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A lone worker is not necessarily the only person on a mine site. The important issue is whether someone works without close or direct supervision and cannot expect immediate assistance. A technician several levels below colleagues or an examiner travelling through inactive workings may therefore be working alone while many other people are underground.
Isolation does not create every hazard, but it can magnify the consequences. A slip, medical event or equipment failure may remain undetected. Underground conditions add restricted visibility, long travel distances, heavy equipment, ground instability, dust, heat and potentially dangerous atmospheres. Rock and mine geometry obstruct signals, while an incident may damage infrastructure (see also: underground mine safety). Detection is only the beginning: responders still need a safe route to the person.
Work processes that can involve isolation include inspecting pumps, sumps, conveyors and ventilation controls; maintaining electrical or communication equipment; geotechnical inspection, surveying and sampling; environmental or gas measurements; security rounds; checking remote headings; and work during shutdowns or outside normal production periods. The mine's risk assessment must establish whether any task can be performed alone. Some work requires a second person, continuous supervision or a formal permit regardless of the monitoring technology available.
The central problem is therefore the interval between an event and effective help. A mine needs to reduce both time to detection and time to response. Britain’s Health and Safety Executive notes that lone workers face the same hazards as other workers but may be at greater risk because help is not immediately available. Its guidance on protecting lone workers (1) emphasises training, supervision, monitoring and support. Technology is one control within that wider system; it does not make an otherwise unacceptable task safe.
An effective lone worker monitoring system must answer five operational questions: Who is at risk? Where is that person (learn more about blasting safety)? Are they moving as expected? Is there evidence of distress or loss of device function? Can the worker and control room communicate? Each answer requires both technology and a defined procedure.
Identity begins with reliable assignment. A wearable, active RFID tag, smart cap lamp, radio, smartphone or badge must be associated with the correct person. The record may also include role, contractor status, competencies, and access permissions. The mine needs a process for forgotten, exchanged, damaged or unreturned devices. A technically perfect location attached to the wrong name is operationally dangerous.
Position must be expressed at a level that supports the response. “Underground” is seldom sufficient. A zone, tunnel segment, level, refuge chamber or coordinate can narrow the search, but required accuracy varies. Detecting entry into a prohibited electrical room may need a tightly defined zone; directing rescuers through a large mine may initially require the last confirmed checkpoint and direction of travel.
Movement and status add context. A stationary worker may be injured, concentrating on a repair, or simply taking a break. A missed check-in may mean distress, a flat battery or a network gap. Systems therefore need rules that combine events rather than treating every signal as certainty.
Communication completes the loop. A person must be able to raise an alarm, while supervisors need a means to verify it, issue instructions and confirm receipt. The HSE’s guidance on training, supervision and monitoring specifically calls for employers to monitor lone workers and keep in touch (2). A dashboard without a staffed response procedure does not meet that practical objective.
Technical monitoring forms a chain: identify the worker, generate observations, transport them, interpret them and present an actionable event. Weakness in any link can produce a late or misleading alarm.
Active RFID tags and connected wearables periodically transmit a unique identifier. Readers or gateways associate that identifier with a location event; the application associates it with a person. A tag can be issued for a shift, permanently assigned or integrated into equipment already carried, such as a cap lamp or radio. Entry readers can automatically place the wearer on the underground personnel list, while exit detection removes them only after a valid passage event.
If a worker enters a controlled zone, the system can compare identity with training or authorisation records and generate a warning. This differs from physically preventing access and depends on integration with access-control or permit systems.
GPS and other satellite navigation signals generally do not penetrate underground workings. Mines therefore use infrastructure-based or hybrid methods. Reader-based active RFID provides zone-level visibility. A tag transmission detected at a portal, level entrance or junction creates a known-location event. It is relatively economical for long tunnels when exact coordinates are unnecessary. Still, the displayed position is normally the last detection zone, not continuous proof that the worker remains at a particular point (nevertheless a zone remains important, e.g. for ventilation on demand).
Bluetooth Low Energy and Wi-Fi can estimate location from nearby beacons or access points, although reflections, machinery and changing tunnel conditions affect accuracy. Ultra-wideband measures radio timing and can provide finer positioning when anchors have suitable geometry and coverage. It usually needs a denser, surveyed installation.
