Friday, August 21, 2015

Why You Shouldn't Worry About Wi-Fi Radiation Exposure


I was recently approached by a client to comment on the growing trend of pseudo-science alarmist claims related to the alleged health risks of radio frequency (RF) exposure from Wi-Fi.   

The concern over RF radiation exposure is not new.  However, despite an ever-growing mountain of scientific evidence debunking claims that exposure to RF radiation from Wi-Fi and cellular phones cause health issues, there seem to be an ever-growing number of subscribers to this belief. Unfortunately, this is not a debate that can be won with reason or scientific evidence.  If that were possible, this would've been resolved a long time ago.  Rather, this is the telecommunication industry's version of the anti-vaccination movement.  It has nothing to do with logic or scientific proof, and is instead all about fear-mongering to push a radical anti-science and anti-technology agenda with a religious zealotry.  Quite plainly, this is one, of unfortunately several, 21st century Luddite movements.   

Nonetheless, this blog post is an attempt to compile several various sources of scientific studies on this topic done by government health agencies around the world, along with the World Health Organization.  It is not by any means an exhaustive list, but is provided as a general reference for a community that keeps being plagued by questions on this issue.

The general consensus of the scientific community is that radio frequency exposure from Wi-Fi in one’s home or work environment is negligible, especially when compared to other types of RF exposure (e.g. cell phones, radio transmitters, microwaves, cordless phones, etc.) that people are regularly exposed to in today’s modern environment.  

Unfortunately, by definition, it is scientifically impossible to prove the absence of something, which is what gets latched on to in order to keep this debate alive.


The Fundamentals

Wi-Fi networks function by using radio waves to transmit information from wired access points to the wireless adapter cards in laptop computers, smartphones, tablets, and network appliances (IoT). The reality is that Wi-Fi APs are limited to around 1 W (30 dBm) of output power at the radio, which is at least 2-3 orders of magnitude less RF energy as always-on sources that we have accepted in our environment without protest for the last 100 years, including cell towers, radio stations, analog TV stations (prior to digital conversion), weather radar systems, and the like.  For comparison with Wi-Fi on 2.4 GHz and 5.2 - 5.8 GHz,  licensed cellular runs on frequencies between 700 MHz to 2.1 GHz, and weather radar is on the UNII-2e portion of the 5 GHz band (roughly 5.5 - 5.7 GHz).  These frequencies are in the range of the electromagnetic spectrum defined as "radio frequency (RF) radiation".  RF radiation (non-ionizing radiation) is much lower in energy than the radiation emitted by x-ray machines (ionizing radiation). The biological effect associated with each type of radiation is very different.

Exposure to high levels of radiation results in tissue and cell heating, which is harmful to health.  The debate centers around the question as to whether low level radiation, where cell and tissue heating is not detected, is also harmful.  Several studies have been conducted to find links between low level RF radiation exposure and cancer, or the effects on pregnant women.  Most studies until now have been concerned with RF emissions from mobile phones, which (as you will see below) provide about 100x the exposure to RF radiation as a Wi-Fi access point. The close distance between the head and the mobile phone and the higher power levels used in mobile devices means that a frequent mobile phone user is exposed to much higher levels of radiation than a person in a residential or commercial Wi-Fi environment. Studies by highly regarded researchers have not shown harmful health effects resulting from either cellular Wi-Fi RF radiation exposure, which are below US regulation limits.  

Several examples of such studies are summarized or referenced below.  Prior to the studies, the assertion that a person gets much more RF radiation exposure from a cell phone or microwave oven than from Wi-Fi access points can be shown mathematically.


Let the Math Happen

(Thanks to Daniel Koczwara at EnGenius for inspiring me to include this section.)
The propagation of all radio signals is subject to Free Space Path Loss (FSPL), which is a mathematical definition of the geometric property that the further away you are located from the source of a radio transmission, the energy level in that signal drops as a function of the square of the distance.  You can think of throwing a pebble into a pond; as the wave ripples out, the energy is spread over a wider and wider area, and the level of energy at any one point is proportionally smaller.

While this is a geometric effect, wavelength is included in the calculation in order to account for the fact that, mathematically, transmission energy is defined as coming from a point source known as an isotropic antenna.  An isotropic antenna is defined as an antenna that radiates energy evenly in a perfect sphere with 0 dBi of gain.  While defining such an antenna is mathematically convenient, it is physically impossible to build.

The following graph shows the free space path loss for Wi-Fi at 2.4 GHz and 5 GHz.

