# Compressed gases in cargo tanks and portable tanks.

- **operation:** document
- **citation:** 49 CFR 173.315
- **title:** Compressed gases in cargo tanks and portable tanks.
- **source type:** regulation
- **agency:** Pipeline and Hazardous Materials Safety Administration
- **status:** current
- **official:** true
- **published on:** Not available
- **effective on:** 2026-08-18
- **summary:** (a) Liquefied compressed gases that are transported in UN portable tanks, DOT specification portable tanks, or cargo tanks must be prepared in accordance with this section, § 173.32, § 173.33 and subpart E or subpart G of part 180 of this subchapter, as applicable. For cryogenic liquid in cargo tank
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- **source url:** https://www.ecfr.gov/on/2026-08-18/title-49/section-173.315
**body:**

(a) Liquefied compressed gases that are transported in UN portable tanks, DOT specification portable tanks, or cargo tanks must be prepared in accordance with this section, § 173.32, § 173.33 and subpart E or subpart G of part 180 of this subchapter, as applicable. For cryogenic liquid in cargo tanks, see § 173.318. For marking requirements for portable tanks and cargo tanks, see § 172.326 and § 172.328 of this subchapter, as applicable.

(1) UN portable tanks: UN portable tanks must be loaded and offered for transportation in accordance with portable tank provision T50 in § 172.102 of this subchapter.

(2) Cargo tanks and DOT specification portable tanks: Cargo tanks and DOT specification portable tanks must be loaded and offered for transportation in accordance with the following table (for purposes of the following table, a column entry with “do” indicates “same as above”):

