Boating Accident Gasoline Explosion- 32 Foot Aluminum Cruiser

TASA ID: 674

Some 10 days before the accident, during a short cruise, it was noticed that the engines were not working properly.  Upon reaching the dock, the owner examined the port engine and noticed water in the fuel.  The day before the accident, he had tried unsuccessfully to start the engines.  Hence, he decided to bring a small portable electric compressor and 10 - one-pint containers of dry gas.  The boat was alongside the dock, connected to the shore power.  He opened the rear hatch on the cockpit, the sliding doors, the gate on the railing, the engine hatches, and all windows that could be opened.  He disassembled the carburetors on both engines, drained water from the fuel filters, and reassembled the engine fuel lines, using paper towels to avoid any gasoline drips from spilling, and discarded the used towels in the trash dumpster at the marina.  Then he added 10 pints of "dry gas" to the fuel tank through the filter line at the aft port side of the vessel.  He put the compressor on the dock and, in order to mix the dry gas with the gasoline in the tank, he removed the fuel tank level gauge, inserted the air compressor hose deep into the gasoline tank, and ran the compressor for 15 to 20 seconds.  At that time, he smelled fumes.  After putting the compressor and tools away on a picnic table, him and his wife went shopping for 2 hours.

After returning to the boat, they never noticed any smell of gasoline, and no gasoline odor was noticed while cooking or eating dinner, which they prepared in the galley in the lower cabin.  They smoked during dinner.  The weather in the marina was calm.  About 6:45, he went to the lazarette, which was still open, as were all the other hatches, and his wife asked if it would be okay to turn the hot water heater on to wash the dishes.  After receiving approval from her husband, she reached for the switch of the water heater, and an explosion occurred immediately.  The owner was thrown from the boat into the water, and his wife was seriously injured and trapped in the boat remains by flying debris. The boat had been all open for some 5 hours after the application of compressed air, and the vapors were probably substantially dissipated in the area of the hatches above the engines and in the area of the hatch of the lazarette. However, vapors were trapped under the floor of the lower cabin and in the compartment where the water heater was located.

CHARACTERISTICS OF THE EXPLOSION

The information contained in the documents reviewed indicates the following:  The lower decking and floors were blown upwards by overpressure in the bilge area, and the upper deck was blown away from the center of the boat.  There was melted wiring insulation in the vicinity of the electric water heater forward of the non-tight bulkhead located under the cabin floor, indicating that flames were present in the vicinity of the water heater.

The wife testified that her clothes were not burned; therefore, no flames developed in the lower cabin or in the 3 steps connecting the lower and the upper cabin, except for some burning of the edge of the carpet under the refrigerator. Also, no flames developed anywhere in the rest of the cabin because the owner's personal effects were not scorched or burned in any way.

DISTRIBUTION OF GASOLINE FUMES

Gasoline as a liquid does not burn.  It is the vapors emanating from the liquid gasoline that can form an explosive mixture when mixed with oxygen in the proper proportion.  These fumes are several times heavier than air and will "sink" or displace air to occupy the lowest position in respect to the surrounding air.  In the case under consideration, as the fumes were "pushed out" of the gasoline tank by the effect of the compressed air used to agitate the gasoline, a very small amount may have been propelled up by the air stream to acquire an elevation of several inches, enabling them to be smelled.

If these fumes went up more than 8" to 10" above the surface of the liquid gasoline, they may have reached the cockpit deck (6" above the top of the tank) and should have drained overboard through the open gate and through the scuppers.  The fumes that were unable to reach the cockpit deck would have fallen to the bilges and  would have advanced, like molten lava of a volcano, toward lowest elevation on the bilges.  Upon reaching the transversal bulkhead forward of the engines, some of the fumes would have drained through the limber holes, like a liquid, towards the forward end of the bilges where the bilge pump was located. More fumes would have continued to accumulate against the bulkhead, leaking forward through its numerous penetrations, framing non-tight seams of plywood and holes cut into the bulkhead connecting the space where the water heater was located.

One of the most popular books regarding boating, Chapman Piloting and Seamanship, which has been reprinted more than 56 times since 1912, indicates a concentration of gasoline in air as low as 1 ¼% - a half a tea cup, a few ounces of gasoline, can create enough explosive vapor mixture to destroy a large boat completely.  The actual explosive range of vapor mixture is from 1.4 to 7.6% in volume.

As the gasoline fumes "fall" to the lower part of the bilges, the vapor will form 3 layers of vapor diffused with air.  The lowest layer would be too rich for flammability. The next layer above will be flammable, and the upper layer will be too lean.  Of course, a sharp and obvious division between layers is not possible unless a condition of calm winds and repose exists for a period of time.  Turbulence created by people walking among the vapors, a natural draft created by differential temperatures (sun and shade), and the availability of two open hatch areas will result in a variation of vapor concentration. but in the bilges and the compartment containing the water heater, no walking or other means of creating turbulence is  possible because of space restrictions. These "pockets" will preserve the existence of the 3 layers. 

This article discusses issues of general interest and does not give any specific legal, medical, or business advice pertaining to any specific circumstances.  Before acting upon any of its information, you should obtain appropriate advice from a lawyer or other qualified professional.

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