Anhydrous ammonia storage rules

This standard covers the design, construction, location, installation, and operation of anhydrous ammonia systems (including refrigerated ammonia storage systems). See 1910.111(a)(1).

• It does not apply to ammonia manufacturing plants or refrigeration plants that use ammonia solely as a refrigerant; those exclusions are listed in 1910.111(a)(1)(ii).
• Use this scope to decide whether your installation must meet the rules in the remainder of 1910.111.

A "cylinder" is a container of 1,000 pounds of water capacity or less built to Department of Transportation specifications. See the definition at 1910.111(a)(2)(ii).

• If your container fits that size and DOT spec, treat it as a cylinder for the rest of 1910.111.

A "container" includes all vessels, tanks, cylinders, or spheres used for transportation, storage, or application of anhydrous ammonia. See 1910.111(a)(2)(iv).

• Use this broad definition when applying marking, construction, and appurtenance rules in the rest of the section.

Gas masks must be approved by NIOSH under 42 CFR part 84 for use with anhydrous ammonia. See 1910.111(a)(2)(x).

• Use only respirators approved and rated for ammonia exposure; unapproved devices do not meet this standard.

Each appurtenance must meet one of the approval paths in [1910.111(b)(1)(i)–(iv)], such as being installed before February 8, 1973 in compliance with specified codes, being certified/listed by a nationally recognized testing laboratory, being inspected and approved by a government authority when no lab will accept it, or being custom-built with a signed engineering attestation. See 1910.111(b)(1).

• If relying on custom design, you must keep on file a signed document from a registered professional engineer or qualified person as required in 1910.111(b)(1)(v).

It means the equipment has been accepted, certified, listed, or labeled by a nationally recognized testing laboratory as safe for the intended use. See 1910.111(b)(1)(ii) and the definition of "listed/labeled" in 1910.111(b)(1)(v).

• For who qualifies as a nationally recognized testing lab, refer to 1910.7 as noted in 1910.111(b)(1)(vi).

Containers used with systems covered in paragraphs (c), (f), (g), and (h) must be constructed and tested according to the ASME Code, except containers built under Table UW12 cannot use a basic joint efficiency under 80 percent. See 1910.111(b)(2)(i).

• This means follow ASME Section VIII requirements, with the specific prohibition on low joint efficiency noted in the standard.

Containers used with systems covered in paragraph (e) must be constructed and tested in accordance with Department of Transportation (DOT) specifications. See 1910.111(b)(2)(v).

• If your system falls in paragraph (e), do not use ASME-only construction; follow DOT regs (49 CFR) for that container.

Containers or systems covered in paragraphs (c), (f), (g), and (h) must be marked with required information such as a notation "Anhydrous Ammonia," compliance code, installation type (underground/aboveground), supplier name/address or trade name, fabrication date, water capacity, design pressure, wall thickness, and the maximum fill level for specified temperatures. See the full list at 1910.111(b)(3)(ii).

• Some markings are required only for underground or aboveground containers as specified in the subdivision (e.g., water capacity and design pressure placement).

Yes. Each applicable container or system must be marked with the notation "Anhydrous Ammonia" and indicate whether it is designed for underground or aboveground installation (or both). See 1910.111(b)(3)(ii)(a) and 1910.111(b)(3)(ii)(c).

• Place the marking on the nameplate or container as required by 1910.111(b)(3)(ii)(j).

Containers must be marked to indicate the maximum level to which the container may be filled with liquid anhydrous ammonia at temperatures between 20 °F and 130 °F. See 1910.111(b)(3)(ii)(h).

• The marking may be on the system nameplate or on the liquid-level gaging device for aboveground and underground containers as specified in 1910.111(b)(3)(ii).

No. The total outside surface area of the container in square feet is required on the system nameplate for underground containers only; there is no requirement to mark total outside surface area for aboveground containers. See 1910.111(b)(3)(ii)(i).

• Check whether your container is installed underground; if so, include that surface-area marking on the nameplate.

Each refrigerated container must have a nameplate on the outer covering showing (1) the notation "Anhydrous Ammonia," (2) builder name and address and fabrication date, (3) water capacity in U.S. gallons, and (4) design pressure. See 1910.111(b)(4)(i)–(iv).

• Additional refrigerated-container markings such as minimum design temperature, maximum allowable test water level, product density, and maximum fill level are listed in 1910.111(b)(4)(v)–(viii).

