Networking & Communications

When Safety Matters: Using Active RFID Down the Mines

February 1, 2004 By: Sven Haagensen Ph.D.

RFID technology can help businesses in many ways. But the greatest promise may lie in enhanced security, access control, and safety for workers in dangerous environments. The RFID system Watcher-ATS has proven particularly useful in mining and offshore oil platform applications.

It's been said that if you think safety is expensive, try an accident. Growing demand for safety in workplaces around the world has resulted in tighter regulations. Keeping track of people and equipment for safety and security can be a personnel-intensive, time-consuming undertaking that diverts attention from an organization's primary business activities. Attempts to automate these basic, but not directly profit-generating, tasks are reflected in a wide range of products. Bar-code and card-based systems dominate the marketplace. However, RFID enjoys several advantages over bar-code systems that make it a better choice for many security and safety situations.

RFID comes in two flavors: passive and active (see "Basics of RFID Technology"). Passive RFID has a reading range of ~1 ft. and is widely used in supply chain and logistics systems. The main advantage is that the tags need not be visible from the reader's position (e.g., to avoid the loss of expensive tools, you can embed tags in the metal).

In an active RFID system the tags have their own power source and transmitter. An active tag can be read up to 300 ft. away, thus broadening the applicability of an RFID system.

Current Security and Safety Systems

An RFID system using active tags is a versatile tool in situations involving restriction of access, movement monitoring, communication between operators and a control system, and locating colleagues in an emergency. You can also tag hazardous equipment, such as gas flasks. In an active RFID system, access control is an inherent feature. Safety and security is the new dimension that opens up.

Let's consider a typical scenario encountered where bar codes or cards are used. A group of people approaches a controlled door. One person will pull out an access card, swipe it, and then courteously hold the door for others?including people the cardholder may not know. If an accident happens, you know who passed the main gate but you do not know where any people in need of rescue are within the facility.

Picture a mine with several tunnel zones. Management is required to know which tunnel each worker is in at all times. Neither workers nor management would accept a system that required all personnel to leave their vehicles so they could pull their ID cards when transiting the zones. Such a system is cumbersome to use and results in greatly reduced efficiency?the frequency could be a stop at every half mile of tunnel! Typical road tolling systems cannot address the problem: If they read the worker's tags in a passing bus at all, few if any systems can read all the tags in a short time frame.

In contrast, a system such as Watcher-ATS can accurately read the tags of an entire busload of workers passing at 40 km/h (25 mph). (See "Watcher-ATS in Action" for a scenario with active RFID.) To achieve this, care has to be taken when tuning the equipment and Watcher software to the application.


Watcher is a software application that is at the heart of the Watcher-ATS system. It is installed on a server. You define PC clients that connect to the server and configure the RFID equipment in the software. You can also integrate additional systems, such as video surveillance and fire alarms.

A tag sends its unique ID to the RFID interrogator (reader). Watcher receives this info, updates tag position in real time, and notes the time of the previous reading. All data, reports, and statistics are handled in the Watcher database. The communication interface is open, so units can exchange data using TCP/IP, RS-232, RS-422, UHF, and VHF.

Watcher-ATS allows you to define and adjust zones while the system is operating. Zones may be overlapping, but field strength measurement still locates the tag (see Figure 1).


Figure 1. Two zones (A and B) each have one antenna. A tag (the red dot) is located between the zones. The tag "belongs" to zone B until the field strength registered by zone A's antenna is greater. Each antenna's signal strength received from the tag is indicated beneath the antenna. Zone B's antenna has a field strength reading of ?15 dB, compared to ?22 dB for zone A's antenna, so the tag is closer to zone B than zone A. The history of the tag (previous readings, indicated by the tinted red dots) indicates that the tag belongs to zone B, because this was the last zone it was in. This history information is especially useful in cases where the field strength measurements are equal or where sudden jumps in the field strengths occur.

The number of zones that can be defined is virtually limitless. Reading ranges can be set between 3 and 300 ft., and the frequency of tag identification can be set to comply with the realistic traffic of tags in the zone (higher frequency in a heavily used entryway and lower frequency in a less-used portion of a tunnel, for instance). The more complex the facility, the more of these options need to be used.

The designer of an active RFID system faces many pitfalls. In order to locate tags, you have to define a geographical zone and locate a minimum of one antenna in the zone. Using several antennas enables more accurate tag positioning using signal strength measurement. There are reflections from walls and equipment to take into account, and in buildings or process industry facilities involving multiple vertical levels, you want to locate the tags on the correct level. In addition, software algorithms must work together with the right equipment to avoid several antennas simultaneously reading a tag or, for a tag within range of several antennas, allocating the tag to one zone.

