Static Electricity during Refueling
Does use of mobile phones at petrol stations cause fires?
Whenever we use mobile phones, they emit microwave to communicate with the nearest antennas around us. According to urban legend, the microwaves emitted could generate a spark that ignite petrol fumes in a petrol station, causing a fire or even an explosion. Thus, we should never use mobile phones at petrol stations. But, is this claim supported by science?
What does it take to cause an electrical spark?
A spark is an electrical current through air. In flowing through air, the current produces so much heat that the temperature exceeds 1000 °C. This can ignite petrol fumes.
But air is typically an electrical insulator. For air to breakdown to allow electrical conduction, a potential difference exceeding approximately 4-30 kV/cm of air is required (https://en.wikipedia.org/wiki/Electric_spark).
Is microwaves from mobile phones strong enough to cause a spark?
Strength of microwaves emitted by mobile phones are of the order of mV/cm (https://en.wikipedia.org/wiki/Signal_strength_in_telecommunications). This is far lower than the order of kV/cm potential difference required to breakdown air. Thus, microwaves from mobile phones are far too weak to cause an electrical spark.
What could have caused electric sparks at petrol station instead?
Friction between our clothing and the car seat causes electrical charges to build up. Charges build up this way could easily amount to tens of thousands of volts (https://www.livescience.com/4077-shocking-truth-static-electricity.html). A sudden discharge in the form of a spark can ignite petrol fumes.
Charging by friction is covered under Static Electricity in our Physics Tuition classes.
Image Source: The Star/ Asia News Network