Underground mine radio - Sending signals through rock

A radio system operating at just below 1000 Hz has been designed to send and receive emergency text messages to miners working underground.

Designed as an addition to the integrated communications cap lamp (ICCL) introduced to miners in 2006, the battery-powered radio will be able to send messages to a depth of 600 m using a relatively simple loop antenna. When a message is received, the cap buzzes and the lamp flashes to display a message of up to 32 characters on a backlit LCD screen. Information can be received individually, in groups or every device on the network can be paged simultaneously.

Each message takes between five and 10 seconds to travel from the surface to the miner and vice versa. The two-way radio system supplements a personal emergency device (PED) that has been used in Australian mines for the last 17 years.

The ability to transmit actual messages allows warnings to be issued and specific information regarding the situation to be sent. For example, the system can let miners know the location of a fire and which evacuation route to take.

Although the final system configuration is yet to be finalised, it is envisaged that the PED module will transmit back to underground base stations which will then transmit through the rock to antennas on the surface that are likely to already be in position for those mines already having a PED system.

Mines deeper than about 600 m will need an additional repeater 'hop' to reach the surface. The underground repeater stations need to be intrinsically safe and their design is continuing. Likely positions for them will be at refuge bays and breathing apparatus changeover stations.

The system has been designed by Tiller+Tiller and developed by Mine Site Technologies.

"The frequencies required to send messages are not practical for voice use, hence text messages via data signals are used," said Denis Kent, business development manager of Mine Site.

"Other systems are used for voice but they are line-of-sight surface networks and do not cover the underground workers."

He said the actual penetration of the radio wave depends on the geology of the mine "but typically a surface antenna can send reliable signals to a depth of 600 to 900 m".

Today, 90% of underground coal mines use PEDs. Some have already started to convert to the latest ICCL including mines at Springvale, Moranbah North, Newlands, and United Clarence. They are also used in metalliferous mines such as Mt Isa, George Fisher and Jundee.

The system is expected to be fully operational by the middle of this year, following tests carried out at BHP's West Cliff colliery in NSW. Mine Site and the CSIRO have worked together to produce this commercially available system.

Mine Site Technologies
www.minesite.com.au

Tiller+Tiller
www.tillerdesign.com