Permanent storage containers must be located at least 50 feet from a dug well or other sources of potable water supply, unless the container is part of a water-treatment installation. See 1910.111(b)(5)(ii).

• Consider both current and future potable water sources when siting a container to meet this distance requirement.

You must consider the physiological effects of ammonia and adjacent fire hazards and locate containers outside buildings or in specially provided building sections. See 1910.111(b)(5)(i).

• Keep storage areas free of readily ignitible materials such as waste, weeds, and long dry grass per 1910.111(b)(5)(v).

All appurtenances must be designed for at least the maximum working pressure of the system portion where they are installed and made from materials suitable for anhydrous ammonia service. See 1910.111(b)(6)(i).

• This means valves, fittings, and gages should match or exceed the pressure rating and be ammonia-compatible materials.

All connections to containers—except safety relief devices, gaging devices, or connections fitted with a No. 54 drill-size orifice—must have shutoff valves located as close to the container as practicable. See 1910.111(b)(6)(ii).

• The intent is to allow rapid isolation of the container in an emergency by placing valves close to the source.

Excess flow valves must close automatically at the manufacturer's rated flows and the protected pipeline must have greater capacity than the valve so it will close on line failure; excess flow and back pressure check valves must be located inside the container or as close as practicable to the container entry, with installation preventing undue strain between the container and the valve. See 1910.111(b)(6)(iii)–(vi).

• Liquid-level gaging devices that vent to atmosphere with flow not exceeding a No. 54 drill-size opening do not require excess flow valves per 1910.111(b)(6)(iv).
• Openings no larger than No. 54 drill size for pressure-gage connections also do not need excess flow valves per 1910.111(b)(6)(v).

Required markings must be on the container itself or on a nameplate permanently attached to it. See 1910.111(b)(3)(ii)(j).

• Ensure markings are permanent and readily accessible for inspection as required by the standard.

Welding to any part of the container subject to internal pressure (shell, head, etc.) must comply with the ASME Code; other welding is permitted only on saddle plates, lugs, or brackets attached by the container manufacturer. See 1910.111(b)(2)(iv).

• Do not perform non-code welding on pressure-retaining parts; that could invalidate the container's construction compliance.

Piping, tubing, and fittings must be made of materials suitable for anhydrous ammonia service. Employers must follow the material suitability requirement in 1910.111(b)(7)(i).

• Use only materials proven compatible with ammonia to avoid corrosion or failure.
• If unsure about a material, get manufacturer documentation showing compatibility with anhydrous ammonia or choose materials specified elsewhere in the rule (see following subsections for specific prohibitions and approved metals).

They must be designed for a pressure at least equal to the maximum pressure they may experience in service. This is required by 1910.111(b)(7)(ii).

• Verify the design pressure with engineering calculations or supplier data.
• Factor in possible overpressure scenarios (temperature rise, pump/compressor discharge, blocked lines) when selecting components.

Refrigerated piping must conform to the Refrigeration Piping Code ANSI B31.5-1966 (with addenda), as referenced in 1910.111(b)(7)(iii) and incorporated by reference via 1910.6.

• Use the ANSI B31.5 standard requirements for design, materials, and fabrication when piping is refrigerated.
• Confirm the specific edition (B31.5-1966 with addenda) referenced by OSHA through 1910.6 if relying on incorporated standards.

Non-refrigerated piping must be at least ASTM A-53-69 Grade B electric resistance welded or electric flash welded pipe (or an equal), with schedule 40 minimum when welded or welded-and-flanged, and schedule 80 minimum when threaded; brass, copper, and galvanized steel are prohibited. See 1910.111(b)(7)(iv).

• Threaded connections may not be back-welded.
• If you use pipe with different specifications, document why it is equal and safe for anhydrous ammonia service.

No; tubing made of brass, copper, or other materials subject to attack by ammonia must not be used. This prohibition is stated in 1910.111(b)(7)(v).

• Select tubing materials that resist ammonia corrosion (consult suppliers or material compatibility charts).

Cast iron fittings are not allowed, except you may use fittings specifically made for ammonia service from malleable, nodular, or high-strength gray iron that meet the listed ASTM specifications. See 1910.111(b)(7)(vi).

• Acceptable fittings must meet ASTM A47-68, ASTM 395-68, or ASTM A126-66 Class B or C as incorporated by reference.
• Always confirm the fitting’s manufacturer documentation shows compliance with the cited ASTM standard and suitability for ammonia.

