Questions the Agency gets asked, with answers.

Update 19 October 2020

What is a Product of Combustion?

Coal is a complex chemical (as illustrated in the example below) made up of mainly carbon and hydrogen with other minor components including oxygen and nitrogen. Not all coals are the same and even the composition within the same coal seam varies, so the products of combustion are not always going to be the same. 

The chemistry of coal combustion is also complex and depends significantly on the amount of oxygen available and the temperature the combustion is taking place at.  If the temperature is very hot and there is enough oxygen (contained in air) all the coal can burn in what is known as complete combustion, with predominately just carbon dioxide and water being produced. 

In an underground coal mine fire, conditions for complete combustion of all the coal involved are unlikely.  As a result there are a wide range of combustion products from incomplete combustion of the coal.  These products are generally made up of the building blocks of the coal molecule, so are primarily carbon and hydrogen, sometimes with some oxygen.  

Image of molecular structure of coalMolecular structure of coal

Because coal is such a complex (and varying chemical) there are wide range of chemicals that can be produced, particularly as the original fire conditions vary.  These products can vary from small gases like carbon monoxide to large aromatic ring-based molecules that at normal temperatures are typically solids.  Another issue is that even without actual burning, heat from the fire is transferred through the coal and it starts to break up into fragments (pyrolysis).  Initially when produced all of these products are hot and travel away from the fire as gases, but when the larger molecules cool they condense (solidify) away from the original fire forming residues.

How were products of combustion found?

We had identified during earlier risk assessments the likelihood of finding products of combustion.

Mine workers noticed a different coloured substance on the ribs (walls) and roof of the drift (access tunnel).  Samples were sent to an independent laboratory, and information on what was found is available on the Agency website.

What additional PPE is required when mine workers go underground?

Along with our normal PPE, face-fitted masks with organic and formaldehyde cartridges and pre-filters for particulates are required to be worn when certain activities are being undertaken. Existing PPE includes coveralls and impermeable gloves.

Image of Chief Operating Officer in full PPE with respiratorChief Operating Officer Dinghy Pattinson in full PPE with fitted P2 face mask (respirator)

Do all workers underground have to wear this full PPE all the time?

Full PPE is required, with the exception of a respirator, which is activity-based. We will continue with our sampling and monitoring programme, the results of which will determine any adjustments to our control measures.

Does it slow down the work underground?

Yes it does add time. It is important and mandatory as the health and safety of our workforce is our number one priority. It’s slightly more cumbersome, and you need to decontaminate and replace for meal breaks and at the end of each shift.

With the two week delay, expert advice, and the new PPE, will this mean the Agency is unlikely to finish the underground recovery by the end of the year?

The effects of the delay does come with a financial cost, but the health and safety of our workforce is our number one priority. We are still confident of finishing the recovery of the drift tunnel by year end and within budget, but in saying this we don’t know what is ahead of us, as this is unexplored territory.

What substances were found and how toxic were they? 

The sampling we undertake is to determine Polycyclic Aromatic Hydrocarbons (PAHs) and Volatile Organic Compounds (VOCs).  We carry out what’s known as a mass scan targeted analysis looking for the following:

  • Formaldehyde
  • Acetaldehyde
  • Acrolein
  • Benzene
  • Toluene
  • Xylenes
  • Ethyl Benzene
  • Trimethyl Benzenes
  • Styrene
  • Naphthalene
  • Benzo(a)pyrene
  • Benzaldehyde
  • Heptanal
  • 2-methylbenzaldehyde
  • 3-methylbenzaldehyde
  • 4-methylbenzaldehyde
  • Acetone
  • Methyl Ethyl Ketone
  • Methyl Butyl Ketone
  • Methyl iso Butyl Ketone

What is Pit Bottom in Stone and why is it significant?

Pit Bottom in Stone starts around 1885m up the mine drift tunnel and has a number of roadways which branch out.  All sorts of mining infrastructure is housed there, including underground electrical substations, switchboards, sumps, pumps and crushers.  This is also the area where Daniel Rockhouse was refuelling a loader when the original explosion happened on 19 November 2010.

