So far I have tried to explain how a vapor cloud develops by discussing Flash Point, Vapor Density, etc. Now I would like to explain how a vapor cloud develops and just how LITTLE energy is needed to be an ignition source. If you ever experience a spill of a flammable/combustible liquid and the temperature of the liquid is even CLOSE TO THE FP, then we MUST treat the spill as a HAZMAT situation. With any materials that have a high vapor pressure and/or low FP, surface area is EVERYTHING. The smaller we can keep the surface area, the less vapor/gas we will have to deal with. Of course if we can get a AFFF foam blanket on the surface of the spill that is even better.
However, regardless of what we do, we will have a vapor cloud of a certain size. as I discussed in the LEL posting, even with a small cloud will have a flammable range within it (at least we should ALWAYS assume this). The mistake a lot of people make is that this could will need to find a flame of some sort to ignite. Like a pilot light, boiler, vehicle, etc. This can be a HUGE ERROR in your planning and assessment. Most solvent vapors have a Minimum Ignition Energy (MIE) of 0.15-1.15 milli Joules (mJ). Hydrogen gas is even lower at 0.02mJ. Combustible dust will range from 1-50 mJ. Just how low is this???? We can not even feel a shock below 10mJ!!!! When you walk across the floor in your sock feet and reach out for a door knob and get shocked…that is around 25 mJ. This is nearly 100 times the energy needed to ignite a hydrogen cloud and PLENTY to set off any vapor cloud.
In closing, cell phones do not cause fires at gas pumps… WE CAUSE fires at gas pumps via static electricity. When we get back into the car and rub our tushes against the seat and get out and the first thing we touch is the nozzle, this is where the spark occurs and is also the likely area for the flammable range to occur. With gasolines VD being around 2.5, the vapors fall quickly when they exit around the nozzle opening, so a cell phone up to our ear is WAY TOO HIGH for it to be a concern. I AM IN NO WAY TELLING ANYONE TO TALK ON THE PHONE WHILE PUMPING GAS! We are transferring one of the most hazardous materials in society and we should be PAYING 100% attention to the task at hand. What I am trying to demonstrate is that the physical properties of Gasoline do not lend themselves to be ignited by a person on a cell phone, but a person who is charged and grabs the nozzle is an ignition source.
Next, I will attempt to explain why filling a 2.5 gallon plastic gas container is SO VERY DIFFERENT than filling a 330 gallon plastic tote. Many of us use small gas containers to get gas for cutting the lawn and as long as these containers are sitting on the ground, it is relatively low risk. HOWEVER, filling 330 gallon plastic totes that are so common in industrial settings with a flammable liquid is like playing Russian roulette.