CFR > Title 29 - Labor > SUBTITLE B—Regulations Relating to Labor > CHAPTER XVII—OCCUPATIONAL SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR (parts 1900 to 1990) > PART 1910—OCCUPATIONAL SAFETY AND HEALTH STANDARDS > SUBPART H—Hazardous Materials (§1910.101 to §1910.126) > 1910.111—Storage and handling of anhydrous ammonia.

1910.111—Storage and handling of anhydrous ammonia.

(a) General— (1) Scope. This standard is intended to apply to the design, construction, location, installation, and operation of anhydrous ammonia systems including refrigerated ammonia storage systems.
(ii) This standard does not apply to:
(a) Ammonia manufacturing plants.
(b) Refrigeration plants where ammonia is used solely as a refrigerant.
(2) Definitions. As used in this section.
(i) Appurtenances. All devices such as pumps, compressors, safety relief devices, liquid-level gaging devices, valves and pressure gages.
(ii) Cylinder. A container of 1,000 pounds of water capacity or less constructed in accordance with Department of Transportation specifications.
(iii) Code. The Boiler and Pressure Vessel Code, Section VIII, Unfired Pressure Vessels of the American Society of Mechanical Engineers (ASME)—1968.
(iv) Container. Includes all vessels, tanks, cylinders, or spheres used for transportation, storage, or application of anhydrous ammonia.
(v) DOT. U.S. Department of Transportation.
(vi) Design pressure is identical to the term Maximum Allowable Working Pressure used in the Code.
(vii) Farm vehicle (implement of husbandry). A vehicle for use on a farm on which is mounted a container of not over 1,200 gallons water capacity.
(viii) Filling density. the percent ratio of the weight of the gas in a container to the weight of water at 60 °F. that the container will hold.
(ix) Gas. Anhydrous ammonia in either the gaseous or liquefied state.
(x) Gas masks. Gas masks must be approved by the National Institute for Occupational Safety and Health (NIOSH) under 42 CFR part 84 for use with anhydrous ammonia.
(xi) Capacity. Total volume of the container in standard U.S. gallons.
(xii) DOT specifications—Regulations of the Department of Transportation published in 49 CFR Chapter I.
(b) Basic rules. This paragraph applies to all paragraphs of this section unless otherwise noted.
(1) Approval of equipment and systems. Each appurtenance shall be approved in accordance with paragraph (b)(1) (i), (ii), (iii), or (iv) of this section.
(i) It was installed before February 8, 1973, and was approved, tested, and installed in accordance with either the provisions of the American National Standard for the Storage and Handling of Anhydrous Ammonia, K61.1, or the Fertilizer Institute Standards for the Storage and Handling of Agricultural Anhydrous Ammonia, M-1, (both of which are incorporated by reference as specified in § 1910.6) in effect at the time of installation; or
(ii) It is accepted, or certified, or listed, or labeled, or otherwise determined to be safe by a nationally recognized testing laboratory; or
(iii) It is a type which no nationally recognized testing laboratory does, or will undertake to, accept, certify, list, label, or determine to be safe; and such equipment is inspected or tested by any Federal, State, municipal, or other local authority responsible for enforcing occupational safety provisions of a Federal, State, municipal or other local law, code, or regulation pertaining to the storage, handling, transport, and use of anhydrous ammonia, and found to be in compliance with either the provisions of the American National Standard for the Storage and Handling of Anhydrous Ammonia, K61.1, or the Fertilizer Institute Standards for the Storage and Handling of Agricultural Anhydrous Ammonia, M-1, in effect at the time of installation; or
(iv) It is a custom-designed and custom-built unit, which no nationally recognized testing laboratory, or Federal, State, municipal or local authority responsible for the enforcement of a Federal, State, municipal, or local law, code or regulation pertaining to the storage, transportation and use of anhydrous ammonia is willing to undertake to accept, certify, list, label or determine to be safe, and the employer has on file a document attesting to its safe condition following the conduct of appropriate tests. The document shall be signed by a registered professional engineer or other person having special training or experience sufficient to permit him to form an opinion as to safety of the unit involved. The document shall set forth the test bases, test data and results, and also the qualifications of the certifying person.
