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Gas safety – when it comes to fuelling our boats' stoves we can't afford to be careless

When using gas, safety should be our first consideration but we should keep things in perspective. To our American friends the word ‘gas’ would be taken to mean gasoline while we in the UK know gas as being a colourless, flammable vapour that, when mixed with air, can be ignited to heat our food. Both are useful fuels. Both are potentially dangerous. They just need proper handling. And gas safety has relevance in both cases.

The stuff that fuels most of our boats’ stoves is described by the acronym LPG – which stands of ‘liquefied petroleum gas’. The word ‘liquefied’ gives a clue as to how it is stored.

LPG as we know it is a cocktail of light hydrocarbons that are gaseous at most normal temperatures but becomes liquid under pressure. The two principal ingredients are butane and propane, with butane being the easiest to store as a liquid, requiring a pressure of only about 2 bar. Those inexpensive plastic lighters we toss about so casually contain butane – a measure of how easily it can be contained.  By contrast, propane must be stored at around 7 bar but rewards the extra effort by turning into a gas at lower temperatures. This makes it more suitable for colder climates. Also propane burns hotter than butane.

Many of the commercial gases we buy are usually a mix of the two, with the proportions adjusted to suit local conditions. However, they may be labelled ‘propane’ or ‘butane’ depending on which is the primary gas and which, if any, is the additive. In the UK propane is usually delivered in red cylinders, butane in blue.

The risks

As a liquid, LPG is lighter than water and will float on the surface until it evaporates. But, in a gaseous state it is heavier than air so will sink to a low level, including into unsealed bilge spaces.

It is this that makes it so potentially dangerous. If the proportion of LPG/air mix falls within the 2% to 10% range it will burn or even explode if ignited. If the concentration is either more or less than these figures, it will be too weak or too rich to ignite.

Undeniably useful though it is, LPG is dangerous stuff. The equipment that contains, delivers and then uses it must be properly designed and installed – and thereafter meticulously maintained.

The precautions

The specifics of how a gas installation should be designed is something of a grey area, with conflicting opinions prevailing in certain countries. Some take the view that the fewer joints there are in the supply line, the lesser the risks of leakage and, therefore, the safer the installation. This might allow the use of flexible hose throughout so long it is of approved type and visible along its entire length.

The British attitude,  on the other hand, prefers the main run of the supply to be in seamless copper or stainless steel pipes with short (no more than 1m) lengths of flexible hose at the cylinder end and also at the cooker (if gimballed). This is a logical solution when pipework is routed behind cabin structure and can neither be inspected or replaced. However, all agree that flexible gas hose should be replaced regularly – every five years being a typical maximum.
Rather than explore all the options, for our purposes let’s stick with the well-regarded CORGI recommendations we’re familiar with in the UK.

The artwork above shows a typical installation. The cylinders are stowed in  a locker, sealed from the boat's interior but vented to the outside, primarily through a drain leading from the locker's base directly overboard above the waterline. The bubbler type gas leak detector shown is not an absolute requirement but is strongly recommended.

It is currently not a legal requirement that work on marine LPG installations must be done by qualified personnel but it does call for an appropriate knowledge of the subject and technical competence. The message is to take no risks. Better by far to employ a qualified gas technician than to bungle the job yourself.