Answer to Question #6962 Submitted to "Ask the Experts"

Magnetic fields are created by electrical currents, and there are lots of electrical currents in a car.  We should not be surprised that measurements of magnetic fields inside or near a car would give positive results and also highly variable results from location to location depending on proximity to electrical wiring. Just think of all the electrical wiring and electric circuits in the body of a modern automobile: inside and outside lighting, radio/CD player, turn signals, blower fans for air conditioning and heater, not to mention the engine itself plus all the unnamed circuits that people who are not auto experts do not begin to understand. One glance at the fuse panel will remind us that each of these circuits carries several amperes of electrical current and so it creates strong magnetic fields. (The actual strength of the magnetic field near a wire with a given amount of electrical current can be readily calculated by consulting equations in a high school physics textbook.) 

It is difficult to interpret the results of magnetic field measurements because the meters commonly used are most likely calibrated to read accurately for 60Hz magnetic fields created by the alternating current in household wiring. In a car the electrical currents are primarily direct current, not alternating current, except of course in the engine itself where the alternator is creating an alternating current, but even this is not a 60Hz frequency. So it is not surprising that a magnetic field meter gives positive indications inside a car, but without a good deal more work by an expert, it would not be possible to intepret these numbers quantitatively.

I do not know of any scientific studies done on the magnetic fields inside automobiles. But there have been reports of measurements of magnetic fields in proximity to household appliances. Common appliances with 60 Hz alternating currents on the order of amperes have magnetic fields on order of hundreds of milligauss.

Also, we all live in the presence of the earth's static magnetic field, which has a strength of about 600 milligauss, more or less, depending on where you live on the planet.   

We do not normally think of common household appliances or of the earth's magentic field as posing human health hazards. There are professional advisory bodies that evaluate reports of health hazards to formulate safety guidelines for hazards like magnetic fields. These include the International Commission on Nonionizing Radiation Protection and the American Conference of Governmental Industrial Hygienists or ACGIH. You will find other helpful information on the Ask the Experts feature of the Health Physics Society website.
 
Gary Zeman, ScD, CHP