personal emergency device

Personal emergency devices, or PED’s, have been used in underground mines since 1987 to enable one-way text messages for emergency situations.

Personal Emergency Devices to save lives

One of the best documented cases to show the value of PED’s for mine safety is the Willow Creek Mine Fire of 1998, where this Utah mine was able to alert underground miners to evacuate before toxic fumes from the fire had filled the mine. (Wikipedia)

The US department of Labor’s Mine Safety and Health Administration relates the story:

On Wednesday, November 25, 1998 at approximately 6:20 pm, a mine fire occurred at the Cyprus Plateau Mining Corporation’s Willow Creek Mine, which is located near Price, Utah. The accident occurred near the longwall tailgate area during normal coal production. No injuries resulted from the incident, however, several longwall crew members were knocked down by the ensuing rush of air. An orange colored flame was observed in the gob that appeared to move toward the face area and then back into the gob. The mine manager ordered an evacuation using a unique system which operates like a pager and is worn by most miners. This “PED” system (Personal Emergency Device), allows for constant contact with the miners, even those working in remote areas. After the accident, a message was sent to the miners — “mine fire-evacuate”. The miners were safely evacuated in about 45 minutes.

The technology behind a personal emergency device (PED)

Through-the-Earth transmission is used to overcome the problem of low or no line of sight (LoS) scenarios, such as in underground mining environments. PED systems are enabled through Ultra Low Frequency (300-3000 Hz) signals from an antenna cable located on the surface of the mine site combined with a high power transmission system to enable signals to travel through hundreds of meters of rock strata all the way into underground mine shafts. This through-the-earth capability means that all areas of an underground mine is within signal range, and that every underground worker can be contacted individually during emergency situations.

PED’s as emergency communication systems in mining

Mining disasters are likely to render underground communications systems that rely on underground cabling inoperable. Through-the-Earth transmission is therefore fundamental to a safe underground mine as it is not affected by underground fires or explosions which would destroy most fixed communication infrastructures; the signal travels through rock face the antenna only has to be placed on surface level, thus significantly minimizing the risk of damage during incidents.

According to Mr M Woodhall from the Southern African Institute of Mining and Metallurgy PED is an extremely effective emergency communication system due to its ability to transmit detailed messages which are vital to issue not only warnings, but specific information regarding an emergency incident, such as evacuations commands.

PED technology for enhancing productivity

Woodhall explains that although Personal Emergency Devices (PED) starts as an emergency messaging application for mines, the Ultra Low Frequency (ULF) technology has grown to include capabilities of remote control of underground equipment such as pumps and fans and centralized blasting initiation.

Using a PED system can enhance productivity through improved communications, such as:

  • Making contact with an underground worker
  • Instructing individuals or groups to move to a specific location
  • Issuing workflow commands, such as attendance to a breakdown
  • Requesting materials or equipment to be brought to a particular location.

Benefits of PED technology in mining

The PED will enhance the total effectiveness and efficiency of underground communications, which in itself benefits mines as every facet of operations benefit from effective communication. Additionally significant savings in electricity use can be expected, where in certain cases the cost of the technology is offset against the savings within a few months. A recent African implementation of PED technology illustrates: ControlPED software enabled the remote control of around 96 underground fans reducing the time and manpower to switch fans on an off around blasting time. In addition electricity wastage was reduced so significantly that the system paid for itself within 5 months.

On top of these benefits the wide coverage provided by ULF technology through the minimal infrastructure means that maintenance of the system is minimal, and signal coverage can typically be provide throughout  the mine for 3 to 5 years of operations without requiring the installation of additional equipment.

In a nutshell

PED systems provide reliable, mine wide communication that is fundamental to a productive and safe underground mine. Because of its minimal infrastructure damage during emergency incidents is reduced making this through-the-earth communication system an ideal complement to two way communication systems such as phones and radios.


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Underground Mine Safety