Thought this may shed some light on this subject:
Boating is an enjoyable pass time for many Canadians. Unfortunately, the dangers associated with this activity are often misunderstood or ignored.
Marine craft present a particular hazard to fire and explosions. According to US Coast Guard statistics, fires and explosions account for the largest single cause of marine property damage. The hazards exist owing to the presence of flammable liquids present within confined, poorly ventilated spaces. Gasoline fuel, which is used to propel the majority of private marine craft presents the most common hazard. Gasoline can be released into boat compartments as a result of equipment failure, spills and improper storage of fuel supply.
Gasoline has a lower explosive limit (LEL) of 1.4% by volume and an upper explosive limit (UEL) of 7.6%. The percentages within the LEL and UEL represent flammable gasoline/air mixtures. Therefore, a flammable gasoline/air mixture can exist when 100 ml (approx. 200 drops) of gasoline liquid is vaporized in 1 cubic metre (approx. 35 cubic feet) of confined air space. Furthermore, gasoline vapour is heavier than air and tends to collect in lower compartments of the boat. Therefore, a small leak or spill can present a significant hazard of explosion and fire.
Diesel fuel presents a reduced explosion hazard owing to its higher flash point which prevents it from readily evaporating to produce a flammable mixture. The LEL for No. 1 grade diesel fuel is 3.5% by volume and the UEL is 6.9%. The LEL is higher and the range is smaller, further reducing the hazard. However, higher temperatures will cause diesel fuel to evaporate more readily resulting in explosive mixtures being present within confined air spaces on marine craft. Temperatures within cabins and engine compartments may be significantly raised by the hot summer sun, increasing this hazard.
In addition to engine fuels, galley stoves, which operate with fuels such as alcohol, kerosene, and propane present significant fire and explosion hazards from improper operation, improper installation, fuel leaks and spills. Propane (LEL = 2.5%, UEL = 4.5%) presents the greatest explosion hazard.
Since it is heavier than air, a propane leak can create and explosive mixture in lower boat compartments. Alcohol can also create explosive mixtures and can cause accidental ignition of combustibles owing to its clear, colourless flame. Therefore, great care should be exercised when using these fuels. Furthermore they should be stored outside or in ventilated compartments sealed from the main cabins and other compartments.
Marine construction materials add to the fire hazard. Fiberglass and wood are the two most popular construction materials used for pleasure craft and small commercial boats. Both of these materials are flammable, increasing the probability of complete destruction of the boat when a fire occurs. This increases coverage concerns.
Preventative measures include proper ventilation, proper refuelling methods, avoiding spillage and overflow, periodic inspection of fuel systems, use of inflammable materials of construction, and installation of fire suppression equipment. Electrical systems should also be properly designed and maintained to reduce electrical ignition sources. Bonding ground systems are preferred for all boats with fixed electrical systems. Fire extinguishing equipment is required by law and can serve to prevent the spread of fire, reducing damage. In addition, exhaust blowers should be running prior to operation of engines.
Refuelling also presents other significant fire and explosion hazards. Fuelling should take place under good lighting conditions and smoking and open flames must be forbidden in the nearby area. Furthermore all electrical and power equipment should be closed and the possibility of static discharge from the fuelling nozzle to the filling port must be eliminated by maintaining continuous contact while fuelling. In addition, all unnecessary personnel should stand clear of the area.
Since the bilge is located at the lowest point in a marine vessel, it represents another area of concern. Released liquid and vapour fuels are heavier than air, and therefore, will flow to this location increasing this hazard. This can result in flammable mixtures being present within the bilge. Frequent flushing and cleaning of the bilge area and good ventilation will reduce this hazard.
Some boaters elect to live on their vessel year round. As a result, heaters are required to provide a comfortable environment. Electrical heaters introduce a possible ignition source for flammable mixtures, not to mention the usual fire hazards associated with this type of equipment. Propane and other LPG heaters are found on some boats. However, most insurance companies will not underwrite marine vessels equipped with appliances with pilot lights as this provides an ignition source for flammable mixtures. This type of equipment should be avoided.
The above information came from http://www.waltersforensic.com/artic...n/vol3-no2.htm
From my own, personal, first-hand experience, I've seen dozens of alcohol fires in galleys. These were fires that got pretty wild in some instances, and could have been catastrophic had the boat's operator not quicky acted with a fire extinguisher. Just filling an alcohol stove underway, even in relatively mild conditions, can result in spills.
I've been using propane for 8 years, a 20-pound tank that is mounted in a special compartment. Never encountered a single problem. I do, however, have a sniffer that can detect a myriad of explosive gasses, including propane, gasoline, diesel, carbon monoxide, etc...
Yesterday I got a call from the marina saying an alarm was going off inside the boat. I told them to not allow anyone near the boat, and quickly drove to the boat to check it out. When I arrived the alarm was not sounding. I opened the outside hatches, stuck my head inside and detected a very slight gasoline odor. I filled the tank the day before, a time when the temperature was in the lower 30s. Yesterday afternoon the temperature rose to the 50s and the sun was beating down on the boat. Apparently, the rise in temperature was just enough to cause the gasoline to expand a bit and a small volume was forced out the tank vent. That tiny amount, which I don't believe was sufficient to prove dangerous, allowed a small volume of vapor to seep into the cabin, thereby triggering the alarm.
I decided to check the alarm and determine just how little gasoline it would take to trip the alarm. As it turned out a single drop of gasoline on a small piece of paper towel and placed six inches from the detector was all it took. WOW! That thing is really sensitive. I also tested it for propane by pressing down on the trigger of a propane light which I use for lighting the stove. I held it down for less than a second and the alarm triggered. This, despite the fact that the lighter was at least 6 inches away and puts out only a tiny amount of propane.
Explosive gas sniffers vary significant in price, depending upon whethe or not it has the word "Marine" associated with the product. The one I purchased came from Amazon.com, it was designed for boats and RVs, and the price was under $40. You can find higher priced models that have selinoid cut-off valves that close automatically with the detection of the slightest amount of explosive gasses present.
The alarms themselves are extremely loud, loud enough so that the person who called me heard the alarm from his condo's third-floor balcony. I seriously doubt that anyone could be aboard the boat and NOT hear the alarm sounding.