Environmental management in cellular and PCS phones: A Saudi Telecom-Assir study

Transcription

1 Environmental management in cellular and PCS phones: A Saudi Telecom-Assir study M. Bayoumi* & S.T. Jerman^ ^Arab Academy for Science and Technology ^Director General of the Assir region ofarabi Saudi Telecom Abstract Saudi Telecom is concerned with the relationship between human health and cellular and PCS phones and their base stations. From the point of view of environmental management principals, it was necessary to review this subject and evaluate the potential impact on human health. It was also necessary to define regional and international criteria to ensure that phones and base stations will meet the safety standards. The above mentioned review and criteria are involved in the actual study. The technical specifications of the 55 base station towers covering the Assir region in the Arabic Saudi Telecom were also given. The study shows that the RF exposure around the tower for the type of antenna and towers used is within the safety limits determined by the Institute of Electrical and Electronics, American National Standards Institute (ANSI / IEEE) and the National Council of Radiation Protection and Measurement (NCRP). The Assir-Telecom company have created a code of practice for working in the controlled spaces which have RF radiation limits above the maximum permissible determined for public. 1 Radiation Human beings are surrounded by both natural and artificial radiation. For example, the sun is the most well known producer of natural radiation. Its wavelength ranges from long wave infra red to ultraviolet. In general, radiation is defined as a sort of energy contained in high-speed particles and electromagnetic waves. If the radiation has enough energy during its interaction with the surrounding atoms; enough to remove tightly bound electrons from their orbits

2 24 Management Information Systems causing an atom to become charged or ionized. This type of radiation is called ionized radiation [1]. If the radiation does not have enough energy to remove bound electron from their orbits around atoms, this type of radiation is called non-ionizing radiation. 1.1 Ionizing radiation According to the above-mentioned definition of ionizing radiation, several types can be identified [2]); X-ray, alpha particles, beta particles, y-rays, Neutrons and cosmic radiation. Ionizing radiations are measured in Gray (Gy) and Sievert (Sv): The quantity of radiation or the doze received by a person is measured in terms of the energy absorbed in the body tissue and expressed in grays. The Sievert is related to the biological effect caused by radiation. One sievert radiation produces a constant biological effect regardless of the type of radiation. The normal background radiation from natural sources is 2 m Sv/year. 1.2 Non-ionizing radiation Some known sources of non-ionizing radiation are ultraviolet, visible light, microwaves, television electromagnetic radiation, AM and FM radiation and power lines electromagnetic fields [2]. In this part we review some non-ionizing radiation sources, applications and discussing their biological effects. Lasers Laser equipment is widely used. The lasers used for surveying and leveling are detailed in certain publications, e.g. [3]. Helium and neon gas laser devices are used for these applications, as the light travels in a straight line over long distances. For accurate leveling for a large area, a motor driven prism reflector may be used to rotate the laser beam [4]. Biological damage may be caused to the absorbing tissues due to laser heating: The human eye may focus on the beam causing thermal burning to retina. The Australian standards [5], related to laser safety, classify the laser devices into four categories or classes. This classification includes the beam energy and other technical specifications. Although the class of the device is determined by the standard , another Australian Standard, , is used as a guide to the safe use of lasers in the construction industry [6]. Microwaves Microwaves, as visible light [6], are non-ionizing radiation and both are a part of the electromagnetic radiation at extremely high frequency radio waves. Microwaves are used in many applications such as radar, satellite communication and much domestic equipment such as microwaves ovens. In ovens the microwaves generated by a magnetron vibrate the water molecules in the food to a frequency of around 2450 MHz. The friction between the vibrated molecules produces the required heat.

