IMO: Interim Guidelines for Safe Use of Liquefied Petroleum Gas (LPG) Cargo as Fuel

Eda Zenic -

The Interim Guidelines for the Use of Liquefied Petroleum Gas (LPG) Cargo as Fuel were approved on 1 July 2024 by the Maritime Safety Committee (MSC) at its 108th session, held from 15 to 24 May 2024.

This approval followed a proposal from the Sub-Committee on Carriage of Cargoes and Containers at its ninth session, held from 20 to 29 September 2023.

The guidelines aim to provide interim guidance on the safe use of LPG cargo as fuel, supplementing the International Code for the Construction and Equipment of Ships Carrying Liquefied Gases in Bulk (IGC Code).

Main Objectives

  1. Safety Assurance: Ensure the safe use of LPG as fuel, comparable to the safety level provided for LNG.
  2. Guidance Provision: Offer specific guidance until permanent provisions are incorporated into the IGC Code.
  3. Industry Response: Address the urgent need for guidelines in the shipping industry.

Scope and Application

These guidelines apply to gas carriers using LPG as fuel, complying with the IGC Code. LPG is composed of propane (C3H8), butane (C4H10), or a propane-butane mixture, with possible minor hydrocarbons and impurities.

Design and Operational Requirements

Safety Goals and Functional Requirements:

  1. Prevent fuel leakage into spaces containing fuel consumers.
  2. Ensure effective ventilation and detection of LPG leaks, considering LPG characteristics.
  3. Ensure fuel composition is suitable for the normal operation of fuel consumers.
  4. Prevent unintended phase changes in fuel supply systems.

Fuel Supply Systems:

  1. Designed to avoid lowering fuel temperature to the dew point when supplied as gas.
  2. Prevent lowering of fuel pressure to vapour pressure when supplied as liquid.
  3. Vent, purging, and bleed lines should not release LPG liquid into the atmosphere.

Supplementary Guidance to Chapter 16 of IGC Code:

  1. LPG can be used in machinery spaces for specific systems like boilers and engines.
  2. Fuel supply systems must comply with relevant IGC Code requirements.
  3. Ensure no external visible flame from LPG fuel consumers and maintain exhaust temperatures below the auto-ignition temperature.
  4. Provide for inerting and venting of gas fuel piping systems to a safe location.
  5. Implement automatic double block and bleed valves for fuel isolation in supply and return piping.

Risk Assessment:

  1. Conduct a risk assessment for LPG fuel arrangements to document equivalent safety levels to LNG.
  2. Address hazards associated with the arrangement, operation, and maintenance of the fuel system.
  3. Consider consequences of fuel leakage and potential accumulation in other spaces.

Machinery Spaces:

  1. Single failures should not lead to gas release in machinery spaces.
  2. Double wall or ducted piping should be used, with continuous outer boundaries.
  3. Air inlets of annular spaces should be located outside machinery spaces.

Fuel Supply Management:

  1. Systems supplying LPG liquid should vent and purge to a fuel tank or gas-liquid separator.
  2. Ventilation inlets for double wall piping should be in non-hazardous areas.
  3. Prevent condensation in fuel supply systems.

Ventilation and Gas Detection:

  1. Ventilation capacity should consider LPG's density and explosion limits.
  2. Numerical calculations (e.g., CFD analysis) should support ventilation designs.
  3. Gas detection heads should be strategically placed where LPG may accumulate.

Combustion Equipment:

  1. Continuous monitoring of gas fuel consumer exhaust temperatures.
  2. Gas turbines should have gas-tight enclosures unless compliant with specific IGC Code requirements.
  3. Evaluate consequences of gas leakage based on risk assessments.

Additional Provisions

  • Ensure inert gas purging interface and means to prevent vapour condensation in fuel supply systems.
  • Ventilation outlets for double wall piping should be located in cargo areas.
  • Consider heating for gas-liquid separators in cold operating areas.
  • Provide means to prevent the release of LPG liquid to the atmosphere during draining processes.

Review and Amendments

The guidelines will be reviewed and amended based on experience and evolving circumstances to ensure ongoing safety and relevance.