Kind of gas Maximum permitted filling density Specification container required Percent by weight (see Note 1) Percent by volume (see par. (f) of this section) Type (see Note 2) Minimum design pressure (psig) Ammonia, anhydrous or Ammonia solutions with greater than 50 percent ammonia (see Notes 14 and 17) 56 82, See Note 5 DOT-51, MC-330, MC-331; See Notes 12, 17 and 27 265; See Note 17. Ammonia solutions with more than 35 percent but not more than 50 percent ammonia See par. (c) of this section See Note 7 DOT-51, MC-330, MC-331; see Note 12 100; See par. (c) of this section. Bromotrifluoromethane (R-13B1 or H-1301); (See Note 9) 133 See Note 7 DOT-51, MC-330, MC-331 365. Butadiene, stabilized See par. (b) of this section See par. (b) of this section DOT-51, MC-330, MC-331 100. Carbon dioxide, refrigerated liquid See par. (c)(1) of this section 95......do 200; see Note 3. Chlorine 125 See Note 7 DOT-51, MC-330, MC-331 225; See Notes 4 and 8. Chlorodifluoroethane (R-142b) (1-Chloro 1,1-difluoroethane); (See Note 9) 100 See Note 7 DOT-51, MC-330, MC-331 100. Chlorodifluoromethane (R-22); (See Note 9) 105 See Note 7 DOT-51, MC-330, MC-331 250. Chloropentafluoroethane (R-115); (See Note 9) See par. (c) of this section See Note 7 DOT-51, MC-330, MC-331 See par. (c) of this section. Chlorotrifluoromethane (R-13); (See Note 9) See par. (c) of this section See Note 7 DOT-51, MC-330, MC-331 See par. (c) of this section. Dichlorodifluoromethane (R-12); (See Note 9) 119 See Note 7 DOT-51, MC-330, MC-331 150. Difluoroethane (R-152a); (See Note 9) 79 See Note 7 DOT-51, MC-330, MC-331 150. Dimethyl ether (see Note 16) 59......do......do 200. Dimethylamine, anhydrous 59 See Note 7 DOT-51, MC-330, MC-331 150. Division 2.1, materials not specifically provided for in this table See par. (c) of this section See Note 7 DOT-51, MC-330, MC-331 See Note 18. Division 2.2, materials not specifically provided for in this table See par. (c) of this section See Note 7 DOT-51, MC-330, MC-331 See Notes 19 and 28. Division 2.3, Hazard Zone A, materials not specifically provided for in this table See par. (c) of this section See Note 7 DOT-51, MC-330, MC-331; See Note 23 See Note 20. Division 2.3, Hazard Zone B, materials not specifically provided for in this table See par. (c) of this section See Note 7 DOT-51, MC-330, MC-331; See Note 23 See Note 20. Division 2.3, Hazard Zone C, materials not specifically provided for in this table See par. (c) of this section See Note 7 DOT-51, MC-330, MC-331; See Note 24 See Note 21. Division 2.3, Hazard Zone D, materials not specifically provided for in this table See par. (c) of this section See Note 7 DOT-51, MC-330, MC-331; See Note 25 See Note 22. Ethane, refrigerated liquid See par. (c) of this section MC-331, MC-338 100; see Note 11. Ethane-propane mixture, refrigerated liquid See par. (c) of this section MC-331, MC-338 275; see Note 11. Hexafluoropropylene 110 See Note 7 DOT-51, MC-330, MC-331 250. Hydrogen chloride, refrigerated liquid 103.0 See Note 7 MC-331, MC-338 100; see Note 11. 91.6......do......do 300; see Note 11. 86.7......do......do 450; see Note 11. Liquefied petroleum gas (see Note 15) See par. (b) of this section See par. (b) of this section DOT-51, MC-330, MC-331; See Note 26 See par. (c) of this section. Methylacetylene-propadiene, stabilized (see Note 13) 53 90 DOT 51, MC 330, MC 331 200. Methylamine, anhydrous 60 See Note 7 DOT-51, MC-330, MC-331. Methyl chloride 84 88.5......do 150. Methyl chloride (optional portable tank 2,000 pounds water capacity, fusible plug)......do See Note 6 DOT-51 225. Methyl mercaptan 80 90 DOT-51, MC-330, MC-331; See Note 23 100. Nitrous oxide, refrigerated liquid See par. (c)(1) of this section 95 DOT-51, MC-330, MC-331 200; See Note 3. Refrigerant gas, n.o.s. or Dispersant gas, n.o.s. (See Note 9) See par. (c) of this section See Note 7 DOT-51, MC-330, MC-331 See par. (c) of this section. Sulfur dioxide (tanks not over 1,200 gallons water capacity) 125 87.5 DOT-51, MC-330, MC-331; See Note 24 150; See Note 4. Sulfur dioxide (tanks over 1,200 gallons water capacity) 125 87.5 DOT-51, MC-330, MC-331; See Note 24 125; See Note 4. Sulfur dioxide (optional portable tank 1,000-2,000 pounds water capacity, fusible plug) 125 See Note 6 DOT-51; See Note 24 225. Trimethylamine, anhydrous 57 See Note 7 DOT-51, MC-330, MC-331 150. Vinyl chloride 84 (see Note 13) See Note 7 MC-330, MC-331 150. Vinyl fluoride, stabilized 66......do......do 250; see Note 11. Vinyl methyl ether 68 See Notes 7 and 13......do 100. Note 1: Maximum filling density for liquefied gases is hereby defined as the percent ratio of the weight of gas in the tank to the weight of water that the tank will hold. For determining the water capacity of the tank in pounds, the weight of a gallon (231 cubic inches) of water at 60 °F. in air shall be 8.32828 pounds. Note 2: See § 173.32 for authority to use other portable tanks and for manifolding cargo tanks, see paragraph (q) of this section. Specifications MC 330 cargo tanks may be painted as specified for MC 331 cargo tanks. Note 3: If cargo tanks and portable tank containers for carbon dioxide, refrigerated liquid, and nitrous oxide, refrigerated liquid, are designed to conform to the requirements in Section VIII of the ASME Code for low temperature operation (IBR, see § 171.7 of this subchapter), the design pressure may be reduced to 100 psig or the controlled pressure, whichever is greater. Note 4: Material must be steel. Packagings must have a corrosion allowance of 20 percent or 0.10 inch, whichever is less, added to the metal thickness. The minimum wall thickness for chlorine packagings is 0.300 inch for stainless steel or 0.625 inch for carbon steel, including corrosion allowance. Note 5: Unlagged cargo tanks and portable tank containers for liquid anhydrous ammonia may be filled to 87.5 percent by volume provided the temperature of the anhydrous ammonia being loaded into such tanks is determined to be not lower than 30 °F. or provided the filling of such tanks is stopped at the first indication of frost or ice formation on the outside surface of the tank and is not resumed until such frost or ice has disappeared. Note 6: Tanks equipped with fusible plugs must be filled by weight. Note 7: Tanks must be filled by weight. Note 8: Chlorine packagings may be shipped only if the contents are to be unloaded at one unloading point. Note 9: This gas may be transported in authorized cargo tanks and portable tanks marked “dispersant gas,” or “refrigerant gas.” Note 10: [Reserved] Note 