• What is the American Conference of Governmental Industrial Hygienists (ACGIH) recommended exposure limit for methane?
• What are the fire and explosion dangers associated with methane?
• Is methane stable when exposed to air, moisture, or heat?
• Are there any conditions to avoid when using methane?
• Does methane have an odour threshold (at what level can I smell it)?
• Is the odour of methane reliable as a warning property?
• How can I work with methane safely?
• What can be done to control hazardous conditions?

What is the American Conference of Governmental Industrial Hygienists (ACGIH) recommended exposure limit for methane?

TIME-WEIGHTED AVERAGE (TLV-TWA): 1000 ppm (Aliphatic hydrocarbon gases: Alkane C1 - C4)

TLV BASIS - CRITICAL EFFECT(S): CNS - central nervous system depression; Cardiac sensitization

TLV COMMENTS:

NOTE: In many jurisdictions, exposure limits are similar to the ACGIH TLVs. Since the manner in which exposure limits are established, interpreted, and implemented can vary, obtain detailed information from the appropriate government agency in each jurisdiction

What are the fire and explosion dangers associated with methane?

Methane is an EXTREMELY FLAMMABLE GAS (can also be a COMPRESSED GAS OR REFRIGERATED LIQUEFIED GAS). Can readily form explosive mixtures with air, which are easily ignited by a static charge. Liquefied methane accumulates static charge. Liquefied methane gas vapourizes under normal conditions and produces 600 volumes vapour for every one volume of liquid. A major release of liquefied methane will produce a large vapour cloud due to condensation of moisture. Small spills of liquefied methane tend to rise and diffuse rapidly above the leak. Large spills of liquefied methane behave like dense flammable vapours and travel over long distances creating a flash back hazard. Direct addition of water (or any other room temperature liquid) to the liquefied gas will cause flash vapourization resulting in an explosion (either immediately or delayed) known as a "boiling liquid, expanding vapour explosion (BLEVE)". The gas can accumulate in confined spaces, resulting in an explosion or asphyxiation hazard. During a fire, toxic gases may be generated. Heat from a fire can cause a rapid build-up of pressure inside cylinders or tanks, which may cause explosive rupture and a sudden release of large amounts of extremely flammable gas.

Is methane stable when exposed to air, moisture, or heat?

Yes, methane is stable under normal conditions.

Are there any conditions to avoid when using methane?

Static discharge, sparks, open flames and other ignition sources

Does methane have an odour threshold (at what level can I smell it)?

Odourless; odourant may be added by supplier.

Is the odour of methane reliable as a warning property?

POOR - odourless; odorant may be added by supplier.

How can I work with methane safely?

Methane is an EXTREMELY FLAMMABLE GAS. It is available commercially as a COMPRESSED GAS or REFRIGERATED LIQUEFIED GAS. This material is an ASPHYXIANT and can displace oxygen necessary for breathing. Methane is a CONFINED SPACE HAZARD. Ensure that any confined space is competently assessed for oxygen deficiency and flammable atmospheres prior to worker entry. Contact with the liquid or with gas escaping from the cylinder can result in frostbite.

Before handling, it is very important that engineering controls are operating and that protective equipment requirements and personal hygiene measures are being followed. People working with this chemical should be properly trained regarding its hazards and its safe use. Maintenance and emergency personnel should be advised of potential hazards.

For large-scale operations using refrigerated liquid or compressed gaseous methane, escape-type respiratory protective equipment should be available in the work area in the event of a leak or spill.

Immediately report leaks, spills or ventilation failures.

Prevent release of gas into workplace air. Consider using closed handling systems for processes involving this material. If a closed handling system is not possible, use in smallest possible amounts in a well-ventilated area, separate from the storage area.

Large-scale operations should have closed handling systems and leak and fire detection systems, oxygen-deficiency alarms and a suitable, automatic fire suppression system.

