Better safe than sorry
On the face of it, keeping employees, contractors and the public safe from potentially hazardous levels of energy generated by RF and microwave transmission facilities doesn’t seem terribly difficult. An organization, such as a commercial wireless carrier or first-responder agency, designates an RF safety officer, who creates a program and administers it. The company’s sites are evaluated in terms of RF radiation levels to determine the level of control that should be employed. These controls, which can include signs, physical barriers and personal RF monitors, are then implemented. Last, but surely not least, affected employees are trained. In theory, this is simple and straightforward — so why are so few companies doing it?
There are several reasons. First, achieving compliance with the FCC’s rules — which are based on IEEE and National Council on Radiation Protection, or NCRP, standards — that dictate maximum permitted exposure (MPE) levels actually is not simple. It requires considerable knowledge about RF safety standards, measurements and technology. Equally important, it requires the experience to make sense of it all. (In lieu of such experience, it requires the sense to realize when to call in a knowledgeable consultant who can assess the situation and provide a road map to establishing an RF radiation safety program.)
In addition, many companies believe that because the FCC has minimally enforced its rules in the past, their chances of being targeted are minimal. And still others say, “I’ve been around this stuff for 30 years and I’m fine, so what’s the problem?”
The answer is simple: Federal law requires every broadcasting organization that generates transmitter power at levels high enough to exceed the MPE to have an RF safety program. For practical purposes, 5 W of transmitter power and above can generate these levels, based on FCC calculations. Rooftops with cellular/PCS, SMR, paging or microwave transmitters very likely will require an RF safety program because they generate more power than this. Co-located sites make exceeding the MPE even more likely and sometimes impossible to control if multiple organizations manage the sites. The FCC’s Office of Engineering and Technology has established a set of calculations to help determine whether an emitter can generate levels above the acceptable limits, although these calculations still may intimidate many people. Moreover, they never should be used as the sole determinant of whether a site needs an RF safety program.
Some may wonder what might happen should they choose not to implement an RF safety program. Looking at the past for guidance, the answer is possibly nothing because the FCC has not strenuously enforced compliance with RF safety guidelines. However, this posture has changed dramatically in recent years, as new test equipment makes the measurement process much easier and less invasive (read: no warning). As a result, several organizations have been fined for non-compliance, and more sites are being investigated every year. In addition, the FCC is not the only organization with which site owners and operators must contend, as demonstrated by an Alaska State Supreme Court case concluded in July. (See sidebar at right.)
While transmitter power levels below 5 W are considered unlikely to result in RF radiation levels that exceed the FCC’s limits, the only way to know for sure is to measure them. This is a task for someone in the organization who has been trained and has experience in both the measurement process and RF safety standards, and who also knows how to interpret the results. (As suggested previously, deferring this task to a third party always is an option, but the qualifications of RF consultants vary widely, so a thorough investigation of a candidate’s qualifications is essential.) The results of the measurement process at the site or sites will reveal where the MPE is being exceeded, by how much, and what safety procedures and controls must be employed to mitigate the threat.
FCC rules establish two tiers of exposure: occupational/controlled and general population/uncontrolled. The two differ by the amount of knowledge and control a person has concerning exposure to RF radiation.
The more stringent uncontrolled rules are designed for the public or untrained workers who are assumed to have no control over their exposure or any technical knowledge about RF radiation, so permissible exposure levels are lower. Controlled exposure levels are higher because it is presumed that trained workers who encounter RF energy in their work know what is not safe and how to avoid overexposure.
A site at which no RF safety program is in place is considered uncontrolled regardless of the RF levels present. However, adding an RF safety program establishes the site as a controlled environment, raising the acceptable exposure levels to the less-stringent range.
There are four categories in which emitters fall. The first does not concern commercial wireless or broadcast organizations because it addresses only transmitters delivering about 1 W of power. However, categories 2 through 4 are relevant to this discussion and are shown on the opposite page, along with the remedies that must be taken to counteract the threat.
Based on the measurement results and analysis, the next step is to implement controls, either engineering, administrative or both. Engineering controls are primarily modifications to the system that will reduce exposure levels to below the MPE anywhere at the site. They could include raising an antenna or moving it to the edge of the roof where someone normally would never be able to get in front of it. Engineering controls are almost always more desirable than administrative changes because they take action to remove potential hazards rather than simply warn people of their existence. However, there are instances where engineering controls are not possible. For example, local zoning laws might restrict the height of rooftop antennas.
