A substantial number of studies have been performed by various organizations to evaluate the impact of RF emissions on the human body. Taking input from these studies, the FCC set exposure limits that “incorporate prudent margins of safety” (according to the FCC’s RF Safety FAQ sheet¹ ). Similarly, Health Canada has issued limits of human exposure to RF radiation in Safety Code 6.
Devices that emit radio energy must be certified by the FCC to meet maximum permissible exposure (MPE) requirements, as specified in FCC 1.1310. The limits specified by the FCC vary based on frequency. The power density limits are specified as an average value over a six-minute period. The power density limit for the 915 MHz band is 0.6 mW/cm².
Health Canada has a similar limit specified in Safety Code 6.² The FCC and Health Canada validate a device using a calculation distance of 20 cm. In the MPE report submitted to the FCC for the communications device used on the REX meter, the transmitter power was measured as 232 mW,
with an antenna gain of 3.66 and at a distance of 20 cm. This results in a calculated power density of 0.169 mW/cm², which is 0.431 mW/cm² below the limit, less than one-third of the limit.
It is important to note these calculations assumed the device was transmitting 100% of the time during the six-minute averaging period, whereas there is no possible scenario existing where a Honeywell smart electric meter or device would transmit at a 100% duty cycle for even a short period, let alone for six minutes.
As highlighted above, raw power density calculations do not take into account how often a device is transmitting. The consumer electronic devices listed above are transmitting nearly continuously when they are in use. In comparison, an electricity meter transmits hardly at all. A Honeywell smart
meter has a transmit duty cycle of less than 1%. The average power density would therefore be 1/100 of the maximum calculated power density.