MN471000, Pressure Safety Manual
Sponsor: Michael W. Hazen, 4000
|Revision Date: November 17, 2008
Replaces Document Dated: May 22, 2008
This document is no longer a CPR. This document implements the requirements of Corporate Procedure ESH100.2.PS.1, Control Pressure Safety Hazards.
IMPORTANT NOTICE: A printed copy of this document may not be the document currently in effect. The official version is the online version located on the Sandia Restricted Network (SRN).
Pressure Safety Manual
5. SELECTING AND ASSEMBLING PRESSURE HARDWARE
Subject Matter Experts: Shane Page and David Paoletta
Contributor: Pressure Safety Committee
MN471000, Issue U
Revision Date: November 17, 2008; Replaces Document
Dated: May 22, 2008
Administrative Changes: June 8, 2010, and May 26, 2011, and January 19, 2012
A pressure manifold is defined as a system of components used to connect a pressure source to downstream equipment. Common examples of pressure sources include gas cylinders, "house" nitrogen supplied by the Facilities Department, air compressors, etc. Common examples of downstream equipment include laboratory instruments such as reaction chambers or pressure vessels, lasers, chromatography applications, vibration-isolation tables, inert gas storage boxes, etc.
Figure 5-1. Typical pressure manifold setup.
Members of the Workforce shall ensure that pressure manifolds:
- Are designed to maintain all components within their maximum allowable working pressure limits. Where high-pressure sources are connected to lower-rated downstream equipment, the pressure must be reduced to the required level.
Note: Pressure regulators (see Figure 5-1) are commonly used to reduce the source pressure to a lower operational downstream pressure.
- That use regulators have overpressure protection based on the potential failure of the regulator (unless the system is rated for the maximum source pressure). Regulators can fail in a variety of ways. One common failure is where a rise in outlet pressure occurs due to internal leakage through the regulator (sometimes referred to as outlet pressure creep). The outlet pressure of the regulator could rise to the full pressure of the cylinder or pressure source.
Note: Pressure-relief valves (see Figure 5-1) or rupture disks are commonly used to protect the system from accidental overpressure from regulator failure or procedural error. Alternate methods, such as automated gas panels with overpressure sensors and automatic shutdown of the pressure source, can also be acceptable.
- Incorporate a means of shutting down or isolating the pressure source.
Note: The gas cylinder valve could be used for system isolation; however, a separate shut-off valve, as shown in Figure 5-1, is recommended.
- Address the safe venting of pressure from any and all parts of the system.
Note: System pressure could be vented through the downstream equipment; however, a separate vent valve is recommended, as shown in Figure 5-1.
Members of the Workforce shall not connect incompatible gases to a common manifold.
Figure 5-1 shows a configuration that complies with the above considerations and can be used for many laboratory applications. Pressure systems that incorporate a downstream pressure or vacuum vessel may require an additional pressure-relief device.
The Restrictive Flow Orifice (RFO) is an option used for Pressure-Relief Valve (PRV) sizing. Consult Safety Engineering SMEs for assistance in manifold design and component selection.
Note: The distribution systems of pressure sources (gas cylinders, air compressors, "house" nitrogen supplied by the Facilities Department, etc.) consist of pressure regulators and manifolds. For a pressure source to be effective and safe, the regulator must take in gas from the supply system and reduce the pressure to a lower working pressure. It is important to obtain the correct regulator, consistent with the gas involved and the operation intended. Manifolds distribute and control gas flow from regulators.
Note: Consult pressure safety SMEs or suppliers for regulator selection criteria.
Members of the Workforce shall:
- Use a proper regulator, rated for the application, for the control of the delivery pressure.
- Store unused regulators in a clean place to avoid particulate contamination that can induce regulator failure.
- Make sure that all hazardous gas has been safely vented (and purged, if required) from the entire regulator before removing it from a flammable, toxic, or radioactive system.
- Make sure that the threads on the regulator's Compressed Gas Association (CGA) connection correspond to those on the cylinder-valve outlet according to the CGA Standard for Compressed Gas Cylinder Valve Outlet and Inlet Connections.
- Never use adapters or force connections that do not fit perfectly.
- Use only oxygen regulators for oxygen service.
Caution: Never use
a regulator for oxygen service unless it is clearly specified and marked
for oxygen use, and has not been used for other purposes.
- Inspect regulators at regular intervals, as appropriate to the application.
- Consider establishing replacement intervals based on system design factors, such as degree of hazard, type of failure mode, compatibilities of soft-seat components, and experience with like components.
- Replace damaged, defective, or unreliable regulators immediately.
- Not make repairs or modifications to regulators.