(v) For the purposes of this paragraph (b)(1), the word listed means that equipment is of a kind mentioned in a list which is published by a nationally recognized laboratory which makes periodic inspection of the production of such equipment, and states such equipment meets nationally recognized standards or has been tested and found safe for use in a specified manner. Labeled means there is attached to it a label, symbol, or other identifying mark of a nationally recognized testing laboratory which, makes periodic inspections of the production of such equipment, and whose labeling indicates compliance with nationally recognized standards or tests to determine safe use in a specified manner. Certified means it has been tested and found by a nationally recognized testing laboratory to meet nationally recognized standards or to be safe for use in a specified manner, or is of a kind whose production is periodically inspected by a nationally recognized testing laboratory, and it bears a label, tag, or other record of certification.
(vi) For the purposes of this paragraph (b)(1), refer to § 1910.7 for definition of nationally recognized testing laboratory.
(2) Requirements for construction, original test and requalification of nonrefrigerated containers. (i) Containers used with systems covered in paragraphs (c), (f), (g), and (h) of this section shall be constructed and tested in accordance with the Code except that construction under Table UW12 at a basic joint efficiency of under 80 percent is not authorized.
(ii) Containers built according to the Code do not have to comply with Paragraphs UG125 to UG128 inclusive, and Paragraphs UG132 and UG133 of the Code.
(iii) Containers exceeding 36 inches in diameter or 250 gallons water capacity shall be constructed to comply with one or more of the following:
(a) Containers shall be stress relieved after fabrication in accordance with the Code, or
(b) Cold-form heads when used, shall be stress relieved, or
(c) Hot-formed heads shall be used.
(iv) Welding to the shell, head, or any other part of the container subject to internal pressure shall be done in compliance with the Code. Other welding is permitted only on saddle plates, lugs, or brackets attached to the container by the container manufacturer.
(v) Containers used with systems covered in paragraph (e) of this section shall be constructed and tested in accordance with the DOT specifications.
(vi) The provisions of subdivision (i) of this subparagraph shall not be construed as prohibiting the continued use or reinstallation of containers constructed and maintained in accordance with the 1949, 1950, 1952, 1956, 1959, and 1962 editions of the Code or any revisions thereof in effect at the time of fabrication.
(3) Marking nonrefrigerated containers. (i) System nameplates, when required, shall be permanently attached to the system so as to be readily accessible for inspection and shall include markings as prescribed in subdivision (ii) of this subparagraph.
(ii) Each container or system covered in paragraphs (c), (f), (g), and (h) of this section shall be marked as specified in the following:
(a) With a notation “Anhydrous Ammonia.”
(b) With a marking identifying compliance with the rules of the Code under which the container is constructed.
Under ground: Container and system nameplate.
Above ground: Container.
(c) With a notation whether the system is designed for underground or aboveground installation or both.
(d) With the name and address of the supplier of the system or the trade name of the system and with the date of fabrication.
Under ground and above ground: System nameplate.
(e) With the water capacity of the container in pounds at 60 °F. or gallons, U.S. Standard.
Under ground: Container and system nameplate.
Above ground: Container.
(f) With the design pressure in pounds per square inch.
Under ground: Container and system nameplate.
Above ground: Container.
(g) With the wall thickness of the shell and heads.
Under ground: Container and system nameplate.
Above ground: Container.
(h) With marking indicating the maximum level to which the container may be filled with liquid anhydrous ammonia at temperatures between 20 °F. and 130 °F. except on containers provided with fixed level indicators, such as fixed length dip tubes, or containers that are filled with weight. Markings shall be in increments of not more than 20 °F.
Above ground and under ground: System nameplate or on liquid-level gaging device.
(i) With the total outside surface area of the container in square feet.
Under ground: System nameplate.
Above ground: No requirement.
(j) Marking specified on the container shall be on the container itself or on a nameplate permanently attached to it.
(4) Marking refrigerated containers. Each refrigerated container shall be marked with nameplate on the outer covering in an accessible place as specified in the following:
(i) With the notation, “Anhydrous Ammonia.”
(ii) With the name and address of the builder and the date of fabrication.
(iii) With the water capacity of the container in gallons, U.S. Standard.
(iv) With the design pressure.
(v) With the minimum temperature in degrees Fahrenheit for which the container was designed.
(vi) The maximum allowable water level to which the container may be filled for test purposes.
(vii) With the density of the product in pounds per cubic foot for which the container was designed.
