Other Types of Non-ionizing Radiation and Their Biological Effects

Recent studies have begun looking at extended exposures to non-ionizing radiation. One example is the evidence that extended exposures to microwaves may be related to development of cancerous tumor in rats. Statistical studies suggest increased rates of leukemia among power station operators, aluminum workers, power and telephone linemen and other workers chronically exposed to electric and magnetic fields. Results of such studies are not conclusive, as yet, regarding harmful effects to humans. The current microwave standard is based on thermal effects in tissue. Other biological effects are under investigation.  

Visual Display Terminals (VDTs):

The applications of computer technology and the accompanying use of video display terminals (VDTs) are revolutionizing the workplaces of America, and their use will continue to grow in the future. For example, in 1984 only 25 percent of the U.S. population used computers at work and less than 8 percent at home; in 1997, more than 49 percent of the population used computers at work, and 71 % at home, and the number continues to grow. Also, more than 20 million people are employed in jobs that often require intensive keying. Along with this expanding use of VDTs have come reports of adverse health effects for VDT operators and many concerns about the use of computers have lead to extensive research on public helath. Some concerns include high voltage electricity, ergonomics, and noise. But the greatest interest is in whether extreme low frequency fields or higher frequency radiation fields emitted by VDTs pose any problem, particularly for pregnant women.

OSHA has no standards that apply specifically to video display terminals or to extreme low frequency electric and magnetic field exposure. However, OSHA does have standards to protect employees against overexposures to radiation, noise, and electrical hazards.

The National Institute for Occupational Safety and Health (NIOSH), the U.S. Army Environmental Hygiene Agency, and others have measured radiation emitted by VDTs. The tests show that levels for all types of radiation are below those allowed in current standards. In fact, some measurements show radiation levels so low that they cannot be distinguished from general environmental radiation (background radiation).

Office automation equipment usage exploded in the 1980s. Along with office automation came controversy of many kinds. One area of controversy is that of safety and health problems related to office automation equipment. Much of the concerns arose from clusters of women office workers who miscarried or bore children with birth defects. One 5 year study found no effect on miscarriages for women who work on VDTs less than 20 hours per week and a 5 % greater incidence of miscarriage for those who work at VDTs more than 20 hours per week. To date there has been no strong link established between VDT use and miscarriages and birth defects. Currently, OSHA has no reliable information that any birth defects have ever resulted from a pregnant woman working at a video display terminal. However, the possible effects of radiation or extreme low frequency fields from VDTs on pregnancies continue to concern employees. Therefore, NIOSH and others are currently conducting major studies to thoroughly investigate any potential problems.

Extremely Low Frequency (ELF)and Electric and Magnetic Fields (EMF):

Extremely low frequency (ELF) radiation includes alternating current (AC) fields and non-ionizing radiation from 1 Hz to 300 Hz. Since ELF frequencies are low (wavelengths are on the order of 1000 km), static electromagnetic fields are created. ELF fields are considered as separate, independent, non-radiating electric and magnetic fields. Electric and magnetic fields (EMFs) at 60 Hz are produced by power lines, electrical wiring, and electrical equipment. Electric fields are produced by voltage and increase in strength as the voltage increases. Electric field strength is measured in units of volts per meter (V/m). Magnetic fields are from the flow of current through wires or electrical devices and increase in strength as the current increases. Magnetic fields are measured in units of gauss (G) or tesla (T). Electrical equipment usually has to be turned on for a magnetic field to be produced. Electric fields are present even when equipment is turned off, as long as it is plugged in. Current research has focused on potential health effects of magnetic fields. This is because some inconclusive epidemiological studies have suggested increased cancer risk associated with estimates of magnetic field exposure. No similar associations have been reported for electric fields. Exposure to EMFs depends on the strength of the magnetic field sources, the distance from those sources, and the time spent in the magnetic field. The American Conference of Governmental Industrial Hygienists (ACGIH) has established occupational Threshold Limit Values (TLVs) for static magnetic fields, sub-radiofrequency (30 kHz and below) magnetic fields, and sub-radiofrequency (30 kHz) and below static electric fields.

Public concern over power transmission lines initially involved aesthetics of towers, property right-of-way issues and nuisance effects. Potential health effects were first noted in the early 1970s in scientific and medical literature. Congress sponsored a review of the ELF health effects. Although there are no federal standards for health, some states have established limits on field strength in right-of -ways.

Principal interest in the U.S. is at 60 Hz since it is used for standard electrical power distribution. Sources of intense exposure include ELF induction furnaces, high voltage power lines, and close proximity to electrical wiring, including electric blankets and water bed heaters.

New area of concern is due to controversial epidemiological studies of leukemia and altered blood chemistry in persons living near electric power distribution lines at exposures of 5-10 mGauss(1/1000th of TLV). Many follow-up studies have been initiated, including a cellular study which showed Human colon cancer cells thrive better in a 60 Hz field.

The body absorbs very little energy at these frequencies, so the safety concepts used at higher frequencies is probably not appropriate for extremely low frequencies. Other mechanisms are under investigation, including molecular resonance as utilized in Magnetic Resonance Imaging (MRI).

ANSI is developing a standard. ACGIH suggests the use of protective devices for fields in excess of 15 kV/m to prevent safety hazards from shock, spark discharge, startle reaction, etc. For unprotected workers, the ceiling limits are 25 kV/m and 10 Gauss.

EMFs In The Workplace

Biohazards of Extremely Low Frequencies (ELF)

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Last Update: January 9, 2007

By: Serdar Z. Elgun