- Not calibrate regulators and regulator gauges obtained from commercial sources.
are not safety devices and shall not be relied on as such. Manufacturer's pressure-relief
valves on regulators are only there to protect the outlet stage of the regulator
(regulator body and diaphragm) and do not serve to protect downstream equipment
or the regulator's low-pressure outlet gauge.
PROTECTIVE PRESSURE-RELIEVING DEVICES
Members of the Workforce shall ensure that all pressure vessels and systems are protected from pressures above maximum allowable working pressure (MAWP) by doing one or more of the following:
- Ensuring that the pressure source is limited to the MAWP. This makes it impossible to overpressurize the system, even in the event of various component failures, fire, or procedural errors.
- Installing a pressure-relief device that is set to begin relieving pressure at a pressure level at or below the system MAWP.
Note: Any and all portions of the system that may be isolated and can be pressurized above the MAWP must be protected with a relief device.
Caution: Never set a relief device higher than the MAWP of the lowest-rated component it is intended to protect. Regulators are not to be used as protection against overpressurization.
Factors in Sizing Protective Devices
Members of the Workforce should consider the following factors when selecting a protective device for a pressure system or a vessel:
- Determine the rate of flow that can be produced by the pressure source(s) in a system.
- Select a device (or multiple devices) of proper capacity.
Determining Rate of Flow
Note: Anything that can provide pressure is considered a pressure source (e.g., pressure cylinders, compressors, pumps, intensifiers, gas generators, explosives or other chemical reactions, and temperature increases in closed systems). See Caution below.
Members of the Workforce should consider the following factors when determining the necessary flow rate:
- Ordinary operation of pressure sources.
- Operational mistakes.
- Equipment failures.
- Unusual circumstances such as fire.
Note: The ASME Boiler and Vessel Code requires a relieving capacity sufficient to prevent the pressure from rising more than 21% above the MAWP in case of exposure to fire.
Note: The rate of flow is the manufacturer's rated capacity if the pressure source is mechanically limited, such as in the following examples:
- Motor-driven compressors.
- Regulator combinations.
Caution: Protection against explosive pressure usually cannot be obtained from safety valves, relief valves, and rupture discs. This is because of the very short time (less than or equal to 10 ms) in which high-level pressure can produce damage and failure. These types of systems should not be treated as pressure system under the precepts of this manual. They are containment vessels, and demonstration of containment is required as specified by MN471011, Explosives Safety Manual.
Selecting a Device of Proper Capacity
Members of the Workforce shall ensure the capacity of a protective device at 110% of the set pressure shall be equal to or greater than the flow that can be produced by all sources.
Members of the Workforce should review the following information for assistance when selecting protective devices:
- ASME Code-Stamped Safety and Relief Valves and Rupture Discs That Meet the ASME Code. These will already be marked with the capacity for that device.
- Non-Code Devices. Record the capacities found in the manufacturer's catalogs in the system data package.
Note: Measure the capacity if it cannot be found in the literature.
Note: When appropriate, convert the safety device capacity from air to another gas.
Special Sizing Problems
Members of the Workforce shall ensure that, for systems in which the pressure source is a gas cylinder with a regulator, the flow capacity of the relief device(s) shall be equal to or greater than the maximum rate at which the regulator will supply gas if it undergoes a failure.
Note: If this flow rate under failure condition is not known, it must either be determined or a component with a known flow-limiting effect must be installed in the system.
Members of the Workforce should be aware that a system that operates at low pressures, but has a high-pressure source, presents special sizing problems, including:
- A vacuum system or laser using a backfill or purge from a standard DOT cylinder. If a failure occurs when the full cylinder pressure is suddenly applied to the system, the normal small relieving device on the system cannot handle the purge and the system will be damaged.
- A brittle vessel pressurized with a standard DOT cylinder. The sudden release of pressure could fracture the brittle vessel before the relief valve has time to function.
Members of the Workforce, to address the problems presented in the examples above, should:
- Use a flow-restricting device on the pressurizing side of a brittle vessel or other system to reduce the rate of pressure increase and to allow time for the relief valve to react to the higher pressure. Types of systems that should use flow-limiting devices include:
- Brittle vessels, because they may not withstand the shock of full pressure applied suddenly
- Small-volume vessels being pressurized from a large-volume source.
Note: Flow-restricting devices and excess-flow valves are available commercially. Metering valves and other components, including regulators, have a physical-design flow coefficient (Cv), which can be considered when determining the flow characteristics of the system. A combination of these and/or multiple relief devices may be required to adequately protect a system. The types of devices used should be selected based on design requirements.
- Other solutions are to:
- Design safety valves in conjunction with other types of restrictions such as tubing or reducer fittings
- Use two or more stages of flow reduction.
