SECTION 26. COMPRESSED GAS AND AIR EQUIPMENT

26.1 BACKGROUND

With high pressure, compressed gases, hazards can result from improper handling. For example, a leaking cylinder could produce a toxic atmosphere, anesthetic, asphyxiate, or explosive; and with a rapid escape, the cylinder becomes a randomly directed missile. The main purpose of properly handling compressed gases is, therefore, to prevent uncontrolled escape of the gas. Various sources, such as OSHA and the Compressed Gas Association (CGA) standards, were used in developing these guidelines. All handling, storing, and utilizing of compressed gases should comply with the CGA standards. Refer to "Handbook of Compressed Gases, 3rd Edition".

26.2 INFORMATION

The following information is offered in order to familiarize personnel with cylinder parts and terminology:

1. Valve hand wheel: used to open and close the cylinder valve. Valves are occasionally not equipped with hand wheels and require special wrenches to open and close the valves.

2. Valve packing nut: contains packing gland and packing around stem. Adjusted only occasionally--usually tightened if leakage is observed around valve stem. Should not be tampered with for diaphragm-type valves.

3. Valve outlet connection: for connection to pressure- and/or flow-regulated equipment. Various types of connections are provided to prevent interchange of equipment for incompatible gases. Usually identified by a CGA number, for example, No. 580 for helium service.

4. Safety device: to permit gas to escape if the temperature gets high enough to endanger the cylinder by increased unsafe pressures.

5. Cylinder collar: holds cylinder cap (6) at all times, except when regulating equipment is attached to cylinder valve.

6. Cylinder cap: to protect cylinder valve.

7. Number signifies the cylinder conforms to Department of Transportation specification DOT-3A governing materials of construction, capacities, and test procedures, and the service pressure for which the cylinder is designed at 2000 pounds per square inch gauge at 70o F.

8. This number is the cylinder serial number.

9. Number indicates the date (month and year) of initial hydrostatic testing. Thereafter, hydrostatic pressure tests are performed on cylinders for most gases every five years to determine their fitness for further use. At this time, new test dates are stamped into the shoulder of the cylinder. Present regulations permit visual tests in lieu of hydrostatic tests for low-pressure cylinders in certain gases free of corrosive agents; special permits allow for hydrostatic pressure tests at ten year intervals for cylinders in high-pressure service for certain gases.

10. Original inspector’s insignia for conducting hydrostatic and other required tests to approve the cylinder under DOT specifications.

11. Valve outlet cap: protects valve threads from damage and keeps outlet clean; not used universally.

26.3 HANDLING CYLINDERS

The rules for handling cylinders are relatively simple and straightforward. If they are followed, the majority of situations where serious accidents might occur will be eliminated.

All cylinders must be marked as to content. Do not accept cylinders with unidentifiable contents.

Store cylinders vertically.

Unless the pressure regulator is attached, keep the valve protection cap on securely.

Cylinders must be made secure with straps, chains, ropes, clamps, or floor-stands to prevent them from falling.

Do not store full and empty cylinders together. Serious “suckback” can occur when an empty cylinder is mistakenly attached to a pressurized system. It is a safe practice to tag cylinders “Empty” or “Full.”

Cylinders must not be stored near sources of heat, ignition, oil, grease, or where they might become part of an electric circuit.

Protect from direct rays of sun, preferably under a canopy or roof overhang.

Cylinders can be stored in the open, but should be protected from the ground to prevent rusting.

Bond and ground all cylinders, lines, and equipment used with flammable compressed gases for long-term storage.

Limit the storage of corrosive gases to about three months. The cylinder valve stem should be worked frequently to prevent freezing. The valve should be closed when not in use.

Cylinders should not be subjected to low temperatures because many steels undergo decreased ductility at low temperatures and could crack.

Avoid subsurface storage locations.

Before connecting a regulator, the cylinder valve should be “cracked” or opened slightly and closed immediately, unless the gas is toxic. When doing this, stand to the side or rear of the valve outlet.

Do not try to force a regulator to fit the cylinder. A poor fit probably indicates that the regulator is not intended for use with that particular compressed gas.

Never use an adapter fitting.

Always open cylinder valve very slowly.

Never attempt to repair or alter cylinders, valves, or safety relief.

OXYGEN CYLINDERS

1. Do not wipe or touch the valve outlet--this may leave organic or hydrocarbon residues (such as various dusts, oils, greases, or hand lotions) which might be subsequently ignited by exposure to high oxygen pressure.

