Wetsuits keep raise workers dry

A Canadian mining contractor working at a project in Indonesia recently resorted to wetsuits to prevent its workers from possibly contacting hypothermia.

Ram Raising of Timmins, owned by Redpath and a specialist in Alimak raise excavation and construction, has been working in a remote mountainous area of the island of Irian Jaya for the past three years. Freeport Indonesia is mining a copper deposit in the area.

A recently completed project, the Fresh Air Shaft Pilot, involved raise pilot excavation three metres in diameter and 345 metres in length between the 3104-metre and 3446-metre levels.

At 3,393 metres — 292 metres above the Alimak raise station — significant water inflow was intersected in three drill holes with pressure measuring 80 lb. per square inch. (The water originated from an elevation about 4,500 metres above sea level and 1,000 metres above the mine.) Work was halted immediately.

A cement grouting program was proposed but the required equipment was unavailable; it was decided the pilot excavation could resume with the possibility the raise could not be completed.

“The first round blasted into the water-bearing seam proved existing ground and water conditions to be worse than anticipated,” said Bruce Mennie, project engineer. “Ground conditions were severe with water inflow estimated at 1,500 litres per minute at a temperature of about 10 degrees C.” While the Alimak raise climber could still operate, the risk of hypothermia to the workers was a serious concern.

To try to reduce the water pressure at the raise face, a 25-cm borehole was drilled down from the raise breakthrough station which intersected the raise face at the footwall. A backup Alimak unit was installed in case an in-raise rescue would be needed.

Diving wetsuits, made of neoprene material which traps a small quantity of water between the suit and skin which helps to retain body warmth, were suggested as a possible solution. “It seemed out of place outfitting hardrock miners in ocean diving wetsuits to work in the raise, but working with the water appeared easier than trying to remain dry,” Mennie said. The wetsuits, shipped in from Australia, were complete with monkey-grip-style gloves and socks all made of the same material. A lining enhanced the thermal properties of the suits.

Work resumed and the remainder of the raise pilot was completed within schedule. “We’re convinced that without the aid of the wetsuits, this raise pilot excavation could not have been completed,” Mennie said.