3 Management Information Systems 25 The microwaves generated cease to exist once the supplied electrical power is turned off. The microwaves are contained inside the designed equipment of the oven itself. In such ovens a safety interlock switch stops the generation of waves once the door is opened. Studies have been carried out to reduce door leakage [7]. Some countries like Australia produced standards for testing and approval of such equipment [8]. The detectors used in testing have standards [9], and the pacemakers must not be susceptible to microwave radiation, any leakage must be within the limits of the standards Radiation from Video Display Terminals (VDTs) VDTs are used to interact with computers. Most VDTs are based on Cathode- Ray Tube (CRT) [10]. This type is designed to emit visible radiation. The CRT is an evacuated tube which has an electron source at one end and a phosphoruscoated screen at the other end. The interaction of electrons with phosphor causes the emission of visible radiation and a small amount of ultraviolet radiation from the screen. Also low energy X-rays, which are absorbed by the glass, and some infra red radiation is found. Radio frequency radiation is emitted by the deflection coil moving the beam by the CRT or the beam high voltage transformer. An extremely low frequency electromagnetic field (EMF) was detected. The RF emissions and the low frequency EMF occur in all directions from the VDT. Some health effects were documented, such as eye problems and skin disorders. Eye problems were observed in operators having close-visual tasks. Skin disorders are due to the build-up of electrostatic charges on the operator's body. The Australian Radiation Laboratory has measured microwave, radio frequency, ultraviolet and X-rays emissions from different models of VDTs [11]. The levels of emission were computed by the limits of exposure given by the International Radiation Protection Association and were found to be within normal limits Marine radar microwaves Some small marine vessels are equipped with radar, with power up to 10 kw [12]. This type of radar emits short pulses of microwave radiation, which may be reflected by objects. This reflection is displayed on the radar screen. The microwave radiation from this radar may therefore reach a crew or people around the vessel. This type of radiation is not hazardous unless its intensity is high enough to cause sufficient heating in living tissues due to the absorption of microwaves and its conversion to heat energy. The Australian Standard specifies a maximum safety limit for microwave exposure [13]. This standard states that persons must not be exposed to a level higher than an average 0.2 mw/cnr, with the peak level not exceeding 1 W/crn^. Measurement [14] showed that at 1 meter from the antenna, the peak level is about 0.5 W/cnf while the average intensity is between 0.5 and 0.8 mw/cnf. At several meters from the antenna the intensity drops to below 0.2 mw/cm".

4 26 Management Information Systems Mobile phone Radio Frequency radiation When a call is made from a mobile phone, RF signals are transmitted between its antenna and the nearest antenna base station [15]. This type of phone emits signals in a frequency ranging from 800 to 2200 megahertz (MHz). These waves or signals are received by a rod like antenna. Two types of antenna are known and can be distinguished far from the base station; whip and sector antenna. The whip antenna is known as a low gain antenna and the sector as a high gain antenna [16]. They can be mounted on a tower or on a building roof, see figure 1. 2 Environmental management in the RF phones issue The present concern that people have about RF exposure implies the application of the environmental management principles to this issue: Starting with a review of the problem, evaluating its state of knowledge, and applying the transparency principle to reach real, and correct, public awareness and ending by finding the limits between the clear and ambiguous elements in the issue under examination. The actual study is applied to the Assir-region in Saudi Arabia. The mobile phone system uses 55 towers serving users in a region of a population about citizens. The actual study can be used to raise public awareness of the RF phones issue. In the next sections, RF used in mobiles is determined in the electromagnetic radiation spectrum. Also, the safe limits of exposure around towers and at roofs are given, accompanied by its scientific credibility basis. Some of the mathematical methods used in the environmental exposure evaluation are reviewed, especially the Near and Far Field RF modeling. 2.1 The mobile RF and the electromagnetic radiation spectrum In the previous sections, the radiation was classified into ionizing and nonionizing radiation, according to its energy, and the possibility that energy affects the human cell or the chemical bonds for elements inside it. It is important to note that sometimes the classification is based on the frequency. It is the same since there is a direct relation between the energy and the frequency through a constant called Planck's constant. The frequency is the rate at which an electromagnetic field changes its direction. From the electromagnetic spectrum shown in figure 2, this spectrum can be classified into non-ionizing and includes the non-thermal, the thermal and optical frequencies extending up to 10^ Hz. Radio waves, microwaves, infrared and ultraviolet waves are also referred to as non-ionizing. The ionizing frequencies include the very high frequency X-rays and those of radiation mentioned in the previous part as a, p, y and neutron radiation. The electric power in Saudi Arabia has 50 Hz frequency. The AM and FM radio frequencies are around 1 MHz and 100 MHz respectively. Microwave ovens have a frequency of 2450 MHz, while X-rays have frequencies up to 1 million MHz. Mobile phones operate at frequencies ranging from 800 to 2200 MHz according to the phone type system.