Joint compounds must be resistant to ammonia. This requirement is stated in 1910.111(b)(7)(vii).

• Use sealing compounds and thread compounds specified by manufacturers for ammonia service.
• Keep manufacturer technical data sheets on file showing ammonia resistance.

Hose used in ammonia service must meet the joint Agricultural Ammonia Institute–Rubber Manufacturers Association specifications, be rated for at least 350 psig working pressure with minimum 1,750 psig burst pressure, and hose assemblies must withstand a 500 psig test; low-pressure-side hoses must meet bursting criteria tied to safety device settings. See 1910.111(b)(8)(i), 1910.111(b)(8)(ii), and 1910.111(b)(8)(iii).

• Ensure hose assemblies are tested after assembly to the 500 psig requirement.
• For hoses downstream of pressure-reducing valves, sizing must support burst pressure of at least 5× the safety device setting (and never less than 125 psig) and connections must be leak-tight.

Hoses used to transfer liquid ammonia should be "wet" hoses equipped with approved shutoff valves at the discharge end and means to prevent excessive pressure; hoses 1/2 inch OD and larger must be etched (or have a permanent nameplate) every 5 feet with "Anhydrous Ammonia," the maximum working pressure, manufacturer, and year of manufacture. See 1910.111(b)(8)(iv) and 1910.111(b)(8)(v).

• If using a nameplate instead of etching, make it permanent and legible.
• Train attendants to inspect the etched information and shutoff valves before transfer operations.

Every container in systems covered by the listed paragraphs must have one or more spring-loaded (or equivalent) safety relief valves, and the relief discharge must be vented upward and unobstructed to the atmosphere. This requirement is in 1910.111(b)(9)(i).

• Position discharge outlets upward and clear of obstructions so vapor can disperse safely.
• Provide rain caps that allow free discharge and prevent water entry per the related paragraph.

Container safety-relief valves must be set to start-to-discharge within the percentage ranges tied to the container design code (for example, ASME-U-68/69 valves: 110–125% of design pressure), must discharge at required rates in accordance with Table H-36 before pressure exceeds 120% of the maximum permitted start-to-discharge setting, and must be arranged to minimize tampering (external adjustments must be sealable). See 1910.111(b)(9)(ii), 1910.111(b)(9)(iii), and 1910.111(b)(9)(iv).

• Verify valve set points and capacities against the container design code.
• Use Table H-36 (flow-rate table) or the surface-area formula for large tanks to size relief capacity as required.

Shutoff valves are generally not allowed between the safety-relief valve and the container, except where the arrangement still always provides the full required relief capacity; safety-relief valves must be plainly marked with “NH3” or “AA”, the start-to-discharge pressure in psig, the actual full-open discharge rate in CFM air at 60°F and atmospheric pressure, and the manufacturer's name and catalog number. See 1910.111(b)(9)(v) and 1910.111(b)(9)(vii).

• Do not restrict relief valve flow capacity with downstream or upstream connections per 1910.111(b)(9)(viii).
• Keep valve markings legible and available for inspection.

A hydrostatic relief valve must be installed between each pair of valves in liquid ammonia piping wherever liquid could become trapped, and it must discharge to the atmosphere at a safe location. This requirement is stated in 1910.111(b)(9)(ix).

• Locate the hydrostatic relief to protect piping and personnel from trapped liquid overpressure.
• Route the discharge to an area where escaping ammonia vapor will not harm workers.

Stationary storage installations must have at least two readily accessible gas masks (NIOSH-approved full-face masks with ammonia canisters are suitable for most outdoor leaks) and an easily accessible shower or a 50-gallon drum of water; vehicle transporters (except farm applicator vehicles) must carry at least 5 gallons of water and be equipped with a full-face mask. For concentrated ammonia atmospheres a self-contained breathing apparatus is required. See 1910.111(b)(10)(ii), 1910.111(b)(10)(iii), and 1910.111(b)(10)(iv).

• Maintain the gas masks and canisters per manufacturer instructions and replace after use or per service life.
• Train employees on when to use NIOSH-approved filters vs. SCBA in concentrated releases.

Filling densities for non-refrigerated containers must not exceed the percent-by-weight and percent-by-volume limits listed in 1910.111(b)(11)(i); aboveground uninsulated containers may be charged to 87.5% by volume only if the ammonia temperature is measured to be not lower than 30°F or charging is stopped at the first sign of frost/ice and not resumed until it disappears. See 1910.111(b)(11)(ii).