Note: Systems using this flow-limiting restriction concept must be carefully engineered for adequate flow reduction.
Note: Engineering reference works such as Mark's Standard Handbook for Mechanical Engineers and commercial fittings catalogs contain orifice and pipe flow equations.
Preferred Pressure-Relieving Devices
Note: Pressure-relieving devices that meet ASME Code requirements are preferred over non-Code devices. However, pressure relief valves 1/2" and smaller in size are generally not subject to ASME Code requirements.
Members of the Workforce shall ensure that ASME Code devices meet the following requirements:
- Pressure tolerances on valves and discs are Code-specified.
- For safety valves marked with a Code stamp, a sample of these safety valves is tested by the manufacturer for capacity.
- Each protective pressure-relief device is marked with
- The manufacturer's identification.
- The design or type number.
- The pipe size of the inlet of the device.
- The flow capacity.
- All safety and relief valves shall be marked with the set test pressure.
- All ASME safety valves shall be marked with a Code stamp.
- Rupture discs shall be marked with a maximum and minimum bursting pressure and associated temperature.
Note: Rupture discs:
- Burst pressure is dependent on temperature.
- Are not marked with the ASME Code stamp.
Note: Correct placement of protective pressure-relief devices in a system is as important to safety as are set pressure and capacity.
Members of the Workforce shall comply with the following rules:
- Do not isolate the relief device from the pressure hardware it is intended to protect.
- All hardware between the system relief device and the component(s) it is intended to protect shall be large enough not to unduly restrict the flow to the relief device.
- All hardware not protected by a relief device shall have an MAWP of at least the maximum pressure possible from the source.
- If a pressure system can be divided into subsystems that may become overpressurized, each portion shall be protected by a relief device set at no greater than the MAWP for that particular pressure section.
- Orient relief devices so that their discharge is not hazardous to people.
Note: A relief device must often be placed on a riser to keep the devices from hot or cold system fluid when:
- The temperature is outside the operating range of the relief device.
- Freezing is a problem.
- Construct, locate, and install pressure-relief devices so that they are accessible for inspection and cannot readily be rendered inoperative.
Caution: Do not use externally adjustable safety valves without the proper safety wiring. They can be adjusted to above system MAWP without the system user's knowledge.
- For all pressure systems containing explosive, toxic, or otherwise hazardous fluids, piping must be used on the outlet of the relief devices to carry the hazardous fluid to a safe discharge area or recovery system. The discharge line shall be large enough not to reduce the capacity of the safety valve below the capacity required to protect the system pressure. When used in liquid service, it shall be designed to facilitate drainage to prevent liquid from lodging in the discharge side of the relief device.
- Test safety and relief valves as follows:
Use rupture discs instead of safety or relief valves where normal system leakage must be minimized, and in dirty, gummy systems. Rupture discs may be used in very high (20,000 psi and above) pressure systems where it is difficult to find reclosable-type safety or relief valves.
- Perform supplier tests before delivery
- Perform line organization inspections and test periodically thereafter (see Table 8-1).
Caution: Do not use rupture discs where it is important to minimize the loss of working fluid. They do not reseal, and unrestricted flow results when pressure is relieved. (Can be used in conjunction with a recovery system, as in rule 7 above.)
- If possible, mark the relief pressure for rupture discs on permanently attached tabs. Otherwise, closely control and identify the discs and tag them appropriately.
- Since rupture disc burst pressure varies with temperature, the disc must be located so that the expected temperatures will not cause the disc either to burst above the system MAWP or to burst prematurely.
- Make certain that the system working fluid does not alter the burst characteristics of the disc.
- Destroy unidentified rupture discs.
Members of the Workforce should be cognizant that a safety-type gauge has a blowout plug or panel in the back of the gauge, the sides and front of the gauge are one integral part, and the cover is made of plastic.
Rules for Using Gauges
Members of the Workforce shall try to use a gauge that meets at least one of the following criteria for commercial pressure gauges that are acceptable for use:
- UL-approved compressed-gas regulator and/or filter gauges with a maximum outside diameter of 3 in.
- Gauges for gas pressure not over 30 psi
- Gauges for liquid pressure not over 200 psi.
Members of the Workforce, when using a gauge that does not meet the above criteria, shall follow the steps below to ensure that the pressure gauge provides equivalent protection:
- Use only safety-type gauges made of materials compatible with the working fluid.
- Protect the gauges against pressure surges by installing one or more of the following:
Locate pressure gauges to minimize exposure to personnel.
Replace glass gauge covers with plastic, replace nonsafe gauges, or install a gauge guard.
- A properly set pulsation damper.
- A restricting orifice.
- A relief valve.
