Radiofrequency and Microwave Radiation

Exposure Limits | Radiofrequency and Microwave Radiation in the Workplace


Exposure limits for RF/MW radiation are designed to keep the RF/MW energy
absorbed by the body well below the lowest levels associated with demonstrated
adverse effects, and to reduce the likelihood of contact shocks and burns.

Since the RF/MW energy absorbed by the body varies with the frequency of
the fields and since the rate of energy absorption is difficult to measure
directly, the exposure limits are expressed in terms of frequency-dependent,
root-mean-square (RMS) electric and magnetic field strengths, or in power
density units (W/m²). Power density measures the amount of radiating
energy crossing a given area in a given period of time.


Occupational exposure of the whole body to RF/MW fields should not exceed the values in Table I.



Table I: Exposure Limits for Radiofrequency and Microwave Exposed Workers Frequency (MHz) Electric Field Strength; RMS (V/m) Magnetic Field Strength; RMS (A/m) Power Density (W/m²) Averaging Time (min)

0.003 - 1	600	4.9	—	6
1 - 10	600/f	4.9/f	—	6
10 - 30	60	4.9/f	—	6
30 - 300	60	0.163	10*	6
300 - 1,500	3.54 f0.5	0.0094 f0.5	f/30	6
1,500 - 15,000	137	0.364	50	6
15,000 - 150,000	137	0.364	50	616,000/f1.2
150,000 - 300,000	0.354 f0.5	9.4 x 10-4 f0.5	3.33 x 10-4	616,000/f1.2
*Power density limit is applicable at frequencies greater that 100 MHz.
Notes: Frequency, f, is in Mhz. A power density of 10 W/m2 is equivalent to 1 mW/cm2. A magnetic field strength of 1 A/m corresponds to 1.257 microtesla (uT) or 12.57 milligauss (mG).

In addition, workers should not be subject to RF contact shocks or burns.
This can be achieved by reducing stray fields and installing appropriate insulation
and grounding, or by ensuring that the electric current flowing between a
worker and an object energized by electromagnetic fields does not exceed the
values in Table II.



Table II: Induced and Contact Current Limits for Radiofrequency and Microwave Exposed Workers Frequency(MHz) Induced Current(RMS) (mA) Through RMS Contact Current (mA)Hand Grip and Through Each Foot Averaging Time Both Feet Each Foot

0.003 - 0.1	2,000 f	1,000 f	1,000 f	1 s
0.1 - 110	200	100	100	0.1 h (6 min)
Note: The limits in Tables I and II are based on Health Canada "Safety Code 6", 99-EHD-237 (1999).

Table III shows which sources of RF/MW radiation may expose workers to levels
in excess of Occupational Exposure Guidelines. Measurements of RF/MW levels
should be carried out around sources with the potential to cause overexposure,
in order to ensure compliance with the Occupational Exposure Limits. Measurements
are not necessary for sources which do not have the potential to produce exposures
in excess of the Occupational Exposure Limits.




Table III: Sources of RF/MW Radiation Source Frequency (MHz) Potential for Over-exposure?

Video Display Terminal (VDT)	0.015 - 0.3	No
Dielectric Heater	1 - 100 (typically 27.12)	Yes
Diathermy Applicator	13.56, 27.12, 915, 2,450	Yes
Communications Transmitters: AM Radio	0.535 - 1.605	Yes
Communications Transmitters: FM Radio	88 - 108	Yes
Communications Transmitters: VHF TV	54 - 72, 76 - 88, 174 - 216	Yes
Communications Transmitters: UHF Radio	470 - 890	Yes
Communications Transmitters: Dish Antenna	800 - 15,000	Yes
CB Radio	27.12	Yes
Cordless Telephone	46 - 5,800	No
Cellular Telephone	824 - 850, 900, 1,800, 1,900	No
Traffic Radar	10,500 and 24,000	No
Microwave Oven	915 and 2,450	No*
*Federal legislation requires that microwave ovens be constructed to meet stringent microwave leakage limits and to have safety interlocks. When these interlocks are defeated, for example, during repair work, there is a risk of overexposure to microwave radiation.

Source:-
http://www.labour.gov.on.ca/english/hs/pubs/radiation/gl_radio_3.php