Controls
One control to prevent microwave injury is limiting exposure. This is accomplished by limiting the intensity of microwaves (the frequency or wavelength one is exposed to) or limiting the duration of exposure. Distance from a source and shielding also can control intensity of exposure. Table 21-1 lists attenuation of various shielding materials. Before implementing controls, one must determine what potential exposures exist through analy- sis, measurements, or both. These are compared with exposure standards to determine if controls are needed. Other controls are signs to warn about radiation hazards or dangers (see ANSI C95 for details), special protective clothing that uses metallized fabric to provide some shield- ing, and protective eyewear that has a closely woven screen for shielding. Workers should handle equipment near microwave sources with insulated gloves to minimize shock and burn hazards. High-power microwave equipment must be grounded to reduce electrical hazards. Access to hazardous microwave locations can be protected by interlocks on doors and regular inspections, and testing ensures that the interlocks are working. During servicing of microwave equipment, lockout and tagout procedures are important.
Standards Microwave exposure standards appear in several publications. One source is OSHA stan- dards,2 which limit power density to 10mW/cm2 for exposure periods of 0.1hr or more. For exposures shorter than 0.1hr, energy density is limited to 1mW-hr/cm2, with limited excursions higher than 10mW/cm2.