Safety First Should be the Guiding Rule for Anyone who Handles Compressed Gases

Recent conversations with customers reveal the harsh fact that the rules of safety that need to be applied when handling compressed gases often slip down in the order of priorities. This is especially true among the more recent entrants who have little or no experience in using gases.

Thus, it has become apparent that it is time for a review of the safe handling practices applied when using compressed gases. A periodic review of safety rules should be a standard in every facility in which personnel are involved with handling gases.

What is a Compressed Gas?

The U. S. Department of Transportation defines a compressed gas as: any material or mixture which exerts in the packaging an absolute pressure of 280 kPa (40.6 psia) or greater at 20?C (68?F).

The handling of compressed gases must be considered more hazardous than the handling of liquids or solids. Compressed gases, by their very nature, present hazards. Even the “safe” inert gases, such as argon, helium, and nitrogen, expose the user to a hazard, simply because it is enclosed in a cylinder at a high pressure; i.e., a large release may cause a dangerous oxygen deficiency. The fact that these are colorless and odorless adds to the potential danger. Other gases are capable of creating hazardous environments—flammable, toxic, corrosive, or highly oxidizing. In fact, many gases present multiple hazards.

In addition to the basic nature of gases, hazards may arise as a result of equipment failure due to improper selection or usage. Additionally, diffusion from systems that are not leak-tight can create explosive atmospheres, an oxygen deficiency that could lead to asphyxiation, or toxic concentrations.

Cryogenic liquids, which have a low boiling point, can cause frostbite on contact with living tissue. But this can also occur upon contact with such liquefied gases as carbon dioxide, propylene, and the fluorocarbon gases.

Good Gas Handling Practices Can Control the Hazards

Simply recognizing that compressed gases pose a potential hazard is a critical step in appreciating the rules for the safe handling of gases.

Next, safe procedures must be developed to ensure safe gas usage. The following general rules should always be followed. They are not offered as a complete treatise on the subject of safety, but are presented as a guideline to good, safe practice.

• Before using any gas, read all of the label information and the Material Safety Data sheet for the gas being used. Never rely on the cylinder’s color to identify the contents. There is no color code standard in the United States.
• Use a proper cylinder hand truck that supports the weight of the cylinder to transport the cylinder.
• Never transport a cylinder without the safety valve cap securely in place.
• When using compressed gases, wear appropriate safety equipment, such as safety glasses or face shield and protective gloves.
• Do not remove the cylinder cap until the cylinder is in place and secure, and you are preparing to use the gas. A variety of devices is available that can be applied to secure cylinders. If the cylinder cap is difficult to remove, do not use a pipe wrench, screw driver, or open-end wrench to remove it. Use a proper tool, such as the wrench shown in.
• Never tamper with the safety devices attached to the cylinder valves or cylinders.
• Never use oil or other lubricants on the cylinder, the valve, or other attachments.
• No part of the cylinder should be subjected to a temperature higher that 125F. A flame should never be permitted to come in contact with any part of a compressed gas cylinder.
• Cylinders stored outdoors should be shaded from the direct rays of the sun and set on a concrete slab or some other non-earthen platform to prevent the cylinder bottoms from rusting. This is particularly important for cylinders of liquefied hydrocarbons, such as propane, because the spring-loaded safety relief devices in the cylinder valve will release gas to relieve the increased pressure due to the heating from the sun.
• Do not store full and empty cylinders in the same location. All gas cylinders should have status tags indicating “empty,” “full,’ or “in service.” Incompatible gases must be segregated from each other in storage by a minimum of 20 feet. Do not store flammable materials with oxidizers or corrosives. If cylinders cannot be segregated by a sufficient distance, a non-combustible partition should be erected to separate gas types, or gas storage cabinets should be employed, such as those shown in Figure 6.
• When corrosive gases are being used, the cylinder valve stem should be periodically opened and closed to prevent “freezing.” The valve should be closed when the cylinder is not in use.

Gas Handling Equipment And Its Proper Application

Pressure regulators are the workhorses of virtually every gas application. They reduce the cylinder pressure to a safe working level.

Before installing a regulator make sure it is the correct one for the application to which it is applied.

• Two-stage or single-stage design
• Proper materials of construction
• Correct delivery pressure range
• Correct inlet pressure rating
• Correct flow capability
• Correct regulator to cylinder connection. Never use an adaptor.
• An outlet valve is recommended on specialty gas regulators

 Consult your supplier before switching regulator gas services. Gases can react with each other and explode or at the least add impurities. For example, use an Oxygen regulator only for oxygen.

The Proper Attachment of a Pressure Regulator to a Cylinder

• Never use Teflon tape or any other thread sealant on CGA connections.
• Inspect the inlet connection and the cylinder valve outlet to assure that they are free of dirt or grease or other foreign matter.
• Prior to attaching the regulator, check to make sure that the cylinder is properly secured to prevent it from falling.
• Tighten the cylinder connection using the proper wrench and gasket, if one is required.
• The correct wrench should be used. Do not use pipe wrenches, vise grips or pliers as these tend to damage the connections and make removal difficult.

The Proper Operation of a Pressure Regulator

After attachment and prior to opening the cylinder valve:

• Turn the pressure adjusting knob counter clockwise until there is no resistance. This closes the regulator.
• Make sure that the outlet valve is closed.
• Open the cylinder valve slowly to bleed the pressure into the regulator inlet, then open the valve fully, but leaving the hand wheel loose as an indicator that it is open.
• Check the inlet pressure gauge to ensure that it is at the expected value. A low reading may indicate a leaking valve and a potential problem. Contact your supplier if you suspect a leaking cylinder.
• Adjust the delivery pressure to the desired value by turning the adjusting knob clockwise
• Open the outlet valve and adjust to achieve the required flow rate.

The Proper Shut-Down Procedure for a Pressure Regulator

• Turn the cylinder valve clockwise to close the valve and shut-off the gas source.
• Allow pressure to drain from the regulator until both gauges read “zero.”
• Turn the pressure adjusting knob counterclockwise until it turns freely. This assures that the regulator is shutoff.
• It is not necessary to remove the regulator from the cylinder unless the cylinder is to be moved or replaced with a full one.
• Never attempt to remove the regulator if there is any pressure indicated on either gauge.

 If the regulator had previously been used on a corrosive gas it should be purged with dry nitrogen before it is removed from the cylinder. Do not store a regulator while it still contains a corrosive gas.

General System Considerations

• Check the specifications of all system components prior to assembly into your system to ensure that each component is compatible with its intended application. Pay particular attention to materials of construction and pressure ratings. If there is a question regarding any component usage contact your supplier.
• Check all equipment installations for leaks with a suitable leak detection solution, prior to full operation.
• Install a flash arrestor, in all flammable gas lines to open the flame equipment. Additionally, all flammable gas lines should be grounded.
• Wear safety glasses whenever using compressed gases.

Summary

While compressed gases naturally present a hazard, proper training of those individuals that will be handling the cylinders and using the gas will go a long way to eliminating potential problems. Whenever in doubt about the correct course of action when handling any compressed gas, contact your supplier before proceeding.

Frank Scornavacca is president of SGD Inc., a single source, full line, wholesale specialty gas equipment supplier to industrial gas distributors with a unique support program. He can be reached at frank@sgd.com.

Specialty Gas Report FOURTH QUARTER 2007 //