FDA Center for Radiation and Health

"...The available science does not allow us to conclude that wireless are absolutely safe, or that they are unsafe. However, the available scientific evidence does not demonstrate any adverse health effects associated with the use of mobile phones or wireless..."

RF safety issues

Brendan Minish 
RF Engineer

When dealing with radio one commonly talks about EIRP this stands for Effective Isotropic Radiated Power.

EIRP is a figure that includes antenna gain, this works by giving the figure for the output power including antenna again (or loss) relative to a theoretical antenna that radiates equally well in all directions, the Isotropic antenna.

This is actually a really useful way to calculate power since it takes into account the bit that matters most, the antenna.

Just to make things a little more complex there are two systems in use to measure / describe power.

Probably the most familiar one is watts and the most useful unit for the wireless network builder is the milliwatt 1 Milliwat = 1 Thousandth of a watt. This is a linear system of power measurement 200 mW is exactly twice 100 mW

However the most useful system for measuring power is the Decibel (dB) system. which is a logarithmic scale. A little harder to understand but well worth the effort.

Decibels by themselves are simply a logarithmic scale so when using Decibels one must always give the reference used.

dBw = Decibels relative to 1 Watt

in this case 0 dBw = 1 W 3 dBw = 2W 6 dBw = 4 w 10 dBw = 10w - 10 dBw = 0.1 W

there is a table Here where you will notice I have rounded off my figures a little

dBm = Decibels relative to 1 Milliwatt (0.001 Watt)
in this case 0 dBm = 1 mW 3 dBm = 2mW 6 dBm = 4 mw 10 dBm = 10mw - 10 dBm = 0.1 mW

There is a table Here

the reason that the dB system is more useful is that one can usually just add dB figures when one is dealing with things like antenna gain. take for example a WiFi card with 32mW output power (a typical output power for a cheap and nasty linksys)

32mW = 15 dBm

Stick on a directional antenna, say a 60 cm 'patch' antenna, the antenna manufacturer tells us that the gain of the antenna is 17 dB

our EIRP is

15+17 = 32 dBm = 1.6w EIRP

But we need to connect our radio to the antenna with cable connectors etc, this incurs some loss, in this case it is a short run so lets say total system loses are 2 dB

15 -2+17 = 30 dBm = 1w EIRP

EIRP is useful because it is the best system we have for calculating system performance

However, the important bit Stick one (1) schoolchild in front of your antenna with 30 dBm (1W) EIRP as in above example and the absolute maximum RF exposure level is only 15 dBm (30 mW).  Why?  Because that's all the power we have put into the system so that's all the power that is available.Antenna gain is got by focusing what you put in, just like the reflector around your torch bulb.

Generally radiological Exposure limits are calculated in W/m2, in our example above we have, right at the antenna 30 mW over an area of 0.36 m2
In the microwave region the current EU safety limit is around 10w/m2, our above example has a peak exposure density at the antenna of 0.0108 w/m2 Around 1,000 times below the exposure limit.

As you can see we are safe by a good margin even right at the antenna, put the antenna up a pole or on a wall above head height (we don't want people breaking our link ) and the exposure levels are Much lower again

In Ireland Comreg organize on site measurements of various transmitter sites, the results are published Here.

There are some good documents that address public concern surrounding the health 'risks' associated with Cellular masts

FCC Document
Cell Phone masts and Safety

I think we should tackle this issue before it even becomes a problem with the anti-mast brigade.

Safety FAQ

http://www.sydneywireless.org/index.php?pagename=Safety%20FAQ

(Portions reproduced from wireless.org.au)

Q: Is 2.4Ghz radiation safe? I've heard it uses the same radiation as my microwave oven? Are you killing me / my chances to reproduce?

A: Only YOU are killing your chances to reproduce. We can't help that.

A microwave oven produces 500 to 1000 Watts of radiation. Typical 802.11b installations will produce 30 to 2000 mW. That's milli-watts.

The energy from a microwave oven is trapped within the faraday cage made up of its metal walls. If you didn't already know, your microwave oven uses a klystron to produce microwave (very short wavelength) radio waves in the 2.4ghz spectrum, which causes water molecules to vibrate in the food, and vibration is heat. The microwave oven is enclosed pretty well to avoid leaking this radiation, and the wavelength is larger than the gaps, holes and the mesh in the microwave door, so you are still quite safe when they put those holes in the microwave door to observe the food cooking. The power output of a microwave outside of the oven is barely noticeable, but it is discernable in the range we're using for 802.11b wireless.

If your microwave has bad seals, the energy can leak out in a concentrated burst & start cooking any water molecules in the area. That means you, the wildlife, the walls, the air, etc. It can be quite lethal at certain exposure levels, as can most kitchen utensils, i.e. treat with care & respect (and a serviceman if your kitchen/computer/antenna area is attracting a lot of inexplicably dead wildlife and people.)