Note: The guard should have appropriate standoffs. It should be made of at least 3/8-in.-thick polycarbonate or 5/8-in. acrylic plastic, undamaged and free of gripper marks, tool chatter marks, and other stress risers.
Pressure gauges should have a full-scale range of about double the operating pressure. The range should never be less than 1.2 times the pressure at which the relief device is to function. When these constraints cannot be met, protective shielding is required.
Do not use gauges whose indicator needles turn twice or more unless:
Place a substantial guard between the back of the gauge and personnel for all gauges with blowout backs, blowout plugs, or open backs.
- A clearly visible total pressure indicator is present.
- A clearly visible warning to read this indicator is posted.
Caution: This guard should not interfere with venting the gauge in case of gauge failure. Require at least 1/2 in. of clear space between the back of the gauge and the guard or panel.
Because there are no ES&H standards requiring the calibration of commercially available pressure gauges that are used in pressure systems, including regulator gauges, Members of the Workforce should be cognizant that:
- The ASME Standard for Pressure Gauges, B40.100, defines gauge accuracy and gives guidance on calibration standards for gauge testing.
- Regulator gauges do not have the accuracy required for use as an indicator for critical pressure functions.
- Instruments in systems that are used for establishing design specifications or health protection are calibrated using CPR100.3.1, Standards and Calibration.
- Instruments used in design-specification or health-protection activities have the necessary accuracy, are appropriately labeled, and are placed in a continuing recall system for periodic calibration, maintenance, and repair.
- For other systems, line operators must make the determination as to whether the indicating devices in use should be calibrated, and so labeled if necessary, for the proper functioning of equipment or accuracy of experimental data.
- These indicators should not be relied upon as safety devices.
- Fail-safe components such as relief valves/burst discs should be designed into pressure systems.
Note: The Department of Transportation (DOT) regulates the design, testing, filling, and transportation of commercially available gas cylinders.
Members of the Workforce shall ensure that:
- DOT-required hydrostatic testing of the cylinder is completed before refilling, if more than a specified time interval has elapsed.
Note: The intervals are specified in 49CFR 49, Transportation.
- The last inspection date is stamped on the valve end of the cylinder.
- For specification DOT-3A or 3AA cylinders, a five-pointed star stamped after the most recent test date indicates that the cylinder may be retested every ten years instead of every five years.
- The cylinder retest interval has not been exceeded.
Members of the Workforce shall verify that all gas cylinders have the following identifying markings:
- Cylinder Certification. The DOT requires that the following information be stamped on the cylinder:
|Type of Cylinder
|Serial Number, Mfgr
- Gas Identification. Each cylinder must be labeled with the name of its contents. Chalk marking or color coding are not acceptable for gas content identification. Since color codes may vary from one supplier to another, always read the label on the cylinder to ensure that you are using the appropriate gas. In addition to the gas identification label, the JIT supplier will apply a barcode to each cylinder in order to meet the requirements of the SNL Chemical Inventory System (CIS). Upon return of the cylinder, the JIT supplier will remove the CIS barcode. It is important to maintain the identity and tracking of all gas cylinders. If either the gas identification label or the CIS barcode begins to peel off or otherwise is deteriorated, please ask the JIT supplier to replace it immediately.
- Cylinder Filling Data. Nonliquefied gases may be filled to the service pressure marked on a cylinder. These markings will appear on the shoulder of the cylinder, e.g., DOT 3AA-2065, which indicates that the cylinder has been manufactured in accordance with DOT specification 3AA and the cylinder filling pressure is 2,065 psig at 70°F. Consult 49CFR 49, Transportation, for filling procedures and restrictions. On the other hand, liquefied gases must be filled by weight.
Members of the Workforce shall plan a course of action in the event of leaks of toxic or flammable gases such as:
- Having a self-contained breathing apparatus available in the event of a toxic gas leak.
- Consulting the industrial hygiene representative on the appropriate division ES&H team to assess the hazards when cylinders of toxic or flammable gases are leaking.
- Consulting the environmental protection representative on the appropriate division ES&H team to remove and dispose of the defective cylinders.
- Not returning leaking cylinders to the supplier until they have been properly emptied and labeled (e.g., as a "leaker", or "has a defective valve", etc.).
Members of the Workforce should observe the following safe practices when handling gas cylinders:
Members of the Workforce should be cognizant that small sample cylinders and calibrated leak cylinders:
- Are commercially available.
- Conform to DOT specifications and comply with DOT regulations.
- Are (mostly) hydrostatically pressure-tested and lot-burst-tested per 49CFR 49, Transportation.
- Like gas cylinders, should not be permanently plumbed into a pressure system. If done so, DOT specification and retest intervals are no longer applicable.