The recovery and forensics of the Pit Bottom in Stone roadways are complex. The recovery consists of the following:

  • A hazard assessment, inspection of all the PBIS roadways (approximately 600m).
  • The seven entrances to these roadways were then barricaded off to prevent entry other than statutory inspections.
  • Continue recovery of the main drift from 1880m to the Rocsil plug located at 2240m, some 360m of roadway which will require re-supporting and removal of a debris field. This will take up to 2 months, providing we don’t find any unexpected unknowns.
  • Install a rated Ventilation Control Device (VCD) 10m out-bye (on the mine portal/entrance side) of the Rocsil plug
  • Tunnel through the Rocsil plug in breathing apparatus to recover to the end of the drift where the roof fall lies.
  • Then fully recover and forensically examine all the PBIS roadways.

Undertaking forensics on this area is going to require some additional expert guidance, and we’re working through this with the New Zealand Police.

When will forensic work begin in the Pit Bottom in Stone area?

After the rated VCD is installed 10m out-bye of the Rocsil plug.

What is VCD2 and where will it go?

A VCD (Ventilation Control Device) is an engineered design as per Schedule 4 of the Health and Safety at Work (Mining Operations and Quarrying Operations) Regulations 2016.

The design of VCD2 to be installed is as below:

Design of VCD2 graphic

The plan is for VCD2 to be installed around 10m outbye of the Rocsil plug.

Operational loader tows the loader driven by Russell Smith from the portal

Loader about to be towed across the White Knight bridge

Loader being towed down to the mine admin area

Loader being checked before moving into storageLoader driven by Russell Smith is stored on siteShifting the loader driven by Russell Smith, recovered from the Pike River Mine drift. 

When did you recover the loader driven by Russell Smith at the time of the explosion?
Tuesday 4 August 2020

What type of loader is it?
Juggernaut (Jug-a-0)

What condition was it in?
The vehicle had obvious signs of corrosion, but was towable.  The condition is as expected given it has been sealed up in a coal mine for 10 years.

How did you recover it?
When we reached the loader we conducted a very deliberate and exacting forensic examination of the vehicle and operational zone, led from the surface by our NZ police investigation team. After that we were ready to hook it up using another loader and tow it down the drift to the portal and then to a covered area near the mine’s administration buildings for storage and further examination.

How long did the forensics underground take?
The forensics work was carried out over about 24 hours of underground working time.

What did the forensics involve?
The New Zealand Police direct our underground team as to what and how they want each area and item to be searched and mapped out.

What sort of planning takes place for this type of recovery?
Our team planned the loader recovery with New Zealand Police for some weeks. Detailed forensic planning for the mapping, recording, search and recovery of the loader and adjacent operational zones has been critical to success. The recovery of the loader has also required detailed planning and risk assessment. Health and safety underground remains our bottom line.

Is the fifth robot at the same location?
The 5th robot was removed at 1566m (before the loader) and was recovered at the end of July.

Why are Police or their experts not underground?
The Police have said publicly that they have confidence in the mining teams they have trained in forensics, and will take an agile approach to going underground. If anything forensically significant is found there would be a reassessment to their approach.

Are you using lidar scanners and cameras underground for the investigation?
Only IS flameproof gear is allowed underground – a very deliberate police methodology of mapping, recording, photographing and videoing is being used in the forensic recovery operations and info can be used to recreate underground topography and equipment placement.

The Agency is pursuing a recently certificated Australian Lidar scanner that we believe is the first in the world for IS Flameproof and use in underground coal mines. Overseas certification does not mean NZ certification and there is a process to go through.

When did the Pike River Recovery Agency recommence after the COVID-19 lockdown?
Miners recommenced working underground at Pike River Mine on Thursday 14 May, following the COVID-19 lockdown and the country moving to alert level 2. 

The mine had been in a ‘care and maintenance cycle’ during COVID-19 Level 4 and 3. 

During this time the Pike River Recovery Agency developed and risk-assessed plans and other documentation required for breaching the Rocsil plug near the end of the drift. We also had a team rostered to maintain the mine site and carry out the statutory functions over that time, in accordance with the mining regulations, and mindful of keeping our team safe.

Under level 3, the mine site, drift access tunnel and specialist equipment were prepared for recommencing operations underground, including all the required safety measures to prevent possible spread of COVID-19.

What was the Agency doing during the Level 4 lockdown?