(viii) With the maximum level to which the container may be filled with liquid anhydrous ammonia.
(5) Location of containers. (i) Consideration shall be given to the physiological effects of ammonia as well as to adjacent fire hazards in selecting the location for a storage container. Containers shall be located outside of buildings or in buildings or sections thereof especially provided for this purpose.
(ii) Permanent storage containers shall be located at least 50 feet from a dug well or other sources of potable water supply, unless the container is a part of a water-treatment installation.
(iii) -(iv) [Reserved]
(v) Storage areas shall be kept free of readily ignitible materials such as waste, weeds, and long dry grass.
(6) Container appurtenances. (i) All appurtenances shall be designed for not less than the maximum working pressure of that portion of the system on which they are installed. All appurtenances shall be fabricated from materials proved suitable for anhydrous ammonia service.
(ii) All connections to containers except safety relief devices, gaging devices, or those fitted with No. 54 drill-size orifice shall have shutoff valves located as close to the container as practicable.
(iii) Excess flow valves where required by these standards shall close automatically at the rated flows of vapor or liquid as specified by the manufacturer. The connections and line including valves and fittings being protected by an excess flow valve shall have a greater capacity than the rated flow of the excess flow valve so that the valve will close in case of failure of the line or fittings.
(iv) Liquid-level gaging devices that require bleeding of the product to the atmosphere and which are so constructed that outward flow will not exceed that passed by a No. 54 drill-size opening need not be equipped with excess flow valves.
(v) Openings from the container or through fittings attached directly on the container to which pressure gage connections are made need not be equipped with excess flow valves if such openings are not larger than No. 54 drill size.
(vi) Excess flow and back pressure check valves where required by the standards in this section shall be located inside of the container or at a point outside as close as practicable to where the line enters the container. In the latter case installation shall be made in such manner that any undue strain beyond the excess flow or back pressure check valve will not cause breakage between the container and the valve.
(vii) Excess flow valves shall be designed with a bypass, not to exceed a No. 60 drill-size opening to allow equalization of pressures.
(viii) All excess flow valves shall be plainly and permanently marked with the name or trademark of the manufacturer, the catalog number, and the rated capacity.
(7) Piping, tubing, and fittings. (i) All piping, tubing, and fittings shall be made of material suitable for anhydrous ammonia service.
(ii) All piping, tubing, and fittings shall be designed for a pressure not less than the maximum pressure to which they may be subjected in service.
(iii) All refrigerated piping shall conform to the Refrigeration Piping Code, American National Standards Institute, B31.5-1966 with addenda B31.1a-1968, which is incorporated by reference as specified in § 1910.6, as it applies to ammonia.
(iv) Piping used on non-refrigerated systems shall be at least American Society for Testing and Materials (ASTM) A-53-69 Grade B Electric Resistance Welded and Electric Flash Welded Pipe, which is incorporated by reference as specified in § 1910.6, or equal. Such pipe shall be at least schedule 40 when joints are welded, or welded and flanged. Such pipe shall be at least schedule 80 when joints are threaded. Threaded connections shall not be back-welded. Brass, copper, or galvanized steel pipe shall not be used.
(v) Tubing made of brass, copper, or other material subject to attack by ammonia shall not be used.
(vi) Cast iron fittings shall not be used but this shall not prohibit the use of fittings made specifically for ammonia service of malleable, nodular, or high strength gray iron meeting American Society for Testing and Materials (ASTM) A47-68, ASTM 395-68, or ASTM A126-66 Class B or C all of which are incorporated by reference as specified in § 1910.6.
(vii) Joint compounds shall be resistant to ammonia.
(8) Hose specifications. (i) Hose used in ammonia service shall conform to the joint Agricultural Ammonia Institute—Rubber Manufacturers Association Specifications for Anhydrous Ammonia Hose.
(ii) Hose subject to container pressure shall be designed for a minimum working pressure of 350 p.s.i.g. and a minimum burst pressure of 1,750 p.s.i.g. Hose assemblies, when made up, shall be capable of withstanding a test pressure of 500 p.s.i.g.
(iii) Hose and hose connections located on the low-pressure side of flow control of pressure-reducing valves shall be designed for a bursting pressure of not less than 5 times the pressure setting of the safety relief devices protecting that portion of the system but not less than 125 p.s.i.g. All connections shall be so designed and constructed that there will be no leakage when connected.
