13 - Laserfiche WebLink

Home Browse Search

Chapter 3: Base Stations and the Public Health 4111 As cellular networks need to deploy more base stations A. RECAP OF ELECTROMAGNETIC to keep up with the public's demand for service, base FIELDS stations are closer to each other and to where people live and work. This naturally causes people to ask the In the last chapter,we learned that cellular base following questions: stations transmit radio waves at frequencies around II Can radio waves from base stations harm me or 850 MHz. Each radio wave comprises two fields— my family? one electric,the other magnetic.The fields are at ■ Are there safety standards for exposure to the radio right angles to each other and to the wave's direc- waves from base stations? tion of travel. But just what are fields? Fields are ■ How do exposures to radio waves from base sta- the way scientists explain certain natural forces. dons compare to those permitted by applicable safe- Until recently,people could only understand forces ty standards? produced by direct physical contact.A spoon on the ground would only move if someone picked it In this chapter, we will answer those questions,in light of the larPtt reported scientific rlarn. up,kicked it,or pulled on a string that was tied to it. If the spoon moved without any direct physical The topic of base stations and the public health contact,magic or a spirit was to blame. was a major area of discussion at the Federal Focus People also had no idea why a spoon knocked off National Symposium on Wireless Transmission a table would always fall down to the ground,never Base Station Facilities.Experts from both the up into the sky.Today,of course,we know that public and the private sectors who participated in the force of the earth's gravity pulls the spoon to the Symposium agreed that the radio signals from the ground.Gravity is one of the natural forces base stations pose no threat to public health. that requires no physical contact between two First,we will see that the magnetic and electric physical objects(the earth and the spoon).Physicists fields that make up radio waves can interact with use the concept of a gravitational field to explain • the atoms and molecules that comprise matter, how the force of gravity arises.Any massive object including living cells.When the fields are weak, such as the earth sets up a gravitational field the interactions are very subtle.Most scientists around it.When another object with mass enters who have investigated those interactions hold that that gravitational field,a gravitational force arises the interactions pose no health risks at the very which tends to pull the two objects together.The low exposure levels associated with cellular base intensity of the force depends on the masses of the stations.While a few scientists have claimed two objects and their proximity to each other. biological effects from fields at frequencies other Today,we also know we can move a stainless steel than those used by cellular base stations,others spoon without directly touching it by bringing a have not been able to reproduce the claimed strong magnet near it.A magnetic force attracts results in laboratory experiments,or the effects the spoon to the magnet.That force arises without have no obvious significance.Stronger fields can any physical contact between the magnet and the produce measurable warming of living tissue.Very spoon.Rather,it arises from the spoon's immersion intense fields can cause significant thermal effects in the magnetic field emanating from the magnet. such as cataracts and temporary sterility in males, but the fields from cellular base stations are far,far There is also an electric force that arises without below the levels required to produce these effects physical contact.You can prove this for yourself in members of the public. by running a hard rubber comb briskly through To protect the general public and workers,various your hair,and then bringing the comb near small pieces of tissue paper on a countertop.Some of the government and private bodies have adopted Stan- bits of paper will fly toward the comb because an dards establishing permissible exposure levels.The electric force causes them to move.As with the public's exposure from base stations is extremely magnet and the spoon,the force arises without low,usually less than one percent of the levels direct physical contact between the comb and the permitted by the standards.And workers who come paper.The force arises from the paper's immersion close to antennas during maintenance activities in an electric field. The electric field results from . can take simple precautions to keep their exposures a static electric charge set up in the comb by the within the limits of the standards. brisk rubbing.t