Liquefied Petroleum Gas (LPG) is not a zero-carbon fuel today, but it offers a mature global supply chain, lower air-pollutant emissions, and relatively simple liquefaction and storage. If renewable LPG (rLPG), bio-LPG, renewable dimethyl ether (rDME), and onboard carbon capture mature over time, LPG could become an important transition option in shipping's energy transition.
The point of LPG is not that it is fully zero-carbon, but that it is available today, backed by mature supply chains, and has potential to extend toward lower-carbon fuels.
LPG is a gas at ambient temperature and pressure, but it liquefies under moderate pressure, so it does not require the cryogenic storage conditions associated with LNG.
LPG's near-term advantages come mainly from low sulphur content, a lower carbon-to-hydrogen ratio, and mature combustion technology, but it remains a hydrocarbon fuel.
Even when fossil-derived, LPG can immediately reduce SOx, PM, and some NOx emissions while also cutting COβ emissions to a certain extent. To meet IMO medium- and long-term GHG reduction goals and regional regulatory requirements, however, it will still need to be paired with solutions such as rLPG, rDME, or onboard carbon capture.
LPG vapour is heavier than air, one of the most important safety-design differences from methane-based fuels.
LPG vapour tends to flow downward and may accumulate in bilges, ducts, pipe tunnels, or other low enclosed spaces. Gas-detector placement and ventilation design therefore need particular attention in low-level areas.
A flammable cloud formed after a leak may ignite some distance from the release point, with the flame travelling back through the flammable mixture toward the source.
Rapid vaporisation of liquid LPG absorbs significant heat and can cause cold burns. Direct contact with deck or hull structures may also create local low-temperature embrittlement risk.
If LPG leaks onto water, it may form a liquid pool and continue to vaporise. Once ignited, the fire can produce intense heat radiation and burn rapidly, often stopping only after the released fuel is consumed.
High concentrations of LPG can displace oxygen in air and may have narcotic effects. Before entering enclosed spaces, ventilation, oxygen content, and flammable gas concentration must be verified.
Double-wall piping, secondary containment, hydrocarbon gas detection, ventilation, emergency shutdown systems, and safety-zone management are key defences in LPG fuel-system design and operation.
The regulatory logic is not identical for a gas carrier using its own cargo as fuel and a non-gas carrier using LPG as fuel.
| Use case | Main regulatory logic | Surveyor reading focus |
|---|---|---|
| Gas carrier carrying LPG cargo and using cargo as fuel | The IGC Code framework is typically used for the construction, equipment, and cargo-as-fuel arrangements of ships carrying liquefied gases in bulk. | Check whether the design boundaries for the cargo containment system, fuel supply system, machinery safety, and class notation are consistent. |
| Non-gas carrier using LPG as fuel | The IGF Code low-flashpoint fuel safety framework is typically used as the basis, together with the IMO interim guidelines for LPG fuel. | Focus on the fuel tank, fuel piping, bunkering station, hazardous areas, ventilation, ESD, and operating manuals. |
| Class notation and approval conditions | The class notation should align with ship type, fuel type, fuel source, and fuel-system design. | Do not rely on the notation name alone; check approved drawings, design basis, risk assessments, and actual installation conditions. |
LPG bunkering can draw on mature LNG bunkering workflows, but safeguards must be rechecked against LPG-specific hazards.
LPG already has relatively mature applications on VLGCs and LPG carriers. Wider adoption across other ship types still depends on engine availability, bunkering infrastructure, and regulatory development.
For two-stroke main engines, ME-LGIP is one of the most representative LPG dual-fuel solutions. Converting an existing ME-C engine usually involves more than replacing injection components; it also touches the gas control block, fuel piping, sealing oil system, control-system upgrades, and subsequent gas-trial verification.
| Fuel Tank Type | Typical condition | Application view |
|---|---|---|
| Refrigerated | Approx. -50Β°C, near atmospheric pressure | Suitable for larger capacity requirements, but low-temperature materials, insulation, and operational control demand more attention. |
| Semi-refrigerated | Approx. -10Β°C, 4-8 bar | Balances capacity and operational flexibility, and is common on LPG carriers that can serve as bunker vessels. |
| Pressurised | Approx. 17 bar | Usually simpler for the receiving vessel and easier to match with different bunker-vessel types. |
The long-term value of LPG lies not only in its current emissions benefits, but also in whether it can connect smoothly to future low-carbon or near-zero-carbon fuel pathways.
Can be produced from renewable electricity or other low-carbon processes. Because its properties are close to conventional LPG, it should be relatively easier to introduce into existing fuel systems in principle.
Can be derived from biomass feedstocks, waste, oils and fats, or by-products from related processes, with potential to reduce lifecycle carbon footprint.
DME has storage and handling characteristics similar to LPG, can be blended at certain ratios, and may use parts of the existing LPG supply chain.
Because LPG combustion produces less COβ than conventional oil fuels, onboard carbon capture may require less COβ storage capacity and lower related cost.
This section focuses on design review, arrangement checks, and operational verification, serving as a practical closing lens for the technical note.
The greatest LPG safety challenge is not only that it is flammable, but where it flows after release, where it accumulates, and when it may meet an ignition source. When reviewing drawings or carrying out onboard inspections, surveyors should therefore consider low-level accumulation risk, ventilation effectiveness, gas-detection coverage, and emergency shutdown logic within the same safety case.
The main value of LPG as a marine fuel is that it offers an alternative pathway available today, with lower air-pollutant emissions than conventional oil fuels, a more mature supply-chain base, and relatively manageable technology risk. It should not be treated as the final zero-carbon solution. But if rLPG, bio-LPG, rDME, and onboard carbon capture mature and scale up, LPG fuel systems could become a transition platform that helps shipowners balance compliance, cost, and practical feasibility during the energy transition.