Compressed Gases are used through out the laboratory for industrial and research use. Compressed Gas Association (CGA) Pamphlet P-1 is cited 29CFRPart1910.101(b) (OSHA) as requirements for the safe operation and use of compressed gases. New York State Fire Code also provides requirements for the safe storage and use of compressed gases. Compressed gases inherently pose pressure safety hazards as well as potential hazards from chemical exposure, oxygen deficiency hazards (ODH) if oxygen concentration can fall below 19.5% by volume. Cryogenic fluid system may also be considered compressed gases.
The following information is provided to help in the use of compressed gases:
Compress Gases are chemicals and are tracked by BNL's Chemical Management System (CMS).
Inert gases (including compressed air) and commonly used gases such as oxygen and propane are typically track by a static/revolving inventory system that identifies the gas, the location stored and the maximum allowed quantity authorized to be stored in that location. Most other hazardous gases are individually tracked by a bar coding system that can allow inventories to be recorded and assessed against regulatory requirements (such as the NYS Building Code). The CMS team attaches the bar code to the cylinder and to a holder that can be attached to the cylinder as shown below. The holder is used to contain bar code information and forms to transfer the chemical (to another user or different location) or to delete the chemical (when emptied). Transfer and deletion can also be performed on-line through the CMS Web Transactions and Forms site.
Either way, a Cylinder Status tag needs to be attached to the cylinder that identifies if the cylinder is full (no contents have been withdrawn), in use (contents have been withdrawn and/or cylinder has been attached to either a distribution system or regulator), or empty (to be returned/disposed).
The Compressed Gas Association (CGA) has established standard valve outlet connections for gas cylinders. Standardized connections make a gas-tight seal and minimize the possibility of connecting a gas to a system not designed to handle that gas. The CGA connections listed in the table below are from CGA Pamphlet V-1 "Standard for Compressed Gas Cylinder Valve Outlet and Inlet Connections." They are for the more commonly used gases and do not include connections specified for gas mixtures. Vendors should be contacted for information on CGA connections for other gases and mixtures
There are several configurations of sizes, male/female orientations, left/right threads and mating surfaces. Regulators should be purchased for the gas to be used and will come with the proper CGA fitting to attach to the cylinder. These fittings should not be removed and changed from regulators. Do not use adapters. The mating surfaces of the majority of fittings are made to be leak tight without the use of aids such as Teflon tape. If leak tight connections cannot be made, then the outlet or attachment surfaces are damaged and should be removed from service.
|Gas||CGA No.||Gas||CGA No.||Gas||CGA No.|
|Ammonia, Anhydrous||240, 660||Halocarbon-13
|Butenes||510||Hydrogen Bromide||330||Phosphorus Pentafluoride||330|
|Carbon Dioxide||320||Hydrogen Chloride||330||Propane||510|
|Carbon Monoxide||350||Hydrogen Fluoride||660||Propylene||510|
|Carbonyl Fluoride||660||Hydrogen Selenide||350, 660||Silane||350|
|Carbonyl Sulfide||330||Hydrogen Sulfide||330||Silicon Tetrafluoride||330|
|Dimethylamine||240||Methyl Chloride||660||Sulfur Hexafluoride||590|
|Dimethyl Ether||510||Methyl Mercaptan||330||Sulfur Tetrafluoride||330|
|Ethyl Acetylene||510||Monomethylamine||240||Vinyl Bromide||510|
|Ethyl Chloride||510||Natural Gas||350||Vinyl Chloride||510|
|Ethylene Oxide||510||Nitric Oxide||660|
Compressed Gas cylinders are provided in standard sizes. The following is a listing of sizes with associated volumes and weight (in pounds of water):
Compressed gases are classified into general safety categories such as: inert, flammable, oxidizer, corrosive, pyrophoric, toxic and highly toxic. Guidance and best practices relating to the storage and use of these gases can at BNL is provided in Working Safely with Compressed Gas Systems.
Air Products is an industry leader in the use of compressed gases and provide "Safetygrams" on various related topics.
"Elevator Compressed Gas Cylinder Caution" image at right is provided as an example when a compressed gas is moved in an elevator.
Compressed gases must be stored, specifically from the hazard of having the cylinder valve protective cap sheared off. The amount of stored energy can cause the cylinder to become a projectile and as demonstrated on the Discovery Channel™ show MythBuster's, can cause the cylinder to go through a concrete wall. When not in use, the cylinder valve protective cap should be installed (some older cylinders do not have caps, it is recommended that these be returned to the supplier). Some gas suppliers provide cylinder valve protection caps that can be used while a pressure regulator is attached.
Insects can build nests inside caps, specially when stored outside. An approved method of control this problem is to install a pourous cover (such as a nylon "footee" (used in shoe stores) over the cap. The cap should only be installed hand tight. However, caps may become stuck on the cylinder. This issue is typical on cylinders stored outside. Only tools that do not enter the cap can be used to help remove the cap (such as a spanner wrench). The use of teflon tape is allowed on the cylinder threads to mitigate this problem.
NEVER use lubricants on the treads. They can contaminate the cylinder valve.
