Doug:

What this is about is an expert said that the weight of the vapors is directly related to the humidity. The discussion was about gasoline vapors ability to rise in a compartment. We were discussing the where the code requirements for 18-inches originated. In the 70’s I was a worker assisting a attorney Edward Downing in Jefferson Parish in conducting test of natural gas water heaters in an enclosed area when gasoline was spilled. At that time there were a number of fires in my area where people were storing gasoline for their lawnmower in their utility rooms. The fire took place when there was a spill of the gasoline. The room was 8X8X8. The spill was from a 1 – gallon container. These test showed that with nothing to disturb the vapors that the vapors would not rise to the 18-inch level to reach the ignition source within the water heater. Additional tests were run where there was movement in the room at different times, with one of the movement times being 41 – minutes after spill. Where we did measure the temperature within the room, which reached between 71 – 88ºF, we did not measure the humidity. Mr. Downing continued this research through the 90’s and his finding were presented to the CPSC. The person said this was due to the level of humidity. I have been trying to find something that would support this contention.

Jim Mazerat
Forensic Investigations Group