Chapter 3. Compressed Gases

I. Compressed gases used in the agricultural setting include a great variety of materials contained in high-pressure cylinders. The gases may be combustible, flammable, explosive, poisonous, corrosive, or in any combination of hazards. All workers working with compressed gases should be familiar with the material safety data sheets (MSDS) that must be available in the work place (see Hazard Communication).

II. Hazards of commonly used compressed gases are included here, however, the worker should refer to the MSDS for complete information prior to using the selected compressed gas.

A. Acetylene has the widest flammable range known and is an asphyxiate. It may contain dangerous amounts of phosphine and arsine in some instances. Under certain conditions it can form spontaneously explosive compounds with silver, mercury or copper. Acetylene is unstable and may explode under low pressures. When contained in small diameter piping systems, 15 psi should not be exceeded. Acetylene can be stored in cylinders at a maximum of 250 psi at 70oF.

B. Ammonia is flammable, colorless, lighter than air, has a piercing odor, and is highly irritating to mucous membranes. Ammonia, or anhydrous ammonia) is toxic to humans. Workers working with this chemical must wear impervious to ammonia gloves, shoe covers, and aprons as well as eye and face protection. Emergency gas masks or respirators must be available in case of accidental spills or other uncontrolled events.

C. Oxygen supports combustion but by itself does not burn. When in combination with other materials, spontaneous ignition may occur. A sudden and violent fire can occur when in combination with oil, grease, or fuel oils. Open flames and smoking is not allowed near oxygen storage areas.

III. Cylinder care.

A. Damage or leaking cylinders should be moved to a safe, isolated area and returned to the supplier. Cylinders should never be dropped or banged against each other.

B. They must be stored upright in a safe, well ventilated area, away from any source of heat and away from electrical wiring. They must be secured by a chain, cable, or other suitable means to prevent them from falling.

C. Except when in use, cylinder valves should remain protected by the steel protective cap threaded completely down.

D. Cylinders should only be moved using a hand truck. When in vehicular transit, cylinders should be lashed to the cradles of the vehicle in as near an upright position as possible.

E. Storage areas must be fire-resistant, clean, free of combustible materials, and well lighted. Oxygen cylinders in storage must be separated from flammable gases a minimum distance of 20 feet or by a noncombustible barrier at least 5 feet high with a fire-resistance rating of 1/2 hour. Empty cylinders should be marked MT (EMPTY) and stored away from full ones.

IV. Compressed air.

A. Workers should be familiar with the air compressor's operating and maintenance instructions.

B. Compressed air used for cleaning purposes should not be in excess of 30 psi. The phrase to "reduce to less than 30 psi" means that the nozzle pressure or opening of a gun, pipe, cleaning lance, etc., used for cleaning purposes will remain at a pressure level below 30 psi for all static conditions. Special nozzles are available that will drop the pressure below 30 psi.

C. Air tanks must be constructed in accordance with appropriate sections of the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code. This information must be stamped permanently on the tank.

D. The drain valve on the air tank should be opened frequently to prevent excessive accumulation of liquid.

E. Air tanks must be protected by adequate safety relief valve(s) and the valve(s) should be tested at regular intervals to be sure they are in good operating condition. There must be no valves between the air tank and the safety valve.

F. The pressure controller and gauge must be maintained in good operating condition.