Most of us are aware that many yachts have use of an auxiliary engine, perhaps a generator (for charging batteries and providing power), a gas-fired oven and hob or a solid fuel stove.
Many have a diesel-fuelled heating system also. The benefits of all these fossil-fuel driven amenities and utilities does come with some drawbacks though and, in particular, requires that we keep relatively large quantities of large and highly flammable fuel onboard.
Diesel is the favoured fuel for boats - and for good reason. Whilst diesel is just as flammable as petrol, it's vapour is not. That has to make it a safer option when carrying hundreds of litres of fuel under your bunk! Another advantage is that diesel generators are less featured in the distressing number of victims of carbon monoxide poisoning.
For cooking, propane or butane gas tends to be favoured. Highly explosive, the gas is without smell naturally but has a scent added. Heavier than air, the danger is that gas spills from the pipes or appliances delivering it and falls into the bilges where is collects, awaiting ignition, perhaps from an electric bilge pump!
To protect ourselves from gas on board, we install a gas detection sensor in the bilges and, in many cases, a carbon monoxide detector to protect against the dangers of the waste gas product from gas ovens. Of course, good ventilation is important when managing the latter.
Smoke alarms in cabins (higher is better) serve to give early warning of fire.
When storing gas on board always stow it securely and in a locker that is ventilated to the outside. Most deck lazarettes are not - so beware! Always ensure that gas appliances and pipes are inspected and serviced regularly by a qualified gas engineer. When running pipes, or stowing kit on board, be sure to avoid damaging pipe runs or detaching connections.
In the event of a gas alarm activation, isolate the gas supply on deck and below and check your bilges for smell. Turn off electric pumps located in the bilges and use the manual pump to help pump out gas. Where possible, open hatches and ventilate the boat. Some advocate using a bucket to bail the gas, although I suspect you'd have to have a big gas leak for that to be very effective!
If gas is not obvious, still ventilate, but consider the possibility that the sensor has been activated either because it's wet or by another form of gas, such as mosquito deterrent or hair spray! If this is suspected, remove the sensor from the bilge area, let it air (or dry) and reinstall.
With diesel fuel, make sure you know where the tanks are located, filled, vented and isolated. Make sure your crew know how to isolate and fill the tanks. In the event of fire, isolate the tank as part of the firefighting routine.
Another gas which can be released on board is the flammable mix of hydrogen and oxygen from batteries. If you have defective batteries you might detect a distinctive smell and a fizzing noise. It's important to ventilate and isolate the batteries to avoid build up of explosive gases.
All in all, the best policy is caution and common sense. Always use a qualified engineer when working with gas pipes and brief your crew on what to do in the case of fire or gas alarm. Carry spare batteries for portable smoke and CO alarms and check them periodically.
Then, enjoy your sailing.