All cylinders containing gases must be labeled, packaged and shipped according to local and national requirements, as well as industry standards. Transportation label diamonds, regardless of color, indicate hazardous materials. Personnel handling any compressed gas should be familiar with the potential hazards before using the gas. In addition to the chemical hazards of compressed gases, hazards accompanying high pressure or low temperature may also be present due to the physical state of the gas (i.e. liquefied or non-liquefied).
It is also recommended that personnel who handle compressed gases engage in pre-job discussion with their supervisor or another knowledgeable coworker before beginning any task. Outline the job step by step. Address potential emergencies and the safe and proper measures necessary to avoid these emergencies. Identify several scenarios that could result in gas leaks or other emergencies to be totally prepared to respond adequately. If there is doubt regarding proper safety procedures, consult your gas supply representative.
Further information concerning the safe handling, storage and use of compressed gases, in addition to the information presented in this article, is available from Scott Specialty Gases and at scottgas.com.
Corrosive - Gases that corrode material or tissue with which they come in contact, or do so in the presence of water, are classified as corrosive. They can also be reactive and toxic and/or flammable or an oxidizer. Most are hazardous in low concentrations over long periods of time. It is essential that equipment used for handling corrosive gases be constructed of proper materials. Use check valves and traps in a system where there is a possibility that water or other inorganic materials can be sucked back into the cylinder. Due to the probability of irritation and damage to the lungs, mucus membranes and eye tissues from contact, the threshold limit values of the gas should be rigidly observed. Proper protective clothing and equipment must be used to minimize exposure to corrosive materials. A full body shower and eye wash station should be in the area. Personnel must be familiar with the work area. Aisles should always be clear and unobstructed in the event that the gas makes contact with the eyes and vision is disrupted.
Flammable - Gases that, when mixed with air at atmospheric temperature and pressure, form a flammable mixture at 13% or less by volume, or have a flammable range in air of greater than 12% by volume regardless of the lower flammable limit, are classified as flammable. They can be high-pressure, toxic, reactive and displace oxygen in air. A change in temperature, pressure or oxidant concentration may vary the flammability range considerably. All possible sources of ignition must be eliminated through proper design of facilities and the restriction of smoking and open flames. Use a vent line made of stainless steel, purge with an inert gas and use a flash arrester. It is important to have (and know how to use) a fire extinguisher in the area where flammable gases are used and stored, as well as a hand-held flammable gas detector to determine if flammable gases are building up. This gas detector can also be used as a leak detector on the lines of the equipment being used. Always remember that the source of flammable gas must be closed or shut-off before attempting to put out a fire involving flammable gases.
Inert - Gases that do not react with other materials at ordinary temperature and pressure are classified as inert. They are colorless and odorless, as well as nonflammable and nontoxic. The primary hazard of these gases is pressure. These gases are often stored at pressures exceeding 2,000 psi (138 bar). Also, they can displace the amount of oxygen necessary to support life when released in a confined place. Use of adequate ventilation and monitoring of the oxygen content in confined places will minimize the danger of asphyxiation. Always wear safety glasses and safety gloves when working with the lines to avoid absorption of the gas through the skin.
Oxidant - Gases that do not burn but will support combustion are classified as oxidants. They can be high-pressure, toxic and reactive, and can displace breathing oxygen from air (except O2 itself). All possible sources of ignition must be eliminated when handling oxygen and other oxidants as they react rapidly and violently. Do not store combustible materials with oxidants. Do not allow oil, grease or other readily combustible materials to come in contact with the cylinder or equipment used for oxidant services. Use only equipment that is intended for this type of service. Use only a regulator that has been clearly prepared for use with this type of service - this regulator should be labeled 'Cleaned for O2 Services.'
Cryogenic - Gases with a boiling point below -130°F (-90°C) at atmospheric temperature are considered cryogenic gases. They are extremely cold and can produce intense burns (similar to heat burns) and tissue necrosis may be even more severe. They can be nonflammable, flammable or oxidizing. Cryogenic liquids can build up intense pressures. At cryogenic temperatures, system components may become brittle and crack. Never block a line filled with cryogenic liquid as a slight increase in temperature can cause tremendous and dangerous buildup of pressure and cause the line to burst. The system should also be designed with a safety relief valve and, depending upon the gas, a vent line. To protect from injury, always wear gauntlet gloves to cover hands and arms, and a cryogenic apron to protect the front of the body. Wear pants over the shoes to prevent liquids from getting trapped inside your shoes. Wear safety glasses and a face shield as cryogenic liquids tend to bounce upward when spilled.
Toxic or Poison - Gases that may produce lethal or other harmful effects on humans are classified as toxic or poison. They can be high pressure, reactive, nonflammable or flammable, and/or oxidizing in addition to their toxicity. The degree of toxicity and the effects will vary depending on the gas; however, death will occur when breathed in sufficient quantities. The permissible exposure levels must be strictly adhered to (please refer to the PELs listed in the Scott Specialty Gases’ Reference Guide or here at scottgas.com). Read your MSDS thoroughly before use and consult with your Scott Representative or a more knowledgeable coworker who has handled the gas before. Never work alone with toxic gases - a backup safety person is essential! Inspect the entire assembly or system that will contain the gas and thoroughly test it for leaks with an inert gas before use. Purge all lines with an inert gas before opening the cylinder valve or breaking connections. Contact your Scott Representative for proper purge procedures. Use toxic gases in a well-ventilated area. For safety purposes and to minimize exposure, it is important to have gas detectors. It is preferable that the breathing apparatus be stored in a safe area immediately adjacent to the work area, so that in the event of an emergency, a person can go directly into the area and close the door and safely put on the apparatus. Full body showers, eye washes, fire alarms and firefighting equipment should be in the area of use and readily accessible. Refer to your local building code for storage and use requirements for toxic gases. Keep your inventory of toxic or poison gases to a minimum. When a project is completed, return leftover cylinders to Scott. They should never be stored for possible future use. This might result in accidental removal of cylinder labeling, making it an unnecessary hazard and greatly increasing the cost of proper disposal.
Compressed - Nonflammable material or mixture that is contained under pressure exceeding 41 psia (3 bar) at 70°F (21°C) or any flammable or poisonous material that is a gas at 70°F (21°C) and 14.7 psia (1 bar) or greater. Most compressed gases will not exceed 2,000 to 2,640 psig (138 to 182 bar) though some go up to 6,000 psig (414 bar).
Nonliquefied Compressed - Chemical or material other than gas in solution that under the charged pressure is entirely gaseous at a temperature of 70°F (21°C).
Liquefied Compressed - Chemical or material that under the charged pressure is partially liquid at a temperature of 70°F (21°C).
Compressed Gas in Solution - Nonliquefied compressed gas that is dissolved in a solvent.
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