![HS-PHS ,[object Object],[object Object],[object Object]](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
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Rf Health&Safety
- 1. Health and Safety (HS-PHS)
- 10. Ionizing vs. Non-ionizing Frequencies
- 11. EME Mechanism of Injury EME at frequencies above UV Light have enough energy to tear electrons from their atoms. This can cause permanent biological changes to the molecular structure of cells.
- 12. RFR Burn vs. Surface Burn A RFR Burn starts at the bone and heats outward towards the skin A surface burn begins at the skin surface and moves inward towards the bone
- 18. General Population Exposure (Uncontrolled)
- 20. Site Safety
- 24. Effects of Reflections of RFR Levels
- 25. EPA Model for Broadcast and Communication Sites Where ERP = Effective Radiated Power, in watts R = Height of antenna, in meters S = Field strength, in µw/cm 2 (For more information, refer to the GWEC module RT-RF Antenna )
- 30. Standards in the U.S. Standards in the U.S. Two major standards are used in the U.S.: IEEE C95.1-1991 (ANSI C95.1-1982) FCC 1997 Regulations IEEE FCC
- 31. Radiation Protection Guide (ANSI C 95.1-1982)
- 33. Liability for Service Organizations
- 34. Compliance
- 39. Summary
Editor's Notes
- © Copyright 2001 Global Wireless Education Consortium All rights reserved. This module, comprising presentation slides with notes, exercises, projects and Instructor Guide, may not be duplicated in any way without the express written permission of the Global Wireless Education Consortium. The information contained herein is for the personal use of the reader and may not be incorporated in any commercial training materials or for-profit education programs, books, databases, or any kind of software without the written permission of the Global Wireless Education Consortium. Making copies of this module, or any portion, for any purpose other than your own, is a violation of United States copyright laws. Trademarked names appear throughout this module. All trademarked names have been used with the permission of their owners.
- Partial support for this curriculum material was provided by the National Science Foundation's Course, Curriculum, and Laboratory Improvement Program under grant DUE-9972380 and Advanced Technological Education Program under grant DUE‑9950039. GWEC EDUCATION PARTNERS: This material is subject to the legal License Agreement signed by your institution. Please refer to this License Agreement for restrictions of use.
- After completing this module and all of its activities, the student will be able to: Explain radiated power and its effects on workers and the general population. Explain OSHA requirements as they relate to RF personal health and safety.
- Electromagnetic Energy ( EME ) is in the radio frequency portion of the non-ionizing radiation spectrum from 3 kilohertz (KHz) to 300 gigahertz (GHz). EME radiates outward from its transmission source (the antenna) in packets of energy called photons. Once generated, these waves of energy travel from the transmitting antenna through space where they are reflected from, refracted through, refracted around, or absorbed by their intended receivers or any object in their path.
- The absorbed energy is a source of health-related concerns. Examples of devices that radiate EME include pagers, radios, and cellular phones.
- Ionizing Radiation (IR) refers to EME or to energetic nuclear particles that are capable of producing ions (charged atoms) directly or indirectly as they pass through matter. This process is called ionization. Ionizing radiation occurs when atoms in a cell are bombarded by radiation and an electron is either added to or taken from the atom, thus giving the atom a charge. The electrically charged particle is called an ion. In the body, such ionization can rupture chromosomes and cause mutations that are responsible for certain cancers. Non-ionizing radiation occurs when there is not enough energy in the radiation to create ions. Instead, the energy is absorbed only as heat. Because of its low energy, EME is non-ionizing radiation. Effects of non-ionizing radiation are not cumulative. Effects of ionizing radiation are cumulative. The ability to ionize is totally frequency dependent. The world’s largest transmitter cannot cause ionization, but an extremely small amount of radioactive material, such as uranium, can cause ionization. Water ionizes at 2.420 GHz (upper limit of UV). Frequencies and energies at or above this level are considered ionizing.
- Concerns about protecting their patients’ health is one of the reasons why doctors keep records of dental and chest x-rays. This helps the doctor ensure someone is not receiving too much ionizing radiation. In extreme cases, Radio Frequency Radiation (RFR) induced heating can cause blindness, sterility, and other serious health problems. These heat-related health hazards are called thermal effects and involve tissue burning.
- Because RFR burns damage tissue under the skin, prompt medical attention is necessary. Skin is designed to grow quickly and replenish itself. Deep tissue has slow growth and requires a longer time to heal.
- Depositing energy into the body increases the response of the body’s thermoregulatory system. The system then responds to the increased thermal load by transferring energy to the surrounding environment through convection, evaporation of body water, and radiation of heat back into the surroundings. The heat is then carried to the extremities of the body and dissipated.