(iv) Where hose is to be used for transferring liquid from one container to another, “wet” hose is recommended. Such hose shall be equipped with approved shutoff valves at the discharge end. Provision shall be made to prevent excessive pressure in the hose.
(v) On all hose one-half inch outside diameter and larger, used for the transfer of anhydrous ammonia liquid or vapor, there shall be etched, cast, or impressed at 5-foot intervals the following information.
“Anhydrous Ammonia” xxx p.s.i.g. (maximum working pressure), manufacturer's name or trademark, year of manufacture.
In lieu of this requirement the same information may be contained on a nameplate permanently attached to the hose.
Table H-36
[Minimum required rate of discharge in cubic feet per minute of air at 120 percent of the maximum permitted start to discharge pressure of safety relief valves]
Surface area (sq. ft.) Flow rate CFM air
20 258
25 310
30 360
35 408
40 455
45 501
50 547
55 591
60 635
65 678
70 720
75 762
80 804
85 845
90 885
95 925
100 965
105 1,010
110 1,050
115 1,090
120 1,120
125 1,160
130 1,200
135 1,240
140 1,280
145 1,310
150 1,350
155 1,390
160 1,420
165 1,460
170 1,500
175 1,530
180 1,570
185 1,600
190 1,640
195 1,670
200 1,710
210 1,780
220 1,850
230 1,920
240 1,980
Code of Federal Regulations 341
250 2,050
260 2,120
270 2,180
280 2,250
290 2,320
300 2,380
310 2,450
320 2,510
330 2,570
340 2,640
350 2,700
360 2,760
370 2,830
380 2,890
390 2,950
400 3,010
450 3,320
500 3,620
550 3,910
600 4,200
650 4,480
700 4,760
750 5,040
800 5,300
850 5,590
900 5,850
950 6,120
1,000 6,380
1,050 6,640
1,100 6,900
1,150 7,160
1,200 7,410
1,250 7,660
1,300 7,910
1,350 8,160
1,400 8,410
1,450 8,650
1,500 8,900
1,550 9,140
1,600 9,380
1,650 9,620
1,700 9,860
1,750 10,090
1,800 10,330
1,850 10,560
1,900 10,800
1,950 11,030
2,000 11,260
2,050 11,490
2,100 11,720
2,150 11,950
2,200 12,180
2,250 12,400
2,300 12,630
2,350 12,850
2,400 13,080
2,450 13,300
2,500 13,520
Surface Area=total outside surface area of container in square feet. When the surface area is not stamped on the nameplate or when the marking is not legible the area can be calculated by using one of the following formulas:
(1) Cylindrical container with hemispherical heads:
Area=overall length in feet times outside diameter in feet times 3.1416.
(2) Cylindrical container with other than hemispherical heads:
Area=(overall length in feet plus 0.3 outside diameter in feet) times outside diameter in feet times 3.1416.
(3) Spherical container:
Area=outside diameter in feet squared times 3.1416.
Flow Rate—CFM Air=cubic feet per minute of air required at standard conditions, 60 °F. and atmospheric pressure (14.7 p.s.i.a.).
The rate of discharge may be interpolated for intermediate values of surface area. For containers with total outside surface area greater than 2,500 square feet, the required flow rate can be calculated using the formula: Flow Rate CFM Air=22.11 A0 82, where A=outside surface area of the container in square feet.
(9) Safety relief devices. (i) Every container used in systems covered by paragraphs (c), (f), (g), and (h) of this section shall be provided with one or more safety relief valves of the spring-loaded or equivalent type. The discharge from safety-relief valves shall be vented away from the container upward and unobstructed to the atmosphere. All relief-valve discharge openings shall have suitable rain caps that will allow free discharge of the vapor and prevent entrance of water. Provision shall be made for draining condensate which may accumulate. The rate of the discharge shall be in accordance with the provisions of Table H-36.
(ii) Container safety-relief valves shall be set to start-to-discharge as follows, with relation to the design pressure of the container:
Containers Minimum (percent) Maximum (percent)
ASME-U-68, U-69 110 125
ASME-U-200, U-201 95 100
ASME 1959, 1956, 1952, or 1962 95 100
API-ASME 95 100
U.S. Coast Guard 95 100
As required by DOT Regulations.