11: MC-330, MC-331 and MC-338 cargo tanks must be insulated. Cargo tanks must meet all the following requirements. Each tank must have a design service temperature of minus 100 °F., or no warmer than the boiling point at one atmosphere of the hazardous material to be shipped therein, whichever is colder, and must conform to the low-temperature requirements in Section VIII of the ASME Code. When the normal travel time is 24 hours or less, the tank's holding time as loaded must be at least twice the normal travel time. When the normal travel time exceeds 24 hours, the tank's holding time as loaded must be at least 24 hours greater than the normal travel time. The holding time is the elapsed time from loading until venting occurs under equilibrium conditions. The cargo tank must have an outer jacket made of steel when the cargo tank is used to transport a flammable gas. Note 12: No aluminum, copper, silver, zinc or an alloy of any of these metals shall be used in packaging construction where it comes into contact with the lading. Note 13: All parts of valves and safety devices in contact with contents of tank must be of a metal or other material suitably treated if necessary, which will not cause formation of any acetylides. Note 14: Specifications MC 330 and MC 331 cargo tanks constructed of other than quenched and tempered steel “(NQT)” are authorized for all grades of anhydrous ammonia. Specifications MC 330 and MC 331 cargo tanks constructed of quenched and tempered steel “(QT)” (see marking requirements of § 172.328(c) of this subchapter) are authorized for anhydrous ammonia having a minimum water content of 0.2 percent by weight. Any tank being placed in anhydrous ammonia service or a tank which has been in other service or has been opened for inspection, test, or repair, must be cleaned of the previous product and must be purged of air before loading. See § 172.203(h) of this subchapter for special shipping paper requirements. Note 15: Specifications MC 330 and MC 331 cargo tanks constructed of other than quenched and tempered steel (NQT) are authorized for all grades of liquefied petroleum gases. Only grades of liquefied petroleum gases determined to be “noncorrosive” are authorized in Specification MC 330 and MC 331 cargo tanks constructed of quenched and tempered steel (QT). “Noncorrosive” means the corrosiveness of the gas does not exceed the limitations for classification 1 of the ASTM Copper Strip Classifications when tested in accordance with ASTM D 1838, “Copper Strip Corrosion by Liquefied Petroleum (LP) Gases” (IBR, see § 171.7 of this subchapter). (For (QT) and (NQT) marking requirements, see § 172.328(c) of this subchapter. For special shipping paper requirements, see § 172.203(h) of this subchapter.) Note 16: Openings, inlets, and outlets on MC 330 and MC 331 cargo tanks must conform to § 178.337-8(a) of this subchapter. MC 330 and MC 331 cargo tanks must be equipped with emergency discharge control equipment as specified in § 178.337-11(a) of this subchapter. Note 17: A Specification MC-330 or MC-331 cargo tank or a nonspecification cargo tank meeting, and marked in conformance with, the edition of the ASME Code in effect when it was fabricated, may be used for the transportation of anhydrous ammonia if it: (1) Has a minimum design pressure not lower than 250 psig; (2) Was manufactured in conformance with the ASME Code prior to January 1, 1981, according to its ASME name plate and manufacturer's data report; (3) Is painted white or aluminum; (4) Complies with Note 12 of this paragraph; (5) Has been inspected and tested in accordance with subpart E of part 180 of this subchapter as specified for MC 331 cargo tanks. (6) Was used to transport anhydrous ammonia prior to January 1, 1981; (7) Is operated exclusively in intrastate commerce (including its operation by a motor carrier otherwise engaged in interstate commerce) in a state where its operation was permitted by the laws of that State (not including the incorporation of this subchapter) prior to January 1, 1981; and (8) Is operated in conformance with all other requirements of this subchapter. Note 18: The minimum packaging design pressure must not be less than the vapor pressure at the reference temperature of the lading plus one percent or 173.4 kPa (25 psig), whichever is less. Note 19: The minimum packaging design pressure must not be less than the vapor pressure at the reference temperature of the lading. Note 20: The minimum packaging design pressure must not be less than 1.5 times the vapor pressure of the lading at 46 °C (115 °F). Note 21: The minimum packaging design pressure must not be less than 1.3 times the vapor pressure of the lading at 46 °C (115 °F). Note 22: The minimum packaging design pressure must not be less than 1.1 times the vapor pressure of the lading at 46 °C (115 °F). Note 23: Packagings must be made of stainless steel except that steel other than stainless steel may be used in accordance with the provisions of § 173.24b(b) of this part. Thickness of stainless steel for shell and heads must be the greater of 7.62 mm (0.300 inch) or the thickness required for the packaging at its minimum design pressure. Note 24: Packagings must be made of stainless steel except that steel other than stainless steel may be used in accordance with the provisions of § 173.24b(b) of this part. Thickness of stainless steel for shell and heads must be the greater of 6.35 mm (0.250 inch) or the thickness required for the packaging at its minimum design pressure. For sulphur dioxide, this Note does not apply until October 1, 1994. Note 25: Packagings must be made of stainless steel except that steel other than stainless steel may be used in accordance with the provisions of § 173.24b(b) of this part. Thickness for shell and heads must be as calculated for the packaging at its minimum design pressure. Note 26: Non-specification cargo tanks may be used for the transportation of liquefied petroleum gas, subject to the conditions prescribed in paragraph (k) of this section. Note 27: Non-specification cargo tanks may be used for transportation of Ammonia, anhydrous and ammonia solutions with greater than 50% ammonia, subject to the conditions prescribed in paragraph (m) of this section. Note 28: For UN1080, Sulfur hexafluoride, a non-specification cargo tank that otherwise conforms to a DOT Specification MC 331 cargo tank except for design pressure and capacity is authorized. Design pressure may not exceed 600 psig. The water capacity range for each tank is 15 to 500 gallons.

