Everyone knows the word flammable and what it means—literally—“will catch fire easily and burn fast”. Inflammable means the same thing and either name in conjunction with a liquid used for cleaning machinery, parts, clothing, etc. can only spell one thing: trouble.
It is surprising to know that many people still believe that it is the liquid itself that burns. All liquid evaporates when open to the air, and it is the vapors of flammables that burn, not the liquid. If the liquid burned, we wouldn’t need complicated carburetors on engines to get the proper air-fuel mixtures. Instead a simple jet could be used.
We all know that a certain combination of oxygen (air) mixture with the vapors must exist before a flame or explosion can occur with any flammable liquid. There is no need to go into detail on the upper and lower explosive limits of the various flammables, which are misused for cleaning purposes. How many of us can tell when these limits are reached? NO ONE CAN without adequate instruments. We know that the leanest vapor-air mixture that will burn is called the lower explosive limit of a substance while the richest vapor-air mixture is called the upper explosive limit. The spread between the two limits is called the “explosive range.” All flammables differ in the spread of the explosive range and the wider the range is, the lower the lower limit will be and the quicker the explosive range will be reached. For instance, gasoline (which is manufactured to explode in an internal combustion engine, to burn in lanterns, stoves, etc. — NOT FOR CLEANING) vapor-air mixture ranges from 1.4% to 7.6% and starts giving off vapor at a -40° F (4 C). Kerosene has a 1% to 6% ratio with vapor range of 115° F(46 C). Diesel oil starts at 130°F (54 C) and the Stoddard Solvents begin around 110°F (43 C).
Another important factor is the rate at which a flammable liquid evaporates, i.e., its volatility at room temperature (usually assumed to be 70°F / 21 C). It’s easy to see that the more volatile a flammable liquid is, the more vapor it will give off into the air per minute or per hour. Therefore, the results will be a larger volume of an explosive mixture and a bigger boom if it’s touched off.
Gasoline must never be used as a cleaning agent, not only from the explosive standpoint, but it is also very toxic and a dangerous “degreaser” to the skin.
Adding just two tablespoons of gasoline to kerosene or any of the other flammable cleaning agents will make a drastic change in the explosive mixture so it is not advisable to use a former gasoline container for other liquids unless you can be positive that it has been thoroughly cleaned. Kerosene and diesel may be used—with proper precautions—but a good Stoddard type solvent is still better. You must remember that heat and especially “Ole Sol” can bring the temperature of any liquid up to its flash-point, and in the hot summertime it’s almost impossible to avoid the upper temperature ranges.
Always do your cleaning or degreasing in the open air since vapors confined in a small area can really create a violent explosion. The use of sprayers for cleaning odd-shaped parts just adds to the hazards involved by causing a more rapid vaporization and possibility of static electricity build-up. The amount of static electricity spark needed to set-off an explosion or fire is so small you can’t feel, see, or taste it.
THINK IT OVER before you start that cleanup job.