I'm presently refitting my gas system on my Grand Banks 42 after numerous failures from a recent BSS inspection. Ive had this article on my website for years so thought id post as an introduction to LPG installations.
Any fuel that produces a flame consumes oxygen when burning and gives off carbon dioxide (CO2) and water vapour. Boats interiors have little volume, and cabin spaces are normally well sealed (they must be to be watertight). The oxygen available in a closed cabin can be consumed quite rapidly. Insufficient oxygen makes the fuel burn improperly and, instead of producing carbon dioxide, it begins to form a deadly carbon monoxide (CO). The combination of oxygen loss and carbon monoxide build up can be fatal-it has caused a number of deaths over the years. Always insure adequate ventilation when burning any fuels; this includes running diesel engines, which sometimes obtain their air via the living spaces in spite of the fact that they should be independently vented. Do not use an appliance for heating unless it is so designed. Never leave a heater on overnight unless it is vented outside the cabin area and adequate air supplies are assured.
LPG (Liquid Petroleum Gas) is kept under pressure as a liquid and when released becomes a heavy flammable gas that is much heavier than air. The aim therefore is to minimise the risk of this gas escaping into your boats interior, where it could quickly accumulate, creating an explosive ‘mix’ of gas and air.
This chapter concentrates on how best to store LPG, how to supply your gas appliances and how to protect the gas system and installation from heat and impact damage. It is always strongly recommend that any work on LPG systems is carried out by a competent gas fitter.
GAS
The two main types of gas in wide spread use are propane and butane. Butane and propane both liquefy at low pressures and temperatures. As gas is pumped into a cylinder at ambient temperatures, these pressures are reached quickly. Then as more gas is pumped in, it liquefies-with temperatures and pressure remaining relatively stable. When a full cylinder is rocked from side to side, the liquid can be heard sloshing around inside. In higher ambient temperatures, pressures in an LPG cylinder will increase somewhat, but never beyond 250PSI; in lower temperatures, it will decrease.
The principle difference between butane and propane is the former
liquefies at higher temperatures and lower pressures for the latter. In
extremely cold weather, liquid butanes rate of evaporation from a
cylinder can slow to the point at which appliances fail to work
properly. In these conditions propane should be substituted.
In the UK appliances operating on Butane do so at a pressure of 28 millibars and Propane at 37 millibars. It is not generally possible to change from one fuel to the other without changing the regulator, hence the cylinders and regulators have different threads and fittings to avoid mishaps. As a point of interest butane has a higher calorific value and a slighter hotter flame temperature.
SAFETY PRECAUTIONS
LPG forms a dangerously explosive mixture when combined with oxygen in the air. LPG is considerably heavier than air-gas leaks sink to the bilges. LPG leaks are particularly dangerous on boats: Small leaks can remain undetected in deep bilges. A tiny spark (which can be generated by static electricity on any boat) can blow the boat apart.
INSTALLATION PRACTICES
Compartment requirements: Gas bottles, both in use and in storage,
must be kept well secured in compartments that are sealed from all
machinery and living spaces, and vented overboard. LPG compartments need
to be vented from the base with a minimum internal diameter of 19mm
(B.S.S exemption to 12mm on older vessels), which slopes continuously
downwards so that no water can form a U-trap, which exit’s the hull
above the waterline at all angles of heel. This is continuously picked
up during surveys, many drain hoses are found to be looped up and
contain water! All gas vents must exit well clear of engine exhausts,
ventilators, and air intakes. Gas cylinders must be secured in an
upright position (again very few cylinders during surveys are secured
properly). If an LPG cylinder tips over, liquid instead of gas might
come out-with potentially dangerous results.
MARINE GAS DETECTION
Suitable means for detecting the leakage of gas should preferably be provided in each compartment containing a gas-consuming appliance. Gas sensor heads should be protected against damage caused by water and other corrosive agents, and the risk of mechanical damage. The consequences of an LP gas leak on board a boat can be disastrous. Every year there are deaths and injuries on board boats, which could have been avoided with the installation of easy to use and cost effective gas detection equipment.
LP Gas is not regarded as poisonous but is explosive and can lead to devastating explosions if it builds up to sufficient levels. It is measured using what's called the Lower Explosive Limit (LEL). This means that when the concentration of gas reaches 100% LEL it becomes explosively dangerous (i.e. if you lit a match it would go bang). Most gas alarms are calibrated to alarm at 10% LEL, well before the gas becomes explosively dangerous.