It's an ongoing debate to define the safe limit of exposure to radiation, and with much thanks to Keith Light body and his article "Wireless Networks in Schools", which also makes reference to the National Standards on safe levels of electromagnetic radiation we know that the safety limit can be summed up with exposure limits:

 High gain, wall or mast mount antennas should be more than 1m from your body.

Dipole antennas on base stations should be more than 60 cm from your body.

The antenna on wireless cards in laptops should be more than 10 to 30 cm from your body, especially your reproductive organs.

 According to the current Australian reference levels standard, safe working environments require a power density of less than 1 mW/cm^2 (one milliwatt per square centimetre) for occupational workers and 0.2 mW/cm^2 for the general public. The proposed standard (which actually has passed into effect recently is 5x higher than the old standard) (extracted from Australian Standards AS/NZS 2772.1 (Int):1998 Maximum RF Exposure Limits (10-300 000 MHz)).

Comcare OHS Fact Sheet No 38 - November 2000 - Radiofrequency Electromagnetic Radiation

Note: This standard is likely to become obsolete very soon. The ACA is moving to adopt the following standard instead:

Radiation Protection Standard Maximum Exposure Levels to Radiofrequency Fields - 3kHz to 300 GHz, developed by the Australian Radiation Protection and Nuclear Safety Agency (ARPANSA). For more information, this is a discussion paper released by the ACA.

 lready the EMR exposure standards for amateur stations have been postponed, to allow the ACA to align them with the new ARPANSA limits.

To give this some perspective and rellivance to you, a mobile phone emits typically 600mw of power (about 28dBm signal) at 900Mhz and/or 1800Mhz, which is also in the microwave part of the spectrum, so the safety limits shown above, for a high gain antenna is appropriate advice for your mobile phone with it's inbuilt/external antenna. I'll check that later too.

 For a cute quip and something you can use to start a wireless discussion between non-wireless friends and members of the opposite sex (to help you get out and reproduce, see the question on safety for the reference), in 1909, Guglielmo (pronounced goo-glee-elmo) Marconi developed the radio, and in 1913 Hedy Lamarr (yes, the Hollywood actress) and George Anthiel developed a patent on a "spread spectrum" device, an anti-jamming device to protect radio-controlled torpedos. It's the basis for FHSS and DSSS and most modern data communications over radio.

Q: Someone mentioned 4w is the max power output allowed. i want "more power" and I'm willing to spend some serious money to boost my signal (and to microwave my neighbours, the people who live in a 10km radius and the surrounding wildlife). How do I do this? Whats the deal with EIRP?

 A: Well, EIRP stands for Emission of Isotropic Radiated Power. The limit for 802.11b compliance in Australia is 4W EIRP. In terms of decibels, that's 36dBm.

 The output power for a Lucent/Orinoco/Agere/Avaya 802.11b PC card is 15 dBm. There is a built in 2 to 3dBi antenna on the card, however they also come with an external connector so that you can plug a much higher gain antenna into. There are some devices with 100mW and 200mW output, this reduces the maximum amount of gain allowed with antenna to remain legal, so bear this in mind.

If you're trying to overcome a problem with a long-distance link, first get bigger antennae, check the link for obstructions and faults with equipment, or move to a different radio spectrum/channel, before you think about upgrading to a more powerful device.

If you attach a 2.4ghz amplifier, you need to be careful that the rated output power does not go over the 36dBm limit once you attach an antenna and a low-loss cable to the amplifier. See the next question for details on how to check this.

Q: How in the heck do i work out my EIRP then?

Example: we have a PC Card with a 14 dBi external antenna (a modded galaxy antenna) and 50 ft (12.7 Metres) of LMR400. We make the assumptions that the total loss for a pigtail adapter is 0.5 dB and the loss for each connector on LMR400 is 0.5 dB. Using a quick formula, here's how we work out the EIRP:

PC card - pigtail adapter - connector - 50 ft (12m) of LMR400 - connector + 14 dBi antenna = ? dB of Total output power 15 dBm - 0.5 dB - 0.5dB - 3.3 dB - 0.5 dB + 14 dBi = 24.7 dBm  The maximum is 36dBm, which makes 4W EIRP.

The resulting signal is roughly 10x stronger than what comes out of the wireless card, and within the safe limits of the EIRP restriction, which is 120x the output power of the card.

For more information on working with decibels (dB), and some lookup tables, check out Power And Gain To Decibels.

Does WLAN Pose a Health Risk?
http://www.netstumbler.com/print.php?sid=324

Being around recently to find out if there are any potential health risks associated with the growing use of wireless LAN technology. We wondered if the growing use of 802.11b technology -- in our homes, cafés, and other public areas -- with the resultant increase in radio traffic all around us should be a cause for concern.