- At frequencies near the body’s natural resonance frequency, RFR energy is absorbed more efficiently and maximum heating occurs. In adults, this frequency is usually between 35-150 MHz if the person is grounded, and 70-300 MHz if the person’s body is insulated from the ground. When looking at energy absorption relative to frequency, energy absorption per kilogram is the same for all people. However, the frequency at which maximum energy is absorbed changes with the height of a person. In addition, the human body in a vertical position absorbs ten times more energy in a vertically polarized field than in a horizontally polarized field.
- Exposure is averaged over time because the primary effect is thermal. It takes the human body about six minutes to fully respond to a change in temperature. Therefore, typical averaging time is six minutes. Limits on peak exposure levels apply only to unusual circumstances like Electro Magnetic Pulse (EMP) testing and military research. This can only be done when exact energy densities are known, such as at broadcast sites where transmitters operate at fixed powers 100% of the time. It is impossible to use time averaging at sites with non-constant duty cycles.
- How much heat can a body absorb before adverse effects are felt? The limbs can tolerate higher levels since the body’s circulatory system acts as a coolant with the remainder of the body functioning as a radiator. Spatial averaging allows the averaging of energy density (EME) to be considered over the entire area of the human body. The normal metabolic rate for humans is 1 W/kg when sleeping and 2.4 W/kg during normal exercise. The maximum rate for healthy young adults over a period of 5 to 6 hours is 4 to 5 W/kg. Most western exposure standards are based on levels of 0.4 W/kg, which is a 10:1 safety factor. This rate “assumes” room temperature. RFR exposure occurring at higher temperatures causes higher metabolic rates.
- Symptoms of overexposure to EME include, nausea, headache, an overall feeling of warmth, perspiration, elevated body temperature, and labored breathing. Severe cases can mimic heat stroke.
- All members of the population fall into this category unless they have been trained in RF safety issues. Examples of uncontrolled/public areas include: Roof-top patios Pools Observation decks Restaurants
- Occupational controlled levels apply to situations in which persons are exposed as a consequence of their employment, and where those persons who are exposed have been made fully aware of the potential for exposure and can exercise control over their exposure. An operator must comply with occupational controlled MPE limits. This includes all people who work at communication sites. Examples of occupations that must be trained to permit the use of the higher MPE limits include: HVAC Roofing Painting Security Wireless technician and engineer.
- In order to understand how to control the safety of a work site, it is necessary to understand the design of typical wireless antennas. (For a more detailed descriptions, see Module RT-RFA: Antennas .) All antennas can transmit many channels and sometimes multiple frequencies at once. For example, a single antenna can be used to transmit many voice conversations at once. A single antenna can also be used to transmit energy on several different frequencies at once. Technical people will refer to the power being radiated, effective radiated power (ERP) of a single channel, when in truth many carriers or channels may be operating at the ERP stated for each single channel. The total ERP being transmitted from the antenna is the number of channels multiplied by the ERP in watts for each single channel. For all antennas over six feet in height, the spatially averaged exposure level is inversely proportional to the antenna height (assuming constant input power). For all antennas less than six feet in height, the spatially averaged exposure level is the same, but hot spots can exist. Contrary to conventional thought, it is the lower gain antennas that can result in the highest exposure levels.
- Often multiple sources contribute to the total exposure level in an area. Each contributor must be analyzed and predicted. Total RFR from all sources must not exceed MPE limits or access to the area must be restricted.
- In order to model the RFR in an area, you must obtain architectural or engineering drawings of the roof or area. You must also identify the location of antennas, doors, walkways, etc. Finally, you must gather antenna parameters. The antenna parameters required for modeling include: X and Y coordinates (in meters) from a reference Exact height (Z coordinate) above the reference plane to the base of the actual antenna Orientation of antenna (polarity) Downtilt of antenna Antenna gain Antenna radiation pattern Trace of transmission line to the equipment cabinet to positively determine licensee or service ERPs and number of carriers at each ERP.
- Worst-case computations consider reflected energy that bounces off the ground or rooftops. If the reflection is as strong as the direct ray and arrives in phase, the field strength, S, could be doubled and the power increased by a factor of 4.
- The EPA model for broadcast and communications sites uses a 60% ground reflection coefficient.
- For surveys to be effective, they should be well planned, conducted by someone that has the necessary skills and knowledge, and well documented. Survey equipment provides accurate measurements and can be used to determine the level of compliance to a particular standard. Survey equipment requires a reasonable level of training before it can be used with confidence. One thing to take into consideration is the fact that survey equipment will not provide continuous monitoring against sudden changes in conditions due to equipment operating on cycles or hardware failures.
- Included in the survey conclusion will be recommendations for possible relocation of antennas and for personal protective equipment (PPE) . PPE is used to protect workers against high levels of exposure. PPE includes: Personal monitors Protective suits (for very high field areas). RFR Personal Monitor sensitivity should be frequency dependent and should match FCC regulations. The monitor sums the energy from all antennas and weighs them per FCC MPE limits.
