetylene, vinyl chloride, tetrafluoroethylene and vinyl fluoride. What are the health hazards associated with compressed gases? Many compressed gases are toxic or very toxic.  They could cause various health problems depending on the specific gas, its concentration, the length of exposure and the route of exposure (inhalation, eye or skin contact).  Contact between the skin or eye and liquefied gases in liquid form can freeze the tissue and result in a burn-like injury. What is the danger of an inert gas? Inert gases, such as argon, helium, neon and nitrogen, are not toxic and do not burn or explode.  Yet they can cause injury or death if they are present in sufficiently high concentrations.  They can displace enough air to reduce oxygen levels.  If oxygen levels are low enough, people entering the area can lose consciousness or die from asphyxiation.  Low oxygen levels can particularly be a problem in poorly ventilated, confined spaces. What are the corrosive hazards of compressed gases? Some compressed gases are corrosive.  They can burn and destroy body tissues on contact.  Corrosive gases can also attack and corrode metals.  Common corrosive gases include ammonia, hydrogen chloride, chlorine and methylamine. Compressed Gas Cylinder Safety Many industrial and laboratory operations require the use of compressed gases for a variety of different operations.   Compressed gases present a unique hazard.  Depending on the particular gas, there is a potential for simultaneous exposure to both mechanical and chemical hazards.  Gases may be: Flammable or combustible Explosive Corrosive Poisonous Inert or a combination of hazards If the gas is flammable, flash points lower than room temperature compounded by high rates of diffusion present a danger of fire or explosion.  Additional hazards of reactivity and toxicity of the gas, as well as asphyxiation, can be caused by high concentrations of even "harmless" gases such as nitrogen.  Since the gases are contained in heavy, highly pressurized metal containers, the large amount of potential energy resulting from compression of the gas makes the cylinder a potential rocket or fragmentation bomb. Careful procedures are necessary for handling the various compressed gases, the cylinders containing the compressed gases, regulators or valves used to control gas glow, and the piping used to confine gases during flow.   Identification The contents of any compressed gas cylinder must be clearly identified.  Such identification should be stenciled or stamped on the cylinder or a label.  Commercially available three-part tag systems may also be used for identification and inventory. No compressed gas cylinder should be accepted for use that does not legibly identify its contents by name.  If the labeling on a cylinder becomes unclear or an attached tag is defaced to the point the contents cannot be identified, the cylinder should be marked "contents unknown" and returned directly to the manufacturer. Always read the label!! Never rely on the color of the cylinder for identification.  Color coding is not reliable because cylinder colors may vary with the supplier.  Additionally, labels on caps have little value because caps are interchangeable. All gas lines leading from a compressed gas supply should be clearly labeled to identify the gas, the laboratory or area served, and the relevant emergency telephone numbers.   The labels should be color coded to distinguish hazardous gases (such as flammable, toxic, or corrosive substances) (e.g., a yellow background and black letters). Signs should be conspicuously posted in areas where flammable compressed gases are stored, identifying the substances and appropriate precautions (e.g., HYDROGEN - FLAMMABLE GAS - NO SMOKING - NO OPEN FLAMES). Handling & Use Gas cylinders must be secured at all times to prevent tipping. Cylinders may be attached to a bench top, individually to the wall, placed in a holding cage, or have a non-tip base attached.  Chains or sturdy straps may be used to secure them. If a leaking cylinder is discovered, move it to a safe place (if it is safe to do so) and inform the Environmental Health & Safety Department.  You should also call the vendor as soon as possible. Under no circumstances should any attempt be made to repair a cylinder or valve. Standard cylinder-valve outlet connections have been devised by the Compressed Gas Association (CGA) to prevent mixing of incompatible gases.  The outlet threads used vary in diameter; some are internal, some are external; some are right-handed, some are left-handed.  In general, right-handed threads are used for non-fuel and water-pumped gases, while left-handed threads are used for fuel and oil-pump gases. To minimize undesirable connections, only CGA standard combinations of valves and fittings should be used in compressed gas installations; the assembly of miscellaneous parts should be avoided.  The threads on cylinder valves, regulators and other fittings should be examined to ensure they correspond and are undamaged. Cylinders should be placed with the valve accessible at all times.  The main cylinder valve should be closed as soon as it is no longer necessary that it be open (i.e., it should never be left open when the equipment is unattended or not operating).  This is necessary not only for safety when the cylinder is under pressure, but also to prevent the corrosion and contamination resulting from diffusion of air and moisture into the cylinder after it has been emptied.   Cylinders are equipped with either a hand wheel or stem valve.  For cylinders equipped with a stem valve, the valve spindle key should remain on the stem while the cylinder is in service.  Only wrenches or tools provided by the cylinder supplier should be used to open or close a valve.  At no time should pliers be used to open a cylinder valve.  Some valves may require washers; this should be checked before the regulator is fitted. Cylinder valves should be opened slowly.  Oxygen cylinder valves should be opened all the way.  Open up the oxygen cylinder valve stem just a crack.  Once the needle on the high pressure gauge has stopped, open up the valve all the way.  This back-seats the valve.  Oxygen cylinders must have the valve opened up all the way because of the high pressure in the cylinder.  There is a back-seating valve on the oxygen cylinder.  