Any fatality is one too many, according to the US National Institute for Occupational Safety and Health (NIOSH). The NIOSH Pittsburgh Laboratory is now working on commercialising its Proximity Warning System (PWS), an innovation that could help reduce avoidable deaths. At the recent Longwall USA conference, W H Shiffbauer explained how.
NIOSH’s proximity warning system has been dubbed HASARD, for Hazardous Area Signalling and Ranging Device. It was developed after much research in both surface and underground operations regarding miner/equipment contact and interaction with all types of equipment, including continuous miners, shuttle cars, highwall miners, conveyor belts and haul trucks.
Schiffbauer noted that sensing technologies such as radar, cameras and mirrors did exist, but that a major disadvantage to visual monitoring devices was that they required continuous observation by the operator. In addition, such tools were typically passive and resulted in many unnecessary “nuisance alarms” due to insignificant detections such as debris and small rocks, leading to a lowering of the operator’s confidence in the apparatus and its reliability.
The NIOSH active sensor system, which is much less susceptible to nuisance alarms and includes a very strong warning indicator, is made up of three components: a signal generating device (Generator), a PAD (personal alarm device) and a wireless remote controller (Controller).
The device works in tandem to measure magnetic fields. The PAD, worn in a miner’s cap lamp (or as a pendant or on a machine), will trigger an alarm when the Generator, along with its associated antenna installed on a vehicle or in a dangerous area, recognizes an object in the magnetic field and communicates with the PAD. The controller, then, can be mounted in most places within the system’s range and is usually used when a remote alarm is needed.
The Generator’s magnetic field is created by a low-frequency current that runs through an attached loop antenna that is wound around a ferrite bar, or bar antenna. The created field can enter solid objects including rocks, water sprays and half-inch-thick steel material, and blankets the monitored area.
The type of antenna used depends on the size of the area and mounting destination, said Schiffbauer, and the marker’s dimensions equate to the amount of current and size of the wire, as well as the amount of wire turns within it. While a loop antenna may be the best choice for long conveyor belts, a bar antenna is typically most efficiently used on continuous miners and other vehicles. These factors also apply to generator size.
For the HASARD warning system, NIOSH chose an indicator that sounds in the lower portion of the Low Frequency bank, or 30-300kHz, as testing results showed that EMI, or electromagnetic interference, can be produced at frequencies below 50kHz. NIOSH, wishing to exceed the EMI frequency, also chose the range because sound below 150kHz generally stays within a small area and does not circulate.
The PAD portion of the system serves as a receiver for the Generator due to a multi-channel active filter that only recognizes the Generator’s signals. With an adjustable threshold to set off the alarm, the microprocessor-based device can identify a distance with precision, typically within about an inch. When the danger enters the magnetic field, the worker can be signalled with a buzzer, lights or a vibration. When the alarm sounds, the HASARD Controller also receives an indication via a short-range wireless data link (WDL) that can alert the equipment operator to the problem.
The Controller is not vital to the system’s performance if the purpose is only to give warning to a single worker. However, because of its inclusion of a WDL, microprocessor and peripheral controls, the options for multiple connection use is possible. The Controller is capable of receiving a unique signal from each PAD being used and can actually trigger a multi-level alert if necessary, and can activate a device’s alarm on one level while deactivating equipment on another level. Additionally, the Controller can also be configured to record radio-frequency identification (RFID), machine number, time of entry, time of exit, distance to machine and the amount of battery life remaining.
NIOSH has been pursuing the use of the HASARD system at underground operations for several years, and an underground instrumentation manufacturer has conveyed an interest in making the system commercially viable. Working together, the vendor and NIOSH have conducted field trials using the agency’s testing plans and the company’s HASARD-based product on a Joy 14 continuous miner at NIOSH to determine the “footprint” the hardware’s magnetic fields produce.
Now that testing has determined the technology’s potential to be life-saving in a dangerous situation underground as well as in other types of mining, another manufacturer is currently in the process of producing a protective shell for the system, according to Schiffbauer. NIOSH, in its constant pursuit of a healthier, safer mining environment, is actively supporting the industry in efforts to bring the HASARD system into commercial use and help save workers’ lives in the future.