The Watcher-ATS system has been successfully installed in the ore mines of Swedish giant LKAB. An oil rig installation is being designed, with yet more challenges: reflections from buildings and equipment, multiple levels, and the fact that the placement and tuning of antennas is influenced by the liquid contents of tanks. Water-based liquids absorb frequencies differently; high frequencies allow higher tag identification rates and give a longer range, but the signals are also more easily stopped by walls and other obstructions.

In the case of an oil rig, RFID equipment must comply with the ATEX standard, meaning that it is intrinsically safe (IS) in an "Eex" environment (where explosive gases are likely to be present). In addition, it must withstand shock, dust, and water according to ingress protection classes (in Europe, the IP rating system).


Figure 3. Searching and finding personnel, both in minor accidents as well as major disasters, is made much easier if each person wears an active RFID tag.

A concrete oil rig platform base clearly illustrates the challenges involved. The space is vast in all dimensions and there is a lot of equipment and changing liquid levels. In an emergency, you need to know where your colleague is, not just that he or she is down on the base (see Figure 3). An access control system typically has registration gates between major structural parts, such as living quarters, production facilities, the oil platform base, and the lifeboat stations. In the mine scenario sidebar, the Carrier is mentioned. This is a handheld searching and communication device supplied by 24-7 Safety Systems. This miniaturized PC with a PDA-like user interface can be used to locate persons wearing tags. Using its own antenna, it acts as a direction finder?helpful to rescue personnel dealing with poor visibility. In noisy environments or locations with poor radio contact, the Carrier's onscreen info may be crucial to rescue personnel. Such an item may come in handy for everyday use as well. An operator can find other colleagues or communicate wirelessly through the system (using a wireless local area network, or WLAN). If you're an automation maintenance worker, you can read a valve positioner without having to bother the control room personnel (during the day, 40%?70% of their time may be devoted to helping maintenance workers). The Carrier may act as the operator's main field-logging and reporting tool, being plugged into a normal screen and keyboard when back in the office.

Making Active RFID Work

Active RFID systems have been improving considerably, and they present a versatile tool for safety, access control, and security. However, to make such a system your extended arm, it must be set up well and have a simple user and maintenance interface. The option of connecting an RFID system to the administrative and process control network multiplies the possibilities and potential payback of such an investment.

Basics of RFID Technology

Performance information of active tags and interrogators in this article is from Identec Solutions of Austria. Selection of equipment depends on the requirements of each application. WTEK makes the software that binds it all together.

A basic RFID system consists of an interrogator, often called a "reader," an antenna, and a tag (see Figure 2).


Figure 2. An overview of the communication flow in a typical Watcher-ATS system. The interrogator uses its antennas to communicate with the tags over 868/915 MHz radio frequency. The Carrier also communicates with the tags and uses a wireless local area network (WLAN) to communicate with the interrogator and Watcher server. Either TCP/IP or RS-232/-485 link the interrogator and the Watcher server; Watcher clients use traditional TCP/IP to connect with the server.

This interrogator is both a transceiver and a decoder; when it transmits a signal through the antenna, the tag answers or reflects the information embedded in it. The advantage over bar-code systems is that the interrogator does not have to "see" the tag or code visually.

The antenna scans its surroundings with signals that will wake up an active tag to reply with its embedded ID or the tag "reports" to the interrogator by itself. The tag identification rate may be adjusted, but has a typical maximum of 100 tags/s. A passive tag has no power source; it uses the power of the antenna signal to respond. An active tag contains its own power source and transmitter.

The server with the Watcher installed is connected to all the interrogators. There may be several clients where system maintenance or configuration is done.

Field strength measurement is used to assess the distance between tag and antenna. To locate a tag, up to four antennas per interrogator may be used. A zone is defined with one or more interrogators, depending on equipment, walls, and other obstacles.

