Magentic fields in the engine room

I've just been fitted with a cardiac defribulator. This device comes with instructions to avoid using cell phone in right ear and keep power-tools 12" away from the device. Seems the risk is that strong magnetic fields may damage the programming and cause the device to reset.

I currently live on a 53' Carver and the engine room has a lot of electrical equipment: 50A Charging / Inverter, 2*Starters / Transformers on the engines and Generator. My concern is that there is the potential for a sizable magnetic field in the engine room and I simply don't (short of saving up a few pennies and getting a crew) know how to avoid or manage the issue.

Questions:

1. Has anybody had to consider this problem? What it a problem? 2. Any clever way I can judge the strength of the magnetic fields?

Thanks,

Dave

Powerful magnets could impact operation of implanted heart devices http://www.healthimaging.com/content/view/5487/89/

Magnets could cause dangerous interference with the operation of pacemakers and implantable cardioverter defibrillators (ICDs), according to a study published in the December 2006 edition of Heart Rhythm.

The study found that common magnets used in homes and offices are not high risk. However, stronger magnets made from neodymium-iron-boron (NdFeB) may cause interference with cardiac devices and pose potential hazards to patients. NdFeB magnets are increasingly being used in homes and office products, toys, jewelry and even clothing.

“Physicians should caution patients about the risks associated with these magnets,” said Thomas Wolber, a cardiologist at the University Hospital of Zurich in Switzerland and lead author of the study. “We also recommend that the packaging include information on the potential risks that may be associated with these types of magnets.”

For the study, two spherical magnets of eight and 10 millimeters in diameter and one necklace made of 45 spherical magnets were tested on 70 patients, 41 with pacemakers and 29 with ICDs. The magnets were shows to have an impact on the device operation in each patient. However, the researchers noted that cardiac devices resumed normal function after the magnets were removed.

Some researchers who have evaluated magnet interference believe that manufacturers who use magnets should be required to put warning labels on their products for optimal patient safety.

More: www.HRSonline.org

The defibrillator probably has two field strengths that it was tested to. IEC61000-4-3 defines the test proceedure for High Frequency phenomena (typically 80-1000MHz) and uses units of Volts per Meter. IEC61000-4-8 defines immunity to Magnetic (Power Frequency) Fields (50/60Hz) and uses units of Amps per Meter.

The manufacturer will know what level the device is immune to. I would cut that level by 3 (which yields half the power) for safety. So if it complies with say 10V/m keep it below 3V/m.

Note: 10V/m will extend 1 meter from a 5W transmitting antennae.

I've tried asking the manufacturer but their 1st response was just their standard instructions. Actually, I have a follow-up in a month or so and I get to meet with a technical representative and I'm hoping to have some measurements by then.

Given the time of year and the fact that I'll have few needs to enter the engine room. Combined with the fact that I can just turn everything off. (Presumption is that there is that there would be a minimal magnetic fields with only a 12v active for lights - Anybody think this is a false assumption?). I can spend some time to fully understand the problem and resolution.

As I make progress I'll make sure to share that with the group as I cannot believe I'm the only one with the question.

Thanks for the inputs,

Dave

Magnetic field strengths are typically measured with a device called a "gauss meter". Here's an example of a reasonably inexpensive, portable one:

http://www.escience.ca/genSci/RENDER/6/1027/1056/11098.html

Once you've determined if there is a problem or not, there is a metal alloy, available in sheet form, called "Mu-Metal" that is used to make effective shielding of magnetic fields. It's available from industrial metal suppliers.

http://en.wikipedia.org/wiki/Mu-metal

Eisboch

I've ordered the meter and I'll provide some feedback when I'm able to map the magnetic fields in the engine room.

Dave

Also; I might check again after the engine/genset is off after a few minutes for risiduals -- so you know if you can shut it down & jump in the engine room.

"Dave Isherwood" <isherwood@att.net> wrote in message