Wireless Local Area Networks (LANS)

Wireless Local Area Networks (LANS)
The safety of users is a primary consideration when VDTs are introduced into the work environment. VDTs are essentially electrically identical to television sets. Both VDTs and television sets produce electromagnetic emissions (sometimes called radiation) from CRT (Cathode ray tube); the phosphor, which is the chemical composition that coats the inside of the CRT screen; and from associated electronic components.

Health and Safety

Wireless LANs operate at very low power (1watt or lower), less energy than is used for most cellular telephones.
Wireless LANs cover relatively short distances, so they can operate using very weak radio waves.
These weak radio waves are far below the exposure limits set by safety standards.

What is a Wireless Local Area Network (LAN) ?

LAN stands for local area network, so a wireless LAN is simply a network linking two or more computers without wires (cables). In many offices today, computers communicate with each other and with printers and other devices by sending information along wires. Using newer technology, computers can be linked by the same method as your cordless telephone operates in your home - by transmitting the signal through air. Just as your cordless telephone frees you to make a phone call from anywhere in your home, the wireless LAN permits workers to use their computers anywhere in the network area, such as an office building or corporate campus. As with the wired network, the computer can access information stored in other computers in the office. Some wireless networks are designed to cover a broader area and are called wide area networks or WANS.

HOW DOES THE WIRELESS NETWORK WORK?

The network operates by linking the computers to the wiring in the office using radio frequency energy, just as the `cordless' portable telephone in your home sends voice information to the telephone wiring in your home. Like the telephone system, it is a hybrid system using both wired and wireless communication. The antenna is small just a few inches, barely noticeable outside of the computer, and the power used is very low, comparable to your cordless telephone.

IS THIS TECHNOLOGY NEW?

The ability to send information across distances by radio frequency energy, or radio waves, is not new. Non-cable television, AM and FM radio, cellular telephones and pagers use this method. However, affordable technology to adapt these techniques for computers in offices has been developed only in the past few years.

A number of applications already exist in which computers are connected by using radio waves instead of wires. Some are wide area networks and some are local area networks. You may have encountered these without noticing. For example, trucks that carry packages for express delivery are liked to the main office by wireless technology. Similarly, an appliance repairman can set up his portable computer in your home and check with the local warehouse to see if the parts needed to fix your refrigerator are available. Wireless LANs are used at airports, by local police and other public service organizations, and in hospitals for nurses and doctors to enter or obtain data at the patient's bedside.

WHAT IS RADIO FREQUENCY ENERGY?

Radio frequency energy, or radio frequency radiation, describes just one category of electromagnetic energy that makes up the electromagnetic spectrum (see figure). The range of radio frequencies in the spectrum - 3000 Hz through 300 billion Hz - has been used to transmit information in various ways. Man-made radio frequency waves have been in the environment as long as we have had radios - almost 100 years. Television, whose signals are also transmitted by radio frequency energy, has been with us for nearly 50 years. The radio frequency range, including microwaves, has many other uses in communication including police, fire, amateur, and Citizens' band radio, marine radios, AM and FM radio, UHF television, and traffic and weather radars. More recently, different radio frequencies have been used for telephones, paging and other personal communication systems.

WHY IS IT CALLED RADIO FREQUENCY RADIATION?

The term radiation simply means that something can spread out from its source, as heat can radiate from a campfire. Radio waves are a type of energy that radiates out from a source, just as light or sound does. The radio frequency energy produced by most sources are transmitted by antennas over distance.

Radio waves are quite different from ionizing or nuclear radiation. As the figure shows, the spectrum of electromagnetic energies includes two categories, non- ionizing and ionizing radiation. The non-ionizing frequencies are those that produce energy that cannot break chemical bonds, or ionize, the chemicals in living tissue. The radio frequencies (RF) are non-ionizing. Infra-red and visible light are also non- ionizing radiation, and as the diagram shows, are higher frequencies than RF.