(b) Maximum permitted filling densities for cargo and portable tank containers for transportation of butadiene, stabilized, and liquefied petroleum gas are as follows:

Maximum specific gravity of the liquid material at 60 °F. Maximum permitted filling density in percent of the water-weight capacity of the tanks (percent) See Note 1 1200 gallons or less Over 1200 gallons 0.473 to 0.480 38 41 0.481 to 0.488 39 42 0.489 to 0.495 40 43 0.496 to 0.503 41 44 0.504 to 0.510 42 45 0.511 to 0.519 43 46 0.520 to 0.527 44 47 0.528 to 0.536 45 48 0.537 to 0.544 46 49 0.545 to 0.552 47 50 0.553 to 0.560 48 51 0.561 to 0.568 49 52 0.569 to 0.576 50 53 0.577 to 0.584 51 54 0.585 to 0.592 52 55 0.593 to 0.600 53 56 0.601 to 0.608 54 57 0.609 to 0.617 55 58 0.618 to 0.626 56 59 0.627 and over 57 60 Note 1: Filling is permitted by volume provided the same filling density is used as permitted by weight, except when using fixed length dip tube or other fixed maximum liquid level indicators (paragraph (f) of this section), in which case the maximum permitted filling density shall not exceed 97 percent of the maximum permitted filling density by weight contained in the table.

(1) Odorization. All liquefied petroleum gas must be odorized as required in this paragraph to indicate positively, by a distinctive odor, the presence of gas down to a concentration in air of not over one-fifth the lower limit of combustibility; however, odorization is not required if it is harmful in the use or further processing of the liquefied petroleum gas or if it will serve no useful purpose as a warning agent in such use or further processing.

(i) The lower limits of combustibility of the more commonly used liquefied petroleum gases are: Propane, 2.15 percent; butane, 1.55 percent. These figures represent volumetric percentages of gas-air mixtures in each case.

(ii) The use of 1.0 pound of ethyl mercaptan per 10,000 gallons of liquefied petroleum gas is considered sufficient to meet the requirements of this paragraph (b). Use of any other odorant is not prohibited so long as there is enough to meet the requirements of this paragraph.

(2) Odorant fade. For cargo tanks or portable tanks being transported from a refinery, gas plant or pipeline terminal and in addition to paragraph (b)(1)(i) of this section, the offeror must ensure that enough odorant will remain in the cargo tank or portable tank during the course of transportation. The offeror must have procedures in place to:

(i) Ensure quantitative testing methods are used to measure the amount of odorant in the liquefied petroleum gas;

(ii) Ensure that, when the odorization of liquefied petroleum gas is manually injected, the required amount of odorant is being added;

(iii) Ensure that, when odorization of liquefied petroleum gas is automatically injected, equipment calibration checks are conducted to ensure the required amount of odorant is consistently added;

(iv) Ensure that quality control measures are in place to make sure that persons who receive cargo tanks or portable tanks that have been subjected to any condition that could lead to corrosion of the packaging or receive new or recently cleaned cargo tanks or portable tanks are notified of this information and that a person filling these packagings implement quality control measures to ensure that potential odorant fade is addressed;

(v) Inspect a cargo tank or portable tank for signs of oxidation or corrosion; and

(vi) Take corrective action needed to ensure enough odorant remains in the cargo tank or portable tank during the course of transportation, such as increasing the amount of odorant added to the liquefied petroleum gas.

(c) Except as otherwise provided, the loading of a liquefied gas into a cargo tank or portable tank shall be determined by weight or by a suitable liquid level gauging device. The vapor pressure (psig) at 115 °F. must not exceed the design pressure of the cargo tank or portable tank container. The outage and filling limits for liquefied gases must be as prescribed in § 173.24b of this part, except that this requirement does not apply to:

(1) A tank containing carbon dioxide, refrigerated liquid or nitrous oxide, refrigerated liquid. Such tank is required to be equipped with suitable pressure control valves and may not be filled to a level exceeding 95 percent of the volumetric capacity of the tank.

