Compressed gases present a variety of potential physical and chemical hazards to workers who handle, use, and store them. This procedure provides methods for controlling these hazards.
This procedure applies to operations involving the use of compressed gases. Its requirements must be incorporated into Job Hazard Analyses, Safe Work Permits, and Standard Operating Procedures. All workers, including contractors, must follow the work practices described in this document.
3.1. Supervisors and Project Managers – Ensure all employees and contractors comply with the work practices described in this procedure.
Check Valve- Equipment in piping systems to prevent the reverse flow of gas or liquids.
Compressed Gas- Gas that is stored and used at pressures greater than nominal atmospheric pressure (15 pounds per square inch absolute). Compressed gas is supplied in cylinders, portable tanks, or through piping systems.
Corrosive- A substance that can cause visible destruction of, or irreversible alterations in, living tissue such as skin, eyes, and lungs by chemical action at the site of contact.
Excess Flow Control- A fail-safe system designed to shut off flow due to a rupture in pressurized piping systems.
Exhausted Enclosure- A non-combustible enclosure, such as a gas cabinet, laboratory hood, or enclosed compartment, which consists of at least a top, back, and two sides and is connected to an approved exhaust ventilation system.
Flammable Gas- A gas that:
- Is ignitable at 14.7 pounds per square inch absolute (psia) when in a mixture of 13 percent or less by volume with air, or
- Has a flammable range at 14.7 psia.
Gas Cabinet- A fully enclosed, non-combustible exhausted enclosure used to store or use gas cylinders. Meets the following criteria:
- Operates at negative pressure in relation to surrounding area
- Provided with self-closing limited access points to give access to equipment controls
- Connected to an exhaust ventilation system
- Provided with self-closing doors
- Constructed on not less than 0.097 inches (12 gauge) steel.
International Fire Code (IFC) - A set of standards established and enforced by government for fire prevention and safety in case of fire as in fire escapes etc.
Incompatible Gases- Gases that, when in contact with each other, have the potential to react in a manner that generates heat, fumes, gases, or byproducts that are hazardous to life or property.
Local Exhaust Ventilation (LEV) - Ventilation provided to remove contaminated air directly from its source.
Lower Explosion Limit (LEL) - The minimum concentration of a combustible gas or vapor in air that will ignite if an ignition source is present.
Maximum Allowable Working Pressure (MAWP) - The maximum pressure at which a vessel or system is designed to operate safely. This is the maximum setting for the primary pressure relief device or secondary regulator.
National Fire Protection Association (NFPA) - An organization charged with creating and maintaining minimum standards and requirements for fire prevention and suppression activities, training, and equipment, as well as other life-safety codes and standards.
Oxidizing Gas- Gas that initiates or promotes combustion in materials through the release of oxygen or other gases.
Physical Hazard- A chemical for which there is scientifically valid evidence that it is a combustible liquid, compressed gas, explosive, flammable, organic peroxide, oxidizer, pyrophoric, unstable/reactive, or water reactive.
Pounds Per Square Inch Gauge (psig) - Measures pressure difference from local atmospheric pressure.
Pressure Relief System- A system designed to relieve excess internal pressure from a pressurized system. Includes pressure relief devices, such as safety valves, relief valves, and rupture disks, and piping or tubing to an approved release point.
Pyrophoric- A substance that may spontaneously ignite in air at a temperature of 130 degrees Fahrenheit (54 degrees Celsius) or below. Specific gases, such as silane, may not ignite in these circumstances or may explosively decompose.
Storage Facility- A building, portion of a building, or exterior area used for the storage of compressed gases.
Threshold Limit Value (TLV) - A guideline value to establish the airborne concentration of a substance to which healthy working adults may be repeatedly exposed day after day over a working lifetime without adverse health effects.
5.0 GENERAL RULES
5.1. Work Planning – Hazard Identification and Control
- Prior to the purchase or use of a compressed gas, the hazards of the gas must be known in order to implement the necessary controls for its hazard classification. Hazard classifications are defined in the International Fire Code (IFC) and, for selected hazard classes, in the definitions of this procedure. Appendix A, Hazard Class of Common Gases, describes the hazard classifications of some common compressed gases.
