The author replies to Jones

I thank Professor Jones for his complimentary remarks. Further, as he states, "[A] liquid can in principle be too far above its [upper] flash point to form a flammable mixture with air." However, a detailed consideration of this principle reveals three further concerns.

First, whenever one has a mixture of a flammable vapor and air in which the proportion of the flammable vapor is above its upper flash point, the only way to get to a guaranteed safe environment is to lower the proportion of flammable vapor in that mixture so that it becomes a mixture that is below the lower flash point. Obviously, in so doing, the proportion of flammable vapor in the mixture passes through the explosive/flammable range. Consequently, it seems to me, to have a mixture of flammable vapor and air in any proportion above 25% of the lower flash point is not desirable.

Second, assuming a typical laboratory room with a volume of 5000 cubic feet requires that 67 kg of n-hexane vaporize to achieve a room-filling vapor-liquid equilibrium at 124 torr. This seems to me to be an unlikely event for a typical laboratory.

Finally, one needs to remember that flash points are determined by laboratory measurement under controlled conditions. It is simply not true that the upper flash point is some kind of limiting number above which a vapor-air mixture will not burn or explode. A flash point is a limiting value on which one can rely only when the conditions duplicate those under which the flash point was determined. I know personally of several fatal accidents involving explosions of vapor-air mixtures in which the proportion of flammable vapor was above the upper flash point. Normal hexane is highly flammable, that is the point at issue, and it is so rated in the CLIP.