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A gas mixture will exhibit the characteristics of its components, with the predominant component determining the final classification of the mixture. An exception is when a component is toxic to a degree sufficient to influence the final classification. The information offered below is assumed to be reliable and is for use by technically qualified personnel at their discretion and risk. Air Liquide does not warranty the data contained herein.

Asphyxiant gases

These are gases that are non- or minimally toxic but which dilute the oxygen in air leading to death by asphyxiation if breathed long enough.

Toxic gases in large enough concentrations can also cause asphyxiation and lead to death by other mechanisms such as interaction with the respiratory system by competing with oxygen (such as carbon monoxide) or causing direct damage (such as phosgene). Because asphyxiant gases are relatively inert, their presence in large quantities may not be noticed until the effects of elevated blood carbon dioxide are recognized by the body. Notable examples of asphyxiant gases are nitrogen, argon and helium.

Corrosive gases

These are gases that corrode material or tissue with which they come in contact, or do so in the presence of water.

They are reactive and can also be 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, mucous 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.

Cryogenic gases

These are gases with a boiling point of -130°F (-90°C) at atmospheric pressure.

They are extremely cold and can produce intense burns. They can be nonflammable, flammable or oxidizing. Cryogenic liquids can build up intense pressures. At cryogenic temperatures, system components can 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. 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 up when they are spilled.

Flammable gases

These are 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.

A change in temperature, pressure or oxidant concentration may vary the flammable range considerably. All possible sources of ignition must be eliminated. Use a vent line made of stainless steel, purge with an inert gas and use a flash arrester. It is important to have a fire extinguisher where flammable gases are used and stored. A hand-held gas detector is also recommended to guard against gas buildup and to detect leaks in gas lines. Remember that the source of gas must be eliminated before attempting to put out a fire involving flammable gases.

Inert gases

These are gases that do not react with other materials at ordinary temperature and pressure.

They are colorless and odorless, as well as nonflammable and nontoxic. Inert gases 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.

Oxidant gases

These are gases that do not burn but will support combustion and they can displace oxygen in air (with the exception of O2 itself).

It is essential that all possible sources of ignition 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 a cylinder or equipment used for oxidant services. Use only equipment that is intended for this type of service. Use only a regulator that is designated and labeled “cleaned for O2 service.”

Pyrophoric gases

Gases such as silane, phosphine, diborane and arsine are commonly used in the semiconductor industry and are extremely dangerous to handle because they do not require a source of ignition to explode or catch fire.

Pyrophoric gases will ignite spontaneously in air at or below 130°F (54°C). Specific gases may not ignite in all circumstances or may explosively decompose. Under certain conditions, some gases can undergo polymerization with release of large amounts of energy in the form of heat.

Toxic or poison gases

These are gases that may chemically produce lethal or other health effects.

They can be high pressure, reactive, flammable or nonflammable, and/or oxidizing in addition to their toxicity. The degree of toxicity and the effects will vary depending on the gas. Permissible exposure levels must be strictly adhered to (click here to download a PELs list). Read the MSDS thoroughly before use. Never work alone with toxic gases – inspect the 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.

Use toxic gases in a well-ventilated area. It is important to have gas detectors, self-contained breathing apparatus and protective clothing on hand. The breathing apparatus must 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 fire fighting equipment should be readily accessible.

Refer to your local building code for storage and use requirements for toxic gases. Keep your inventory of toxic or poison gases at a minimum. When a project is completed, return leftover cylinders to Air Liquide. 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.