Members of the Workforce shall comply with the following storage requirements:
Figure 5-2. Approved Gas Cylinder Storage Configuration
- Containers shall be protected from any object that will produce a harmful cut or other abrasion in the surface of the metal. Containers shall not be stored near elevators, gangways, or unprotected platform edges, or in any location where heavy moving objects may strike or fall on them.
- Liquefied gas containers, except those designed for use in a horizontal position on tow motors, etc., shall be stored and used valve-end up. Acetylene containers shall be stored and used valve-end up. Storage of acetylene containers valve-end up will minimize the possibility of solvents being discharged. ("Valve-end up" includes conditions where the container axis may be inclined as much as 45° from the vertical.)
COMMON COMPRESSED GASES
Before Using Compressed Gases
Members of the Workforce shall:
- Have permanent gas system installations and storage areas designed and installed through the Facilities Management & Operations Center (10800) or Facilities Planning and Engineering (8512). This ensures that the appropriate codes and standards will be reviewed for applicability and compliance.
- Review other available information as applicable to ensure that their systems are in compliance. Under 29 CFR 1910.1200, Hazard Communication, manufacturers, importers, and distributors of compressed gases are required to label their containers and to provide Material Safety Data Sheets.
- Provide employees with information and training on the hazards in their work areas.
- Ensure that the applicable information is reviewed and made available to all users of the system. A list of relevant codes and organization source references that are applicable to the use of compressed gases is provided at the end of this chapter.
Note: Acetylene, which sometimes carries the trade name Prestolite, is a colorless gas with the odor of garlic and is highly flammable and explosive under certain conditions.
Acetylene is an anesthetic and, when breathed in large quantities, may cause death.
Members of the Workforce shall:
- Never use copper fittings or pipe on acetylene cylinders.
The combination of acetylene with copper produces an explosive compound.
- Not pipe acetylene at pressures greater than 15 psig without special precautions.
- See the Compressed Gas Association (CGA), Handbook of Compressed Gases Pamphlet G-1, Acetylene, for a more thorough discussion on the properties of acetylene and the safe use of acetylene cylinders, and review NFPA 51, Standard for the Design and Installation of Oxygen-Fuel Gas Systems for Welding, Cutting, and Allied Processes, for design and installation requirements.
Note: Ammonia gas is less toxic than chlorine but deserves similar respect in handling.
Members of the Workforce shall:
- Have appropriate respirators or shields readily available in places where ammonia is used.
- Discuss protective clothing and respiratory equipment needs with the appropriate division ES&H team.
- Store and use ammonia cylinders in an upright position to keep the liquid away from valves.
- Not allow ammonia to come into contact with copper, zinc, or alloys containing copper as a major element.
- Consult the Facilities Management & Operations Center (10800) safe standard piping requirements for anhydrous ammonia. Never remove check valves because suckback into the ammonia tanks may cause an explosion.
Note: Carbon dioxide is a heavy, inert gas that is colorless and odorless. Although it is neither an anesthetic nor an irritant, an atmosphere of the gas will not support life. It is in liquid form in a cylinder.
Note: Chlorine is a greenish-yellow nonflammable gas, about 2 ½ times heavier than air. It is a corrosive, suffocating, and irritating gas. It is shipped as compressed liquefied gas.
Members of the Workforce shall:
- Have appropriate respirators or shields readily available where chlorine is used.
- Discuss protective clothing and respiratory equipment needs with the appropriate division ES&H team.
- Store and use chlorine cylinders in an upright position to keep liquid away from valves.
Note: Hydrogen is the lightest gas known. Hydrogen is colorless, odorless, nontoxic, and tasteless. It is flammable and will burn in concentrations between 4.1% and 74.2% in air.
Note: When questions arise, consult with Facilities Fire Protection Engineering for specific requirements and guidelines on the use and storage of hydrogen.
Members of the Workforce shall:
- For small systems (<400 cu. ft.), comply with the following requirements:
- Install small systems in a room having high-point exhaust ventilation and no pockets where hydrogen can accumulate under the ceiling, under an upper floor, or under a roof.
Note: Hydrogen systems should be shut off during nonoperational hours in buildings where full-time ventilation is not provided.
- Protect cylinders from the sun's rays and from all heat sources.
- Protect cylinders from physical damage
- Carefully remove leaking cylinders from the building and tag them as leaking.
- Keep combustible material 12 inches or further from any high-pressure pipe or upstream of the regulator valve. Under the right conditions, hydrogen passing through a piping leak to the atmosphere can self-ignite.
- Mark each hydrogen installation with a sign stating:
HYDROGEN, FLAMMABLE GAS
- Place shut-off valves where they are readily accessible.