• Always monitor liquid temperature during charging when approaching the higher volume limits.
• Implement written procedures and training for attendants to stop charging immediately if frost appears.

During liquid transfer, the ammonia must be at a temperature suitable for the receiving container's construction and design; a trained attendant must be continuously present during the transfer; containers may only be charged or used with owner authorization; and gaging/charging must occur in the open atmosphere or in specifically provided buildings/areas. See 1910.111(b)(12)(i), 1910.111(b)(12)(ii), 1910.111(b)(12)(iii), and 1910.111(b)(12)(iv).

• Keep an attendant close enough to stop the transfer immediately in an emergency.
• Use designated charging areas with appropriate ventilation and emergency equipment.

Pumps used for transferring ammonia must be manufactured for that purpose and positive-displacement pumps must have a constant differential relief valve discharging back to the suction port sized to carry full pump capacity at the relief setting; pumps must be designed for at least 250 psig working pressure; a 0–400 psig gauge must be installed on the pump discharge before the relief valve line; and plant piping should have shutoff valves as close as practical to pump connections. See 1910.111(b)(12)(v)(a), 1910.111(b)(12)(v)(b), 1910.111(b)(12)(v)(c), and 1910.111(b)(12)(v)(d).

• Follow the pump manufacturer’s installation recommendations for relief valve settings and line sizing.
• Calibrate and inspect pressure gages regularly.

Compressors must be recommended by the manufacturer for ammonia service and designed for at least 250 psig working pressure; plant piping must have shutoff valves close to compressor connections; a relief valve large enough to discharge the compressor’s full capacity must be connected to the discharge before any shutoff valve; and compressors must have suction and discharge gauges graduated to at least 1.5 times the maximum pressure that can be developed. These are required by 1910.111(b)(12)(vi) and its subparagraphs (vi–(d)).

• Make sure relief valve sizing and location protect the compressor and downstream equipment.
• Verify gauge ranges exceed expected maximum pressures to ensure accurate monitoring.

You determine required discharge rate by first calculating the container’s total outside surface area (using the formulas for cylindrical, spherical, or other heads) and then finding the matching flow-rate in Table H-36; for containers with surface area greater than 2,500 sq ft you must calculate required flow using the formula Flow Rate CFM Air = 22.11 × A^0.82 where A is surface area in sq ft. See the surface-area calculation formulas and the flow-rate table referenced in 1910.111(b)(9)(i).

• Use the stated formulas to compute surface area when nameplate markings are missing or illegible.
• Interpolate Table H-36 values for intermediate surface areas; for very large containers (>2,500 sq ft) use the mathematical formula provided.

On all hose one-half inch outside diameter and larger used for transferring anhydrous ammonia liquid or vapor, the following must be etched, cast, or impressed at five-foot intervals: “Anhydrous Ammonia”, the maximum working pressure in psig, the manufacturer's name or trademark, and the year of manufacture; alternatively, the same information may be provided on a permanently attached nameplate. See 1910.111(b)(8)(v).

• Inspect hose markings regularly to ensure legibility and replace hoses with missing or illegible information.
• Record hose age and service life based on the year of manufacture marking.

A valve marking example could be “NH3 250-4050 Air”, which means the valve is suitable for anhydrous ammonia (NH3), is set to start-to-discharge at 250 psig, and has a full-open discharge rate of 4,050 cubic feet per minute of air at 60°F and atmospheric pressure; the marking must also include the manufacturer's name and catalog number. See 1910.111(b)(9)(vii).

• Keep valve documentation and test records to verify the stated discharge rate and set pressure.
• Replace or re-certify valves if stamped data does not match test results.

Yes; the employer must require the continuous presence of an attendant in the vicinity during any time ammonia is being transferred. This duty is stated in 1910.111(b)(12)(ii).

• The attendant should be trained to stop transfers, activate emergency response, and use protective equipment.
• Document attendant assignments and training as part of transfer procedures.

A shutoff valve is not allowed between the safety-relief valve and the container except when the valve’s arrangement is such that full required relief flow capacity is always afforded even with that shutoff valve present. See 1910.111(b)(9)(v).

• If a shutoff is needed for maintenance, ensure an alternative means preserves the full relief capacity at all times.
• Document the design and provide verification that capacity is not restricted.

When transferring liquid from one container to another, a "wet" hose is recommended and such hose should be equipped with approved shutoff valves at the discharge end; provisions must be made to prevent excessive pressure in the hose. See 1910.111(b)(8)(iv).