5 2.2 Safety standards and RF safety limits Management Information Systems 27 The scientific credibility of the RF safety standards is based on a number of studies [17-24]. Common agreement between these studies can be grouped into three important aspects. The first states that the extensive radio waves studies reveal that radio waves, even for those frequencies not used in mobiles, can cause related heat damage at high rates of exposure. This damage is common in all applications such as radar, ovens, etc. In mobile application, public exposure cannot exceed the safety limits, as antenna power intensity is designed to be fixed at a certain power. The second indicates that the biological effects of radio waves depend on the absorption rate of energy. The third shows that mobile phones are an application like any other well established application; it only needs a scientific public awareness. Regarding the safety standards, for many countries there are national and international standards of public exposure to RF. The most widely used standards are developed by International Commission on Non-Ionizing Radiation Protection (ICNIRP) 17], the Institute of Electrical and Electronics Engineers [18] (IEEE) and the National Council on Radiation Protection and Measurements (NCRP) [20]. These societies, which are international or governmental societies with great scientific credibility, gave radio frequency standards expressed in "plane wave power density" and measured in mw/cnf. The definition of "plane wave" will be detailed below. These societies give exposure standards of 1.2 mw/cnf for the general public (IEEE) and 0.57 mw/cnf (NCRP). It must be noted that all measurements take into consideration a safety factor superimposed on the lower limit of exposure causing damages. For this reason the technicians working in this field may be exposed to higher rates knowing, of course, the real exposure limits. Knowing the standards for safety exposure limits, it was important to test these values around the tower or the roof. Two studies [25] were effectuated for an antenna mounted at 40 ft which is similar in height to the Assir-Telecom towers. The studies showed that the ground level power density at its higher value was mw/cnr, which is much lower than the standard. Power density inside a building will be lower by a factor of 3 to 20 than outside. 2.3 RF modeling As mentioned in the previous section, the radio frequency exposure standards are expressed in "plane wave power density". This expression comes from the fact that the field radiates from an antenna like a ripple on the water [26] after a pebble is thrown. Before detailing the antenna models, it must be noted that the expression plane wave means that it is far from the source or a far field case. This explains that the safety standards are measured and applied at far field conditions.

6 28 Management Information Systems Cylindrical model For a rod-like antenna in a vertical position, the power density can be calculated using a circular radiation pattern and the height of the antenna. At a distance X cm from the antenna and for a total antenna power P in mw, the power density D (mw/cnf) can be calculated, forming a cylinder around the antenna of height h (cm), by the formula D = 2%Xh (m W/cnf) From this formula, the shorter the antenna, the higher the field intensity for the same antenna power. Also at the closer distance, the higher the field intensity. Spherical model In far field situations, the antenna is considered as the point source. The power density can be calculated by the formula D = PG (m W/cnr) where G is the gain ratio of antenna. RF environmental energy management As mentioned before, there is no problem with exposure, except at the roof area where an array of antenna is located. Below the roof the intensity is reduced by a factor from 3-20 times that in an open air. This means that the exposure for the public is within the safe limits. Only the roof, at which antenna is located, must be inspected and modeled to determine the intensity map at the roof level to prevent RF levels exceeding the safe procedures for working and maintenance in the roof area. The above equations are used in the modeling. It will be interesting to compare the theoretical models for calculating the near field and the far fields power densities around the antenna. The RF emission from 1000 W power gain is represented in figure 3, the top view of power density close to the antenna. The curve represents the power densities calculated from the equations are a power given. This means that these equations can be used later to predict the power densities around the antenna of the Assir towers in order to put an environmental energy management plan for technical assistance and maintenance for antenna and its supporting constructions in a building roof level and near an antenna tower into action.