(iii) Safety relief devices used in systems covered by paragraphs (c), (f), (g), and (h) of this section shall be constructed to discharge at not less than the rates required in paragraph (b)(9)(i) of this section before the pressure is in excess of 120 percent (not including the 10 percent tolerance referred to in paragraph (b)(9)(ii) of this section) of the maximum permitted start-to-discharge pressure setting of the device.
(iv) Safety-relief valves shall be so arranged that the possibility of tampering will be minimized. If the pressure setting adjustment is external, the relief valves shall be provided with means for sealing the adjustment.
(v) Shutoff valves shall not be installed between the safety-relief valves and the container; except, that a shutoff valve may be used where the arrangement of this valve is such as always to afford full required capacity flow through the relief valves.
(vi) Safety-relief valves shall have direct communication with the vapor space of the container.
(vii) Each container safety-relief valve used with systems covered by paragraphs (c), (f), (g), and (h) of this section shall be plainly and permanently marked with the symbol “NH3 ” or “AA”; with the pressure in pounds-per-square-inch gage at which the valve is set to start-to-discharge; with the actual rate of discharge of the valve at its full open position in cubic feet per minute of air at 60 °F. and atmospheric pressure; and with the manufacturer's name and catalog number. Example: “NH3 250-4050 Air” indicates that the valve is suitable for use on an anhydrous ammonia container, is set to start-to-discharge at a pressure of 250 p.s.i.g., and that its rate of discharge at full open position (subdivisions (ii) and (iii) of this subparagraph) is 4,050 cubic feet per minute of air.
(viii) The flow capacity of the relief valve shall not be restricted by any connection to it on either the upstream or downstream side.
(ix) A hydrostatic relief valve shall be installed between each pair of valves in the liquid ammonia piping or hose where liquid may be trapped so as to relieve into the atmosphere at a safe location.
(10) General.
(i) [Reserved]
(ii) Stationary storage installations must have at least two suitable gas masks in readily-accessible locations. Full-face masks with ammonia canisters that have been approved by NIOSH under 42 CFR part 84 are suitable for emergency action involving most anhydrous ammonia leaks, particularly leaks that occur outdoors. For respiratory protection in concentrated ammonia atmospheres, a self-contained breathing apparatus is required.
(iii) Stationary storage installations shall have an easily accessible shower or a 50-gallon drum of water.
(iv) Each vehicle transporting ammonia in bulk except farm applicator vehicles shall carry a container of at least 5 gallons of water and shall be equipped with a full face mask.
(11) Charging of containers. (i) The filling densities for containers that are not refrigerated shall not exceed the following:
Type of container Percent by weight Percent by volume
Aboveground-Uninsulated 56 82
Aboveground-Uninsulated 87.5
Aboveground-Insulated 57 83.5
Underground-Uninsulated 58 85
DOT—In accord with DOT regulations.
(ii) Aboveground uninsulated containers may be charged 87.5 percent by volume provided the temperature of the anhydrous ammonia being charged is determined to be not lower than 30 °F. or provided the charging of the container is stopped at the first indication of frost or ice formation on its outside surface and is not resumed until such frost or ice has disappeared.
(12) Transfer of liquids. (i) Anhydrous ammonia shall always be at a temperature suitable for the material of construction and the design of the receiving container.
(ii) The employer shall require the continuous presence of an attendant in the vicinity of the operation during such time as ammonia is being transferred.
(iii) Containers shall be charged or used only upon authorization of the owner.
(iv) Containers shall be gaged and charged only in the open atmosphere or in buildings or areas thereof provided for that purpose.
(v) Pumps used for transferring ammonia shall be those manufactured for that purpose.
(a) Pumps shall be designed for at least 250 p.s.i.g. working pressure.
(b) Positive displacement pumps shall have, installed off the discharged port, a constant differential relief valve discharging into the suction port of the pump through a line of sufficient size to carry the full capacity of the pump at relief valve setting, which setting and installation shall be according to the pump manufacturer's recommendations.
(c) On the discharge side of the pump, before the relief valve line, there shall be installed a pressure gage graduated from 0 to 400 p.s.i.
(d) Plant piping shall contain shutoff valves located as close as practical to pump connections.
(vi) Compressors used for transferring or refrigerating ammonia shall be recommended for ammonia service by the manufacturer.
