Cellular Phone and Base Station
Radiofrequency (RF) emissions from antennas used for wireless transmissions such as cellular and PCS (personal communication systems) signals result in exposure levels on the ground that are typically thousands of times less than safety limits. These safety limits were adopted by the Federal Communications Commission (FCC) based on the recommendations of expert organizations and endorsed by agencies of the federal government responsible for health and safety. Therefore, there is no reason to believe that such towers could constitute a potential health hazard to nearby residents or students.
Other antennas, such as those used for radio and television broadcast transmissions, use power levels that are generally higher than those used for cellular and PCS antennas. Therefore, in some cases there could be a potential for higher levels of exposure on the ground. However, all broadcast stations are required to demonstrate compliance with FCC safety guidelines, and ambient exposures to nearby persons from such stations are typically well below FCC safety limits.
The "Minimum Safe Distance" from a mobile phone base antenna is described by the Food and Drug Administration/FCC as follows: "To be exposed to levels at or near the FCC limits for cellular or PCS frequencies an individual would essentially have to remain in the main transmitted radio signal (at the height of the antenna) and within a few feet from the antenna . . . . In addition, for sector-type antennas RF levels to the side and in back are insignificant." Note that the quote about safe distances applies to the actual radiating antenna, not to the tower (or building or structure) the antenna is on. For a mobile phone base station antenna mounted on a tower that is 5+ meters high (about 15 feet), there should be no areas that will come anywhere close to the RF radiation safety guidelines, so the concept of a "minimum safe distance" doesn't really apply to generally occupied areas.
In general this will not be a problem. The roof of the building will absorb large amounts of the RF energy. Typically a roof would be expected to decrease signal strength by a factor of 5 to 10 (or more for a reinforced concrete or metal roof). In addition, the FCC requires RF radiation evaluations of high-power rooftop transmitters. Even a worst-case calculation predicts that power density on the floor below an antenna will meet all current RF safety guidelines, and actual measurements in top-floor apartments and corridors confirm the power density is far below all current RF safety guidelines.
Hands-free cell phone car microphones have been tested by the manufacturers and meet the current American National Standards Institute (ANSI)/Institute of Electrical and Electronics Engineers (IEEE) standards for R) radiation safety. These are the same standards that the FCC enforces under the Telecommunications Act of 1996, and they place limits on the specific absorption rate of RF energy in the body. There has been no substantiated information that the car microphones emit more RF than any other item used with cell phones.
Whenever they are turned on, cell phones communicate at infrequent intervals with a nearby base station even when they are not being used for a call. This is necessary to tell the system where the user is in case a call should come in. Thus, even while they are inactive, the phones are a source of (very low) RF energy exposure to the user.
Hands-free kits reduce exposure to a user by removing the phone from the vicinity of the head. There is no identifiable health benefit in using the kits, but there is no detriment either, and using them may increase a user's peace of mind. In your case, the cell phone and hands-free kit are clearly an important link to the outside world and I would not hesitate in using them. There may be comfort issues with having the earpiece in place for a long time, but RF radiation exposure should not be a concern at all. The hands-free kits will reduce exposure below that which you would receive if the phone were kept close to your head.
There are a number of opportunistic gadgets on the market to allegedly protect the user from hazards of cellular phones. You can search the Internet to find the latest, ranging from antenna shields to whole-body shielding materials. Most experts believe that these devices take advantage of customers' misunderstanding and unfounded fears to sell products with no real value. First of all, cell phones that operate within the guidelines established by national and international safety panels have never been shown to pose a health risk to the user (see answers to other questions on cell phone safety on this page). Secondly, placing any kind of shield over the antenna of a cell phone will in most cases cause it to increase its RF output as it attempts to compensate for signal loss in the shield and maintain a quality phone call.
The best single reference is the Federal Communications Commission Website. Look for:
- Bulletin 56, "Questions and Answers about Biological Effects and Potential Hazards of Radiofrequency Electromagnetic Fields."
- Bulletin 65, "Evaluating Compliance with FCC Guidelines for Human Exposure to Radiofrequency Electromagnetic Fields."
- "A Local Government Official's Guide to Transmitting Antenna RF Emission Safety: Rules, Procedures, and Practical Guidance."
An excellent technical paper with field measurements of cell-tower emissions was published by R.C. Petersen and P.A. Testagrossa in the journal Bioelectromagnetics, volume 13, page 527ff, 1992.
The issue of banning mobile phone use in hospitals is a subject of some controversy. For a snapshot of the controversy it is useful to look at an article that was published in March 2003 in the British Medical Journal (BMJ 326:460, March 2003). The authors concluded: "Mobile phones in hospitals are not as hazardous as believed and should be allowed at least in nonclinical areas."
At least as interesting as the article itself are the online responses to the article. This is what we know:
- Mobile phones can interfere with medical equipment.
- The interference is relatively rare and generally goes away when the phone is turned off or moved away.
- There appear to be no confirmed reports of life-threatening interference.
- The two-way radios used by emergency-service personnel and hospital transport aides (porters) are a bigger source of interference than consumer mobile phones.
- Other sources of RF radiation (for example, digital TV broadcasts and other medical equipment) have also caused interference with medical devices.
- Many (most?) hospitals ban mobile phones, but the basis for their bans is generally vague, and the bans are often very poorly enforced on visitors or on staff.
I am unaware of any general governmental bans on the use of mobile phones in hospitals. In the United States, this would fall under the jurisdiction of the Center for Devices and Radiological Health of the Food and Drug Administration and to date the Food and Drug Administration has not taken a position on the subject. The bottom line is that interference with medical equipment by devices that produce RF radiation is an issue for hospitals and medical-equipment makers, but the source of the problem is not limited to mobile phones.
It's a question of signal strength. Interference with medical devices has been observed only very close to transmitting antennas where there is strong signal strength. Interference has been observed in some medical electronics due to hand-held cell phones. Rooftop antennas are some distance away from any susceptible electronics. In addition to proximity, the directionality of the antennas is important. Most rooftop antennas have strong gain in the forward directiontowards the horizonand very low gain in the vertical direction. Finally, there are layers of building materials shielding the interior areas from the rooftop antennas. Proximity, directionality, shieldingall go towards reducing the signal strength inside a building due to the antennas on the roof so that interference is not generally an issue. This does not mean that you cannot receive the signals from the rooftop antennas inside the building; it simply means that the received signals are not strong enough to cause interference.
It is not clear that mobile phones do produce brain tumors, or any serious health effects for that matter. A number of epidemiology studies have been almost completely negative on the issue. See the article by Kenneth Foster and John Moulder in IEEE Spectrum magazine and also Moulder's FAQ on mobile phones and health. There has been a lot of discussion over the years about the possible mechanisms by which microwave energy such as emitted by cell phones might produce biological effects. The one proven mechanism is the heating of tissue, but mobile phones operate at power levels that are too low to cause noticeable heating in the user. Scientists have speculated about other mechanisms, but these theories remain unproven and many of them have been challenged on biophysical grounds.
Whatever may be the risks or nonrisks of mobile phone radiation, a hands-free kit is an effective way for the user to reduce his or her exposure to RF energy while using a mobile phone. If you have serious concerns, limited or no use of a cellular phone might be a consideration for you.