What are RF exposure limits?
RF exposure is limited to prevent heating of body tissue. In the US, 47 CFR 1.1310 sets maximum permissible exposure (MPE) as power density, e.g. for the general population 1.0 mW/cm² from 1,500 MHz to 100,000 MHz and f/1500 mW/cm² (f in MHz) from 300 to 1,500 MHz, averaged over 30 minutes. Portable devices near the body are evaluated by specific absorption rate (SAR), with a general-population limit of 1.6 W/kg averaged over 1 g of tissue for partial-body exposure.[1]
How is safe distance estimated?
In the far field, power density is S = EIRP/(4πR²). Solving for R at the MPE limit gives the minimum separation: R = √(EIRP/(4πSlimit)). Example: 4 W EIRP at 2.4 GHz with S = 1 mW/cm² = 10 W/m² gives R ≈ 0.18 m.[1]
What about occupational limits?
Occupational/controlled limits are five times higher in power density in the upper bands (5 mW/cm² above 1,500 MHz) with 6-minute averaging, and apply only when people are aware of and can control their exposure.[1]
Do other countries use the same limits?
Many countries follow ICNIRP guidelines, which differ in detail (e.g., SAR of 2 W/kg over 10 g for localized head and trunk exposure). Product compliance must follow the rules of each market.
Frequently asked questions
Is RF exposure ionizing?
No; RF photons lack the energy to ionize, and limits address heating.
What is SAR?
Specific absorption rate, power absorbed per unit mass of tissue, in W/kg.
Do Part 15 devices need RF exposure evaluation?
Yes, intentional radiators must address RF exposure under FCC rules.
See also
References
Online sources accessed October 21, 2026; printed works cited by edition. See all sources.
- “47 CFR 1.1310: Radiofrequency radiation exposure limits”. U.S. Federal Communications Commission, via eCFR. current.