Wednesday, June 1, 2011

Write -Up by A M JOSHI; Need for more than 3 m seperation bet. Tower and next Bldg.

From: Ashok Joshi

Date: Sun, May 29, 2011 at 6:42 PM

Subject: Write -Up by A M JOSHI; Need for more than 3 m seperation bet. Tower and next Bldg.


Subject: Write -Up by A M JOSHI; Need for more than 3 m seperation bet. Tower and next Bldg.

[ Possible Arguments to counter W B & Other State Govt.'s 3m separation stipulation / Rules ]

1. In the situation described , let us assume that the Centre of the Antenna is 1.5 m above the 3 m clearance from roof top / terrace top i. e. the Centre is 4.5 m above the terrace /roof top. Horizontal seperation for nearby building [ assuming of similar height ] is 3 m. Hence, from the geometry of right angle triangle, the distance from the centre of antenna to the adjoining building edge will be square root of 4.5 m square plus 3m square i. e. say approx. 5.4 m

2. Radiation from the cell tower

A GSM900 base station antenna transmits in the frequency range of 935 - 960 MHz. This frequency band of 25 MHz is divided into twenty sub-bands of 1.2 MHz, which are allocated to various operators. There may be several carrier frequencies (1 to 5) allotted to one operator with upper limit of 6.2 MHz bandwidth. Each carrier frequency may transmit 10 to 20W of power. So, one operator may transmit 50 to 100W of power [ at any instant ] and there may be 3-4 operators on the same roof top or tower, thereby total transmitted power may be 200 to 400W. In addition, directional antennas are used, which typically may have a gain of around 17 dB (numeric value is 50), so effectively, several KW of power may be transmitted in the main beam direction. Operators are now also assigned frequencies in 1800 MHz band , in addition to 900 MHz band.

2.1 Radiated power density from the cell tower

Power density Pd at a distance R is given by the following formula [ available in text books also ]
Pd = Pt X Gt divided by 4 X 3.14 ( i. e. Pi ) X R square
where, Pt = Transmitter power in Watts
Gt = Gain of transmitting antenna
R = Distance from the antenna in meters

For Pt = 20 W, Gt = 17 dB = 50 ( In numerical terms ) , Pd for various values of R is given in Table 1 below.

Table 1 – Power density at various distances from the transmitting tower

Distance R (m)      Power density                  Power density
                             Pd in W/ square m           Pd in µW/m2

1                           79.6                                 79,600,000

3                           8.84                                 8,840,000

5                           3.18                                 3,180,000

10                         0.796                               796,000

50                         0.318                               31,800

100                       0.008                               7,960

500                       0.000318                         318

The power density values given in Table 1 are for a single carrier and a single operator.

Multiple carriers are being used and multiple operators are present on the same roof top or tower,

then the above values will increase manifold. Assuming 5 carriers are used at a time by an operator --not uncommon in metro cities due to heavy traffic --- the value of Pd at 10 m will be 3.98 W/m2 . For three operators it will be 3 times say 11.98 W / m2 say 12 W / square meters. At any given tower, all the operators main beam is generally expected to be in the same direction to cover a specific road /colony etc.

2.2 At present , India [ Dot ] follow the International Commission on Non-Ionising Radiation Protection (ICNIRP) guidelines for Radiation,[ from radio wave transmitters on earth's surface ] which allow a radiation rate of 4.5 watts/sq metre at 900 MHz and 9.2 watts/sq metre at 1,800 MHz to be emitted from cell phone towers . (Inter-ministerial Committee --IMC Report, pp 31-32). India follows the latter reference level. The Dot has issued a rule in this regard ,a couple of years back , which hardly any practical value to a common man ] The ICNIRP limit has a serious flaw. It specifies this limit for only 6 minutes continuous exposure. In practice , the Cell Tower radiation is round the clock for 365 days of year ! hence, much lower limit is called for . Unfortunately , the Indian Medical Council of Research [ ICMR ] has not acted in this area effectively. As the tower has many directional antennas , transmitters etc. only actual measurement will allay any doubt of radiation in the vicinity as precise calculations will be difficult and will not give mental satisfaction. Below the tower , there is less problem , but in the nearby building esp. those who are at near tower height or just below, are the worst exposed. This value of of 12 W/m2 at 10 m is very high compared to ICNIRP stipulation indicated below [ ref. IMC Report , page 29 ,para 5.1 ]

India has adopted the following ICNIRP guidelines for basic restrictions and reference levels for limiting Electromagnetic fields exposure in the band upto 2000 MHz is f / 200 W /m2 where f is the frequency in MHz. This is 4.5 W /m2 at 900 MHz band and 9 W /m2 at 1800 MHz band. These guidelines are based on short term exposure of 6 minutes and not H24 / 365 days exposure encountered in Cell Tower radiation exposure.

2.2.1 Following the outcry reg . cell towers radiation health hazard over last few years, the DOT appointed an Inter Ministerial Committee [ IMC ] with rep. of Min. of Health , Environment also. The latter Ministries forced the Dot rep. in the IMC to agree to lower the limit by 10 times but it it is still to be notified by Govt.

The IMC Report [ year 2010 ] also addresses health hazard from cell phone handsets also besides Cell Tower Radiation Hazard ] The IMC 's suggested that the radio frequency exposure limits in India may be lowered to 1/10th of the existing reference level. They have however not given any cogent reasoning how and why they thought of 1/10 . Possibly this was a thumb rule compromise in the IMC .