- A monitor will beep every 1-2 seconds when the field level is just over the monitor’s threshold. The monitor beeps faster with higher field levels, similar to a radar detector. The repetition rate is a rough indication of the magnitude of the field and whether or not you are moving toward or away from the energy source. The monitor threshold facing forward is set for 25% – 50% of FCC MPE for Occupational Controlled standards. The monitor is about half as sensitive to signals from the side and overhead. The person’s body blocks the monitor from detecting signals behind them. Occasional alarm sounds at the minimum repetition rate of 3-4 times/sec can safely be ignored when on rooftops or at ground level. If a monitor alarms at the minimum rate for more than 15 seconds or at a high repetition rate, it may mean the person wearing the monitor is in a red danger zone and should move away from the antennas until the monitor alarm ceases. Waiting a couple of minutes before re-entering the area should stop the alarm from sounding, but if the alarm conditions repeat, power to the antennas must either be reduced or shut off before work can continue in the area.
- It is acceptable to allow the RFR monitor to alarm at a low repetition rate briefly in order to climb past an antenna. Use the two-way radio to coordinate with ground personnel that can control the transmitters. Human exposure to RF emissions clearly is a part of the quality of the human environment. Filings for construction not only address the direct impact on humans, but also the impact to other areas such as forests, lakes, wetlands, and historic districts. The National Environmental Policy Act of 1969 requires federal agencies to evaluate the effects of their actions on the quality of the human environment.
- FCC regulations govern the emissions from transmitting facilities and are concerned with human exposure. The Occupational Safety and Health Administration (OSHA) is concerned with employee safety and exposure to RF energy. Regulation ANSI C95.1-1982 was adopted by the FCC in 1986. It was the first SAR -based ( specific absorption rate -based) or frequency dependent standard to be used worldwide. SAR, given in W/kg, represents localized power absorbed in a small area of the body rather than the whole body average or external power density. The human body most easily absorbs transmissions that occur in the range of 30-300 MHz. Exercise care when working in and around antennas that operate within this range. The 1997 FCC Occupational/Controlled regulations are identical to the 1982 ANSI-based levels. The MPE levels for the new General Population/Uncontrolled tier are five times more restrictive ( 3MHz) than the Occupational/Controlled levels. Induced and contact current limits expect to be added in the near future.
- Since October 15, 1997 all new applicants and license renewal must conform to the 1997 regulations. All sites were required to be in compliance with the new regulations by September 1, 2000. Compliance is site based. If a site adds an operator that must obtain a license or if any operator is up for a license renewal, the site must be brought into compliance immediately. In the IEEE C95.1-1991/ANSI C95.1-1982 standard limits are usually expressed as a Whole Body Average. The FCC has stated that time and spatial averaging are acceptable. Spatial peak SAR’s may exceed whole body average by a factor of 20. The NCRP 1986 standard includes time averaging, but does not include spatial averaging.
- OSHA has an outdated standard still on record, but now uses more modern standards under its “General Duty Clause”. Individual state OSHA enforcements are much more aggressive than those of the federal OSHA. State OSHAs support the 1997 FCC regulations. State OSHAs also consider total exposure level, regardless of the source or ownership, and has authority to levy large fines and suspend operations, if required, for compliance. Other government organizations, local, state, and federal, are likely to use the FCC regulations as a basis for evaluating site compliance. Employees of site owners and site managers are covered by OSHA regulations. Whenever the field level from their antenna exceeds 5% of the applicable MPE in an area of non-compliance, operators of antenna-based systems are liable for any site-related compliance issues. The operator is jointly responsible for corrective action with all other operators that also exceed the 5% rule, as well as the site owner/manager.
- Service organizations are liable for the safety of their employees under OSHA regulations. A safety program allows the service organization to work at levels up to the Occupational MPE.
- This section examines the important topic of compliance. Once you understand the concepts and principles used in RF safety, you must know what to do about them. Compliance only ensures that no worker or member of the public will be exposed in excess of MPE limits. Compliance means assuring a healthful work environment by: Identification of unsafe areas Education and training of safe working procedures for sites Development of support mechanisms Documentation of compliance
- If a site is compliant by design, it is designed so that anywhere an individual can walk, the individual cannot be exposed to RFR above the General Population (uncontrolled) MPE levels. It is very difficult to make tower sites compliant by design.
- There are three options for determining compliance. Calculations Can be very useful for simple broadcast sites. They are of little value for co-located wireless services. Computer Modeling Requires very good information on every emitter and antenna. Useful for predicting prior to construction, major renovations, or the addition of new services. Measurements The “on demand” nature of most wireless services dictates that care be exercised to insure a worst case condition is measured.
- The slide above highlights information about health and safety as covered in this module.