---
kind: "section"
citation: "46 C.F.R. § 154.1735"
title: "46"
number: "154.1735"
heading: "Methyl acetylene-propadiene mixture."
url: "https://uscodex.org/cfr/46/154.1735"
---

# §154.1735. Methyl acetylene-propadiene mixture.

- (a) The composition of the methyl acetylene-propadiene mixture at loading must be within the following limits or specially approved by the Commandant (CG-OES):
  - (1) **One composition is—**
    - (i) Maximum methyl acetylene and propadiene molar ratio of 3 to 1;
    - (ii) Maximum combined concentration of methyl acetylene and propadiene of 65 mole percent;
    - (iii) Minimum combined concentration of propane, butane, and isobutane of 24 mole percent, of which at least one-third (on a molar basis) must be butanes and one-third propane; and
    - (iv) **Maximum combined concentration of propylene and butadiene of 10 mole percent.**
  - (2) **A second composition is—**
    - (i) Maximum methyl acetylene and propadiene combined concentration of 30 mole percent;
    - (ii) Maximum methyl acetylene concentration of 20 mole percent;
    - (iii) Maximum propadiene concentration of 20 mole percent;
    - (iv) Maximum propylene concentration of 45 mole percent;
    - (v) Maximum butadiene and butylenes combined concentration of 2 mole percent;
    - (vi) A minimum saturated C 4 hydrocarbon concentration of 4 mole percent; and
    - (vii) **A minimum propane concentration of 25 mole percent.**
- (b) A vessel carrying a methyl acetylene-propadiene mixture must have a refrigeration system without vapor compression or have a refrigeration system with the following features:
  - (1) A vapor compressor that does not raise the temperature and pressure of the vapor above 60 °C (140 °F) and 1.72 MPa gauge (250 psig) during its operation and that does not allow vapor to stagnate in the compressor while it continues to run.
  - (2) Discharge piping from each compressor stage or each cylinder in the same stage of a reciprocating compressor that has:
    - (i) Two temperature actuated shutdown switches set to operate at 60 °C (140 °F) or less;
    - (ii) A pressure actuated shutdown switch set to operate at 1.72 MPa gauge (250 psig) or less; and
    - (iii) A safety relief valve set to relieve at 1.77 MPa gauge (256 psig) or less.
  - (3) A relief valve that vents to a mast meeting [§ 154.805](/cfr/46/154.805.md) and that does not relieve into the compressor suction line.
  - (4) An alarm that sounds in the cargo control station and in the wheelhouse when any of the high pressure or high temperature switches under paragraphs [(b)(2)(i)](#b-2-i) and [(b)(2)(ii)](#b-2-ii) of this section operate.
- (c) A vessel carrying a methyl acetylene-propadiene mixture must have separate cargo piping, vent piping, and refrigeration equipment for methyl acetylene-propadiene that are segregated from other cargo piping, vent piping and refrigeration equipment on the vessel.

## Notes

### Amendments

[CGD 74-289, 44 FR 26009, May 3, 1979; 44 FR 59234, Oct. 15, 1979; CGD 82-063b, 48 FR 4782, Feb. 3, 1983]

### Authority

Authority: 46 U.S.C. 3703, 9101; Department of Homeland Security Delegation No. 0170.1.

### Source

Source: CGD 74-289, 44 FR 26009, May 3, 1979, unless otherwise noted.

### Amendments

[CGD 74-289, 44 FR 26009, May 3, 1979; 44 FR 59234, Oct. 15, 1979; CGD 82-063b, 48 FR 4782, Feb. 3, 1983]