Each miner cap lamp is equipped with a very low frequency (VLF) tag, and the locator unit is kept on surface. VLF was selected as it offers pronounced through-rock penetration capabilities.
In the event of a rescue situation the VLF locator and the antenna are then taken underground by the rescue team. This handheld locating device is used to transmit a signal which is then acknowledged by the tag in the miner’s cap lamp.