7 3 Assir mobile phones network Management Information Systems 29 The phone system is composed of 55 towers. Most of them are on separate towers except those located at the Assir hospital, the Abha prison, the intermediate school, the old water station, the PTT Compound and the Intercontinental Hotel. 3.1 The system and network The technical information for GSM table: used in Assir region is given in the following Types of antennae Direction of coverage No. of antennae Antennae function Type of link Frequency Duplex 1 way 1 antennae Receive & transmit Up link MHz Antennae Omni Frequencies Multi way Receive & transmit Down link MHz Sectorize 1 way 3 antennae 2 receive & 1 transmit 3.2 Electromagnetic energy management and awareness In the previous section, it has been mentioned that the higher levels of RF energies exist in the near field around the antenna sites. For this reason the administration or the sites manager must prepare the necessary routine and emergency procedures to be applied in these sites existing in the near field area. The site plan must raise the worker's awareness of RF radiation and equipment issues including antenna, antenna selection, antenna sites, building sites, towers, different RF levels and corresponding zones, documentation, operation guidelines, warning tags and caution signs etc. Antenna sites There are two common sites used for antenna installation; the building and the towers. The most suitable building is the highest, and the antennas are mounted on the roof at a certain height from the roof ground. The antenna is mounted on a tubular structure and separated by at least 3 ft distance. It must be note that while the RF field from one antenna may be below the maximum permissible energy level, several antennas located near each other may give levels exceeding the

8 30 Management Information Systems occupation or the controlled maximum permissible energy level. Roof-View and Tower-Calc [27] made a software modeling program for antenna sites. Zone one includes the lowest EME levels in the site, which is below 20% of the occupational maximum permissible level. Zone two is any area in the near field. Figure 4 shows RF fields with five antenna transmitting. It can be seen that the combined field produces levels over the MPE and the near field area requires exposure controlling. Towers are usually used as antennas supporting structures in isolated areas. The height of the tower depends on the required coverage. It was found that the cellular configuration gives less EME exposure to workers on the tower than the two-way tower configuration. The site manager must be aware that, in two-way towers, a worker may be climbing the faces of several antennas at various locations with different powers up to 200 Watts. Without going into technical detail, the EME level depends on the number of antennas located at the tower. Figure 5 shows the EME mapping of a tower carrying 5 antennas. It can be seen that the EME levels for 5 activated antennas exceed the limits. The workers must be acquainted with this EME mapping. This gives an example of the necessity to an EME management to secure the safety of the workers: This responsibility lies with the site manager. 3.3 EME management factors Some important factors for the site manager to consider are: 1 - The type of antenna supporting construction, building or tower. 2- The uptime period for the same antennas. 3- The training of workers. The ideal objective of the site manager is to find the best environment for the workers, with the lowest exposure conditions possible. As discussed in the previous section the site manager must have an EME mapping for the site. This enables the worker to go through the working area knowing all exposure conditions. Also it was found that transmitters activities vary during the day and night. This variation may reach 30% and tests and measurements could produce an uptime period. So the site manager must locate the uptime periods since it affects the EME exposure levels on a site. The training of a worker on-site is a must. No worker should pass into the controlled access of the antenna site unless he has received specific technical training and EME awareness information. The site manager must issue "guidelines" for working in a radio frequency environment. 3.4 Guidelines of the Assir Telecom company for working in a radio frequency environment After surveying all the previous information and seeking advice from experts in this field, the Assir Telecommunication administration created guidelines divided into three sections:-

