For years after the introduction of mobile phones, there was widespread controversy about whether the use of cell phones could cause brain tumors. http://www.fumento.com/media/cellphone.html. Cell phones were suspect, because of the energy released by the high frequency radio or microwaves while the antenna is next to the head. Like any form of energy, these waves can and do (in a miniscule way) liberate heat and, due to its location next to the skull, heat the brain, but so does lifting up one's arms or walking a few steps (due to increased blood flow). Now that hundreds of millions of people use cell phones routinely and an epidemic of brain tumors has not yet materialized, the worry has largely dissipated, though research continues.
A new cell phone fear has arisen-that cell phones can cause gasoline vapor explosions while pumping gas. Some newspaper articles and numerous highly-circulated E-mails have described any number of such explosions and have warned that cell phones must be shut off before dispensing gasoline to avoid a fire or explosion.
Exxon in the U.S. and Shell in the Orient instructed at least some of their gas station operators not to use or allow customers to use cell phones. Numerous other stations have signs prohibiting the same, though many or most such signs are the result of pre-cell phone laws requiring signs prohibiting any electronic devices near gas pumps.
In the U.K., the Health and Safety Executive, their equivalent of the U.S.'s OSHA, issued an official instruction in Feb, 2005 that gas station employees and customers should not use cell phones while pumping gas. The risk of explosions was not the reason, however. Their stated reasons were "Generally mobile telephones are not designed and certified for use in explosive atmospheres. Their use can also create a serious distraction for people carrying out dispensing activities". In other words, neither the safety certification agencies nor the cell phone manufacturers have approved cell phones for use in explosive atmospheres, and, besides, cell phones could be a distraction that could lead to spilling gasoline.
Many or most manuals that cell phone manufacturers provide with the phones warn about sparks in hazardous atmospheres that could cause serious injury or death.
At least one gas station explosion that was widely described in newspapers and TV as confirmed by a police report as originating from a cell phone later turned out to have nothing to do with a cell phone. http://www.esdjournal.com/static/cell/nycellfire.htm.
Snopes.com and urbanlegends.com have tried to verify some of the exploding gas station-cell phone stories circulated on the internet, but have been unable to document a single case. Some of the newspaper stories appear to have been knock-offs of internet stories rather than original reporting. Exxon decided to put warnings on all its pumps in the U.S. despite the fact they have no such accidents at their stations and knew of none at other stations.
Motorola contracted an engineering consulting firm to investigate the issue worldwide. http://www.motorola.com/mot/doc/0/203_MotDoc.pdf. And they concluded that "there is no sound technical basis to prohibit the use of mobile phones in gasoline stations or single them out as hazards.” Others have come to the same conclusion, including government agencies, industry groups and Shell Oil, which has the strongest rule against the use of these phones.
Cell phone-gas station stories have wide acceptance, because many people believe that the slightest spark can set off an explosion if the gasoline vapor to air ratio is within a certain range. As a matter of fact, all flammable vapors require the spark to have a particular strength to cause ignition, called the minimum ignition energy, which is measured in milliJoules. For gasoline that number is .24 mJ. That is not much energy, but it is 10 times higher than for hydrogen mixtures, for example. The .24 mJ energy level rules out the possibility that operation of the phone or its antenna could cause a gasoline vapor explosion.
However, the possibility of the battery in these phones causing a spark of sufficient strength cannot be theoretically ruled out; the vast experience with these batteries indicates that, practically speaking, any such risk is miniscule.
Shell International states its policy in this way: "Although driving whilst using a cellular phone is perfectly safe, we do not allow them to be used on the forecourt [of a service station] in case an electronic fault in the phone causes a spark." Shell has it exactly backwards. It is better to use a cell phone while the car is parked in front of a gasoline pump than it is to use one while the car is on the road.
A much greater risk than a cell phone spark is the risk of static electricity discharged while the driver's hands are close to the open gas tank. A static charge can build on the driver's body from contact with the car seat. Typically, any static electricity on the driver's body is dissipated by touching metal parts of the car or the gasoline nozzle. Most people can't even get out of their cars without touching a metal part. Young, athletic drivers may do so, but they are likely to touch the car door to close it or touch the metal lid over the gas tank filler tube or a metal part of the gas pump before their hands reach the area with a hazardous vapor concentration. To get an explosion this way requires a combination of low humidity, static producing clothes and car seat, and an unlikely set of actions in getting to an open gas tank without losing the static charge. This very low risk increases if the car or the gas pump has an electrical grounding defect. The risk is not zero, so there will be an explosion once in a while, and so the fire department and reporters will ask if a cell phone was nearby.
