What happened at Pike River?

VIDEO footage from Pike River indicates the main ventilation fan may have gone offline for at least a few minutes before the first tragic explosion last week. ILN talks to underground coal mining safety academic David Cliff.
What happened at Pike River? What happened at Pike River? What happened at Pike River? What happened at Pike River? What happened at Pike River?

Underground at Pike River before the explosions hit the mine this month. Image courtesy of PRC.

Blair Price

While the second explosion yesterday ended hopes for the missing 29 miners, the exact cause of the first explosion alone could take many months to identify.

At a media conference two days ago, Pike chief executive Peter Whittall analysed the CCTV footage taken outside the mine entrance, revealing how the ventilation operated before and after the explosion.

With a little piece of rag attached to a wall on the sunlit side of the mine entrance, Whittall pointed out how the rag was angling into the mine as the functioning ventilation system pulled in fresh air.

But for a “few minutes” before the pressure wave from the explosion made its way to the surface, the rag stopped pulling in towards the entrance and went vertical as gravity became the only force at play.

“It just goes still.

“So there’s nothing going into the tunnel or going out and you can watch that as the blast starts,” Whittall said before the footage showed the pressure wave and associated dust and debris spewing out of the mine entrance.

He said the rag started to flap back into the mine after the blast as ventilation was restored very quickly, but he specified this was natural ventilation “not mechanical”.

The footage could therefore indicate the main ventilation fan went offline before the explosion.

“He [Whittall] seems to suggest to me from his comment on the video that the fan had stopped, it was not operating normally, when he starts the video,” Cliff told ILN.

The amount of time the main ventilation fan might not have been working is unclear given the short length of the video.

If the main ventilation fan stops it can allow methane to dangerously accumulate.

On the other hand, the fan might have been taken out by the explosion. This and the associated pressure wave might have ripped through at speeds of up to 60 kilometres per hour, so whether the fan played a role in the disaster depends on how long the ventilation was down for.

In Australian underground coal mines an evacuation would be underway if the main fan stops for more than 30 minutes.

But with long-established real-time gas monitoring systems in place, an evacuation would start in far less time as rising gas levels are detected.

Cliff said he was not clear about the level of sophistication of the gas monitoring underground at the Pike River mine.

A tube bundle system had not yet been implemented as the small, behind-budget mine aimed to adopt more safety measures during future development.

Cliff believed the monitoring in place would have largely been on machine methane detectors, along with handheld devices used by the deputies, but he did not know the extent of the real-time monitoring.

“So it’s not as comprehensive as you would normally get in underground coal in an Australian mine,” he said.

Cliff noted the New Zealand safety regulations did not appear to require real-time monitoring to take place in underground coal mines.

The relevant law under the NZ Health and Safety in Employment (Mining – Underground) Regulations 1999 are covered in only a 35-page document and the lack of detail can cost lives.

While there is a requirement to constantly monitor flammable gases, Cliff had not found any specific requirements to routinely monitor ambient gases.

To ensure fresh air requirements underground, the regulations state this compliance can be met by taking measurements at “suitable intervals, and at suitable locations, using methods and measuring devices capable of giving accurate results”.

Cliff said the applicable legislation in Queensland and New South Wales stated minimum requirements for which gases must be monitored at which locations and using a specific type of system, while many mines installed systems that far exceeded these requirements.

“So I don’t know what fixed monitoring they have in place,” he said of Pike River.

Ventilation design, possible causes and recovery

Before the second explosion yesterday, Engineering, Printing and Manufacturing Union national secretary Andrew Little told ILN the main fan was powered by a substation connected to the grid and there were two diesel generators to provide backup power.

Little was not able to confirm whether the mine used real-time monitoring systems.

While it is still not known whether ventilation problems contributed to the disaster, Cliff noted it was unusual that the mine also had an auxiliary fan near the main shaft.

Once methane levels are high in a mine, there is a wide range of potential causes of ignition, including spontaneous combustion and friction ignition.

The thick gassy seam at the mine was drained using in-seam drilling but methane could still come from a sudden outburst, problems with the drainage line, goaf areas from hydro-mining or control failures at development headings.

While Cliff did not want to speculate too much on these matters, he was surprised there had been such a big explosion at such a small mine, referring to the first blast a week ago.

The second explosion yesterday appeared to be on a much larger scale, according to reports.

The mine could eventually be sealed off at the surface but Whittall made it clear the families would want the men out of the mine, even if they were not alive.

For the recovery effort, Cliff suggested the mine might have to be completely inertised and the Queensland Mines Rescue Service’s GAG unit might need to be used for the job.

The inertisation unit uses a jet engine and its emissions consist of carbon dioxide, nitrogen and water at a high capacity to overwhelm the present methane and remove the threat of another explosion.

Rescue teams could then enter the mine with breathing apparatus for search and recovery.

Yesterday ILN sought comment from QMRS on whether it would send over its GAG unit, and reports this morning indicate it is on its way to the Pike River mine.

ILN also sought comment from Pike and NSW industry-owned Coal Services, which recently held the seventh International Mines Rescue Competition in Wollongong, but understandably they were both occupied with the recent events.

Cliff is an associate professor at the University of Queensland’s Minerals Industry Safety and Health Centre and is highly experienced in fighting fires in underground coal mines.