Per FCC and other worldwide government regulations, a Wi-Fi signal, at most, has a maximum initial power of  30 dBm (1 W, or 1000 mW), and within the first 3 feet over 40 dB of energy is lost (100 W), meaning that the level of exposure 3 feet away is below -10 dBm (0.0001 W, or 0.1 mW). 

Comparative Example 1:  Microwave Oven   A microwave oven operated on the 2.4 GHz bands at around 1000 W (60 dBm). Granted microwaves are shielded, but the shielding is not perfect and deteriorates over time, which is why microwave ovens typically interfere with Wi-Fi when in operation, because they put out more energy on the 2.4 GHz band than an AP and this flood the channel, causing wideband interference.  Three feet away from a leaky microwave oven, the 2.4 GHz energy level decreases by 40 dB to 20 dBm (0.1 W, or 100 mW), or about 1000x higher than a Wi-Fi access point.

Comparative Example 2:  Ham Radio  A ham radio typically operates at 50 W (47 dBm) at 440 MHz.  The FSPL at three feet away (i.e. where the operator is sitting) is about 25 dB (approximately 0.32 W or 320 mW), leading to an exposure level of 22 dBm (0.16 W or 160 mW), or about 1600x higher than a Wi-Fi access point.

Comparative Example 3:  Cell Phone  A typical cellular phone operates at 23 dBm (0.25 W or 250 mW).  However, it operates very close to your head when on a call (about 2 inches), which provides a minimal FSPL of only 3.5 dB (0.0022 W, or 2.2 mW) at 700 MHz (Verizon LTE). This leads to an exposure level of 19.5 dBm (90 mW or 0.09 W), or approximately 100x higher than a Wi-Fi access point.

Comparative Example 4:  Cell Tower  It's somewhat interesting that the output of an entire city or town from a nearby cell tower is never brought up in the debate, though again the math explains this.  A typical cellular tower operates around 40 W (46 dBm).  At 700 MHz (Verizon LTE), the FSPL at about 1/2 mile - 1 mile away is about 90 dB, leading to an exposure level of -44 dBm (0.00004 mW or 0.00000004 W), or about 4000x lower than from a Wi-Fi access point.

Short answer: you get more exposure to RF energy from using your cell phone on the cellular network than you do from Wi-Fi.

Some Highlighted Scientific Studies

The Federal Communications Commission (FCC), the Occupational Health & Safety Agency (OSHA), the Institute of Electrical and Electronics Engineers (IEEE), and the International Commission on Non Ionising Radiation Protection (ICNIRP) have established standards and guidelines for general public and occupational exposure to radio frequency radiation.

Prestigious organizations have conducted surveys of the RF radiation field levels encountered in the presence of wireless networks. For example, a 2007 published paper entitled Radiofrequency Exposure from Wireless LANs UtilizingWi-Fi Technology discusses a study in which measurements were conducted at 55 sites in four countries, and measurements were conducted under conditions that would result in the higher end of exposures from such systems. An excerpt from the abstract states “.…In all cases, the measured Wi-Fi signal levels were very far below international exposure limits (IEEE C95.1-2005 and ICNIRP) and in nearly all cases far below other RF signals in the same environments.”

In 2007, Princeton University commissioned the New Jersey Department of Environmental Protection (NJDEP) to perform a survey of the RF levels associated with the wireless network at Princeton’s Firestone Library.  Spot RF levels in the line of sight with the antennae were measured in addition to spatially-averaged levels in the vicinity of the antennae. NJDEP limits for RF radiation exposure are defined specifically in terms of spatially averaged values, averaged over the dimensions of the human body, rather than for ‘spot’ measurements.  Measurements were also made within an Office of Information Technology (OIT) closet, a student carrel (because cable runs overhead and a map indicated that an antenna was located overhead), and at the ceiling in the vicinity of a radiating (‘leaky’) cable.  One of the most noteworthy points of these measurements is that the RF levels present in all locations were so low that the levels were close to the lower limit of detection of the RF survey equipment. The maximum spatially-averaged level measured was 10.9 Volts2/meter2, directly below an access point antenna. This measurement should be compared to NJDEP’s allowable limit of 20,000 Volts2/meter2, spatially averaged over the dimensions of the human body. The NJDEP limit does not differentiate between exposure of the general public and occupational exposure.

