Reverse Implementation of Radio Frequency Identification (RFID) Technology

for Personnel Tracking in Underground Mines

Objective

To develop a method for tracking underground mine 

workers that provides: (1) potential improvements in

accuracy when compared to conventional, zone-based 

radio frequency identification (RFID) methods, (2) the 

ability to interface to a variety of mine communications 

infrastructures, (3) a higher degree of survivability after a 

mine disaster, and (4) ease of installation and 

maintenance.

Background

The Mine Improvement and New Emergency 

Response Act (MINER Act) of 2006 calls for 

improvements in underground coal mine accident 

preparedness and response. One of the requirements is that 

each mine provide a method for aboveground personnel to 

determine the location of all underground personnel after 

an accident or mine emergency. Researchers at the 

National Institute for Occupational Safety and Health 

(NIOSH) Office of Mine Safety and Health Research 

initiated a study of personnel tracking systems that could 

be applied to underground mining. A new methodology 

was proposed that reverses the way conventional RFID 

tracking systems are normally implemented. A 

conventional RFID system uses fixed tag readers (which

are typically line powered, mounted in the mine, and 

connected via wire, fiber, or through a wireless link) to 

transmit location data to a surface tracking system 

computer. Battery-powered tags, worn by the miners,

transmit an ID that is detected as a miner walks near an 

RFID tag reader. This allows the system to locate a miner 

within a certain zone where the zone size is determined by 

the spacing between readers. A reverse RFID system 

reverses the conventional implementation of RFID 

components by locating the RFID tags at fixed, known 

locations in the mine, and making the tag readers portable 

and worn by the miners (Figure 1).

Figure 1. The reverse RFID concept with tags mounted on the mine roof 

and portable, belt-worn readers.

Approach

In 2007, NIOSH awarded a contract to L3 

Communications (Chantilly, Virginia) to develop and test 

the reverse RFID concept. L3’s prototype was 

implemented with ultra-wideband (UWB) technology. 

Each tag broadcasts its location identifier five times per 

second. The system’s tag readers (worn by the miners) 

receive this information and sense the received UWB 

signal strength associated with the tag transmissions. This 

measurement of signal strength allows an estimation of 

distance between the reader and the nearest tags. A UWB 

transmission scheme was used because its low power 

requirements allowed long tag battery life, and the pulsed

signal offered decreased interference from multipath 

signal reflections. 

The miner’s location information is sent via a radio

from the miner’s tag reader to the existing mine 

communications system. The information is then 

processed and displayed on a mine map by the tracking 

system computer located at the surface. The distance 

estimation technique and the provision for a high density 

of tags throughout the mine can provide location tracking 

No. 543 September 2011 
accuracies that surpass those of other conventional 

tracking systems.

Test Results

Using a NIOSH-approved test plan, L3 

Communications conducted tests of the final mine-ready 

system at an underground coal mine in Pennsylvania. The 

test area consisted of two entries and extended 

approximately 2,000 ft. Tags were mounted on the roof

with various spacings. Installation time averaged around 

three minutes for each tag and consisted of hanging the tag 

in the center of a crosscut and recording the tag ID and 

location of the tag into the tracking system database. Most 

of the testing was conducted with tags mounted at every 

other crosscut, which achieved a balance of accuracy and 

practicality.

The miner’s tag reader was worn on the belt with the 

UWB antenna tethered to the cap lamp. A radio was 

packaged inside the same enclosure as the tag reader, 

which transmitted the location information to the mine’s 

existing leaky feeder communications system. The leaky 

feeder system then relayed the position estimate to the 

tracking system computer at the surface. With tags at 

every other crosscut (approximately 200 ft between tags), 

the location of a miner was determined to within an 

average of 42 ft as the miner walked down the entry

(Figure 2). 

These initial tests also highlighted some challenges

related to system updates and component packaging. 

Tracking information could only be updated if the miner 

was within range of and had a link to the mine’s 

communications system (in this case, the leaky feeder

system). Also, components worn on miners’ belts (tag 

reader and radio) can be cumbersome. To lighten the

burden, the additional components can be integrated with

existing cap lamp components.

Figure 2. Comparison of surveyed distance from starting point 

and the tracking system’s calculated distance for tags at every 

other crosscut.

Summary

Possible benefits of the reverse RFID approach 

include: (1) higher tracking accuracies that can average 

under 50 ft with tags at every other crosscut, (2) the 

flexibility to use a mine's existing communications 

infrastructure, (3) potentially higher system survivability 

because the tracking tags mounted in the mine are selfcontained and wireless (Figure 3), i.e., there are no 

interconnecting wires to be damaged and, if some tags are 

lost in a fall of ground or explosion, tracking will resume 

when other intact tags are encountered, and (4) low-cost 

tags that can be quickly and easily mounted and recorded

at fixed, known locations in the mine, which allows for 

easy expansion as mining progresses. However, as with

many other tracking systems, a disadvantage is that 

tracking information will not be updated after a mine 

incident or emergency if the communications 

infrastructure is not operational.

The technology described in this article is available 

through L3 Communications (Chantilly, Virginia) and is 

marketed as the Tru-Tracker Precision Location System

[http://www.gses.l-3com.com/mine_safety/tracking.php].

The reverse RFID approach is also being tested by other 

personnel tracking system manufacturers.

Figure 3. MSHA-approved UWB RFID

tag with an estimated 10-year battery life.

For More Information

For more information on this technology and its use, 

contact Todd Ruff (TRuff@cdc.gov) or the Health 

Communications Coordinator (OMSHR@cdc.gov), 

NIOSH Office of Mine Safety and Health Research, P.O. 

Box 18070, Pittsburgh, PA 15236-0070.

To receive NIOSH documents or for more 

information about occupational safety and health topics, 

contact: 1-800-CDC-INFO (1-800-232-4636), 1-888-

232-6348 (TTY), e-mail: cdcinfo@cdc.gov, or visit the 

NIOSH Web site at http://www.cdc.gov/niosh

Mention of any company name or product does not 

constitute endorsement by the National Institute for 

Occupational Safety and Health.

DHHS (NIOSH) Publication No. 2011–209