Over 50 cases of human cataract induction have been attributed to microwave exposures, primarily encountered in occupational situations involving acute exposure to presumably relatively high-intensity fields. The following are three reported incidents of cataracts caused by microwave radiation:

(a) A 22-year-old technician exposed approximately five times a 3 GHz radiation at an estimated average power density of 300 mW/cm2 for 3 min/exposure developed bilateral cataracts.
(b) A person was exposed to microwaves for durations of approximately 50 hr/month over 4- year period at average power densities of less than 10 mW/cm2 in most instances, but with a period of 6 months or more during which the average power density was approximately 1 mW/cm2.

A3-mm-thick panel of aluminum alloy (k 177 w/m-k, c 875 j/kg-k and ? = 2770 kg/m) is finished on both sides with an epoxy coating that must be cured at or above t,-150°c for at least 5 min. the production line for the curing operation involves two steps: (1) heating in a large oven with air at ts,0-175°c and a convection coefficient of h, 40 w/m2. k, and (2) cooling in a large chamber with air at 25°c and a con- vection coefficient of he 10 w/m2.k. the heating portion of the process is conducted over a time interval te which exceeds the ime required to reach 150°c by 5 min (h = r + 300 s). the coating has an emissivity of ? = 0.8, and the temperatures of the oven and chamber walls are 175 and 25°c, respectively. if the panel is placed in the oven at an initial temperature of 25°c and removed from the chamber at a safe-to-touch tempera ture of 37°c, what is the total elapsed time for the two-step curing operation?