Pike River: 'GAG unit' flown in to West Coast

The jet engine arrives at Hokitika Airport. Photo / NZPA

Facing a volatile mix of gases and the threat of an unquenchable fire in the Pike River mine's tunnel, officials are considering a drastic, high-tech strategy to recover the 29 bodies inside.

A large jet engine which stabilises gases arrived in Hokitika on a Royal New Zealand Air Force Hercules about 6.30am today.

The engine, termed a "GAG unit", has been flown in from Australia, along with 16 crew from the Queensland Mines Rescue Service, to dampen fires and explosive gases in the mine, Queensland Mines Rescue Service manager Wayne Hartley told Radio New Zealand today.

"It's used for controlling underground coalmine fires particularly by inerting the atmosphere and displacing explosive gases or methane gases, extinguishing any fires and suppressing any sparking or sources of ignition," he said this morning.

The Gorniczy Agregat Gasniczy engine is placed at the mouth of a mine. It pumps gas with very low concentrations of oxygen that will not sustain a fire in the mine. Steam is also pumped in. Over time this starves the fire of the oxygen and smothers it.

In 2003 a similar engine was used at the Loveridge Mine in West Virginia to put out a fire that had been burning 200m underground for two months. It took 10 days of continuous use but was months quicker than letting the fire burn itself out.

Despite a brief stabilisation in the mine on Tuesday night, the 2.8km network of tunnels has refilled with potentially explosive methane and poisonous carbon monoxide.

Wednesday afternoon's enormous explosion briefly burned away some of the hot gases but with no working ventilation in the mine shaft further blasts cannot be ruled out.

Pike River chief Peter Whittall said: "The situation that ... did happen [on Wednesday] could equally happen again today, tomorrow, or the next day."

The impetus for swift action was the prospect of a coal fire.

Tests taken through a borehole into the mine's main tunnel indicated that gas fires were burning inside. If the flames spread to the coal seam, emergency services could face a month-long battle with fire before a recovery mission could take place.

"We need to move quickly because if it progresses into a coal fire where the walls in the tunnel begin to burn, then it makes it much, much more difficult to put it out," said Mr Whittall.

Engineering and mining geologist David Bell said the worst coal fires could burn for decades. The Strongman 2 mine, also on the West Coast, burned for eight years before Solid Energy could extinguish it.

Starving the tunnel of oxygen would not quench a coal fire, because it could exist as heat for a long period before re-igniting again.

Superintendent Gary Knowles, the officer in charge of the recovery operation, yesterday said mining experts were discussing a number of options for recovery, with safety the key priority.

One option was the use of inert gas generators, like the GAG jet engine unit.

Smaller versions of the jet engines could also be used - called "low flow" generators - which pump gas into the mine at 0.5m3 per second.

Mine explosion and gas analysis expert David Cliff said: "The low flow devices may be adequate because of the small size of the mine. But if speed is required the GAG jet engine unit is the only real option."

Another option was pouring water into the mine. This would be difficult because the tunnel sloped uphill from the entrance. There was a possibility water could be poured through the newly drilled borehole.

Mr Bell said he understood flooding the mine with water would be the preferred option but this tactic made the recovery of bodies difficult.

Sealing the mine was another way of coping with the fires and gases but relatives of the dead miners have asked Mr Whittall not to make the mine into a tomb.

Even if a coal fire does not occur, the wait for recovery is likely to be several weeks. Mr Whittall and Mr Knowles repeatedly emphasised that families must be patient.

Mr Knowles pointed out that at a similar mine disaster in the United States, emergency services took four months to retrieve a body from inside.

"This is not a quick fix. It will take some days, some weeks. The worries have not changed. The whole focus still is the stability of the environment."

OPTIONS ON PIKE RIVER

STARVE A FIRE
Starving the tunnel of oxygen would not quench a coal fire because it could exist as heat for a long period before re-igniting.

USING INERT GAS
An "engine" could force gases such as nitrogen or carbon dioxide into the mine to stabilise the atmosphere. Over time this starves the fire of oxygen and eventually smothers it.

FLOOD THE MINE
Difficult at Pike River because the tunnel slopes uphill from the entrance. There is a possibility that water could be poured through the newly drilled borehole. However, this tactic makes the recovery of bodies difficult.