(2) A tank containing ethane, refrigerated liquid; ethane-propane mixture, refrigerated liquid; or hydrogen chloride, refrigerated liquid. Such tank must be filled to allow at least two percent outage below the inlet of the pressure relief valve or pressure control valve under conditions of incipient opening, with the tank in a level attitude.

(d) If the loading of cargo tanks and portable tank containers with liquefied gases is to be determined by weight, the gross weight shall be checked after the filling line is disconnected in each instance. The gross weight shall be calculated from the tank capacity and tare weight set forth on the metal plate required by the specification, and the maximum filling density permitted for the material being loaded into the tank as set forth in the table, paragraph (a) of this section.

(e) If the loading of cargo tanks and portable tank containers with liquefied gases is to be determined by adjustable liquid level device, each tank and each compartment thereof shall have a thermometer well, so that the internal liquid temperature can easily be determined, and the amount of liquid in the tank shall be corrected to a 60 °F. basis. Liquid levels shall not exceed a level corresponding to the maximum filling density permitted for the material being loaded into the tank as set forth in the table in paragraph (a) of this section.

(f) When the loading of cargo tanks and portable tank containers with liquefied gases is determined only by fixed length dip tube or other fixed maximum liquid level indicator, the device shall be arranged to function at a level not to exceed the maximum permitted volume prescribed by the table, paragraph (a) of this section. Loading shall be stopped when the device functions.

(g) Containers, the liquid level of which has been determined by means of a fixed length dip tube gauging device, shall not be acceptable for stowage as cargo on vessels in commerce subject to the jurisdiction of the United States Coast Guard. Nothing contained in this section shall be so construed as to prohibit the transportation on car floats or car ferries of motor vehicles laden with containers nor cargo tanks the liquid level of either of which has been determined by means of fixed length dip tube devices.

(h) Each cargo tank and portable tank, except a tank filled by weight, must be equipped with one or more of the gauging devices described in the following table which indicate accurately the maximum permitted liquid level (for purposes of the following table, a column entry with “do” indicates “same as above”). Additional gauging devices may be installed but may not be used as primary controls for filling of cargo tanks and portable tanks. Gauge glasses are not permitted on any cargo tank or portable tank. Primary gauging devices used on cargo tanks of less than 3500 gallons water capacity are exempt from the longitudinal location requirements specified in paragraphs (h)(2) and (3) of this section provided: The tank length does not exceed three times the tank diameter; and the cargo tank is unloaded within 24 hours after each filling of the tank.

Kind of gas Gaging device permitted for filling purposes Anhydrous ammonia Rotary tube; adjustable slip tube; fixed length dip tube. Anhydrous dimethylamine None. Anhydrous monomethylamine Do. Anhydrous trimethylamine Do. Aqua ammonia solution containing anhydrous ammonia Rotary tube; adjustable slip tube; fixed length dip tube. Butadiene, stabilized Do. Carbon dioxide, refrigerated liquid Do. Chlorine None. Dichlorodifluoromethane Do. Difluoroethane Do. Difluoromonochloroethane Do. Dimethyl ether Do. Ethane, refrigerated liquid Rotary tube; adjustable slip tube; fixed length dip tube. Ethane-propane mixture, refrigerated liquid Do. Hexafluoropropylene None. Hydrogen chloride, refrigerated liquid Do. Liquefied petroleum gases Rotary tube; adjustable slip tube; fixed length dip tube. Methyl chloride Fixed length dip tube. Methyl mercaptan Rotary tube; adjustable slip tube; fixed length dip tube. Monochlorodifluoromethane None. Nitrous oxide, refrigerated liquid Rotary tube; adjustable slip tube; fixed length dip tube. Methylacetylenepropadiene, stabilized Do. Refrigerant gas, n.o.s. or Dispersant gas, n.o.s None. Sulfur dioxide Fixed length dip tube. Vinyl chloride None. Vinyl fluoride, inhibited Do.

(1) The design pressure of the liquid level gauging devices shall be at least equal to the design pressure of the tank.

(2) If the primary gauging device is adjustable, it must be capable of adjustment so that the end of the tube will be in the location specified in paragraph (h)(3) of this section for at least one of the ladings to be transported, at the filling level corresponding to an average loading temperature. Exterior means must be provided to indicate this adjustment. The gauging device must be legibly and permanently marked in increments not exceeding 20 Fahrenheit degrees (or not exceeding 25 p.s.i.g. on tanks for carbon dioxide, refrigerated liquid or nitrous oxide, refrigerated liquid), to indicate the maximum levels to which the tank may be filled with liquid at temperatures above 20 °F. However, if it is not practicable to so mark the gauging device, this information must be legibly and permanently marked on a plate affixed to the tank adjacent to the gauging device.