• Use hoses specifically designed for liquid transfer (not vapor-only hose) and verify valve operation before transfer.
• Use pressure-limiting devices or relief protection to prevent over-pressurization during filling.

Adequate means you must provide a device such as a drainable liquid trap on the compressor suction to minimize liquid entering the compressor. Employers must follow the requirement in 1910.111(b)(12)(vi)(e) by installing a drainable trap or equivalent arrangement and maintaining it so liquid cannot accumulate and be carried into the compressor.

• Inspection and maintenance: regularly drain and inspect the trap so it functions as intended.
• If you use an alternate means, it should provide the same protection against liquid carryover as the trap described in the standard.

(See 1910.111(b)(12)(vi)(e).)

You must protect loading and unloading systems with backflow check valves, properly sized excess-flow valves, or remotely operated shutoff valves to prevent emptying the storage container if a hose is severed. The rule in 1910.111(b)(12)(vii) requires installation of such devices where necessary; if those valves are not practical, you may install remotely operated shutoff valves instead.

• Common options: back-pressure check valve + excess-flow valve, properly sized excess-flow valve alone, or remotely operated shutoff.
• Verify sizing and functionality: excess-flow and check valves must be sized and tested for the expected flow conditions to reliably stop product loss on hose severance.

(See 1910.111(b)(12)(vii).)

You must ensure unloading is done by trained, reliable people, display caution signs until unloading and disconnection are complete, keep the siding track substantially level, and set brakes and block wheels on cars being unloaded. These duties are specified in 1910.111(b)(13) and its subsections, including the sign requirements in 1910.111(b)(13)(iii), the level track requirement in 1910.111(b)(13)(iv), and the brakes/wheel blocking in 1910.111(b)(13)(v).

• Signs: must be metal or other suitable material, at least 12 x 15 inches, and say "STOP - Tank Car Connected" or "STOP - Men at Work" with specified letter heights.
• Personnel: unloading must be performed by reliable, instructed people who have the authority to ensure procedures are followed.

(See 1910.111(b)(13)).

Gaging devices that vent product to the atmosphere must limit the bleed valve opening to No. 54 drill size unless an excess-flow valve is provided, and fixed-tube liquid-level gages must indicate when a container reaches 85% of its water capacity. These requirements are in 1910.111(b)(14)(iii) and 1910.111(b)(14)(v).

• Bleeding gages (rotary tube, fixed tube, slip tube): maximum bleed valve opening = No. 54 drill size, unless an excess-flow valve is installed.
• Fixed-tube gages: must be designed/installed so they show when the container reaches 85% of its water capacity.

(See 1910.111(b)(14)(iii) and 1910.111(b)(14)(v).)

Columnar gage glasses are allowed only for stationary storage installations and must have shutoff valves with metallic handwheels, excess-flow valves, extra heavy glass in a manufacturer-applied metal housing, and shielding from direct sunlight. These conditions are set out in 1910.111(b)(14)(vi).

• Limitations: restricted to stationary storage—do not use on mobile or portable containers.
• Required features: shutoff valves (metallic handwheels), excess-flow valves, heavy glass protected by a metal housing applied by the gage manufacturer, and shielding against direct sun.

(See 1910.111(b)(14)(vi).)

Filling connections must have back-pressure check/excess-flow or equivalent arrangements, most liquid and vapor connections must have excess-flow valves, each storage container must have a 0–400 p.s.i. pressure gage for ammonia service and vapor return valves, and vent pipes must be at least the same diameter as the relief-valve outlet connection. These requirements come from 1910.111(c)(2)(i)–(iv) and 1910.111(c)(3)(iv).

• Filling connections: require combination back-pressure check + excess-flow valve, or equivalent positive shutoff plus internal check/excess-flow device (1910.111(c)(2)(i)).
• Connections: except for specified exceptions, liquid and vapor connections must be equipped with excess-flow valves (1910.111(c)(2)(ii)).
• Gauges and vapor returns: containers must have a pressure gage graduated 0–400 p.s.i. for ammonia service and vapor return valves (1910.111(c)(2)(iii) and 1910.111(c)(2)(iv)).
• Vent pipes: vent piping must not be restricted or smaller than the relief-valve outlet connection (1910.111(c)(3)(iv)).

(See 1910.111(c)(2) and 1910.111(c)(3)(iv).)