9 Section A: General Section B: Normal Working to ^Practice Section C: Emergency and Accidental Working Practice. Management Information Systems 31 General This section includes the site information, the appointed workers and the required protection equipment. The site manager must map the working spaces and transfer this knowledge to appointed worker and must determine the site signs containing all the guidelines related to the site. The regions with RF levels above the MPE for public must have a special sign. The site manager must create guidelines for the appointed workers including the necessity of ensuring that the working area carries the correct signs according to the RF mapping delivered by the site manager and that the transmitters are not operating without shields. The site manager must determine the correct RF monitors to be used by the workers at the site. The correct functioning of these monitors is directly related to worker safety. In addition, the site manager must detenuine the proper protective clothing used in the controlled area. Normal working practices This section includes all details beginning with approaching the site to working inside and to leaving the site. Examples of these details are: "Before going into the site to work with antenna, the worker must notify the manager and disable the transmitters." The worker must be aware that human error may occur; the worker must verify that all requirements set out for him are obeyed. The worker also must obey all signs in the controlled area. Emergency and accidental working practice The site manager creates a working practice code for any emergency. This is important since working in restricted sites may include trouble-shooting of some working radio transmitters. The site manager is responsible for choosing the most suitable worker for this task. The transmitters are usually supplied with shields to prevent strong RF radiation from reaching the workers. The code must contain regulations for occasions when the shield is removed to ensure that it is returned to its place before starting the transmitter. The Assir Working Practice code includes a special section for emergency and accidental cases. 4 Conclusions In this study the Assir Telecommunication Management (ATM) reviews ionizing and non-ionizing radiation. This was carried out from the point of view of comparing the known used non-ionizing radiation to show where ATM can place the RF radiation used in mobile phones. The literature showed that the RF radiation levels in worldwide systems, including mobile phones, are lower than the maximum permissible limit determined by the Institute of Electrical and

10 32 Management Information Systems Electronics Engineers (IEEE), the American National Standards Institute (ANSI) and the American Federal Commission (FCC). In the working area where levels exceed the maximum permissible for the public, the ATM created guidelines for working in radio frequency environments. Those with technical and managerial experience developed this code into three sections. This code of practice would help to prevent accidents in restricted areas. The detailed regulation of the code of practice would improve worker training and understanding of the RF radiation. Consequently this improves the working conditions of the telecommunications section. References [1] Radiation related terms- Dept. Nuclear Engineering- Oregon State University- \v\vw.ne.orst.edu/rhp//terms.html [2] Non-Ionizing Radiation nir.html [3] Charschan, S.S. (ed.)., Lasers in industry. New York: Van Nostrand, [4] Harry, I.E., Industrial lasers and their applications. New York: Mcgraw- Hill, [5] Standards Association of Australia. Laser Safety. North Sydney, A.S [6] Standards Association of Australia. Guide to the safe use of lasers in the construction industry, A.S [7] National Health and Medical Research Council, Seventy-third Session, Canberra, October [8] Standards Association or Australia. Australian Standard "Approval and Test Specification for Particular Requirements for Microwave Ovens" [9] Standard Association of Australia. Australian Standard "Microwave Oven Leakage Detectors for Household Use". [10] Radiation Emissions from Video Display Terminals- vvww.healtlmov.au /arl/is_vdtrd.html [11] Video Display Terminals- Health Concerns and Radiation Emissions. [12] Marine Radars Mounted on Small Craftwww.heaJth.uov.au/arl/is marin.html [13] Australian Standard 2772 (1985)- "Maximum exposure levels- Radiofrequency radiation 300 khz to 300 GHz." Standards Association of Australia, North Sydney, NSW. [14] D W Peak, D L Conover, W A Herman, R E Shuping- "Measurement of power density from marine radar." US Dept of Health, Education and Welfare publication (FDA) , [15] Mobile Telephone Communication Antennas: Are They a Health Hazard?- anten.html [16] Cellular Phone Antennas and Human Health-