(3) A dip tube gauging device consists of a pipe or tube with a valve at its outer end with its intake limited by an orifice not larger than 0.060 inch in diameter. If a fixed length dip tube is used, the intake must be located midway of the tank both longitudinally and laterally and at maximum permitted filling level. In tanks for liquefied petroleum gases, the intake must be located at the level reached by the lading when the tank is loaded to maximum filling density at 40 °F.

(4) Except on a tank used exclusively for the transportation of carbon dioxide, refrigerated liquid or nitrous oxide, refrigerated liquid, each opening for a pressure gauge must be restricted at or inside the tank by an orifice no larger than 0.060 inch in diameter. For carbon dioxide, refrigerated liquid or nitrous oxide, refrigerated liquid service, the pressure gauge need only be used during the filling operation.

(i) Each tank must be provided with one or more pressure relief devices which, unless otherwise specified in this part, must be of the spring-loaded type. Each valve must be arranged to discharge upward and unobstructed to the outside of the protective housing to prevent any impingement of escaping gas upon the tank. For each chlorine tank the protective housing must be in compliance with the requirements set forth in the applicable specification.

(1) The safety relief valves on each tank must meet the following conditions:

(i) The total relieving capacity, as determined by the flow formulas contained in Section 5 of CGA S-1.2 (IBR, see § 171.7 of this subchapter), must be sufficient to prevent a maximum pressure in the tank of more than 120 percent of the design pressure;

(ii) The flow capacity rating, testing and marking must be in accordance with Sections 5, 6 and 7 of CGA Pamphlet S-1.2.

(iii) For an insulated tank, the required relieving capacity of the relief devices must be the same as for an uninsulated tank, unless the insulation will remain in place and will be effective under fire conditions. In this case, except for UN portable tanks, each insulated tank must be covered by a sheet metal jacket of not less than 16 gauge thickness. For UN portable tanks where the relieving capacity of the valves has been reduced on the basis of the insulation system, the insulation system must remain effective at all temperatures less than 649 °C (1200.2 °F) and be jacketed with a material having a melting point of 700 °C (1292.0 °F) or greater.

(iv) An MC 330 cargo tank that has relief valves sized by Fetterly's formula dated November 27, 1928, may be continued in service.

(2) Each safety relief valve must be arranged to minimize the possibility of tampering. If the pressure setting or adjustment is external to the valve, the safety relief valve must be provided with means for sealing the adjustment and it must be sealed.

(3) Each safety relief valve on a portable tank, other than a UN portable tank, must be set to start-to-discharge at pressure no higher than 110% of the tank design pressure and no lower than the design pressure specified in paragraph (a) of this section for the gas transported. For UN portable tanks used for liquefied compressed gases and constructed in accordance with the requirements of § 178.276 of this subchapter, the pressure relief device(s) must conform to § 178.276(e) of this subchapter.

(4) Except for UN portable tanks, each safety relief valve must be plainly and permanently marked with the pressure in p.s.i.g. at which it is set to discharge, with the actual rate of discharge of the device in cubic feet per minute of the gas or of air at 60 °F (15.6 °C) and 14.7 p.s.i.a., and with the manufacturer's name or trade name and catalog number. The start-to-discharge valve marking must be visible after the valve is installed. The rated discharge capacity of the device must be determined at a pressure of 120% of the design pressure of the tank. For UN portable tanks, each pressure relief device must be clearly and permanently marked as specified in § 178.274(f)(1) of this subchapter.

(5) Each safety relief valve must have direct communication with the vapor space in the tank.

(6) Each connection to a safety relief valve must be of sufficient size to provide the required rate of discharge through the safety relief valve.

(7) [Reserved]

(8) Each pressure relief valve outlet must be provided with a protective device to prevent the entrance and accumulation of dirt and water. This device must not impede flow through the valve. Pressure relief devices must be designed to prevent the entry of foreign matter, the leakage of liquid and the development of any dangerous excess pressure.

(9) On tanks for carbon dioxide, refrigerated liquid or nitrous oxide, refrigerated liquid each safety relief device must be installed and located so that the cooling effect of the contents will not prevent the effective operation of the device. In addition to the required safety relief valves, these tanks may be equipped with one or more pressure controlling devices.

