###### Editorial Note on [Part 151](/current/title-46/part-151?toc=1)

#### Editorial Note:

Nomenclature changes to part 151 appear by USCG-2009-0702, [74 FR 49236](https://www.federalregister.gov/citation/74-FR-49236), Sept. 25, 2009, and USCG-2012-0832, [77 FR 59784](https://www.federalregister.gov/citation/77-FR-59784), Oct. 1, 2012.

###### Editorial Note on [Subpart 151.50 of Part 151](/current/title-46/part-151/subpart-151.50?toc=1)

#### Editorial Note:

Nomenclature changes to subpart 151.50 of part 151 appear by CGD-95-072, [60 FR 50465](https://www.federalregister.gov/citation/60-FR-50465), Sept. 29, 1995, and CGD-96-041, [61 FR 50732](https://www.federalregister.gov/citation/61-FR-50732), Sept. 27, 1996.

#### § 151.50-30 Compressed gases.

(a) All tank inlet and outlet connections, except safety relief valves, liquid level gauging devices, and pressure gauges shall be marked to designate whether they terminate in the vapor or liquid space. Labels, when used, shall be of corrosion-resistant materials and may be attached to valves.

(b) *Venting.*

(1) Except as provided in [paragraph (b)(2)](/on/2024-09-23/title-46/section-151.50-30#p-151.50-30(b)(2)) of this section each safety relief valve installed on a cargo tank shall be connected to a branch vent of a venting system which shall be constructed so that the discharge of gas will be directed vertically upward to a point at least 10 feet above the weatherdeck or the top of any tank or house located above the weatherdeck.

(2) Safety valves on cargo tanks in barges may be connected to individual or common risers which shall extend to a reasonable height above the deck. Where the escape of vapors from the venting system may interfere with towing operations, the installation shall be acceptable to the Commandant, and the arrangement shall be such as to minimize the hazard of escaping vapors. Arrangements specially provided for venting cargo tanks forming part of the hull on unmanned barges will be given special consideration by the Commandant.

(3) The capacity of branch vents or vent headers shall depend upon the number of cargo tanks connected to such branch or header as provided in Table [151.50-30(b)(3)](/on/2024-09-23/title-46/section-151.50-30#p-151.50-30(b)(3)).

Table [151.50-30](/on/2024-09-23/title-46/section-151.50-30)(b)(3)—Capacity of Branch Vents or Vent Headers

| *Number of cargo tanks* | *Percent of total valve discharge* |
| --- | --- |
| 1 or 2 | 100 |
| 3 | 90 |
| 4 | 80 |
| 5 | 70 |
| 6 or more | 60 |

(4) Return bends and restrictive pipe fittings are prohibited. Vents and headers shall be so installed as to minimize stresses on safety relief valves and their mounting nozzles.

(5) When vent discharge risers are installed, they shall be so located as to protect against physical damage and be fitted with loose raincaps.

(6) When vent discharge risers are installed and their installation in accordance with the provisions of this paragraph results in restrictions in the operation of the barge due to navigation clearances, the vents may be designed so as to be collapsible when passing under such low clearance obstacles.

(c) *Repairs involving welding or burning.*

(1) Repairs involving welding or burning shall not be undertaken on the cargo tanks or piping while cargo in either the liquid or vapor state is present therein.

(2) Repairs involving welding or burning on parts of the barge other than cargo tanks or piping may be undertaken provided positive pressure is maintained in the tanks or the tanks have been vented or washed internally.

(d) *Respiratory equipment.*

(1) At least one approved self-contained breathing apparatus shall be available in a readily accessible location off the barge at all times during the cargo transfer operations. This equipment shall not be considered to be part of the barge equipment, and the barge shall not be required to carry this equipment en route.

(2) The approved self-contained breathing apparatus, masks, and all respiratory protective devices shall be of types suitable for starting and operating at the temperatures encountered, and shall be maintained in good operating condition.

(3) Personnel involved in the cargo transfer operations shall be adequately trained in the use of the respiratory equipment.

(e) *Filling densities and container design pressure.* For compressed gases transported at or near ambient temperatures, the maximum filling densities and minimum design pressure of container as indicated in Table [151.50-30(e)](/on/2024-09-23/title-46/section-151.50-30#p-151.50-30(e)) shall apply. Deviations from the tabulated values shall be submitted to the Commandant for approval. Where cargo is to be carried at temperatures below ambient, the tank shall be designed in accordance with [§ 151.15-3(b)(3)](/on/2024-09-23/title-46/section-151.15-3#p-151.15-3(b)(3)) and the maximum amount of cargo shall be in accordance with [§ 151.45-6(b)](/on/2024-09-23/title-46/section-151.45-6#p-151.45-6(b)).

Table [151.50-30](/on/2024-09-23/title-46/section-151.50-30)(e)—Filling Densities and Container Design Pressures

| Kind of gas | Maximum permitted filling density (percent by weight, see [§ 151.03-21](/on/2024-09-23/title-46/section-151.03-21)) | | Minimum design pressure of tank (pounds per square inch gauge) | |
| --- | --- | --- | --- | --- |
| Uninsulated tanks | Insulated tanks | Uninsulated tanks | Insulated tanks |
| Ammonia, anhydrous | 57 | 58 | 250 | 215 |
| Chlorine | 125 | 125 | 300 | 300 |
| Dichlorodifluoromethane | 123 | 125 | 147 | 127 |
| Dimethylamine | 61 | 62 | 46 | 36 |
| Methyl chloride | 85 | 87 | 131 | 112 |
| Monochlorodi-fluoromethane | 110 | 113 | 243 | 211 |
| Vinyl chloride | 86 | 87 | 81 | 67 |

(f) The shell and head thickness of liquefied compressed cargo tanks shall not be less than five-sixteenths inch.

(g) The special requirements for ammonia (anhydrous) in [§ 151.50-32](/on/2024-09-23/title-46/section-151.50-32), for argon in [§ 151.50-36](/on/2024-09-23/title-46/section-151.50-36), for chlorine in [§ 151.50-31](/on/2024-09-23/title-46/section-151.50-31), for nitrogen in [§ 151.50-36](/on/2024-09-23/title-46/section-151.50-36), and for vinyl chloride in [§ 151.50-34](/on/2024-09-23/title-46/section-151.50-34) also apply to the carriage of those gases.

[CGFR 70-10, [35 FR 3714](https://www.federalregister.gov/citation/35-FR-3714), Feb. 25, 1970, as amended by CGD 88-100, [54 FR 40040](https://www.federalregister.gov/citation/54-FR-40040), Sept. 29, 1989]