Nesting depends on a three-point contact system such that all cylinders must be in contract at three points either with a secure wall or with another cylinder. The following are examples of properly nesting compressed gas cylinders and storage in racks:
Note: A chain is required when in the storage rack to provide the third point of support and is recommended when nested.
Compressed gas cylinders need to be properly secured when being stored or in use. Cylinder racks typically provide the required three (3) point of contact when being stored. When in use, cylinders need to be secured. Appropriate means of securing include manufactured clamps that are installed on vertical surfaces such as walls or benchtops. If no vertical surfaces are available, then floor stands should be used.
Transport carts do not provide as safe of a securing method as clamps and stands unless specifically designed (see "Misuse of Gas Transport Cart" Lessons Learned). However, if the use is temporary in nature, then cylinders can be used on cylinder carts* provided the following:
* See the OSHA Standard Interpretation on allowed provisions for the use and stowage of Oxygen/Acetylene (Oxyacetylene) systems on carts.
Hazard Evaluation Tools provides tools for determining oxygen concentrations and ODH classifications using either cryogens or compressed gas that can be recorded in a data base maintained by Safety Engineering. Also a tool for Carbon Dioxide is available that will give potential CO2 exposure levels.
Storage of Flammable gases with flammable materials is not allowed. This includes storing small gas cylinders, such as propane bottles in flammable cabinets. OSHA provided a Standard Interpretation on April 19, 1999 reinforcing this requirement.
Oxygen/Acetylene (Oxyacetylene) systems used for welding and torch work. OSHA provided a Standard Interpretation on May 8, 2005 on their use and storage.
To safely use compressed gases, pressure reducing regulators are used. The two (2) primary types are single stage and dual (2) stage regulators. Both are safe as long as they are used per the manufacture's recommendation. Single stage regulators use one reducing assembly. They can be used where high flows are needed however the output pressure is subject to changes in cylinder (input) pressure. 2-Stage regulators provide stable output pressures for a large range of input pressure. For more detail information see Fisher-Rosemount Technical Monograph 27, the " Fundamentals of Gas Pressure Regulation." To avoid catastrophic failure of regulators, pressure relief devices are installed. The chart gives VICTOR regulator models (typically used at the laboratory) along with there respective output pressure ranges and relief valve part numbers and relief settings. Note: Regulators internal pressure relief devices are designed to protect the regulator body from the source pressure and therefore represents the maximum pressure that the regulator can put out in any failure condition.
|Model||Pressure Range (psi)||Relief Valve Part Number||Relief Setting|
|VTS 450A||2-15||0600-0016||300 psi|
|VTS 450B||2-40||0600-0016||300 psi|
|VTS 450D||5-125||0600-0018||400 psi|
|VTS 450E||10-200||0600-0023||500 psi|
|VTS 452A||2-15||0600-0070||300 psi|
|VTS 452B||2-40||0600-0070||300 psi|
|VTS 452D||5-125||0600-0071||400 psi|
|VTS 452E||10-200||0600-0067||500 psi|
|VTS 452MD||5-125||0600-0071||400 psi|
|VTS 452ME||10-200||0600-0067||500 psi|
|VTS 453B||2-40||0600-0016||300 psi|
|VTS 453D||5-125||0600-0018||400 psi|
|VTS 453E||10-200||0600-0023||500 psi|
Typically compressed gas uses tubing or hoses to supply the system. Pressure rating and material compatibility is essential for their safe use. The following information is provided for reference in the choice of tubing/hoses:
If the tubing/hose is purchased with connectors, the user should ensure that it is marked with its pressure rating. If the end fittings are installed by the user they might require the use of pressure rated clamps. Note that typical worm-type clamps (i.e. automobile radiator clamps) do not have a pressure rating (a typical automobile cooling system is only pressurized to 16 psig). The type of clamps used should not cause damage to the tube/hose and must prevent the connection from loosening. If clamps are used on barbed fittings, they must be placed at the proper location on the fitting. If the tube/hose does not have a manufacturer's pressure rating (stamped or printed), then a proof test (at 110% of operating pressure) needs to be performed and documented.
It is important that if sealant are used on threaded connections (a.k.a. doping), that the material is compatible with the fluid (gas/liquid) used. Note, Sealant need to be used on all National Pipe Taper (NPT) threads and fitting. The most common forms of Pipe Dope are Pipe thread compounds and Polytetrafluoroethylene (PTFE) tape (commonly referred to as Teflon tape).
When selecting the pipe thread compounds, check the fine print very carefully to insure the product is listed as approved for the application you intend to use it for as some of these products have a very limited range of applications. White compounds are typically not compatible with flammable gases or oxygen. Specific applications include:
As the PTFE tape industry evolved into more products, they adopted a standardized color code (Always read the packaging to ensure compatibility).
PTFE tape is only approved as a thread seal when applied correctly. To apply you begin at the end of the pipe and wrap the tape under tension in the direction of the thread turns. Each successive layer should overlap the previous layer by ½ to 2/3 and continue wrapping until the entire threaded portion of the pipe is covered. (Minimum of 3 full turns).