The Agency was operating according to its business continuity plan:

  • Ongoing government department reporting; health and safety steering committee meeting and management team meetings
  • Providing regular updates to the Family Reference Group and wider families; daily COVID 19 updates to staff and contractors via email and on a dedicated Agency web page; along with weekly wellbeing checks
  • Daily remote monitoring of the mine – (gas monitoring, strata monitoring and electrical supplies onsite), weekly scheduled site inspections and scheduled site maintenance
  • Reviews of PHMPs, PCPs and draft of the risk assessment on breaching the plug
  • Plans developed for how the mine would operate under Level 3 and Level 2 Covid-19 alert levels

Before the lockdown:
Our team were carrying out a detailed forensic scene examination of each recovered section of the drift.  As they proceed, some items not essential for the investigation are removed to allow vehicle access.  The teams underground work closely with New Zealand Police on site to discuss the removal and processing of any potential evidence.

After more than nine years with no maintenance, there are several sections in the mine drift which require new bolting of the roof, and that task takes some time in each section.  As each section is recovered, air, water, communications, gas monitoring and ventilation is installed to the recovery point.  A refuge chamber is moved to be reachable as the team progresses.

Why did Cabinet give you an extra $15 million?
A number of factors have put extra pressure on the Agency’s ability to complete the mandated recovery of the 2.3km drift access tunnel.  They include:  The ongoing need to attract and retain key staff with a range of specialist skills; the ongoing time and costs to ensure the mine is compliant with regulations; the time (more than 29,000 hours) and costs (including engaging leading international expertise) to develop all the required planning and safety management processes and documentation; the cost, availability and reliability of specialised mining equipment (in short supply and high demand and no longer available in New Zealand); prevailing weather conditions which impinge on the significant amount of helicopter work required; the dynamic atmospheric conditions underground where no maintenance has been carried out for the more than nine years the mine drift has been inaccessible; confirmation of the extent of forensic work underground being carried out by mining staff rather than NZ Police; geotechnical requirements underground.

When did you step through the 170m barrier, and who did it?
A team went in on Tuesday 17 December 2019.  They checked for any hazards, inspected the state of the tunnel’s roof and walls, and had a brief forensic scan.  Included were:  Chief Operating Officer Dinghy Pattinson, Acting Underviewer Kirk Neilson, Mine Deputy Bryan Heslip, and Geotechnical Engineer Chris (Rick) Lee.

How do you control the atmosphere in the mine drift without the 170m barrier?  
Our Ventilation and Gas Management Plan (2019)(external link)   provides for a number of ventilation control devices (VCDs).  The first, a Rocsil “plug” remotely inserted using boreholes close to the roof fall was completed in early November; with another confirmed VCD just 10m outbye the Rocsil plug.  This seal will provide a stable atmosphere for an extensive investigation of the 600 metres of tunnel and mining infrastructure housed in the pit bottom in stone area. 

This plan was further updated in July this year:  Ventilation and Gas Management Plan Access to Fall.

When did you first re-enter the Pike River Mine drift?
On Tuesday 21 May 2019 a re-entry team comprising Chief Operating Officer Dinghy Pattinson, Mine Deputy Kirk Neilson, and geotechnical engineer Chris Lee opened the airlock doors at the 30m wall and stepped through back into the mine drift.

What’s the method of recovery?
Single entry – our manned re-entry is being carried out in fresh air, apart from the final few metres between the Rocsil plug and the end of the drift.  Suitable safety controls are in place. 

How can anyone guarantee safety?
By assessing the risks, and implementing the controls required to mitigate or lessen the likelihood of those risks occurring, we believe it’s safe to re-enter and recover the mine.  People work safely in underground coal mines around the world.  No-one wants anyone further to be injured or killed at Pike River Mine.  Safety is paramount.

What about a second means of egress for the recovery?
One of the options we were considering included a new small tunnel to intersect with the main drift in the vicinity of Pit Bottom in Stone.  However the complexity and associated risk involved in its development outweighed any benefit.  This issue is discussed more fully in “Report – Pike River Mine Drift Re-entry and Recovery dated 31 Oct 18”.

Isn’t there a requirement for an underground mine to have a second means of egress?
The Health and Safety at Work Act (Mining Operations and Quarrying Operations) Regulations 2016 require that by 2024 that will be mandatory.  While it would be good to have a second means of egress, it’s down to the level of risk that is acceptable.  The complexity and associated risk with the option to build a new small tunnel to provide a second means of egress outweighed any benefit. 

