Should LPG and CNG Vehicles Ride a Ferry?

Yes, with conditions. Ferries routinely carry LPG and CNG cars and campervans with gas bottles, provided the fuel valves are shut, the bottles are within limits and the crew knows they are aboard. The IMDG Code exempts such vehicles on ro-ro decks if nothing is leaking, and UK guidance caps camping gas at three cylinders totalling 47 kg. The risk is in the exceptions.

Gas-fuelled vehicles matter because their tanks are pressure vessels. In a fire, a liquefied-gas tank whose relief device fails or is overwhelmed can rupture violently, which a petrol or diesel tank rarely does. The rules are built to keep that hazard small and known, and they only work if the controls at the ramp are actually applied.

What the IMDG Code says

A gas-fuelled vehicle on a ro-ro deck is normally outside the dangerous-goods regime, on condition. Special Provision 961 of the IMDG Code exempts vehicles stowed in vehicle, special category or ro-ro spaces, or on the weather deck of a ro-ro ship, provided there are no signs of leakage from the engine, fuel tank, compressed gas cylinder or battery. Outside that ro-ro exemption, SP 961 treats a flammable-gas vehicle as non-hazardous only if its fuel tanks are empty, the positive pressure in the tank does not exceed 2 bar and the fuel shut-off or isolation valve is closed and secured.

A vehicle that meets neither condition becomes dangerous goods under UN 3166, assigned to class 9 under Special Provision 962. For flammable-gas vehicles, SP 962 requires the fuel shut-off valve of the tank to be securely closed. In practice the line between exempt and declared turns on two things the crew rarely checks in person: whether the valve is shut, and whether anything is leaking.

What ferry operators require

Operators add their own conditions on top of the Code, and they are broadly similar. UK guidance in the Maritime and Coastguard Agency's MGN 545 sets the baseline for private vehicles:

• Camping gas: cars, campervans, motorhomes and caravans may carry butane or propane for lighting, cooking or heating only, up to three cylinders with a combined weight of no more than 47 kg.
• Shut off and secured: the gas supply must be shut off at the cylinders, which must be secured against movement and stowed away from sources of ignition and heat.
• Gas-fuelled cars: only recognised manufacturers' models of standard specification, or conversions where there is evidence of work by a competent certified mechanic.
• Declaration: operators such as Irish Ferries and CalMac require gas to be declared at check-in, and require LPG and CNG vehicle tank valves to be closed while on board.

Not every crossing accepts them. Some operators of enclosed shuttle services refuse LPG vehicles outright, including dual-fuel cars. The variation is itself a risk: a driver used to one operator's rules may not expect another's.

Why gas tanks are a fire hazard on deck

A liquefied-gas tank engulfed by fire can fail as a boiling liquid expanding vapour explosion, and on a car deck that would happen beside other vehicles. In fire tests on toroidal LPG vehicle tanks with their safety devices removed, all ten tanks failed in under five minutes, with a fireball, a blast wave and fragments over a wide area. Modern tanks carry relief valves to prevent exactly this, which is why an unmodified, correctly maintained system matters more than the fuel itself.

Camping gas adds a second risk. Bottles left open to a cooker, heater or fridge can leak into a closed campervan, and a vehicle deck with ventilation running can carry a leak further. A leak of heavier-than-air propane or butane collects low, around the wheels and underside of nearby vehicles.

What operators should check at the ramp

• Ask, don't assume. Make fuel type and gas bottles a booking and check-in question for cars, campervans and caravans.
• Look at the conversion. Aftermarket LPG conversions without certification are the case MGN 545 excludes; ask for evidence.
• Confirm valves are shut. A quick visual or verbal check at boarding is the control both SP 961 and SP 962 rely on.
• Stow with intent. Keep known gas vehicles where the crew can reach them and away from the heaviest fire loads.
• Tell the bridge. Fire teams and shore responders need to know where gas vehicles are before they open a deck, not after.

Sources

• 1. IMO — IMDG Code, Special Provisions 961 and 962 (as amended by Amendment 42-24, mandatory from 1 January 2026): ro-ro exemption where there is no leakage; flammable-gas vehicles non-hazardous if tanks are empty, positive pressure not above 2 bar and the shut-off valve closed and secured; otherwise class 9 under UN 3166 with fuel shut-off valves securely closed.
• 2. UK Maritime and Coastguard Agency — MGN 545 (M+F), 'Guidance on the transport of dangerous goods as defined by the IMDG Code when carried in a private vehicle not in commercial use or by a foot passenger on a Ro-Ro ship' (read in full): butane/propane, maximum 3 cylinders, combined weight not over 47 kg, for lighting, cooking or heating only; gas supply shut off at the cylinders, secured and stowed away from ignition and heat; gas-fuelled cars only recognised standard models or certified conversions.
• 3. Irish Ferries — 'Fuel, gas, air and oxygen cylinders and dangerous gases': LPG, LNG and CNG vehicles accepted with cylinders closed and secured; camping gas up to 47 kg in 3 cylinders, declared at check-in.
• 4. CalMac Ferries — 'Can I bring dangerous goods on board?': gas cylinders declared to port staff or deck crew; LPG car tank valves closed before shipment.
• 5. Journal of Loss Prevention in the Process Industries (2018) — 'Experimental investigation of consequences of LPG vehicle tank failure under fire conditions': ten toroidal LPG tanks without safety devices all failed as a BLEVE in under five minutes.
• 6. DNV GL — 'Fires on Ro-Ro Decks' (2016): identified causes of 35 ro-ro deck fires 2005–2016, none attributed to a vehicle gas fuel system.