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106 Advances in Productive, Safe, and Responsible Coal Mining

of view with measurement rates up to 50Hz. Like radar, it is only useful in line-of-
sight applications and cannot differentiate between objects and humans; however,
it does have high accuracy and does not require an MWC.

7.4 NIOSH research on magnetic-based proximity

7.4.1 Early NIOSH research (HASARD)

NIOSH first developed electromagnetic proximity detection technology in 2000 as the
Hazardous Area Signaling and Ranging Device (HASARD) [6]. This system used an
electromagnetic-field generator to create a magnetic-field measurable by an MWC
thereby giving a rough indication of the distance between the generator and the
MWC, as illustrated in Fig. 7.2. The HASARD system was based on the use of
low-frequency (73kHz) magnetic fields and the concept that the strength of the field
decreases approximately proportional to the cube of the distance from the source.
It is important to emphasize that HASARD is a two-part active system composed of
a single transmitter and one or more receivers, depending on the circumstances. The
transmitter is installed on-board the CMM. The receiver is worn by the CMM oper-
ator, helper, and other miners working near the CMM. The HASARD receiver was
designed to be an omnidirectional (direction-independent) magnetic-field strength
meter. Multiple antennae detect the field, and the internal electronics amplifies and
filters the signal and converts it to a DC voltage level. This signal level is compared

Increasing distance from generator

MWC

Generator

Increasing magnetic field strength

Fig. 7.2 Conceptual drawing of proximity detection operating principle.