Radar mount on mast vs post at stern

[Bob Kuba]

I found this article on Radar Safety Issues on Sailnet. Considering the fact that safety issues are concerned, and the article is educational in nature, I copied it without permission.

http://www.sailnet.com/forums/seamanship-articles/18989-radar-safety-microwave-exposure.html

Jim Sexton  
Contributing Authors   
Radar Safety and Microwave Exposure

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In recent years, affordable prices and user-friendly systems have greatly increased the number of radar units in use on sailboats. But this surge in radar use has come with some risk of exposure to microwave radiation. Given the size of these sailboats, radar scanners are often mounted in close proximity to crew, or even to people on nearby docks or other boats. It is possible, although not probable, that these persons can be exposed to levels of microwave radiation that can exceed the recommended safe limits.

Microwaves (RF energy at radar frequencies) can be hazardous if the intensity is sufficiently high. Microwaves are absorbed by the water in living tissue and their energy is converted to heat that may easily damage some organs, particularly the eyes, which may develop cataracts. For safety, always avoid looking directly into a scanner whether the radar is transmitting or not. It is well known that microwaves will interfere with cardiac pacemakers and it is common place to see the warning signs in public areas where microwave ovens are in use.

It has also been shown that long-term exposure to low levels of microwave radiation can induce a variety of physiological effects in small laboratory animals. The importance of these effects and their relevance to humans are not yet fully understood. Again for safety reasons, you should avoid long-term exposure and radar units should be operated only when needed for navigation or safety. When the radar is not needed, it should either be in standby mode (not transmitting) or turned off.

Obviously, the radiation levels associated with marine radar units will vary according to the particular make and model. A radar unit of three kilowatts up to approximately 0.5 watts per centimeter squared, operating in the X-band at 3-1/2 feet from and at the same height as the scanner, can be encountered. OSHA has determined that the recommended maximum safe level of exposure to microwaves is 0.2 milliwatts per centimeter squared. The average intensity can be as high as 0.8 (milliwatts per centimeter squared) when the scanner is stationary. At a distance of 7 to 10 feet from the scanner, the average intensity drops to safe levels (i.e. below 0.2 mW/cm2).

At points above or below the scanner's horizontal plane, the radiation level is lower than that measured at a corresponding point on that plane. However, it must be noted that the average radar has a rather large vertical beam width (20 to 25 degrees) and microwave radiation is beamed about 10 to 12 degrees above and below the horizontal plane. At 5 feet from the scanner and 1-1/2 foot below the scanner, the average intensity can still be in excess of the OSHA safety limit.

For these reasons, the scanner should be mounted as high as possible. You should also ensure that the radar is not transmitting when crewmembers are aloft or working in the area of the scanner. Crewmembers should be briefed about the hazards of RF energy and instructed to avoid the scanner by a minimum horizontal distance of 6 feet and a vertical distance of 2 feet when the radar is operating. Crewmembers should be briefed to not remain within the hazardous area for prolonged periods.

During normal radar operation, the average exposure is reduced, because the scanner rotates and a person is exposed only when the beam sweeps past. For example, a person standing three feet away from a four-foot rotating scanner is exposed to less than 20 percent of the average radiation level of a stationary beam. Exposures to microwave radiation above the recommended safe limits are most likely to occur in the immediate vicinity of a transmitting scanner when it is stationary. When the scanner is rotating for normal radar operation, average exposure is below the recommended safe limits; even at points as close as 3 feet.

Some radar units are designed to prevent emission unless the scanner is rotating. Other models, however, lack this safety feature. In these cases some care is required on the part of the operator to prevent unnecessary exposure of crewmembers. Operating procedures should be adopted which ensure that no microwave radiation is emitted except when the scanner is rotating.

A good rule of thumb for all small marine radar units is that the equipment should be turned off when not required, particularly in areas of high population density (e.g. at dockside and when moored in the area of other boats).