- Because a regulator valve could fail, a relief valve shall be positioned to protect the low-pressure system from excessive pressure. The relief valve shall discharge or be piped to a safe location.
- For small-volume laboratory systems, installing an exhaust hood over the equipment will usually suffice to remove leaking gas.
- Consider possible hydrogen embrittlement when choosing containers, piping, and fittings.
- Leak-check piping, using an inert gas, after installation and after any modification to the piping.
Liquefied Petroleum Gas (LPG)
Note: Liquefied petroleum gases are known under various trade names, the most common being Insto-gas, Pyrofax, and Phil-gas, and are either propane, isobutane, propylene (propenes), butylenes (butenes), butane, and any mixtures of these hydrocarbons. These gases are flammable, colorless, and odorless and are required to have an odorant added to indicate the presence of gas in case of leakage.
Liquid Air, Liquid Oxygen, and Liquid Nitrogen
Members of the Workforce who handle cryogenic fluids shall:
- Wear protective clothing when handling cryogenic fluids as specified by the appropriate division ES&H team.
- Transport and store cryogenic fluids, until used, in the supplier's insulated containers, which provide means for the venting of gas as the liquid vaporizes. The outlet of such containers should never be obstructed. Empty containers shall be kept clean and returned promptly to the supplier.
- Never store cryogenic fluids in small, closed compartments without adequate ventilation. A well-ventilated storage space shall always be provided.
- To prevent spontaneous combustion, never store or use containers of liquid oxygen or mixtures of liquid oxygen where they may come in contact with combustible gases or other combustible materials.
- Entrust handling of cryogenic fluids only to competent persons trained to use them. Because of their extremely low temperature (about 320°F below zero), these liquids will seriously burn the skin much as hot liquids would. Never permit them to come in contact with the skin or be allowed to soak clothing.
- Never pour liquid oxygen on clothing, fabrics, rags, waste, or other combustible materials.
- Do not allow the gaseous oxygen arising from liquid oxygen to penetrate clothing. Combustible substances in the presence of oxygen are extremely flammable.
- Never store or use liquid oxygen in proximity to an open flame. Any flame may expand enormously in an oxygen-enriched atmosphere, which may result in an explosion. Liquid air or liquid oxygen shall never be put in containers contaminated with oil, grease, or carbonaceous materials of any kind. They shall never be used in combination with other substances without knowing what the result may be.
- Because the composition of liquid air changes as the liquid evaporates, if liquid air is allowed to remain in the container, the proportion of oxygen will increase. If it is allowed to remain in a container until a large portion of the liquid is evaporated, an analysis shall be made before it is used for any purpose where high oxygen content would be dangerous. The proportion of oxygen in mixtures of liquid oxygen and nitrogen will also increase if allowed to remain in the container. The liquid mixture shall be analyzed before it is used for any purpose where a high oxygen content would be dangerous.
- Do not allow air to become entrapped in insulation around nitrogen pipes as it may be liquefied at points where the nitrogen vaporizes within the pipe system. Oxygen-enrichment of the liquefied air can result in an explosive hazard in combustible insulation.
Note: See GN470100, Safe Handling of Cryogenic Fluids, for cryogenic fluids handling precautions.
Note: Oxygen is a colorless, odorless, and tasteless gas. Although it is nonflammable, it readily supports combustion and greatly enhances the rate of burning.
Members of the Workforce shall not permit oil and grease to come in contact with oxygen cylinders, valves, regulators, gauges, or fittings. Explosive mixtures can result when oxygen and hydrocarbons are combined.
Members of the Workforce shall ensure the same level of safety is observed for the piping in pressure systems as for the vessel and other components.
High-pressure systems may not have a safety factor of 3.5. When in doubt, additional information and analysis are necessary to document the safety of these systems.
Members of the Workforce may use commercial piping obtained from a reputable supplier provided that it meets the requirements of ASME B31.1, Power Piping, at its specified rating. The suppliers' catalogs or technical bulletins specify the minimum bending radius or other restrictions that should be observed when installing this equipment. Special tools, such as bending tools, may be available.
Note: When there is doubt concerning the rating or use of any commercial component, additional investigation and/or consultation may be justified.
Flexible hose should not be bent beyond its rated minimum bend radius. Over-bending will introduce hazardous stress risers.
Recommendations for Selecting Wall Thickness
The following recommendations are provided for Members of the Workforce when selecting wall thickness of piping:
- Commercially supplied piping should have the appropriate wall thickness for the intended use and pressure rating. Consult the supplier or the appropriate catalog/product guide.
- Where commercial piping is not available for a specific application, design piping and tubing in accordance with ASME specifications where applicable.
