Table 1: Table 1: Magnetic field exposure standards at 20kHz, expressed in microtesla.
|Comm. of Massachusetts (1986)||1.99|
Table 1 lists magnetic field exposure standards, culled from the summaries by Kavet and Tell (1991) and Haes and Fitzgerald (1995), which apply between 10kHz and 20kHz, and which do not apply exclusively to VDT emissions. Standards originally quoted in units of Amps/meter, including the ANSI/IEEE standard, were converted to microtesla using a conversion factor of T/(A/m).
The standard which is most relevant to use of the Articulograph in most of the United States is probably the consensus standard which was composed by the Institute of Electrical and Electronic Engineers (1991), and which was approved by the American National Standards Institute in 1992 as ANSI C95.1-1991. The ANSI/IEEE standard recommends that the average exposure, averaged over any six minute period and over a cross section of the human body, should not exceed 205uT. Less stringent standards apply to partial-body exposures, but the less stringent standards specifically do not apply to the eyes.
The IEEE standard is designed to keep the induced current in biological tissue at least a factor of ten below the lowest reported stimulation thresholds for electronically excitable cells. The current standard is less stringent than the 1982 version of the standard (ANSI C95.1-1982), because recent studies with detailed heterogeneous human models have shown that there is no danger of tissue heating at the new threshold level.
In designing the standard, the committee considered peer-reviewed articles describing the health effects of electromagnetic fields in fourteen different areas, without regard for the mechanism causing the effect. The mechanisms of tissue heating and cell stimulation were chosen as the basis for standard exposure thresholds because they are quantifiable, and because ``no reliable scientific data exist indicating that nonthermal (other than [electric] shock) or modulation-specific sequelae of exposure may be meaningfully related to human health.''
Several of the other standard exposure levels listed in table 1, with the exception of the Federal Republic of Germany standard, are lower than the ANSI/IEEE standard. Kavet and Tell (1991) suggest that the lower standards may be incorporating additional safety factors, in an attempt to guard against possible nonthermal and chronic effects of exposure, which are not at present sufficiently well documented to suggest any specific quantitative exposure threshold.
The American College of Governmental Hygienists (ACGIH) recently raised their recommended threshold limit value to match that of the IEEE/ANSI standard. In the 1993-1994 edition of their Threshold Limit Values and Biological Exposure Indices, they recommended a maximum exposure of 2.01uT. In the 1996 edition of the same book, the maximum recommended exposure has been raised to 200uT, as shown in the chart above.