The answer seems to be... Maybe -- if you are one of the growing band of people who use home-made equipment to increase the range of 802.11b hotspots.

Understandably, in the wider world, there isn't the same level of concern about the radiation emissions from relatively low-power WLAN kit as there is about, say, living next to a cellular tower. And apparently, as long as you're using standard-issue commercial wireless LAN kit, the Federal Communications Commission (FCC) in the U.S. and other regulatory bodies worldwide tightly controls the emission levels.

However, some of people working outside of the strictly commercial WLAN market -- boosting the range of their local wireless community sites with Pringle can antennas, for instance -- could potentially be taking a risk, according to David Sifry, CTO at open-source WLAN mavens, Sputnik Inc.

"I'm not a doctor, nor do I play one on TV," he writes in an email reply to Unstrung. "So please take this for what it is worth -- one engineer's understanding of the current issues, and some extrapolation of current physical research into the 2.4GHz spectrum.

"Current FCC regulations limit power output to 1 Watt EIRP (Effective Isotropic Radiated Power) for 802.11b (2.4GHz) devices. Most cards are 30 milliwatt, and there are a few 100mW and 200mW cards out there. Compare this with microwave ovens, which can emit 500 to 700 Watts to heat up your dinner. Of course, microwave ovens are shielded, but even a small amount of leakage would emit more radiation than these 802.11 devices."

However, Sifry fears that some of the more outré methods being used to boost the range of WLAN systems could prove to be hazardous: "Of course, if you illegally crank up the power or narrow the beam [exactly as the Pringles can antenna does], the EIRP goes way up, so there are potential health threats associated with using illegal equipment."

Now, these kinds of booster devices tend to be placed on rooftops and thus generally away from people, in order to get the best line-of-sight access. So it is hard to gauge exactly how much of a risk there is from such signal amplification. And common sense suggests that you don't walk in front of your home-made antenna if you are really trying to crank up the range of your 802.11b system (Unstrung health tip number one).

Despite the low emissions of commercial WLAN equipment, Jack Gold, VP of the mobile and pervasive computing group at Meta Group sums up just how much we don't know about the effects of widespread use of wireless technology.

"I'm not sure anyone knows the long-term effect of walking around in lots of radio fields… I think it may take years before we have proof one way or the other about the effects," he says. "Of course, I am not a medical researcher, so I am not able to give a medical opinion -- but from all that I've read, the jury is still out on this."

— Dan Jones, Senior Editor, Unstrung
http://www.unstrung.com

Health Issues

http://www.wirefreelondon.com/faq.html?b=health

When people are concerned with the health issues surrounding wireless networks, they are talking about the effects of radio wave radiation. Radio waves are lower down the electromagnetic spectrum than x-rays, gamma rays and other harmful radiation and there has been no medical correlation to any form of disease in the range that wireless equipment uses.

A typical 802.11b wireless network card will transmit at around 30 milliwatts and operates in the 2.4 GHz frequency band. The average GSM mobile handset has a power output of around 600 milliwatts, which is about 20 times that of a wireless network transmitter. Furthermore, the transmitter is far away from your body and the resultant signal strength decreases by the inverse square of the distance from the source. This means that by being even a few feet away has the effect of the emissions being negligible by comparison. If using a mobile phone is a risk when considering health issues, it is clear that by comparison the risk of wireless network equipment is small.

Regional and national regulatory authorities such as the FCC and CEC also subject to equipment certification and operating requirements establish wireless network equipment.

Standards and Guidelines

http://www.who.int/peh-emf/en/

- EMF World Wide Standards Database
- Framework for Harmonization of Standards
- Model Legislation

A number of national and international organizations have formulated guidelines establishing limits for occupational and residential EMF exposure. The exposure limits for EMF fields developed by the International Commission on Non-Ionizing Radiation Protection (ICNIRP) - a non-governmental organization formally recognized by WHO, were developed following reviews of all the peer-reviewed scientific literature, including thermal and non-thermal effects. The standards are based on evaluations of biological effects that have been established to have health consequences. The main conclusion from the WHO reviews is that EMF exposures below the limits recommended in the ICNIRP international guidelines do not appear to have any known consequence on health.

The International EMF Project has compiled a worldwide standards database limiting exposure to EMF.

Because disparities in EMF standards around the world has caused increasing public anxiety about EMF exposures from the introduction of new technologies, WHO commenced a process of harmonization of electromagnetic fields (EMF) standards worldwide. With 54 participating countries and 8 international organizations involved in the International EMF Project, it provides a unique opportunity to bring countries together to develop a framework for harmonization of EMF standards and to encourage the development of exposure limits and other control measures that provide the same level of health protection to all people.