(10) Each tank for carbon dioxide, refrigerated liquid also may be equipped with one or more non-reclosing pressure relief devices set to function at a pressure not over two times nor less than 1.5 times the design pressure of the tank.

(11) Each portion of connected liquid piping or hose that can be closed at both ends must be provided with a safety relief valve without an intervening shut-off valve to prevent excessive hydrostatic pressure that could burst the piping or hose.

(12) Subject to conditions of paragraph (a) of this section for the methyl chloride and sulfur dioxide optional portable tanks, one or more fusible plugs examined by the Bureau of Explosives and approved by the Associate Administrator may be used on these tanks in place of safety relief valves of the spring-loaded type. The fusible plug or plugs must be in accordance with CGA Pamphlet S-1.2, to prevent a pressure rise in the tank of more than 120 percent of the design pressure. If the tank is over 30 inches long, each end must have the total specified safety discharge area.

(13) A pressure relief device on a chlorine cargo tank must conform to one of the drawings in Chlorine Institute, Inc. Pamphlet 49, “Recommended Practices for Handling Chlorine Bulk Highway Transports” (IBR, see § 171.7 of this subchapter).

(j) Consumer storage containers. (1) Storage containers for liquefied petroleum gas or propane charged to five percent of their capacity or less and intended for permanent installation on consumer premises may be shipped by private motor carrier under the following conditions:

(i) Each container must be constructed in compliance with the requirements in Section VIII of the ASME Code (IBR, see § 171.7 of this subchapter) and must be marked to indicate compliance in the manner specified by the respective Code. Containers built in compliance with earlier editions starting with 1943 are authorized.

(ii) Each container must be equipped with safety devices in compliance with the requirements for safety devices on containers as specified in NFPA 58, Liquefied Petroleum Gas Code (IBR, see § 171.7 of this subchapter).

(iii) The containers must be braced or otherwise secured on the vehicle to prevent relative motion while in transit. Valves or other fittings must be adequately protected against damage during transportation. (See § 177.834(a) of this subchapter).

(iv) Storage containers of less than 1,042 pounds water capacity (125 gallons) may be shipped when charged with liquefied petroleum gas in compliance with DOT filling density.

(2) Storage containers with a water capacity not exceeding 500 gallons charged with liquefied petroleum gas to more than five percent of their capacity and intended for permanent installation on consumer premises may be transported by private motor carrier one-way only from the consumer's premises to the container owner's nearest facility under the following conditions:

(i) Each container must be constructed in compliance with the requirements in Section VIII of the ASME Code and must be marked to indicate compliance in the manner specified by the respective Code.

(ii) Maximum permitted filling density may not exceed that specified in paragraph (b) of this section.

(iii) Prior to loading on a motor vehicle, the container must be inspected by a trained and qualified person for leaks, corroded or abraded areas, dents, distortions, weld defects, or other condition that may render the container unsafe for transportation. A record of the inspection must be legibly signed and dated by the person performing the inspection and retained by the container owner for two years. The signature on the inspection record represents a certification that the container has been inspected and has no defects that would render it unsafe for transportation under the HMR. The record of inspection must include the date of inspection, the inspector's contact information (such as a telephone number), the container's serial number and container size (water capacity), estimated amount of hazardous material, and the origin and destination of shipment.

(iv) Only one storage container may be transported on a motor vehicle.

(v) For loading on a motor vehicle, the container must be lifted by slings, which must be completely wrapped around the container. Lifting lugs may not be used. The slings must be rated to a weight sufficient to accommodate the container and its lading and shall comply with ASME B30.9 on slings used for lifting purposes, and must be visually inspected prior to each use. A sling showing evidence of tears, fraying, or other signs of excessive wear may not be used.

(vi) The storage container must be secured on a motor vehicle so that the container is completely within the envelope of the vehicle and does not extend beyond the vehicle frame.

(vii) The storage container must be placed on the vehicle in a manner, such as in a cradle, which ensures that no weight is placed on the supporting legs during transportation.

(viii) The storage container must be secured against shifting during transportation. Bracing must conform with the requirements of paragraph (j)(1)(iii) of this section and § 177.834(a) of this subchapter and with Section 6-5.2 of NFPA 58, Liquefied Petroleum Gas Code. Straps or chains used as tie-downs must be rated to exceed the maximum load to be transported and conform to the requirements in §§ 393.100 through 393.106 of this title.

(ix) Tow trailers used to transport storage containers in accordance with this paragraph (j)(2) must provide rear end protection that conforms to requirements in § 393.86 of this title.

(k) A nonspecification cargo tank meeting, and marked in conformance with, the edition of Section VIII of the ASME Code in effect when it was fabricated may be used for the transportation of liquefied petroleum gas provided it meets all of the following conditions:

(1) It must have a minimum design pressure no lower than 250 psig.

