This article is based on Q&M magazine articles published in past issues and a web feature written by Simon Nathan produced by the government’s NZ History team.
In ruins and entombing 29 workers, the Pike River Mine is a sorry monument to our coal mining history, and even more tragic that it occurred in the 21st century as one of the world’s worst mining disasters. It was always going to be a difficult project and its development history could provide the answers to the mysterious explosion caused by a sudden build-up of methane to an explosive level and then ignited.
A rich resource begging for extraction
The Brunner coal measures and the deeper Paparoa measures make up our largest coal field, located 45 kilometres northeast of Greymouth near the top of the Paparoa Range.
The Brunner seam is estimated to contain just over 58.5 million tonnes of recoverable high-grade coal, with an additional eight million tonnes in the Paparoa seam.
The coalfield was first explored just after WW2 near the crest of the Paparoa Range from which the Pike Stream flows into the Grey Valley. The large resource of bituminous coal exposed along a steep escarpment in the headwaters of the Punakaiki River that extended east to the Hawera Fault, was recognised as the highest-grade coal found at such high elevation. Such quality coal, sought after by steel mills around the world, is usually found at depths.
This coal resource was buried in small basins about 35 million years ago and uplifted to form the present mountains, which was also the cause of the faulting and fracturing of this coal seam that complicates underground mining on the West Coast.
At the time of this exploration, the government-owned State Coal Mines held mining and prospecting leases over all the major coalfields on the West Coast except Pike River. In 1979, geologists explored the large coal reserves through a drilling programme. The Pike River Coal Company was formed in 1982 to hold exploration rights to the area and, in 1988, was bought by New Zealand Oil and Gas.
The Paparoa National Park had been created in 1987, but the area of the Pike River coalfield excluded from it. However, sitting in conservation land, DoC permission was required for access and other activities (such as the mine access road and ventilation shaft) outside the boundaries of the coalfield.
The mine project was pushed long by private investment and the state (think royalties) by the global demand for high-quality hard coking coal with low ash content (one percent compared to eight percent in premium Australian coking coals) and the high-fluidity valued by international coke and steel producers, who use it as a fuel and a catalyst. From the mid-1980s the overseas market for West Coast coking coal grew, with over one million tonnes exported in 1994, and more than double that in 2002.
Over a 13-year period, the Pike River Coal Company undertook further exploration and acquired the necessary authorisations to develop a mine. The board of New Zealand Oil and Gas initially wanted to develop the mine in partnership with an established mining company, but then considered the venture too risky and decided that the Pike River Coal Company should undertake the project itself although, at that stage, no one in the company had any expertise or experience in coal mining.
Peter Whittall, an Aussie mining engineer with 24 years’ experience with BHP, was appointed technical manager in 2005 with the task of creating the new coal mine.
The project design involved a new 11-kilometre access road over several bridges that began in December 2005 across steep, bush-covered hillsides to the mine entrance where a 2.3 kilometre tunnel would be driven uphill at an angle of about five degrees through solid rock until it crossed the Hawera Fault and penetrated the Brunner coal seam.
The mine development
This Pike River Coal Mine was designed to go into large scale production in 2008 producing one million tonnes per year over a projected 18-year life. However, getting the mine into production proved a saga of delays caused by rockfalls, and engineering challenges that ended up with the unconventional choice of an extractor fan located at the bottom of the ventilation shaft.
The mine tunnel was the largest and longest built here since the second tunnel at the Manapouri hydro plant was completed in 2001. As a mining company Pike River could have developed its own adit, but instead opted to let a fast-track design-build civil contract for the job to McConnell Dowell Constructors (NZ).
Most of the problems resulted from the failure of the mining company to undertake adequate geological and geotechnical investigations before starting work, as it was assumed the adit would be cut through such tough rock that little structural support would be needed. In reality, as discovered in the first full face blast in mid-September 2006, around 80 percent of the tunnel passed through fractured rock and the D-profile 5.5 metre-wide, 4.5 metre-high access tunnel would require a lot of reinforcing with expensive rock bolts, reinforcing mesh, and robotic shotcreting with polyolefin structural fibres. Consequently, the tunnel took twice as long as anticipated, and cost more than twice as much had been budgeted.
One of the big engineering hurdles was a major fracture zone called the Hawera fault. It took crews over five weeks to drill and blast their way through the 60-metre zone of crushed rock. The constant threat of methane gas infiltration meant explosion-proof equipment had to be brought in.
The tunnel crossed the Hawera Fault into coal in November 2008, and on the 27th the mine was officially opened to mark the imminent start of production, once ventilation was in place.
A major ventilation shaft was sunk close to the Hawera Fault in late 2008 powered by a large fan to extract methane from the mine and draw in fresh air along the tunnel.
Mining could not begin until this ventilation system was working. In February 2009, however, the bottom part of the shaft collapsed and filled with fallen rock. It was decided to abandon the collapsed section and construct a new bypass shaft.
The original plan was to install the ventilation fan at the top of the new shaft. Because of operational difficulties on DoC land (such as no road access to the shaft top), the fan was placed within the mine at the bottom of the shaft. This contradicted industry practice as it made the ventilation system vulnerable to power failure, fire or explosion. At the time there were no regulations to stop the fan being placed in the mine. Nor did the Pike River mine have a dedicated ventilation officer, which is a statutory requirement in Australia and most other countries with a coal-mining industry.