Leaky-feeder, private cellular, Wi-Fi and mesh systems primarily provide connectivity, although location functions may be added through radio nodes, access-point association or separate tracking infrastructure. Inertial sensors can estimate steps, direction and changes in orientation between known points. This relative or dead-reckoned movement accumulates error over time, so map constraints and periodic absolute fixes are important.
No single technology is always best. A mine may use RFID at strategic junctions, a communication network across production areas and higher-precision positioning near mobile machinery. NIOSH is researching wireless technologies for underground mine safety (3), specifically recognising that narrow tunnels, large obstacles and moving vehicles can affect communication performance.
Accelerometers and gyroscopes in a wearable can detect impact, orientation change and inactivity. Software may flag a possible fall, an unusual angle or immobility beyond a configured period. The thresholds must reflect the task: a mechanic lying beneath equipment, a vehicle operator sitting still and an examiner walking a route produce very different movement patterns.
A local pre-alarm reduces false dispatches. The device first vibrates, flashes or sounds; an uninjured worker cancels it within a defined interval. If there is no response, the alarm escalates with identity, last known location, device status and event type. The inability to cancel is evidence requiring investigation, not a diagnosis.Geofencing adds movement context. The platform can detect entry into a restricted zone, unexpected route deviation or failure to leave an area before blasting or shutdown. Relative positioning can also protect workers around machinery by measuring their relationship to a vehicle or hazardous envelope. NIOSH describes underground proximity research that monitors worker positions relative to machines and safety zones. (4)
The term “life signal” needs disciplined use. A device heartbeat confirms that the wearable or tag has reported recently; it does not confirm that the wearer is healthy. Motion confirms activity, not consciousness. A manual welfare check requires the worker to acknowledge a scheduled prompt and offers stronger operational evidence, but a missed acknowledgement still has several possible causes.Physiological measurements—such as heart rate, skin temperature, or blood oxygen—require suitable sensors, proper contact, and validated interpretation. Consumer-style readings should not be treated as a clinical diagnosis. For many mining applications, dependable SOS, man-down, immobility and check-in functions offer clearer safety value than ambiguous biometric data.
Wearables may also receive environmental data from personal or fixed gas, dust, heat or oxygen sensors. This can connect a person and location to an exposure alarm. However, a lone worker system should preserve the distinction between the worker’s condition, the device’s condition and the surrounding environment.
A dedicated SOS control should be reachable with gloves and designed to prevent accidental activation. Automatic alarms can cover man-down, immobility, missed welfare checks, restricted-zone entry, low battery and loss of connectivity. Priorities and display formats must help operators distinguish a possible injury from a maintenance warning.
One-way communication can broadcast evacuation instructions by text, sound, light or vibration. Two-way voice or messaging lets the control room ask about injuries, hazards and escape routes. Delivery confirmation shows that the device received a message; a deliberate worker acknowledgement provides stronger confirmation that it was noticed. The two should not be confused.As a regulatory example, the US Mine Safety and Health Administration addresses post-accident wireless two-way communication and electronic tracking in its communications and tracking guidance (5). Requirements differ by jurisdiction and mine type, so system design must be checked against the rules that apply to the operation.
Monitoring becomes protection only when an event reliably triggers appropriate action. A typical workflow begins with SOS activation, an automatic man-down alarm, a missed check or a hazardous environmental event. Where appropriate, the wearable gives a short pre-alarm. If the worker does not cancel it, the platform sends the event to a continuously supervised function.The operator should receive the worker’s identity, role, alarm type, timestamp, last confirmed location, direction or recent route (where available), and battery and connection status. The first step may be a voice call or message, but failed contact must not reset or indefinitely delay escalation. The response plan should define who investigates, who dispatches mine rescue or first aid, which supervisors are notified and when external assistance is called.
Location history helps responders choose a search area, but it must display uncertainty honestly. “Last detected at Junction 14 six minutes ago” is safer than presenting a stale marker as a live coordinate. The control room should also consider ventilation, gas, fire, ground conditions, equipment movement and access restrictions before sending anyone into the area. A lone-worker alert must never create a second casualty through an unplanned rescue.
Key steps should be time-stamped to support review of detection time, response time, false alarms and coverage failures. Drills must test human actions as well as radios, readers and software.
The same identity and location data can strengthen emergency accountability. OSHA’s emergency action plan standard includes procedures to account for employees after evacuation (6). For a mine, the applicable legal framework will be different. Still, the operating principle remains valuable: reconcile who entered, who exited, who reached a safe location and who remains unaccounted for.