Breaching the 30m seal (21 May 2019):

What does breaching the seal mean?
As part of the original specification for the 30m seal, a set of man doors were built into the wall so the seal was “reversible”. A concrete cutting specialist drilled holes through around 800mm of concrete around the perimeter of the man door and fed a wire concrete cutting string through the holes to cut 2m x 1m block sections out of the seal until the man doors were exposed. Another 1m x 1m hole was cut out to allow for the ventilation ducting to pass through. Once this and all requirements under the ventilation plan were completed, manned re-entry took place.

What happened after the opening of the airlock doors 30m into the drift?
Fresh air ventilation was established up to the existing 170 metre wall and the door there closed.  A fully engineered barrier was established at 170 metres.  Re-entry teams working in fresh air cleared away the rest of the infrastructure up to that point (weirs, barriers, gabion baskets etc) to enable full access by mining equipment.  At the same time, plans for going beyond the 170 metre barrier were finalised with assistance from our international experts.  WorkSafe, the regulator, provided input and feedback to the Agency about its plans and accepted they are safe.  After fresh air trials, a team stepped through the 170m barrier on 17 December 2019.  The barrier was removed early in 2020.  After that, the teams continue to move carefully and deliberately up the drift observing actual conditions, pausing and replanning as required, and identifying anything of potential forensic interest.

Ventilation:

Recovery where the nitrogen is replaced by air seems risky. You risk creating an explosive mixture.  Why not keep the nitrogen in the mine / drift and enter with breathing apparatus? 

Recreating an explosive mixture: Nitrogen is an inert gas.  By using nitrogen pressure in combination with a remotely placed (Rocsil) ventilation plug to separate the mine workings from the drift we eliminate the risk of explosive mixtures.  Since the explosion, the mine had been stable with an atmosphere of around 96% methane.  The gas management plan we are executing purges the methane from the drift and the mine workings, by venting through upper level boreholes (methane being lighter than air/nitrogen). The residual methane originating from the workings (approx. 30 l/sec) is managed in the same way.   We will follow the same process now we have introduced fresh air into the drift as far as the Rocsil plug.  This way we don’t get an explosive mixture of methane and air.

Breathing apparatus: We have previously considered using breathing apparatus. This however would create additional risk and potentially compromise the forensic examination. We will use breathing apparatus to examine the area at the very end of the drift beyond the Rocsil plug.

How is the nitrogen produced?
The Agency has hired a nitrogen producing plant, which filters nitrogen from fresh air, compressing it to be piped at about 98% pure nitrogen into the Pike River Mine. 

Photo of the nitrogen-producing plant at the Pike River Mine

 

 

 

 

 

 

 

 

 

 

 

The nitrogen-producing plant at the Pike River Mine.

Does the nitrogen displace methane in the mine workings area, as well as in the drift?
Methane continues to be emitted at a rate of around 20 litres/second, and is being vented through boreholes in the mine workings, as it is displaced by nitrogen. The reason the nitrogen and methane mixture is vented through the boreholes is to prevent an unwanted pressure and methane build-up.  Nitrogen is being pumped into the mine workings and the chamber between the roof fall at the end of the 2.3km drift and the nearby Rocsil Plug.  The drift contains fresh air up to the Rocsil Plug.

We’ve heard you have flushed out the methane, then pumped the mine full of nitrogen to make it inert, before introducing fresh air.  What prevents methane from continuing to be produced in the mine?
The drift access tunnel is largely cut from stone, the mine workings are in coal which will continue to emit methane, and that’s why we will continue to pump nitrogen through the top of the mine where the mine workings are, and over the area where the roof fall occurred, to keep the mine atmosphere inert.  Methane will continue to be produced from the coal in the mine, but in small quantities that can be managed well with the nitrogen present in the drift and mine workings area.

Images of the plug being installed undergroundUnderground images of the Rocsil plug in place in the drift.

Doesn’t the remote ventilation control device/”Rocsil” foam plug cover up forensic evidence? 
The “Rocsil” plug (Rocsil is the brand name for a phenolic plug) covers the width of the drift (about five metres), from floor to roof and a distance of between 10 and 15 metres from one end to the other, so between five and seven metres either side of where the borehole sits in the drift.  Using a camera lowered down a borehole, we photographed as much of the area as is possible before the foam was pumped in, and Police experts have indicated they are unable to see any items of interest in the area where the foam sits.  Safety of our underground team remains our paramount principle, and the use of the foam barrier is a key safety measure in our Ventilation and Gas Management Plans .