Ionizing radiations, which include X- and gamma rays are the highest frequencies in the spectrum. This type of energy, found at frequencies higher than visible light, carry sufficient energy to alter molecular structure or break chemical bonds.

Figure, the SPECTRUM labeling IR and NIR

WHAT DO WE MEAN BY STRONG OR WEAK RADIO FREQUENCY FIELDS?

The two important characteristics used to describe electromagnetic energy are the frequency at which the wave is transmitted, and the strength of the RF electromagnetic energy. The frequency (cycles of the wave per second), shown in the Figure of the electromagnetic spectrum, is measured in Hz. The strength of the RF energy is measured by the concentration in space, called the power density, measured as watts per square meter.

At any frequency, the energy can be strong or weak, just as a high frequency sound wave, producing a high pitched sound, can be either strong (loud) or weak (soft).

DOES THE RF ENERGY FROM WIRELESS LANS AFFECT HEALTH?

The RF energy from wireless LANs does not effect the function or the health of living things. The RF energy is extremely low because these systems operate at very low power (1 watt), less energy than is used for most cellular telephones. A radio station, for example, may transmit at 50,000 watts. Because they operate at low power, the RF energy from LANS is well below the exposure limits recommended by radio frequency standards; in fact RF fields from LANS are hundreds of times below the exposure limits recommended in health based standards.

Health-based standards refer to any regulation or exposure guideline that provides specific limits on emissions from sources, or on concentrations in the air or water, for the purpose of protecting human health. The most widely recognized source of standards in the U.S. is the American National Standards Institute (ANSI). ANSI adopted the RF standard that was developed by the Institute of Electrical and Electronic Engineers (ANSI/IEEE, 1992).

HOW ARE THESE STANDARDS DEVELOPED?

The potential effects of low levels of exposure can be determined from scientific research studies, and from the basic principle that safety is directly related to limiting or reducing exposure.

The ability of RF energy to affect living things depends on the strength, or intensity. Over the years, scientific studies have indicated that below a certain intensity level, RF energy does not effect living organisms. Several scientific and technical organizations have developed exposure guidelines or standards, which recommend limits on exposure to ensure that no adverse effects occur. At levels above the recommended exposure limits, exposure to RF fields can increase the temperature of biological tissues. Below these limits, however, even prolonged exposure to RF energy has not been shown to affect, or cause any changes, in living organisms.

HOW DO WE KNOW WHETHER LOW LEVELS OF RF CAN EFFECT HEALTH?

The biological effects of RF exposure, and the RF intensity levels at which effects could occur, are identified from scientific studies of exposed cells, animals, and humans. These research studies are used to develop health and safety standards that specify permissible exposure levels. Over the years, hundreds of studies have been undertaken to determine how, and under what circumstances, RF energy can affect animals and people. This research has been reviewed on several occasions by different groups of scientists in the U.S. and by other national and international organizations. Wireless LANS operate at such low power that RF levels could not reach or exceed the limit specified in the health based standard used in the U.S., the ANSI/IEEE (1992) standard.

In research studies, laboratory animals have been exposed for long periods of time to RF energy at levels below those that cause heating. Studies of people are inherently limited, so additional information from carefully controlled experimental studies in animals is important. Low level exposure has not been shown to effect pregnancy, contribute to cancer, affect eyes, or affect human health in any manner. Studies of workers exposed to RF energy have not provided evidence of increases in cancer or other health effects.

CAN CUMULATIVE EXPOSURE CAUSE HARM?

People often wonder whether exposures from various sources can add together to reach a harmful level. Exposures from wireless LANS are too low for this to happen. For instance, if exposure from a wireless LAN is several thousand below the standard, it would take several thousand similar sources in the same place all and operating at the same time and in the same direction to reach the exposure limit specified in the standard.

It is highly unlikely that any significant addition of RF could occur: the intensity is very low; different sources are not likely to be operating in the same area or operating toward the same direction; and the low-intensity radio waves get even weaker with distance from the source.