Note: Pressure Installers should be cognizant of the vendors' restrictions on bending radius of piping and tubing. Special tools should be used when called for. Supplier's catalogs or technical representatives should be consulted.
Anchoring Rigid Piping
Members of the Workforce shall ensure that rigid piping is properly installed following these rules:
- Configure piping to allow for thermal expansion and contraction.
- Support the piping to avoid vibration, using adjustable wrought-iron or malleable-iron hangers at 8-foot intervals.
- Anchor piping to withstand thrust, torsion, and other operating conditions. This extends the service life of the piping and provides protection in the event of line failure.
- Tubing will have hangers spaced not over 5 feet apart.
- Minimize runs of pipe.
When working with flexible hoses, Members of the Workforce shall:
- Attaching tiedowns securely to the hose (not the termination) because hose failures usually occur when the hose releases from the termination.
- Ensuring that anchoring devices, such as whip-checks, must be capable of withstanding a force greater than 50% of the MAWP times the cross-sectional of the hose's OD.
COMPRESSED AIR SYSTEMS
House Air Systems
Note: House or shop air systems provide compressed air to drops or hose reels at 150 psi or less. Generally the air source is from a compressor.
Members of the Workforce should be cognizant of potential injuries that can occur when working with pressurized air or gas. Examples of potential injuries from the misuse of pressurized air or gas include the following:
- A strong blast of air or gas from a hose can dislodge an eye from its socket, rupture an eardrum, or induce hemorrhaging.
- An air jet from a 100-psi line released through a 1/8-inch diameter or smaller opening at skin surface can enter through a cut or sore and inflate the flesh, and even cause air embolism (bubbles) in the bloodstream.
- A highly compressed gas stream needling through a very small opening that contacts the skin can pierce the skin, permeate the flesh in depth, and cause tissues to inflate, causing excruciating pain from expansion of the gas.
- A stream of air from a hose at a pressure of 30 psi or more can drive metal chips at speeds that make them missile threats to eyes or face.
Blowing or Dusting
Members of the Workforce shall not use compressed air for cleaning purposes (blowing or dusting) except where pressure is reduced to less than 30 psi, and then only with effective chip-guarding and personal-protective equipment. The pressure source must be regulated to less than 30 psi or a safety-type nozzle, which restricts the output to less than 30 psi, must be installed on the line.
Members of the Workforce shall observe the following precautions:
- Do not exceed the maximum air pressure of 30 psi.
- Wear safety glasses or safety glasses with a face shield.
- Do not blow dust or chips if other people are in the immediate area or without wearing adequate chip guards.
- Do not dust off clothing with air or any other compressed gas.
- Sweep up metal chips that are too large or heavy for blowing at this pressure.
- Install the safety nozzles on the air supply hose when they are being used for blowing or dusting.
Note: Placing signs reading "Caution - 30 psi Max for Dusting" in the vicinity of the air supply outlet is recommended to remind people of the requirement.
Note: Several brands of safety air nozzles are available, such as "SAFE-T-BLOW" and "Guardair", and may be ordered through the Just-in-Time system. These nozzles restrict the pressure at the output of house air (100 psi maximum) systems to less than 30 psi without having to regulate the pressure.
SUPPLIERS AND THEIR PRODUCTS
Just-in-Time (JIT) Procurement
The JIT contract for pressure hardware imposes quality program requirements on suppliers that are consistent with Supply Chain Management documents and the SNL Suspect/Counterfeit Items Program to ensure that various types of pressure or vacuum components supplied to Sandia are free of suspect or counterfeit parts and are adequately tested and certified. The Sandia Pressure Safety Committee (PSC) has determined that material furnished to Sandia can be used without further testing or certification.
For the purpose of evaluating JIT contract proposals pertaining to pressure and vacuum equipment, the PSC should appoint one or more members to provide technical assistance in evaluating the proposals and suppliers.
Pressure Installers shall:
- Ensure that non-JIT purchases of vacuum and pressure hardware meet the requirements of Chapter 4, "Procuring Pressure Vessels and Special System Components."
- Be aware of the information in Supply Chain Management documents and the SNL Suspect/Counterfeit Items Program
Hardware procured from sources other than through the JIT contract may require additional investigation, analysis, inspection, or testing. Members of the Workforce should consult their organizational Pressure Advisor regarding this hardware.
Pressure Installers who purchase pressure components should obtain vessels and components consistent with the requirements of Supply Chain Management documents and the SNL Suspect/Counterfeit Items Program, when deemed applicable.
Requirements Source Documents
National Codes and Standards
ASME B31.3, Chemical Plant and Petroleum Refinery Piping, American Society of Mechanical Engineers, 345 East 47th Street, New York, NY 10017.