A strong smell of gas can be noticed when the concentration is only 0.5% to 1% LEL because gas suppliers add a harmless but strong smelling chemical to the gas. Despite the strong smell this level is not dangerous and therefore the alarm will not sound. This reduces the possibility of false alarms.
Any fuel that produces a flame consumes oxygen when burning and gives off carbon dioxide (CO2) and water vapour. Boats interiors have little volume, and cabin spaces are normally well sealed (they must be to be watertight). The oxygen available in a closed cabin can be consumed quite rapidly. Insufficient oxygen makes the fuel burn improperly and, instead of producing carbon dioxide, it begins to form a deadly carbon monoxide (CO). The combination of oxygen loss and carbon monoxide build up can be fatal-it has caused a number of deaths over the years. Always insure adequate ventilation when burning any fuels; this includes running diesel engines, which sometimes obtain their air via the living spaces in spite of the fact that they should be independently vented. Do not use an appliance for heating unless it is so designed. Never leave a heater on overnight unless it is vented outside the cabin area and adequate air supplies are assured.
LPG (Liquid Petroleum Gas) is kept under pressure as a liquid and when released becomes a heavy flammable gas that is much heavier than air. The aim therefore is to minimise the risk of this gas escaping into your boats interior, where it could quickly accumulate, creating an explosive ‘mix’ of gas and air.
This chapter concentrates on how best to store LPG, how to supply your gas appliances and how to protect the gas system and installation from heat and impact damage. It is always strongly recommend that any work on LPG systems is carried out by a competent gas fitter.
GAS
The two main types of gas in wide spread use are propane and butane. Butane and propane both liquefy at low pressures and temperatures. As gas is pumped into a cylinder at ambient temperatures, these pressures are reached quickly. Then as more gas is pumped in, it liquefies-with temperatures and pressure remaining relatively stable. When a full cylinder is rocked from side to side, the liquid can be heard sloshing around inside. In higher ambient temperatures, pressures in an LPG cylinder will increase somewhat, but never beyond 250PSI; in lower temperatures, it will decrease.
As long as an LPG cylinder is kept upright, there will always be gas
at the top, liquid at the bottom, and stable pressure-until the cylinder
is almost empty. At this point the pressure begins to fall as the last
of the liquid evaporates.
The principle difference between butane and propane is the former
liquefies at higher temperatures and lower pressures for the latter. In
extremely cold weather, liquid butanes rate of evaporation from a
cylinder can slow to the point at which appliances fail to work
properly. In these conditions propane should be substituted.
In the UK appliances operating on Butane do so at a pressure of 28 millibars and Propane at 37 millibars. It is not generally possible to change from one fuel to the other without changing the regulator, hence the cylinders and regulators have different threads and fittings to avoid mishaps. As a point of interest butane has a higher calorific value and a slighter hotter flame temperature.
SAFETY PRECAUTIONS
LPG forms a dangerously explosive mixture when combined with oxygen in the air. LPG is considerably heavier than air-gas leaks sink to the bilges. LPG leaks are particularly dangerous on boats: Small leaks can remain undetected in deep bilges. A tiny spark (which can be generated by static electricity on any boat) can blow the boat apart.
INSTALLATION PRACTICES
MARINE GAS DETECTION
Suitable means for detecting the leakage of gas should preferably be provided in each compartment containing a gas-consuming appliance. Gas sensor heads should be protected against damage caused by water and other corrosive agents, and the risk of mechanical damage. The consequences of an LP gas leak on board a boat can be disastrous. Every year there are deaths and injuries on board boats, which could have been avoided with the installation of easy to use and cost effective gas detection equipment.
LP Gas is not regarded as poisonous but is explosive and can lead to devastating explosions if it builds up to sufficient levels. It is measured using what's called the Lower Explosive Limit (LEL). This means that when the concentration of gas reaches 100% LEL it becomes explosively dangerous (i.e. if you lit a match it would go bang). Most gas alarms are calibrated to alarm at 10% LEL, well before the gas becomes explosively dangerous.
A strong smell of gas can be noticed when the concentration is only 0.5% to 1% LEL because gas suppliers add a harmless but strong smelling chemical to the gas. Despite the strong smell this level is not dangerous and therefore the alarm will not sound. This reduces the possibility of false alarms.