2.3 The Inter Ministerial Committee of the Govt. of India ( IMC) has also accepted that the existing standards are based on thermal (heating) limits and do not address non-thermal (or low intensity) exposures which are reported to cause Biological effects. Lot of other medical reports are also available pointing to the need for lowering the ICNIRP guidelines. The IMC has also stated that the present ICNIRP / FCC ( USA ) limits are insufficiently protective of public health and require reconsideration and has recommended lowering the above limit by a factor of 10. It has also referred to the Bio-initiative report, [ published in USA in 2007 ] which has recommended 1000 microwatt/m^2=0.001W/m^2 for outdoor exposure and 100 microwatt/m^2 for continuous indoor exposure [ pl see Section 5.4, page 32 of IMC Report ]

2.4 One should also take note of see the limits lower by 100 or more time times adopted by many other countries [ ref. page 30 of IMC Report and Prof. Kumar's doc ] . China has adopted 0.4 W /m2 standard , 0.1 W / m2 by Poland / Hungary ,Paris and 0.001 W/m2 . These countries must have done this after careful consideration of Health hazards from radiation exposure.

2.5 Radiation pattern of the antenna

It is accepted that the , radiation density will be much lower in the direction away from the main beam and the above mentioned scenario may not be encountered for an adjoining building , every time. The simulated radiation pattern of GSM900 antenna of approximately 17 dB gain at 950 MHz of size 2400 mm x 30 mm is shows radiation in two planes – horizontal and vertical. There is one main lobe and several side lobes. For the main lobe, half-power beam-width (HPBW – defined as angular range over which maximum power decreases to half of its value) in the horizontal direction is 65 degrees and HPBW in the vertical direction is 6 degrees. There are several side lobes, whose maximum levels are about -13 to -20 dB below the main level.

One should know actual radiation pattern of the antenna (which unfortunately is not made public) to calculate exact radiation density at a point , but the above formula can give reasonable estimation. One cannot go on doing calculations for each tower and each building . Again estimating actual radiation pattern , integrating patterns for the antenne of 3-4 operators will also be a complex task Actual measurements would be desirable but may not be practicable , every time .

2.5.1 One should be aware that compliance with present standards is left by the DoT to self certification by the service providers. Even this is not being done and a large number of towers are unauthorised – illegal. As the Tower no. in India has crossed 5.88 lakhs , this a real serious problem which needs attention of Policy Makers / Ministers.

The DoT had invited comments from stake holders on the IMC Report by 31st March 2011. Final decision on this proposal of lowering the limits is awaited. But all such reforms will be on paper only because the DoT has no manpower to verify conformity. Public outcry should force the service provider to carry out measurements in the presence of enlightened public rep.s

3. International Telecommunication Union ( ITU ) , Geneva , Recommendation

The ITU - T Rec. K.52 on Guidance on complying with limits for human exposure to electromagnetic fields is also important . In Appendix II --p. 25 , 26 etc. , examples of simple evaluation of EMF exposure at ground level and at an adjacent buildings are given. From the curves , given therein ; it is apparent that maximum exposure hazard is there for horizontal separation upto about 10 -15 meters .

4. Case study of Usha Kiran Building, Mumbai

Through the help of the above typical radiation pattern, Prof. G. Kumar has analyzed the news reported in Mid- day, Mumbai dated Jan. 3, 2010, which stated - “Mumbai's swanky Usha Kiran building says the four cancer cases there could be linked to mobile towers installed on the facing Vijay Apartments . The towers are seperated by more than 10 -15 metes from this building . People living in the 6th, 7th and 8th floor in the opposite building [ Ushakiran ] will get maximum radiation as they are in the main beam direction. People living on the other floors will receive lesser radiation as beam maxima is reduced considerably as can be observed from vertical radiation pattern. In the horizontal direction again, people living in the front side of the antenna will receive much higher radiation compared topeople living in the back side of antenna.

From Table 1, it may be noted that for a single transmitter, power density at R = 50m is equal to 0.0318W/m2 = 31,800 µW/m2. Even for 3 transmitters in the same direction, it comes out to be approximately 0.1 W/m2 = 100,000 µW/m2, which has caused cancer to several people in a duration of 2 to 3 years.

4. 1. Measurement at a cancer’s patient residence [ From Prof. G Kumar's Report ]

Since the radiation effect on the human body is cumulative, a hand held broadband radiation monitor (Frequency range of 800 to 2500 MHz) has been developed to measure the total received power. Radiation measurements were carried out in a lady’s apartment, who had developed cancer within one year of installation of cell tower. The layout of the apartment . The measured readings show that the radiation level is very high and it is between – 4 to -10 dBm. At 900 MHz, -10 dBm received power is equivalent to 7,068 µW/m2, again implying that safe radiation norms must be reduced considerably than adopted by India, which is 4.7W/m2 = 4,700,000 µW/m2.

5. It is hoped that the above , will make it apparent that the if 3m separation specified in W. B . / Maharashtra / Delhi Govt. Notification / Rules is NOT Safe for human exposure to Cell Tower radiation. It is particularly harmful when one is exposed to main beam. The 3m seperation distance specified in W.B Govt. and other State Govt. 's Notification / Rules is not adequate to protect the residents in nearby buildings and in such matters caution would be a better option. It took many years for the Govt. to ban Smoking in public places and to ban the use of Asbestos. Let us not repeat this in case of cell Tower radiation exposure.

1 comment:

  1. Dear Sir , I am a victim of mobile towerradiation staying on TOP Floor. Pl. let me know Whom should I address & What is the email id ? Thanks.