This prevents the high-pressure gas from leaking out through the threaded stem. When opening the valve on a cylinder containing an irritating or toxic gas, the user should position the cylinder with the valve pointing away from them and warn those working nearby.  Cylinders containing flammable gases such as hydrogen or acetylene must not be stored in close proximity to open flames, areas where electrical sparks are generated, or where other sources of ignition may be present. Cylinders containing acetylene shall never be stored on their side. An open flame shall never be used to detect leaks of flammable gases.  Hydrogen flame is invisible, so "feel" for heat.  One common practice is to use a natural bristle broom to "sweep" the air in front of you.  All cylinders containing flammable gases should be stored in a well-ventilated area. Oxygen cylinders, full or empty, shall not be stored in the same vicinity as flammable gases.  The proper storage for oxygen cylinders requires that a minimum of 20 feet be maintained between flammable gas cylinders and oxygen cylinders or the storage areas be separated, at a minimum, by a fire wall five feet high with a fire rating of 0.5 hours.  Greasy and oily materials shall never be stored around oxygen; nor should oil or grease be applied to fittings. Regulators are gas specific and not necessarily interchangeable! Always make sure that the regulator and valve fittings are compatible.   If there is any question as to the suitability of a regulator for a particular gas, check with Environmental Health & Safety Services or call your vendor for advice.  After the regulator is attached, the cylinder valve should be opened just enough to indicate pressure on the regulator gauge (no more than one full turn) and all the connections checked with a soap solution for leaks.  Never use oil or grease on the regulator of a cylinder valve. The following rules should always be followed in regards to piping: Copper piping shall not be used for acetylene. Plastic piping shall not be used for any portion of a high-pressure system. Do not use cast iron pipe for chlorine. Do not conceal distribution lines where a high concentration of a leaking hazardous gas can build up and cause an accident. Distribution lines and their outlets should be clearly labeled as to the type of gas contained. Piping systems should be inspected for leaks on a regular basis. Special attention should be given to fittings as well as possible cracks that may have developed. A cylinder should never be emptied to a pressure lower than 172 kPa (25 psi/in2) (the residual contents may become contaminated if the valve is left open).  When work involving a compressed gas is completed, the cylinder must be turned off, and if possible, the lines bled. When the cylinder needs to be removed or is empty, all valves shall be closed, the system bled, and the regulator removed.  The valve cap shall be replaced, the cylinder clearly marked as "empty," and returned to a storage area for pickup by the supplier. Empty and full cylinders should be stored in separate areas. Where the possibility of flow reversal exists, the cylinder discharge lines should be equipped with approved check valves to prevent inadvertent contamination of cylinders connected to a closed system.  "Sucking back" is particularly troublesome where gases are used as reactants in a closed system.  A cylinder in such a system should be shut off and removed from the system when the pressure remaining in the cylinder is at least 172 kPa (25 psi/in2).  If there is a possibility that the container has been contaminated, it should be so labeled and returned to the supplier. Liquid bulk cylinders may be used in laboratories where a high volume of gas is needed.  These cylinders usually have a number of valves on the top of the cylinder.  All valves should be clearly marked as to their function.  These cylinders will also vent their contents when a preset internal pressure is reached, therefore, they should be stored or placed in service where there is adequate ventilation. Always use safety glasses (preferably with a face shield) when handling and using compressed gases, especially when connecting and disconnecting compressed gas regulators and lines.     All compressed gas cylinders, including lecture-size cylinders, must be returned to the supplier when empty or no longer in use.   Transportation of Cylinders The cylinders that contain compressed gases are primarily shipping containers and should not be subjected to rough handling or abuse.  Such misuse can seriously weaken the cylinder and render it unfit for further use or transform it into a rocket having sufficient thrust to drive it through masonry walls. To protect the valve during transportation, the cover cap should be screwed on hand tight and remain on until the cylinder is in place and ready for use. Cylinders should never be rolled or dragged. When moving large cylinders, they should be strapped to a properly designed wheeled cart to ensure stability. Only one cylinder should be handled (moved) at a time.   To complete the Compressed Gas Cylinder Training Module, please take the Quiz. Compressed Gas Cylinder Quiz If the regulator to an oxygen cylinder is difficult to thread, you should: Oil the threads Return the cylinder or regulator to the supplier Use a crescent wrench to tighten it Use a regulator from a nitrogen cylinder If you find a compressed gas cylinder without a label, you should: Make your best guess as to what the gas is, based on cylinder color Attach a regulator and test the gas Mark the contents "unknown" and return immediately to the supplier Segregate in a storage closet until identification can be made safely It is safe to conduct minor repairs on the valves of cylinders containing "harmless" gases. True False Cylinders may safely be secured by: Duct tape Bracing the cylinder on two sides by non-movable objects such as a refrigerator and storage bench Chains All of the above When equipment is left unattended or not operating, cylinder valves should always be: Closed Left open Oxygen cylinder valves should be opened all the way True False Which type of cylinder should never be stored on its side? Acetylene Helium Self-Contained Breathing Apparatus Oxygen Cylinders containing flammable gases shall not be stored near: Areas where electrical sparks might be generated Bunsen burners Pilot lights All of the above It is acceptable to use plastic piping for parts of a high pressure system True False Cylinders should never be rolled or dragged True False   Quiz Answers B C B C A A A D B A