At the planning stage, it had been agreed that coal would be extracted by a combination of coal-cutting machinery and hydro-mining – a system that uses a high-pressure water jet to carve out the coal seam and wash it downhill to storage facilities.
Water and gravity carried the crushed coal to the pit bottom coal handling facilities where it was further crushed to 35mm and pumped via the water-fed slurry pipeline 10 kilometres to the coal preparation plant at the bottom of the Pike River valley. When fully commissioned, the hydro monitors were designed to cut coal at an average rate of more than 2000 tonnes a day. First hydro coal started in the 2010 quarter, with 14,000 tonnes already stockpiled and the company was expecting to ship 20,000 tonnes to 30,000 tonnes in its first coal shipment in the first quarter of 2010. In February 2010, the first export shipment of 20,000 tons of coal was delivered to India for use in steel production.
Hydro-mining had been used effectively elsewhere on the West Coast, but did pose problems. In particular, collapse of the coal face could cause large and unpredictable methane pulses in the mine.
In the face of this challenge, the coal-cutting machines initially obtained for the mine kept breaking down in the rugged conditions. More worryingly, they also sparked small methane explosions when the cutting tool hit hard sandstone.
More trouble looms
Although coal was being extracted from the Pike River mine in 2010, it was still in start-up mode and considerably behind schedule. Costs blew out because of the problems with the ventilation and hydro-mining systems, and machinery breakdowns. The company needed to go back to its investors and other lenders for more funds. Because of the continuing delays, the board dismissed Gordon Ward, the general manager, in mid-2010 and replaced him with Peter Whittall.
By 2010, there was ample evidence of dysfunction at senior management level at the mine. Six different people held the statutory position of mine manager in 2009-2010, and there was a very high turnover of experienced technical staff.
Signs of methane
From the time the tunnel penetrated the Brunner coal seam there had been frequent alarms about methane levels and many small ignitions that were, perhaps, often not acted on as warning signs because of the pressure to increase coal production, and a planned methane detection system was never fully installed or calibrated.
At one stage the Inspector of Mines, employed by the Labour Department, considered closing down the mine until the methane and ventilation problems were sorted out, but the mine management convinced him that they had these issues under control.
A shipment of coal was due to be made early December 2010, and the mine was under pressure to meet that production.
On the early afternoon of Friday 19 November miners from Pike River Mine worked alongside employees of five different contracting companies, and chance played a big part in deciding the 31 men who were underground at 3.44 p.m. when the first explosion disabled power and communication into the mine. Workers from McConnel Dowell had just finished a shift and had exited the mine, as a new shift prepared to enter.
Of the 31 workers left in the mine there were only two survivors. The other 29 were either killed by the force of the explosion or suffocated by noxious gases. Further explosions on 24, 26 and 28 November made it clear that it would be too dangerous to attempt re-entry, and the mine was subsequently sealed until 2018.
The Royal Commission
As in the case of enquiries into the previous eight coal mine explosions in which men were killed, it says the mine’s management had overlooked or played down the risk of a methane explosion.
There is little doubt that the first explosion on 19 November was caused by the ignition of a large volume of methane. Methane is only explosive when it mixes with air at a ratio between 5 and 15 percent. A level what would have gas alarms blaring and automatic machinery cut offs activated, one would presume.
The Commission report says the project to mine coal at Pike River was flawed from the start. The vision of driving a 2.3-km tunnel uphill though solid rock, across a fault into a gassy coal seam, with no alternative tunnel or shaft for ventilation or exit, ignored international coal-mining experience and was probably the only mine in the world in which the main ventilation fan was sited underground.
The plans for the mine received virtually no independent scrutiny because government authorities no longer had any responsibility to check that mine design was prudent or safe.
The report of the Royal Commission also highlighted widespread, systemic problems in the mining industry. The specific issues at Pike River were exacerbated by inadequate oversight of the mine by regulatory organisations and deficiencies in the laws covering health and safety. Since 1992 the level of regulatory oversight had been progressively reduced, and by 2010 there were only two mine inspectors for the whole country.
Under the heading, ‘A failure to learn’, the report noted that “New Zealand’s health and safety record is inferior to that of other comparable countries.”
Following recommendations from the Royal Commission, the government established WorkSafe New Zealand, a Crown Agency dedicated to safety, with an independent board.
Following publication of the Royal Commission report, the Department of Labour laid charges against the Pike River coal company under the existing Health and Safety in Employment Act. The company, then under the control of receivers, did not appear at the hearing. In finding the company guilty, Judge Jane Farish commented on ‘a systematic failure of the company to implement and audit its own (inadequate) safety plans and procedures’.
Subsequently, in December 2014, charges against Peter Whittall under existing health and safety legislation were dropped. It was agreed to pay the remaining funds from the Pike River Coal company ($3.41 million) to the families rather than proceed with legal action.
Then the coal market collapses
In sad irony that by 2012 the international price of coking coal had fallen dramatically, leading to the closure of a number of coal mines and Solid Energy, New Zealand’s main exporter of coking coal, went into voluntary administration in 2013 and was wound up. It is speculated that, had there been no explosion, it is likely that Pike River would have shut down by 2013 as there was no longer a market for the coal it was producing. Q&M