Eliminate all ignition sources, (e.g. static discharge, sparks, open flames, hot surfaces). Keep away from heat and welding operations. Post "NO-SMOKING" signs. It is very important to keep areas where this material is used clear of other materials which can burn (e.g. cardboard, sawdust). Keep aisles and exits free of obstruction.

Use non-sparking ventilation systems, approved explosion-proof equipment and intrinsically safe electrical systems in areas of use. During transfer operations, cylinders, vessels and equipment should be electrically grounded to prevent the buildup of a static charge. Use piping and equipment designed to withstand the pressures and temperatures encountered with the particular operation.

Do not use with incompatible materials such as strong oxidizers (e.g. peroxides and perchlorates) and halogen compounds.

Make sure cylinders are labelled clearly. Avoid damaging cylinders. Do not handle cylinders with oily hands. Move cylinders by hand truck or cart designed for that purpose. Do not drag, drop, roll or slide cylinders or permit them to bang against each other.

Leave cylinder cap on until cylinder is secured and ready for use. Always secure cylinders to a wall, rack or other solid structure in an upright position. Use the appropriate pressure regulator. Ensure equipment is compatible with cylinder pressure and contents. Follow supplier recommendations. Before connecting the cylinder for use, make sure that back feed from the system into the cylinder is prevented. Do not open cylinder if damaged. Never use excessive force when opening. Open cylinder valve slowly to prevent rapid decompression and damage to valve seat. Keep cylinder valves clean and free from contaminants (particularly oil and water). Make sure valves on gas cylinders are fully opened when gas is used. Open and shut valves at least once a day, while cylinder is in use, to avoid valve 'freezing'. Shut flow off at cylinder valve and not just at the regulator after use. Replace outlet caps or plugs and cylinder caps as soon as cylinder is disconnected from equipment. Keep empty cylinders under slightly positive pressure. Do not use cylinders as rollers or for any other purpose than to contain the gas as supplied. Regularly check cylinders for evidence of corrosion or leakage.

Have suitable emergency equipment for fires, spills and leaks readily available.

Follow handling precautions on Material Safety Data Sheet. Practice good housekeeping. Maintain handling equipment. Comply with applicable regulations.

Additional information for handling refrigerated liquefied methane:

Ensure receiving container is constructed of a material capable of withstanding extremely low temperature. All cryogen dewars should be clearly labelled and operated in accordance with the manufacturer's instructions. The pressure relief devices should be periodically inspected for ice formation.

Insulated gloves and other personal protective equipment must be worn to prevent all skin/eye contact with cryogenic liquids. It is good practice to remove metal jewelry such as rings, bracelets and watches from your hands and wrists before working with cryogens (it may freeze to skin if accidentally exposed to boil-off gas or cryogenic liquid).

Use care when filling portable dewars; do not overfill. If using a thermos flask with a screw top, do not screw the lid in, but allow it to rest on the rim. This allows evaporating gas to safely escape. If the lid is screwed in, pressure can build up and an explosion can result.

Proceed slowly when filling containers or inserting objects into liquid to minimize boiling and splashing. When transferring to another container, cool the receiving container first. Transfer or pour cryogens slowly to minimize boiling and splashing. Use a phase separator or special filling funnel. If the liquid cannot be poured, use a cryogenic liquid withdrawal device for the transfer (follow manufacturer's instructions).

What can be done to control hazardous conditions?

Engineering control methods to reduce hazardous exposures are preferred. Methods include mechanical ventilation (dilution and local exhaust), process or personnel enclosure, control of process conditions, and process modification (e.g. substitution of a less hazardous material). Administrative controls and personal protective equipment may also be required.

Provide sufficient local exhaust and general (dilution) ventilation to maintain the methane concentration below the exposure limit. Use a non-sparking, grounded ventilation system separate from other exhaust ventilation systems. Exhaust directly to the outside. Supply sufficient replacement air to make up for air removed by exhaust systems.

For large-scale operations, closed handling systems should be used. In addition, consider the installation of leak and/or oxygen monitors as well as fire detection equipment and a suitable automatic fire suppression system.

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Document last updated on December 11, 2006

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