(2) It must have a capacity of 13,247.5 L (3,500 water gallons) or less.

(3) It must have been manufactured in conformance with Section VIII of the ASME Code prior to January 1, 1981, according to its ASME name plate and manufacturer's data report.

(4) It must conform to the applicable provisions of NFPA 58, except to the extent that provisions in NFPA 58 are inconsistent with requirements in parts 178 and 180 of this subchapter.

(5) It must be inspected, tested, and equipped in accordance with subpart E of part 180 of this subchapter as specified for MC 331 cargo tank motor vehicles.

(6) Except as provided in this paragraph (k), it must be operated exclusively in intrastate commerce, including its operation by a motor carrier otherwise engaged in interstate commerce, in a state where its operation was permitted by law (not including the incorporation of this subchapter) prior to January 1, 1981. A cargo tank motor vehicle operating under authority of this section may cross state lines to travel to and from a qualified assembly, repair, maintenance, or requalification facility. The cargo tank need not be cleaned and purged, but it may not contain liquefied petroleum gas in excess of five percent of the water capacity of the cargo tank. If the vehicle engine is supplied fuel from the cargo tank, enough fuel in excess of five percent of the cargo tank's water capacity may be carried for the trip to or from the facility.

(7) It must have been used to transport liquefied petroleum gas prior to January 1, 1981.

(8) It must be operated in conformance with all other requirements of this subchapter.

(l) Anhydrous ammonia must not be offered for transportation or transported in specification MC 330 and MC 331 cargo tanks constructed of quenched and tempered (“QT”) steel except as provided in this paragraph.

(1) The ammonia must have a minimum water content of 0.2 percent by weight. Any addition of water must be made using steam condensate, deionized, or distilled water.

(2) Except as otherwise provided in this paragraph, each person offering for transportation or transporting anhydrous ammonia shall perform a periodic analysis for prescribed water content in the ammonia. The analysis must be performed:

(i) From a sample of the ammonia in storage taken at least once every 7 days, or each time ammonia is added to the storage tanks, whichever is less frequent; or

(ii) At the time the cargo tanks are loaded, then a sample of the ammonia taken from at least one loaded cargo tank out of each 10 loads, or from one cargo tank every 24 hours, whichever is less frequent; or

(iii) At the same frequency as described in paragraph (l)(2)(ii) of this section, from a sample taken from the loading line to the cargo tank.

(3) If water is added at the time of loading:

(i) The sample for analysis must be taken from a point in the loading line between the water injection equipment and the cargo tank; and

(ii) Positive provisions must be made to assure water injection equipment is operating.

(4) If water injection equipment becomes inoperative, suitable corrective maintenance must be performed after which a sample from the first loaded cargo tank must be analyzed for prescribed water content.

(5) The analysis method for water content must be as prescribed in CGA G-2.2, “Tentative Standard Method for Determining Minimum of 0.2 percent water in Anhydrous Ammonia,” (IBR, see § 171.7 of this subchapter).

(6) Records indicating the results of the analysis taken, as required by this paragraph, must be retained for 2 years and must be open to inspection by a representative of the Department.

(7) Each person receiving anhydrous ammonia containing 0.2 per cent water by weight may offer for transportation or transport that ammonia without performing the prescribed analysis for water content provided:

(i) The ammonia received was certified as containing 0.2 percent water as prescribed in §§ 172.203(h)(l)(i) and 177.817(a) of this subchapter; and

(ii) The amount of water in the ammonia has not been reduced by any means.

(m) General. (1) A cargo tank that is commonly known as a nurse tank and considered an implement of husbandry transporting anhydrous ammonia and operated by a private motor carrier exclusively for agricultural purposes is excepted from the specification requirements of part 178 of this subchapter if it:

(i) Has a minimum design pressure of 250 psig, meets the requirements of Section VIII of the ASME Code (IBR, see § 171.7 of this subchapter), and is marked with a valid ASME plate.

(ii) Is equipped with pressure relief valves meeting the requirements of CGA Standard S-1.2 (IBR, see § 171.7 of this subchapter);

(iii) Is painted white or aluminum;

(iv) Has a capacity of 3,000 gallons or less;

(v) Is loaded to a filling density no greater than 56 percent;

(vi) Is securely mounted on a farm wagon or meets paragraph (m)(3) of this section; and

(vii) Is in conformance with the requirements of part 172 of this subchapter except that shipping papers are not required; and it need not be marked or placarded on one end if that end contains valves, fittings, regulators or gauges when those appurtenances prevent
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