Selection should start with hazards and response decisions, not a preferred radio technology. The mine should define where lone work is allowed, the maximum tolerable delay, required location resolution, alarm types, communication functions and who owns each response. A coverage map can then translate these needs into reader, beacon, anchor and network placement.
System validation should measure more than nominal accuracy. Important criteria include update rate, end-to-end alarm latency, availability, location uncertainty, false-alarm rate, missed events, battery endurance and recovery after a network or power interruption. Underground layouts change, so tests must be repeated as headings advance, equipment moves and infrastructure is extended. The current standard ISO/IEC 18305:2016 (7) provides performance metrics and test scenarios for localisation and tracking systems, mainly in indoor environments.
Wearables must suit the work: rugged construction, glove-friendly controls, secure attachment, manageable weight, charging discipline and compatibility with PPE. Equipment intended for gassy or otherwise hazardous areas may require specific approval or certification. In the United States, MSHA states that certain products require approval for underground coal and gassy underground metal mines and provides a dedicated page for communications and tracking equipment. (8)
Resilience is equally important. The design should address backup power, damaged cables, failed gateways, local buffering, network supervision, low-battery warnings and defined behaviour outside coverage. A maintenance alarm must reach somebody before infrastructure loss silently removes protection.
Finally, monitoring affects privacy and trust. Mines should define its purposes, restrict access, set retention periods and explain what is monitored. Workers need training on device assignment, SOS use, charging and what happens after an alert. A system people bypass or misunderstand is not dependable.
Usually not. Satellite signals are too weak to provide dependable positioning through rock and deep underground infrastructure. GPS can support surface operations and register a worker before portal entry. Still, underground monitoring generally requires RFID, Bluetooth, Wi-Fi, ultra-wideband, radio-network association, inertial sensing or a combination of these. The appropriate method depends on whether the mine needs checkpoint, zone or coordinate-level information.
No. Man-down detection uses motion and orientation sensors to identify patterns such as a fall or prolonged immobility. It cannot establish the worker’s medical condition. A device heartbeat only confirms recent device communication. Physiological monitoring uses dedicated sensors and requires appropriate validation. An alarm should therefore be presented as a condition requiring verification, not as proof that somebody is unconscious, injured or safe.
Accuracy should match the hazard and response. Zone-level location may be enough to direct responders along a tunnel network or confirm arrival at a refuge chamber. Machinery interaction or access to a compact hazardous area may require much finer resolution and faster updates. Mines should specify accuracy alongside latency, availability, confidence, and last-update age; a precise but stale or unreliable position can be less useful than a dependable zone event.
A lone worker monitoring system should combine verified identity, fit-for-purpose positioning, movement alarms, device-status checks and dependable communication with a rehearsed response process. It must reduce uncertainty without pretending that connectivity or motion proves a worker is safe. During an evacuation, the same foundation can support e-mustering by reconciling entries, exits and arrivals at safe points, highlighting unaccounted-for personnel and their last known locations so that rescue decisions begin with clearer, faster information.
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Absolute positioning reports a worker’s location in a mine coordinate system or on a surveyed map, allowing the control room to identify a defined zone or point. Relative positioning reports location in relation to another object, such as a miner’s distance and direction from a vehicle, reader or previous position. Relative measurements can support proximity warnings or dead reckoning; absolute results support map-based tracking. Some systems combine both, converting relative observations through surveyed reference points. (9)
References:
(1) https://www.hse.gov.uk/pubns/indg73.htm
(2) https://www.hse.gov.uk/lone-working/employer/training-supervision-monitoring.htm
(3) https://www.cdc.gov/niosh/mining/about/projects.html
(4) https://www.cdc.gov/niosh/mining/topics/machinery-struck-by-injuries.html
(5) https://www.msha.gov/compliance-enforcement/compliance-assistance/program-policy-letters/p14-v-01
(6) https://www.osha.gov/laws-regs/regulations/standardnumber/1910/1910.38
(7) https://www.iso.org/standard/62090.html
(9) Rainer Mautz, Indoor Positioning Technologies (ETH Zurich, 2012), especially the discussion of absolute and relative position. https://www.research-collection.ethz.ch/server/api/core/bitstreams/756bd2d9-30e2-4632-a3c0-dcf6735b6a9e/content
Note: This article was partly created with the assistance of artificial intelligence to support drafting. The head image was created by AI.