11 Management Information Systems 33 [17] International Commission on Non-Ionizing Radiation Protection: Health issues related to the use of hand-held radiotelephones and base transmitters. Health Physics 70: , [18] IEEE Standards Coordinating Committee 28 on Non-Ionizing Radiation Hazards: Standard for safety levels with respect to human exposure to radio frequency electromagnetic fields, 3 khz to 300 GHz (ANSI / IEEE c ), The Institute of Electrical and Electronics Engineers, New York, [19] International Commission on Non-Ionizing Radiation Protection: Guidelines for limiting exposure to time-varying electric, magnetic and electromagnetic fields. Health Physics 74: , [20] National Council on Radiation Protection and Measurements: Biological effects and exposure criteria for radiofrequency electromagnetic fields. NCRP Report No. 86, [21] National Radiation Protection Board: Restrictions on human exposure to static and time varying electromagnetic fields and radiation. Doc NRPB 4:1-69,1993. [22] CG Likkle et al: Alteration of life span of mice chronically exposed to 2.45 GHz CW microwaves. Bioelectomag 15: ,1994. [23] MA Stuchly: Biological concerns in wireless communications. Crit Rev Biomed Eng 26: ,1991. [24] J Juutilainen and R de Seze: Biological effects of amplitude-modulated radiofrequency radiation. Scand J Work Environ Health 24: ,1998. [25] RC Petersen et al: Radiofrequency electromagnetic fields associated with cellular-radio cell-site antennas. Bioelectromag 13: ,1992. [26] Specifically, the ICNIRP standard is 0.40 mw/cm-sq for cellular phone frequencies and 1.00 mw/cm-sq for PCS phone frequencies. [27] Roof-Wiew and Tower-Calc - stp/eme.htmi

12 34 Management Information Systems fj * \' 1 POI0Mcunt Pole Mount Loimy Grgtin (whip) * es; % b oo O O 0 ODD P O O O O O "Roof* Mount %E3% D 0 O ODD POO ODD 'Penthouse* Figure 1 : Antenna mounting The Electromagnetic Spectrum static aower AM FM radio microvtave heat tanning medical line radio TV oven tamp booth x-rays * Of* 1 1 0^ 1 1 0*2 1 or* 1 cr 1 or i i.r'-:' Wavelength (met ers^i F re q u en c y ( Hz ) i cr- i rr' i a* I [f 10^ '^, I 0*^' 10''...-. ELF Ra< ^_ (R J.'f Mjcrowave "^S?^ «Utravk ^ (wv*o ^ ' 4 (UV3 L y N< DH- Ionizing ^. ionizing Non -thermal ' ThermaJ ' Optical ' Broken bonds * Low induced High currents ^ induced Electronic currents exctatbn ^ DNA Damage V V Heating Photochemcal effects AM radio 300 ] m ] 1 Of!»-n I vv'aveienglh 1 r mquef^cy 1 0 0kHz < GOO v. H^: 1997, JEMb»Jd«r YHF-TV UHF-TV MW Oven FM radio I ' ucn i 3 i rn 30 i cn'i T?. cm i U MK-iZ 1 00 MHZ MH- ' :J <_»; iz r t "CB* "cordless* phones phones Figure 2 : The electromagnetic spectrum

13 Management Information Systems 35 RF Emissions from a 1000W(ERP) Low-Gain Antenna (Top Yi«w of the Power Oensty Close to the Antenna) 40ft 40 40ft Figure 3 : Top view of the power density Five Transmitting Antanoas Four Transmrtting Antennas Figure 4 : (1 to 5) Activated antennae Figure 5 : 1 and 5 Activated antennae