Recognizing our current lack of knowledge about VLF fields with strengths of more than a few microtesla, there are certain institutions around the world which have recommended exposure limits which are more strict than the limits suggested in ANSI C95.1-1991; some of these stricter standards are shown in table 1. For example, Canadian health regulations (Stuchly, 1989) and Commonwealth of Massachusetts labor regulations (Comm. of Mass., 1986) both prohibit long-term exposure to fields as strong as those produced by the Articulograph.
Recent studies, including the review study published by the IEEE in connection with ANSI standard C95.1-1991, seems to suggest that these lower standards are not necessary. The ACGIH has recently raised their published threshold limit value, and it is possible that other organizations will do the same. Since some of the remaining regulations have the force of law, however, researchers in areas with such regulations (e.g. Canada and the Commonwealth of Massachusetts) should obtain current copies of the relevant standards before purchasing a Carstens Articulograph. If acute exposure to the fields produced by the Articulograph is not permitted, such researchers may wish to consider purchasing the other commercially available EMMA system, the Botronic Movetrack.
Hoole and Nguyen (1996) review three EMMA systems, including the Carstens Articulograph, the Botronic Movetrack system (Hägersten, Sweden), and the MIT system (Perkell et al., 1992). They report that the Movetrack and the MIT systems both expose subjects to fields of less than 1uT, which is below the maximum permissible exposure specified by both Canadian and Massachusetts regulations. The MIT system is, however, not a commercial product. The Movetrack system is a commercial product, but because of its two-transmitter construction, the Movetrack is considerably more susceptible than the Articulograph to tracking errors caused by misalignment of the receivers (see Hoole and Nguyen, 1996, or Perkell et al., 1992, for a more thorough discussion).