Administrative controls include placing warning signs in various places and barriers in front of antennas to prevent exposure to the high levels of RF radiation that exists directly in front of them. Personal RF monitors also are considered administrative controls. Their ability to “sniff” radiation that is at or approaching MPE thresholds makes them desirable regardless of whether other administrative controls are in place. Not surprisingly, some of the largest wireless carriers mandate that affected employees and contractors wear them. (Standard RF monitors that alarm at or below the exposure limits are of less value because they will produce continuous false alarms and thus are not an effective control.)
It is important to ensure a clear rationale exists for sign placement, a road map for which is provided above. Signs must be deployed consistently to be effective and should not be overused. The FCC’s rules allow site-specific text to be inserted under the warning symbol, which is a great advantage in some complicated environments. Custom signs that could include site-specific safety procedures in multiple languages are inexpensive and readily available.
A good approach to rooftop signage would include notification signs at the entrance(s) to the roof and caution signs to educate the user as to what areas are off-limits. Category 3 or 4 emitters (such as broadcast towers) require multiple controls, from barriers and signs on the tower (where levels warrant based on measurements) to RF-shielded clothing when working on a tower and commonly accepted industrial “lock-out/tag-out” procedures.
Finally, the importance of training cannot be overemphasized. It should cover the health effects of RF energy and the standards that govern RF safety, and it should provide clear information about the controls the company will employ, such as signage and RF monitors. Employees also need to know what to do when they think they have been exposed to high levels of RF radiation. The RF safety program must be audited periodically to ensure it is functioning as intended and to determine whether it is still needed or needs improvement. Because transmitting environments often are dynamic, knowledge about changes — especially at multi-transmitter/multi-operator sites — may not be available.
Although this article provides only the most basic information about creating an RF safety program, the reference material below provides a wealth of information about RF safety standards, measurements and protection programs. But all the educational resources in the world are worthless without a sincere desire to comply with FCC rules in order to protect workers and public. With that as a driver, implementing and maintaining an RF safety program is not just work — but an accomplishment.
Robert E. Johnson is director of instrument products at Narda RF Safety Test Solutions and has been involved in RF safety products and standards for 20 years. A member of the AIHA, IEEE and ASSE, Johnson has conducted hundreds of RF safety classes for thousands of students. He can be reached at [email protected].
|CONTROLS||Category 2||Category 3||Category 4|
|Safe work practices||•••||○||●|
|Control of source power||•••||○||○|
|Personal or area monitors||○||●||●|
|PERSONAL PROTECTIVE EQUIPMENT|
|RF suits, gloves||•••||○||○|
|RF safety awareness||○||●||●|
|RF and medical devices||○||●||●|
|Sources of additional info||•••||○||○|
|Ancillary hazard assessment||○||○||○|
|LEGEND: ● Required ○ Optioal ••• Not applicable|
RF safety and the law: A chilling example
In Orchitt v. AT&T Alascom (a satellite communications provider), John Orchitt, an employee of AT&T, accidentally was exposed to RF radiation emitted by a leaky waveguide feeding a satellite communications uplink antenna while working at a site in 1998. The transmitter serving the antenna was supposed to have been turned off, but another was mistakenly turned off instead. Consequently, the transmitter serving the waveguide on which Orchitt was working delivered about 90 W of power at 6 GHz. Orchitt later filed for workers’ compensation benefits claiming he had suffered head, brain and upper-body injuries as a result of overexposure to RF radiation. AT&T disagreed, and after a contested hearing, the Alaska Workers’ Compensation Board awarded him temporary total disability and medical benefits.
AT&T unsuccessfully appealed in superior court, alleging that procedural irregularities deprived it of due process and that the board’s decision was not supported by competent scientific evidence. AT&T then appealed to the state supreme court, which ruled that substantial evidence supported the compensation board’s findings and — because the board’s procedural decisions did not deprive AT&T of due process — the superior court’s judgment that affirmed the board’s ruling should stand.
The lesson here is that while the disability benefits themselves may not have been huge in monetary terms, the case resulted in a string of expert witnesses on both sides, eight years of litigation, tens of thousands of dollars (or more) in legal fees for AT&T — and still the company lost. This precedent should be a warning to any company that believes RF safety couldn’t cost them dearly.
— Robert Johnson
FCC Office of Engineering and Technology, Bulletin 65, Aug. 1997
Supreme Court of the State of Alaska: AT&T Alascom v. John Orchitt and The State Of Alaska, Department of Labor and Workforce Development, Division Of Workers’ Compensation
IEEE Standard C95.1-1991: IEEE Standard for Safety Levels with Respect to Human Exposure to Radio Frequency Electromagnetic Fields, 3 kHz to 300 GHz
IEEE Standard C95.7-2005: IEEE Recommended Practice for Radio Frequency Safety Programs, 3 kHz to 300 GHz
Note: IEEE membership is required to obtain standards.