AWS Z49.1, Safety in Welding and Cutting, American Welding Society, 550 N.W. LeJeune Road, P.O. Box 351040, Miami, FL 33135.
API 620, Recommended Rules for Design and Construction of Large, Welded Low Pressure Storage Tanks, American Petroleum Institute, 1220 L Street, N.W., Washington, DC 20005.
ASME Boiler and Pressure Vessel Code (Section VIII, Unfired Pressure Vessels), American Society of Mechanical Engineers, 345 East 47th Street, New York, NY 10017-2392.
ASTM G88, Guide for Designing Systems for Oxygen Service, ASTM, 1916 Race Street, Philadelphia, PA 19103-1187.
Code of Federal Regulations, Title 49 CFR (Transportation), Superintendent of Documents, U.S. Government Printing Office, Washington, DC 20402.
Compressed Gas Association, Handbook of Compressed Gases, Compressed Gas Association, 1235 Jefferson Davis Highway, Arlington, VA 22202. (Appendix 4 of the handbook lists the CGA Pamphlets and Bulletins that address the safe transportation, handling, and use of compressed gases.) These publications are available on microfilm in the Design Information Center.
DOE Pressure Safety Guidelines, M-089.
Material Safety Data Sheets (provided by supplier).
Matheson Gas Data Book, 6th ed., Matheson Gas Products, Inc., Secaucus, NJ 07094 (1980).
National Board Inspection Code - A Manual for Boiler and Pressure Vessel Inspectors, National Board of Boiler and Pressure Vessel Inspectors, 1055 Crupper Avenue, Columbus, OH 43229.
NFPA 70, National Electrical Code, National Fire Protection Association, 1 Battery March Park, Quincy, MA 02269.
National Fire Protection Association Codes Pertaining to Compressed Gases
||Storage of Gaseous Oxidizing Materials
||Standard on Fire Protection for Laboratories Using Chemicals
||Hazardous Chemicals Data
||Standard for Bulk Oxygen at Consumer Sites
||Standard for Gaseous Hydrogen Systems at Consumer Sites
||Standard for Liquefied Hydrogen Systems at Consumer Sites
||Standard for the Design and Installation of Oxygen-Fuel Gas Systems for Welding, Cutting and Allied Processes
||Standard for Acetylene Cylinder Charging Plants
||Standard for Fire Prevention During Welding, Cutting and Other Hot Work
||Standard for Compressed Natural Gas (CNG) Vehicular Fuel Gas Systems
||Recommended Practice on Materials, Equipment, and Systems in Oxygen-Enriched Atmospheres
||National Fuel Gas Code
||Liquefied Petroleum Gas Code
||Utility LP-Gas Plant Code
||Standard for the Production, Storage, and Handling of Liquefied Natural Gas (LNG)
||Standard for Health Care Facilities (supersedes NFPA 3M, 56A, 56B, 56C, 56D, 56E, 56G, 56HM, 56K, 76A, 76B, and 76C
The contact for these codes is NFPA, 1 Battery March Park, Quincy, MA 02269 (Telephone: 1-800-344-3555).
Occupational Safety and Health Administration
The Occupational Safety and Health Administration (OSHA) under the United States Department of Labor promulgates regulations "to assure safe and healthful working conditions for working men and women." These OSHA regulations are published in Title 29 of the Code of Federal Regulations under Part 1910 relating to General Industry Standards, Part 1915 relating to Shipyard Employment, and Part 1926 relating to Construction Industry Standards.
Under the General Industry Standards of 29 CFR Part 1910, the following sections will be of particular interest to users of compressed gases:
- 29 CFR 1910.94, Ventilation
- 29 CFR 1910.95, Occupational Noise Exposure
- 29 CFR 1910.101, Compressed Gases (general requirements)
- 29 CFR 1910.102, Acetylene
- 29 CFR 1910.103, Hydrogen
- 29 CFR 1910.104, Oxygen
- 29 CFR 1910.105, Nitrous Oxide
- 29 CFR 1910.110, Storage and Handling of Liquefied Petroleum Gases
- 29 CFR 1910.111, Storage and Handling of Anhydrous Ammonia
- 29 CFR 1910.251, Subpart Q, Welding, Cutting, and Brazing
- 29 CFR 1910.307, Hazardous (classified) Locations
- 29 CFR 1910.1000, Air Contaminants
- 29 CFR 1910.1047, Ethylene Oxide
- 29 CFR 1910.1200, Hazardous Communication
DOE Worker Safety And Health Program
10 CFR 851, Worker Safety and Health Program.
International Fire Code, 2000, International Code Council, 5203 Leesburg Pike, Suite 600, Falls Church, VA 22041
Shane Page, firstname.lastname@example.org
Al Bendure, email@example.com
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