Features Passive Tag Systems Active Tag Systems
Basic applications Asset tracking, logistics, access control Access control, safety, security, movement tracking
Transmitting tag No Yes
Tag battery life No battery Typically 1-5 yr.; strongly influenced by number of transmission per day
Tag identification range ~1 ft. Up to 300 ft.
Tag identification rate Varying Up to 100 tags/s
Tag dimension/weight Small button Similar to small cell phone, ~1.7 oz.
Applicability in explosive environments (ATEX/Eex zones) Easy to adopt tags because of their intrinsically safe (IS) circuitry; other equipment requires special (IS) encapsulation Tags and other parts need special (IS) encapsulation
Frequencies Low frequencies 125-134 kHz, 13.56 MHz High frequencies 433 MHz, 868/915 MHz, 2.45 GHz, 5.8 GHz
Tags within a zone Varying Max. 2000
Note: A wide variety of RFID specifications exist. The above figures are typical for most systems.

An RFID system of today should have these features:

Software independent of the hardware, so that future RFID interrogators and higher-specification tags can be adopted easily.

Module-based software as well as tag and zone anti-collision algorithms and hardware.

Graphical user interfaces with actual maps of the site, building, or tunnel system. Maps can be added and edited in real time.

Zones, reading ranges, etc., that can be added, removed, or adjusted in real time while the system is running.

Zones that can be defined as in/out zones, enabling a quick overview of personnel inside and outside a major site structure, such as a building, a platform leg, or tunnels of a mine.

Reports that can be generated at predefined times for different criteria.

Integration with other systems, such as fire alarms, gates, and process control systems.

SMS or email messaging capabilities.

Data logging to backtrack tag movements (in countries permitting this, within personal privacy rules).

Watcher-ATS in Action: One Day in the Mine

tunnelIn Norway, occupational health and safety regulations demand an overview of personnel below surface; specifically, the state says, "a system must exist to determine who is located below surface and their most likely location." Watcher-ATS does just that, as the following scenario illustrates.

The mine in our example has both above- and underground installations. As a mine truck with Tom and Nina on board approaches the gate, an inductive loop in the ground senses the vehicle and triggers an antenna to scan the area for tags. As the tags on the two miners and their truck respond and are recognized, an LED display flashes a handshake signal that three readings have been made and stored in the system database. The truck's tag is recognized, and the system knows Tom and Nina are cleared personnel at this time of the day, so the gate opens. So far, the system functions like any other access control system. Beyond this point, it also functions as a safety system.

  Personnel Mobile Objects
IN 120 30
OUT 180 20

As the truck approaches the mine entrance, the LED display located there indicates the number of personnel and objects inside and outside the mine.

The truck passes the entrance, where there is an interrogator inside a cabinet. The interrogator is connected to antennas on either side of the cabinet. Both antennas register that the truck is approaching, but the antenna closer to the exit has a greater field strength reading. As soon as Tom and Nina's truck passes the entrance, the inner antenna has the greater reading, and the truck is now registered as "inside the mine." The outside LED display adds two personnel and one object inside the mine and subtracts two personnel and one object from outside the mine.

The truck now passes a bus with 30 visitors heading out of the tunnel. Before this bus entered the tunnel, it received a stop signal from the LED display. The display then showed the number of tags registered inside the bus, and the bus driver counted the number of people in the bus to ensure that every visitor was wearing a tag.

This truck is equipped with its own RFID interrogator, and on an LCD screen inside the truck, small red dots are displayed when the interrogator locates tags. The screen has a box resembling the truck itself, and on the left side of this box red dots indicate the tags in the passing bus. This function prevents people and equipment from being run over in mines where visibility is poor (giant trucks do roll over pickups in such circumstances).

Suddenly, the truck engine breaks down and smoke fills the tunnel. A smoke detector triggers an alarm on all system operator locations. At the rescue control station, the alarm triggers a flashing red light. A text message is received on the mobile phones of the two smoke divers on duty. The rescue control operator checks the map and notices a red flashing light in the zone where the truck is. He clicks it on the screen to get detailed information; the names and other relevant information about Tom and Nina instantly pop up.

The smoke divers take their Carriers (handheld searching and communication devices supplied by 24-7 Safety Systems) and head for the accident zone. Smoke has reduced visibility, so they click the zone on the Carrier, which now displays two red dots and the corresponding information on Tom and Nina's personnel tags. The Carrier antenna is oriented to take the bearing on the tags, and their LED indicators begin to blink so they are seen more easily. If a fire or explosion had knocked out the antenna system, all information at the time of blackout would have been available on the Carrier; tracking using the Carrier's antenna is independent of the RFID antenna system.

These two miners had left the truck but didn't find their way out of the smoke. This incident was likely to end with only minor smoke poisoning, because the rescue personnel knew where to find them. And this is the core of it: Getting there in time.

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