Another survey report,
ACRBR EME In Homes Survey: Final Report was conducted by the Australian Centre for Radiofrequency Bioeffects Research in 2009.  Radio frequency radiation levels were measured in 20 suburban homes in Melbourne, Australia. The survey assessed RF levels from individual devices (cordless phones, Wi Fi, etc) in isolation, as well as their cumulative exposure. The results generally indicated very low levels with the highest level being less than 1% of the limits in the Australian RF Standard. For individual devices, the highest level was less than 10% of the limits in the Standard. Having all RF devices on simultaneously in a home (cumulative exposure) had little effect on the results. The authors conclude that the use of RF devices in an average suburban home results in very low RF exposure (compared to the Australian Standard), even when numerous RF devices are operating simultaneously. 

The ultimate authority on this in the USA is the FCC.  They have an official statement, primarily related to cell phones but. as demonstrated, also applicable to Wi-Fi.  Basically, it states that the FCC regulates all radio devices sold in the USA and there is no scientifically proven causal relationship between RF energy and health.  Health Canada presents, in my opinion, a more in-depth analysis of the issue, reaching the same conclusions as the FCC.   As a reminder, Wi-Fi's regulated frequencies and power limits are identical in the USA and Canada, and fairly similar throughout the rest of the world.

On the access point front itself, there is a 2005 position white paper by Cisco indicating that they are in compliance with FCC, European, and World Health Organization regulations and guidelines for their equipment.  All AP vendors, including EnGenius, comply with these, else they would not be able to sell equipment in these world markets.  The paper has some interesting secondary references as well.


Additional Resources

If the above was not sufficient to convince, these are several additional studies and papers that I've come across. 

  1. Lin, J, Update of IEEE Radio Frequency Exposure Guidelines, IEEE Microwave Magazine; 2006.
  2. Lin, J, Safety Standards for Human Exposure to Radio Frequency Radiation and Their Biological Rationale, IEEE Microwave Magazine; 2003.
  3. Osepchuk, JM, and Petersen, RC, Safety Standards for Exposure to RF Electromagnetic Fields, Microwave; 2001
  4. World Health Organization. ElectromagneticFields and Public Health: Mobile Phones. Fact Sheet No. 193; October 2014
  5. Australian Radiation Protection and Nuclear Safety Agency. Maximum Exposure Levels to Radiofrequency Fields - 3 kHz to 300 GHz.  Radiation Protection Series Publication No. 3; 2002.
  6. Australian Radiation Protection and Nuclear Safety Agency.  An Explanatory Question & Answer Guide to the ARPANSA Radiation Protection Standard for Maximum Exposure Levels to Radiofrequency Fields – 3 kHz to 300 GHz. 2002.
  7. M. Kundi.  The Controversy about a Possible Relationship between Mobile Phone Use and Cancer. Environmental Health Perspectives; 2009.


  1. Howdy. Glad I found your blog as I find it very informative and helpful -- thank you for doing it. Also, wondering if we ever intersected during the IHTFP times ;) I think after you've written this post, FCC has upped the limit to 4W for some channels (see I haven't checked FCC's official documents (because I find them unreadable), but thought you'd probably know for sure, and might be interested in updating the post. Again, thanks for a terrific blog!

    1. Alas, most MIT professors' lectures and textbooks have proven to be less cryptic than FCC documents, though I did not think so at the time. :)

      The 4W of output power has to do with the effective isotropic radiated power (EIRP), which is the power out of the antenna, after accounting for the antenna gain. The power output on UNII-3 is allowed for 1W (30 dBm) of transmit power for the radio with an antenna gain of up to 6 dBi, leading to 4W (36 dBm) total EIRP. If you want to use a higher gain antenna, for a point-to-(multi)point link, the FCC regulations mandate lowering the AP transmit power such that the EIRP still does not exceed 4W (36 dBm).

      In practice, most installers are neither aware of nor follow this FCC restriction, and it is only ever enforced if someone else (a) notices and (b) complains to the FCC. For the purpose of the conclusions of this blog, this doesn't really matter. Even assuming an installer uses a 20 dBi gain (100x) antenna, leading to a total EIRP of 100 W (50 dBm), the power levels are still in the "noise" in terms of exposure, and with free space path loss, power levels only a few feet away are still at very minimal levels.

  2. what about mistaken exposure to the chest area at 1ft @ 45dBm for about 10-20 seconds

  3. 45 dBm is a tad under 40W. I would expect that you would get far more exposure from an X-Ray or other medical scan, and that is ionizing vs. RF which is non-ionizing. Those of us who work in Wi-Fi regularly get exposed to far more RF, with several APs in a small lab broadcasting at full blast for hours at a stretch, without any ill effects.