Answer to Question #13181 Submitted to "Ask the Experts"

There are two cell towers on the roof of my office building, one from AT&T and one from T-Mobile. I purchased a handheld reader to test the radiofrequency (RF) levels and it reads a peak of 8–12 mW m^-2. That seems much higher than the "safe" levels I have read about. Should I investigate this further, and if so, how would I do that?

To fairly assess the levels of exposure to RF energy within the building would require a trained technician using specialized (and very expensive) equipment. Consumer grade RF meters cannot be trusted to be even approximately correct. Also, since there are many sources of RF energy in modern environments (including any cell phones close to the measurement site) the source is not clear for the RF fields you were measuring. 

That said, the exposure levels you mentioned, about 10 mW m^-2 are not impossible within a building directly beneath a set of cell base station antennas mounted on the roof. They could come from cell base stations or other communications transmitters on roofs of nearby buildings, or even from a cell phone in your pocket. Similar field levels might be found in the vicinity of a microwave oven when it is in use. 

Exposure limits in effect in the United States and most other countries depend on frequency, but are about 5–10 watts m^-2 at frequencies used by cell phones. In other words, the levels you mentioned are roughly 1,000 times below safety limits in the United States and most other countries for cellular telephone signals.

The RF levels you mention would not trigger any requirements for remediation, and are far below US safety limits. Health agencies have repeatedly studied the large body of scientific literature related to RF fields and health, and consistently conclude that no clear evidence exists that RF exposure levels below international limits produce any health effects, although they all recommend that more research be done. Some individuals report nonspecific symptoms such as headaches when they consider themselves to be exposed to RF fields at levels far below safety limits, but controlled studies have failed to link the symptoms to actual RF exposure, as opposed to the belief of an individual that he/she has been exposed.

Before doing anything further, I suggest you would check your readings. Were all RF devices in the area (including all cell phones) turned off during your measurements? Are there other antennas on neighboring buildings that could contribute to the signal you measure? Do your meter readings change when you move to the lower floors of the building? If you really want to know the source of the RF signals and their actual levels, it can be done but I am not sure what you would gain from such information. An RF survey by a qualified engineer is not likely to result in actionable information, for RF compliance purposes, and it will probably be quite expensive.

However, if you want to go that route, you might commission a professional engineer to carry out an exposure assessment using professional-grade equipment that can determine the source of the RF fields and exposure levels in the rooms—they may be different from what you measure and may come from a different source than the cell base station antennas. Accurate information from a trusted RF professional may help to reassure you. That being the case, I strongly suggest hiring an expert who does not sell "remediation" services, who might try to scare you into expensive remediation services, and insist that the expert uses professional-grade instrumentation that can determine the frequency (and hence the source) of any RF signals in the rooms.

Kenneth R. Foster, PhD