- Prior to the purchase, delivery, or acceptance of a compressed gas, the user must verify that the existing facilities, engineering controls, and proper work practices are adequate to safely use, store, and dispose of the compressed gas with respect to its hazards.
- Requirements of this procedure must be incorporated into Work Planning documents required for the activity, if any, to include Job Hazard Analyses (JHA), Safe Work Permits (SWP), and Standard Operating Procedures (SOP).
- Necessary work authorizations must be completed prior to using compressed gases, such as completion of work planning documents, Job Briefings, etc.
5.2. Gas Cylinders
- Purchase. Workers must strive to purchase cylinders that can be returned to the provider when empty or no longer needed. For gases that cannot be purchased in returnable containers, the purchaser must verify in advance with the EH&S Department that arrangements can be made for proper disposal. Due to the potentially high cost for disposal of compressed gas cylinders, the purchasing organization may be charged for disposal, including transportation and handling costs.
- Transportation. Transportation of cylinders outside of buildings must be done with suitable motor vehicles (e.g., trucks, properly equipped lift trucks, mancars, etc.) with the cylinder properly secured, the regulator removed, and the cylinder valve protection cap in place. Cylinders may not be transported in the passenger compartment of a motor vehicle or in the trunk of a passenger car. All Department of Transportation (DOT) regulations apply (e.g., placarding, driver qualifications, etc.) when cylinders are transported over public roadways. (Note: Exceptions may be allowed by the EH&S Department for transport of small, low pressure cylinders intended for general public use, such as propane cylinders for hand torches.)
- Moving Cylinders. Large cylinders must be moved by means of a suitable hand truck with the cylinder secured with a chain or belt. The regulator must be removed and the cylinder valve protection cap in place when the cylinder is being moved.
- Securing. Cylinders must be secured in place to a suitable wall, a bench, or other firm support, or placed in a cylinder stand to prevent falling. Cylinders in use, including spare or back-up cylinders in the work place, must be individually secured.
- Cylinder Valve, Caps, and Plugs. Gas cylinders equipped with removable caps and valve outlet caps/plugs must have these devices in place except when the cylinders are in use.
- Separation of Incompatible Gases. Hazardous gases must be separated from incompatible gases by distance, barriers, gas cabinets, or laboratory hoods as noted in the following table. When a gas is classified in more than one category, the most stringent separation must be used. Nonhazardous gases may be stored with any hazard category. Portable oxygen/fuel gas welding equipment must be stored at least 20 feet from combustible materials and away from elevators, stairs, or means of egress.
- Appendix A: Hazard Class of Common Gases
Gas Cylinder Separation by Hazard Class Gas Hazard Category
1 Cylinders may be stored adjacent to each other.
2 Distances can be reduced without limit when cylinders are 1) separated by a ½ hour rated non-combustible barrier, such as 12 gauge steel, that extends not less than 18 inches above and to the sides of the gas cylinders, or 2) stored in separated gas cabinets or laboratory hoods.
3 Does not apply to oxygen/fuel cylinders in actual use or attached for use.
5.3. Storage Facilities
- Storage and use of gas cylinders in exit corridors is prohibited.
- Flammable gases must be stored away from sources of ignition, open flames, ordinary electrical equipment, and intakes of ventilation or air-conditioning equipment or separated from these sources by placement in an approved gas cabinet.
- Cylinder storage areas must be posted with an NFPA 704 diamond panel hazard warning sign and areas with flammable gases must be posted with a “NO SMOKING” sign.
- Cylinders in storage must be grouped by hazard classification. Full and empty cylinders must be grouped separately.
- Storage locations must be properly ventilated and dry.
5.4. Central Gas Systems
- Central gas systems, such as house-systems or closed systems for scientific research must be designed and installed in accordance with applicable standards.
- Appropriate Work Planning processes must be completed to identify the necessary controls to be incorporated in the system, which may include but is not limited to: - Check Valves
- Excess flow controls
- Exhausted enclosures
- Local exhaust ventilation
- Maximum Allowable Working Pressures
- Pressure relief systems
5.5. Warning Labels and Signs
- Cylinders. Cylinders must be labeled with a Department of Transportation (DOT) label.