(a) Compressors shall be designed for at least 250 p.s.i.g. working pressure.
(b) Plant piping shall contain shutoff valves located as close as practical to compressor connections.
(c) A relief valve large enough to discharge the full capacity of the compressor shall be connected to the discharge before any shutoff valve.
(d) Compressors shall have pressure gages at suction and discharge graduated to at least one and one-half times the maximum pressure that can be developed.
(e) Adequate means, such as drainable liquid trap, shall be provided on the compressor suction to minimize the entry of liquid into the compressor.
(vii) Loading and unloading systems shall be protected by suitable devices to prevent emptying of the storage container or the container being loaded or unloaded in the event of severance of the hose. Backflow check valves or properly sized excess flow valves shall be installed where necessary to provide such protection. In the event that such valves are not practical, remotely operated shutoff valves may be installed.
(13) Tank car unloading points and operations. (i) Provisions for unloading tank cars shall conform to the applicable recommendations contained in the DOT regulations.
(ii) The employer shall insure that unloading operations are performed by reliable persons properly instructed and given the authority to monitor careful compliance with all applicable procedures.
(iii) Caution signs shall be so placed on the track or car as to give necessary warning to persons approaching the car from open end or ends of siding and shall be left up until after the car is unloaded and disconnected from discharge connections. Signs shall be of metal or other suitable material, at least 12 by 15 inches in size and bear the words “STOP—Tank Car Connected” or “STOP—Men at Work” the word, “STOP,” being in letters at least 4 inches high and the other words in letters at least 2 inches high.
(iv) The track of a tank car siding shall be substantially level.
(v) Brakes shall be set and wheels blocked on all cars being unloaded.
(14) Liquid-level gaging device. (i) Each container except those filled by weight shall be equipped with an approved liquid-level gaging device. A thermometer well shall be provided in all containers not utilizing a fixed liquid-level gaging device.
(ii) All gaging devices shall be arranged so that the maximum liquid level to which the container is filled is readily determined.
(iii) Gaging devices that require bleeding of the product to the atmosphere such as the rotary tube, fixed tube, and slip tube devices shall be designed so that the maximum opening of the bleed valve is not larger than No. 54 drill size unless provided with an excess flow valve. (This requirement does not apply to farm vehicles used for the application of ammonia as covered in paragraph (h) of this section.)
(iv) Gaging devices shall have a design pressure equal to or greater than the design pressure of the container on which they are installed.
(v) Fixed tube liquid-level gages shall be designed and installed to indicate that level at which the container is filled to 85 percent of its water capacity in gallons.
(vi) Gage glasses of the columnar type shall be restricted to stationary storage installations. They shall be equipped with shutoff valves having metallic handwheels, with excess-flow valves, and with extra heavy glass adequately protected with a metal housing applied by the gage manufacturer. They shall be shielded against the direct rays of the sun.
(15) [Reserved]
(16) Electrical equipment and wiring. (i) Electrical equipment and wiring for use in ammonia installations shall be general purpose or weather resistant as appropriate.
(ii) Electrical systems shall be installed and maintained in accordance with subpart S of this part.
(c) Systems utilizing stationary, nonrefrigerated storage containers. This paragraph applies to stationary, nonrefrigerated storage installations utilizing containers other than those covered in paragraph (e) of this section. Paragraph (b) of this section applies to this paragraph unless otherwise noted.
(1) Design pressure and construction of containers. The minimum design pressure for nonrefrigerated containers shall be 250 p.s.i.g.
(2) Container valves and accessories, filling and discharge connections. (i) Each filling connection shall be provided with combination back-pressure check valve and excess-flow valve; one double or two single back-pressure check valves; or a positive shutoff valve in conjunction with either an internal back-pressure check valve or an internal excess flow valve.
(ii) All liquid and vapor connections to containers except filling pipes, safety relief connections, and liquid-level gaging and pressure gage connections provided with orifices not larger than No. 54 drill size as required in paragraphs (b)(6) (iv) and (v) of this section shall be equipped with excess-flow valves.
(iii) Each storage container shall be provided with a pressure gage graduated from 0 to 400 p.s.i. Gages shall be designated for use in ammonia service.
(iv) All containers shall be equipped with vapor return valves.
(3) Safety-relief devices.