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Why are there so many requirements for fuel, electrical and ventilation on boats?
History and accident investigations have shown that one of the most devastating and damaging accidents that can happen on a boat is a an explosion or fire. There is simply no where for you to go and it usually happens so fast, there is no reaction that can be made to prevent much of the damage and injuries that occur. So, over the years safety standards have been developed to prevent this.
Fires and explosions require three conditions before they can occur. This is called the fire triangle and has been around for many, many years. It is, oxygen, a source of ignition, and fuel. On boats the oxygen obviously is present, the source of ignition is usually the boats electrical system, and the fuel is generally gasoline. Do not be fooled though. Even though diesel is much less volatile than gasoline and fires occur much less frequently, diesel powered boats need to follow the same rules.
So, if one side of the fire triangle can be eliminated, then the explosion and fire can be prevented. Each of the standards dealing with fuel systems, electrical systems and ventilation is designed to eliminate one of the sides of the fire triangle.
Ventilation: Fires and explosions occur within a very narrow range of conditions called the lower explosive limit (LEL) and upper explosive limit (UEL). This is the ratio of fuel to air. The range for gasoline is between a ratio of seven parts air to one part fuel vapor, and fourteen parts air to one part fuel vapor. 7 to 1 to 14 to 1. A ratio greater than 14 to 1 is too lean to explode (too much oxygen) and less than 7 to 1 is too rich to explode (too much fuel). This is why your car won't start when it's flooded. Too much fuel. Ventilation is designed to keep the LEL way below 14 to 1 so you never reach the lower explosive limit. Pour in lots of air and you should never reach that ratio. Big block engines especially need lots of air to breath properly so a well designed ventilation system is very important.
Fuel: The fuel system standard is designed to do one thing. Stop leaks!. The hose specified is to insure that the hose will withstand the heat, humidity, and most importantly, the components of the fuel, without getting hard, or too soft, cracking or splitting. The hose is also designed to withstand fire for 2 ½ minutes so that should a fire occur, the hose doesn't just become a steady source of fuel for the fire. The fuel system fittings are designed to prevent leaks where they most frequently occur, at the fitting. Eliminate as many fittings as possible. Keep it simple!
Electrical: Last but not least, the electrical system has to be designed to eliminate sparks; sources of ignition! This is the why there is an ignition protection requirement. But also, there is a need for over current protection, to eliminate the short circuit that causes the wire to get red hot and melt, setting off a fire. There are other safety considerations for electrical systems.
Shock hazard is a big consideration today. Twenty years ago most boats had a 12 Volt DC system. Few boats had 110 volt AC systems. They were generally only found on large yachts. Today it is very common to have extensive AC systems on even small cruisers in the 25 and 26 foot range, and on cruising sailboats in the 30 foot range. Larger yachts are installing 220 and 600 volt systems. Shock hazards are very real.
Galvanic Corrosion!: Galvanic corrosion is a very real problem on boats, particularly boats with both AC and DC systems. Even if your boat is well protected, the one next to you in the marina may not be. A poorly designed system can eat the stern drives right off your boat in a few days!