- Gas Lines. Gas lines must be labeled with the name of the gas at each critical shutoff valve, every 20 feet, upon entering/exiting a wall, and when located over a doorway. Labels must be durable and display the name of the gas and direction of gas flow.
- Work Area Entrances. NFPA 704 diamond panel hazard warning signs must be posted at entrances to work areas (e.g., laboratories, welding shops, etc.) containing compressed gases having a Health, Fire or Reactivity hazard rating of 3 or 4, or an Oxidizer or Simple Asphyxiant hazard rating.
- Gas Cabinets. Gas cabinets must be labeled with the NFPA 704 diamond panel hazard warning sign including the names of the gases contained in the cabinet.
- Storage Facilities. Storage facilities must be posted with an NFPA 704 diamond panel hazard warning sign and with a “NO SMOKING” sign if flammable gases are present.
5.6. Quantity Limitations
- The quantity of gas used and/or stored in an area must comply with the requirements of the International Fire Code (IFC) and applicable National Fire Protection Association (NFPA) standards. The applicable standards and allowable quantities may vary depending on the location (i.e., surface or underground) and type of occupancy/activity (e.g., laboratory, maintenance shop, storage area, etc.) and will be determined on a case-by-case basis. The EH&S Department should be contacted for guidance and assistance.
- The quantity limitations will be affected by the hazard controls provided, with greater quantities generally allowed in facilities equipped with automatic fire sprinklers and/or when Exhausted Enclosures or Gas Cabinets are provided. These controls will be addressed during work planning activities related to compressed gases.
- Dedicated ventilation systems may be required for storage and/or use of compressed gases based on the controls identified during Work Planning activities. The ventilation requirements may include, but are not limited to, Exhausted Enclosures (including laboratory hoods), Gas Cabinets, and Local Exhaust Ventilation. Ventilation systems may be used as an engineering controls to address the hazards of:
- Ambient atmospheres potentially containing less than 19.5% oxygen (i.e., oxygen deficient),
- Corrosive, toxic or highly toxic atmospheres potentially exceeding the Threshold Limit Value (TLV) or some other recognized hazard criteria, and
- Flammable atmospheres potentially exceeding 10% of the Lower Explosive Limit (LEL) of the gas (es) used or stored.
• Basic requirements for dedicated ventilation systems include:
- Mechanical ventilation must be provided, and
- The exhausted area (e.g., gas cabinet, hood) must be at negative pressure in relation to the surrounding area.
- Exhaust must be discharged to an acceptable area. 5.8. Continuous Gas Detection
• Continuous gas detection may be required for storage and/or use of compressed gases based on the controls identified during Work Planning activities. Compressed gas hazards that may require continuous detection may include:
- Highly toxic in quantities >1 ft3,
- Pyrophoric if quantities > 1 ft3 and concentration >1%,
- Flammable gases where it is determined that a leak will result in concentrations greater than 10% of the LEL
- Corrosive gases if quantities >1 ft3and that have physiological warning properties at a higher level than the TLV, and
- Gases that if accidentally released may create an oxygen deficient atmosphere (<19.5%).
- Hazard Communication Training is required for workers who handle, use, or may potentially be exposed to compressed gases.
- Additional training may be required and documented in the JHA or SOP based on the specific hazards presented by the storage and/or use of compressed gases.
5.10. Emergency Preparedness
- Specific emergency response procedures required for compressed gas, if any, must be included in Job Hazard Analyses, Safe Work Permits, or Standard Operating Procedures.
6.0 REFERENCE AND RELATED DOCUMENTS
• Compressed Gas Association (CGA)
- IFC, Compressed Gases
- IFC, Hazardous Materials
- Occupational Safety and Health Administration (OSHA) General Industry Standards, Compressed Gases
- OSHA General Industry Standards, Acetylene
- OSHA General Industry Standards, Hydrogen
- OSHA General Industry Standards, Permissible Exposure Limits
- OSHA General Industry Standards, Hazard Communication
- OSHA General Industry Standards, Occupational Exposure to Hazardous Chemicals in Laboratories
- NFPA, Fire Protection for Labs Using Chemicals
- NFPA, Compressed and Liquefied Gases in Portable Containers