Is the plug able to be removed?
Our intent when we reach that point is to cut a small doorway through the plug and recover the remaining drift to the roof fall. 

How much did the foam plug work cost?  Approximately $1 million.

Image of the venturi at Gray BrothersThe venturi at Gray Brothers in Greymouth.

What is a venturi?  What does it do?
A venturi is a piece of equipment (pictured) which works to extract gases from the borehole it is attached to.  Here’s the one the Agency procured, which was fabricated at Gray Brothers Engineering in Greymouth.

General:

Where is the rock or roof fall located in the mine drift?  The roof fall is around 2300m in from the portal and believed to be up to 50m long.

The 30m door is opened on 21 May 2019The 30m door is re-opened on 21 May 2019

Who went into the mine first? 
The first re-entry on Tuesday 21 May 2019 was led by Agency Chief Operating Officer / Site Senior Executive Dinghy Pattinson, with Mine Deputy Kirk Neilson and geotechnical engineer Chris (Rick) Lee.  All people involved in recovering the drift are trained in working underground.

How far have the families been underground?
On Thursday 3 October, 26 family members of the Pike 29 chose to go underground by driftrunner up to the 170m barrier.  Some family had previously gone underground as far as the 30m barrier.

Are you planning to re-enter the mine proper past the roof fall?
Our remit is for a safe, manned re-entry of the drift access tunnel, to investigate the area to try and discover what happened, and to recover any remains found. Our role is also to rehabilitate the area.  The Government decided (Cabinet decision published 17 March 2020) there will be no work beyond the roof fall into the mine workings proper.

How much will the re-entry and recovery cost?
The current best estimate for the project using the preferred approach is $51 million.  There are still some ‘unknowns’ that may affect the final actual cost of the project.

Forensics:

Are Police going underground – how will the forensics be carried out?
The Police role is to complete a forensic scene examination of as much of the drift as is safely possible, as well as any functions required on behalf of the Coroner.  Police, the PRRA, WorkSafe NZ and their respective experts have agreed that the safest option for Police staff is for the drift to be fully recovered before Police consider deploying into the drift, rather than a staged approach.  However Police will adopt an agile approach in the event of a critical find, such as the discovery of human remains.  This means that, in certain circumstances, Police will consider deploying staff into the drift before it is fully recovered.  Should this situation arise then Police will consult with the PRRA and independent experts to assess and understand the stability of the mine and the underground emergency management measures at that point.  Police will only deploy staff into the drift if they consider it safe for their staff.

What are the chances you’ll recover bodies?
The last known location of the men placed them in the mine workings beyond the roof fall.  Given it was shift change at the time of the explosion, with men going in and out, there is a possibility that human remains could be found in the drift.  As part of the detailed forensic examination, any human remains that are found will be treated and recovered with care and respect. 

In terms of recovering evidence, what pieces of equipment do you expect to bring out?
Whatever items are identified as being of interest, where we are able to bring them out, we will.  If something is a particularly big and heavy piece of equipment, it might mean dismantling it and bringing parts out. On Tuesday 4 August 2020 we were able to recover the loader driven by Russell Smith at the time of the explosion.

In terms of other forensic clues, what else could be in there?
The New Zealand Police has developed a forensic search plan which includes all of the underground equipment, as well as any items of interest in the drift.

Are images from the drift and items found in it available to the media and public?
All images of the Pike River Mine drift taken during the recovery are potentially relevant to the ongoing criminal investigation. The same applies to any items of interest found within the drift. For this reason, as a general rule, Police will not be authorising the public release of this imagery beyond what is available on the Agency website.

Is this approach unique to the recovery of the Pike River Mine drift?
No. Police do not routinely release images of crime scenes to the media and public during the course of an active criminal investigation. Police are adopting the same approach here.

Who can authorise the release of images that are taken during the recovery of the drift?
Only the senior Police member in charge of the criminal investigation can authorise the release of any images taken during the recovery of the drift.

glossary of mining terms from the Royal Commission on the Pike River Mine Tragedy is available on the Pike River Recovery Agency website.