2. Use only oxygen pressure-reducing regulators to control the supply of oxygen.

3. Make sure the regulator is clean and free from organic or hydrocarbon residues and a clean filter is installed in its inlet nipple.

4. Before opening the cylinder valve, release the pressure-adjusting screw by turning it counterclockwise until it turns freely.

5. Stand to one side of regulator while very slowly opening the valve.

Do not empty a cylinder completely. This will prevent “suck-back” and possible explosive mixtures.

When discharging gas into liquid, a trap or suitable check valve should be used to prevent liquid from getting back into the cylinder or regulator.

Do not use copper tubing with acetylene.

Avoid rolling or dragging cylinders, even for short distances. Move cylinders only on a cylinder hand truck. Make sure it is secured on the hand truck with a chain. Do not lift cylinders by the cap.

Never drop cylinders or allow them to strike each other violently.

Must not be charged except by the owner.

Use soapy water or commercial leak detector to detect gas leaks.

If a cylinder develops a leak, the valve-packing nut should be tightened. If leakage persists, move the cylinder to a location outside where it can vent safely. Avoid areas of ignition sources in the case of leaking flammable gas. If the gas is flammable or toxic, place an appropriate sign at the cylinder warning of these hazards. Notify the Site Safety Officer and gas cylinder supplier immediately.

TOXIC GASES

Cylinders containing toxic gases require special consideration and handling. The same general safety procedures apply; however, extreme care is required when connecting these cylinders to regulators, tubing, manifold systems, or other equipment. Cylinders of toxic gases should never be changed by only one person. Preferably, two persons should be involved, with a third person waiting in a safe area. The use of an approved respirator will greatly increase the margin of safety for the people performing the cylinder change.

In some situations it may be advisable to investigate the need for self-contained breathing apparatus. Such equipment must be matched to the specific hazard and requires operator training. Contact the Site Safety Officer if use of a self-contained breathing apparatus is desired.

Examples of gases considered to be extremely toxic are:

chlorine
arsine
boron triflouride
bromine
fluoride
phosgene
phosphines

There are many others that are not listed here. Certain gases may require special equipment to make them safe to use, such as stainless steel tubing or special regulators.

26.4 LEAK PROCEDURE

The risk of a leak developing while a cylinder is installed in place is somewhat less, but still a possibility which should be considered. A variety of systems are available which continually monitor the air. In the event of a leak, an alarm is activated. These can be interfaced with other reporting systems thereby providing a 24-hour alarm system.

In case of a toxic gas cylinder leak, the following minimum instructions are provided:

- evacuate the area immediately;
- activate an alarm pull box as you exit the area, if applicable;
- notify the Site Manger or the designated responsible person;
- stay near the scene and inform emergency response personnel of any pertinent
information.

26.5 COMPRESSED AIR EQUIPMENT

Compressed air is used for many purposes throughout APO and the following safety guidelines should be observed:

- inspect lines regularly;
- portable air lines should be stored so they do not hang or extend into machine
work areas or traffic patterns. Provide suitable spring hangers; sway bracing, vibration dampers, etc.;
- a pressure gauge or a valve connection for a pressure gauge should be located at the outlet of each pressure-reducing valve;
- air receivers should be installed so all drains, hand-holes, and manholes therein are easily accessible. Air receivers should be supported with sufficient clearance to permit a complete external inspection and to avoid corrosion of external surfaces. Under no circumstances should an air receiver be buried underground or located in an inaccessible place. The receiver should be located as close as possible to the compressor or after-cooler in order to keep the discharge pipe short;
- a drainpipe and valve should be installed at the lowest point of every air receiver to provide for the removal of accumulated oil and water. Adequate automatic traps may be installed in addition to drain valves. The receiver should be completely drained frequently and at such intervals as to prevent the accumulation of excessive amounts of liquid in the receiver;
- every air receiver should be equipped with a visible pressure gauge with one or more spring-loaded safety valves. The total relieving capacity of the safety valves should prevent pressure in the receiver from exceeding the maximum allowable working pressure of the receiver by more than 10%;
- no valve of any type is to be placed between the air receiver and its safety valve or valves;
- safety appliances, such as safety valves, indicating devices, and controlling devices, are to be constructed, located, and installed so they cannot readily be rendered inoperative by any means;
- all safety valves are to be tested frequently and at regular intervals to determine whether they are in good operating condition;
- compressed air for cleaning the work site may only be used under the conditions referred to in Section 22.4, “Compressed Air for Cleaning.”