Afterdamp in New Zealand

Afterdamp – [n] – a toxic mixture of gases (including carbon dioxide and carbon monoxide and nitrogen) after an explosion of firedamp in a mine.

There was hope, following last Friday’s explosion at a coal mine in New Zealand. And there were expectations of another mining miracle. It was barely a month ago, after all, that 33 miners in Chile were safely rescued after a cave in left them trapped underground for more than eight weeks.

But today came the terrible news of a second blast from underground at the Pike River mine and an announcement by police authorities that all 29 miners still in the shattered tunnels were dead. “New Zealand is a small country — a country where we are our brother’s keeper,” said prime minister John Key.  “So to lose this many brothers at once strikes an agonizing blow.”

Scorching around New Zealand mine after Friday's explosion (International Business Journal)

But – if we’re honest about the chemical nature of coal mines – not an unexpected one. The uplifting comparisons to the Chilean rescue were unrealistic – and ultimately cruel.  That was a gold-and-copper mine, damaged by an earth collapse, but fundamentally a stable structure that allowed for weeks of rescue work to take place.

Coal mines, by their very nature are unstable. To maintain safety, operators must manage them as if they were bombs just poised on the edge of detonating.

U.S. Government Test of a Coal Dust Explosion

As miners drill into coal seams, the flammable gas methane – sometimes called by the old mining term “firedamp” – seeps out. The amount of methane in air has to be very carefully monitored. The gas is only combustible when it builds up to levels between 5 and 15 percent in the surrounding air. Below that range, there’s not enough to ignite and above it, the mixture is too dense to be explosive (although it can be suffocating). Chemists say that the riskiest amount of methane in the air is when it reaches 9.5 percent saturation – achieving a perilously unstable balance with naturally explosive oxygen. In that situation, it only takes one spark from a piece of machinery to ignite the gases into a literal fireball.

That would be the first explosion at Pike River. Some people believe that such a blowout clears the mine of deadly gases. But, unfortunately, that’s not true. Instead, the explosion tends to peel open new seams in the coal, releasing more trapped methane. It layers the area with explosive coal dust. And in the aftermath of the fire, levels of carbon monoxide – known in old-time mining lingo as afterdamp – starts to rise.

Carbon monoxide is famously a product of incomplete combustion. If the flammable gas methane ignites in a mine, it tends to act as a fuse to highly explosive coal dust. In the resulting blast, the carbon-rich gases, dusts, and other materials burn. In the low-oxygen environment of the mine, they often burn incompletely, leaving residual carbon to attach to whatever oxygen is still jittering around underground. In last spring’s disaster in the United States, at the Upper Big Branch mine in West Virginia, 29 miners died in an explosion. The blast was followed by a horrifying rise in carbon monoxide.

After the April explosion at the Upper Big Branch Mine (

In fact, readings taken from bore holes drilled into Upper Big Branch after the explosion measured carbon monoxide (CO) levels at 14,000 parts per million. The maximum safe level, according to safety standards, is 50 parts per million. Carbon monoxide is a very bad actor. It’s a poison – displacing oxygen in the bloodstream and suffocating its victims – and it’s a very explosive gas.

An explosion at a Chinese mine

This would be the second fiery blast – late Wednesday afternoon in New Zealand. After the earlier explosion, authorities measured rising levels of both methane and carbon monoxide in the mine shafts. They also detected smoke, suggesting that a fiery residue still burning below. They refused to let rescue workers go into such a dangerous environment and although this enraged waiting family members, that was a painfully right decision. “The blast was … just as severe as the first blast,” said a police commander.

Coal mines have ticked like waiting bombs since we first started tunneling them out, excavating earth’s waiting – and dangerous – treasure trove of fossil fuels. By nature, they breed explosive and flammable gases. The deadliest mining accident in New Zealand history was in 1896,  a gas explosion in a mine on the same coal seam as Pike River that killed 65 people.

All the world’s worst mining disasters have been stories of methane and coal dust explosions: In France, in 1907, 1,099 dead; in Japan, in 1914, 687 dead;  China, in 1942, 1549 dead; in South Africa in 1960, 437 dead. In the year 2010, so far, six fatal mine explosions (including New Zealand) have occurred world-wide, killing nearly 250 people.

1968 explosion at the Farmington Mine in West Virginia

That we no longer see a thousand people die in a single explosion says a lot about how much safer mines have become over the last hundred years, about their reliance on use of ventilation, monitors, coal-dust removal techniques. But things go wrong – ventilation systems fail, maintenance gets a little careless, human beings, as ever, get overconfident – the fuse gets lit and the waiting bomb goes off.

We forget, we don’t even think, about the courage that it takes to go down into a ticking mine every day, about the risks taken to provide us with our daily dose of energy. Consider this a reminder. Our best wishes, our sympathy and our deepest respect to the miners of Pike River and their families, and to the thousands of miners around the world, working somewhere underground today.

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19 Responses to Afterdamp in New Zealand

  1. Dee (NZ) says:

    Thanks for your very insightful and compassionate article Deborah, it’s been linked on the NZ Herald website as a resource, and I think it’s a piece that contributes a lot of much needed information and understanding at this time. It’s horrifying to read about those past and all too recent deaths – let’s hope strides continue to be made into making this industry safer and ensuring as much as possible that the workers return home safely at the end of their shifts.

  2. Deborah Blum says:

    I’m with you, Dee. And I think we just have to keep telling these stories until people just don’t forget. I appreciate your kind words and am glad the information is useful. Best wishes to you all.

  3. Adam (NZ) says:

    Thank you for such a factual and sensitive article. I hope it brings some peace to those affected by this terrible tragedy.

  4. Deborah Blum says:

    Me too. Thanks so much for writing. My best wishes to all of you.

  5. Philip [NZ] says:

    RIP our mining brothers, fathers, sons…

  6. Calli (NZ) says:

    Thanks for this article ( linked on my site ) and the previous one as both give a helpful insight into what the cause and conditions were at Pike River. I am glad I read it and have passed it on to several Kiwis given I now know why a rescue/recovery attempt could not be contemplated. It eases the pain a bit.

  7. Mick Rogers says:

    I read this with sadness my neighbours and I have watched this nightmare here in Australia, on TV we all felt for the families.
    I will go and show them this article as we too argued about why the rescue attempt was not attempted

  8. Lisa Cunningham says:

    What a load of shit! Those guys are ALIVE. You wait and see.

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  10. Marie (NZ) says:

    Many thanks for your article. I too have shared it with friends.

  11. Curtis Jones says:

    Your definition of Afterdamp is incorrect, and defining all coal mines as ticking time bombs is similarly incorrect. Some seams make a little carbon dioxide and little more. Some are gas rich, but directional gas drainage drilling can and does reduce the gas content to a safe and mineable level (Tahmoor in NSW is a good example), plus can be used to cogenerate power. I disagree with your theory that the second blast was mainly due to CO – while it does have a wide flammability range it has a narrow range of explosivity. I’m more convinced that the second explosion was a smaller methane explosion that in turn triggered a coal dust whompf, said dust being liberated by the first explosion – which stripped off any stone dusting and should have tripped any installed water barriers. I also disagree with your theory that initial blasts dont remove flammable gases – they do indeed remove flammable gases and there MAY be a subsequent window of opportunity to effect a quick entry by teams wearing closed circuit breathing apparatus. I point to Moura No 4 as one example. Leaving the mine open to ventilate I think was an error, and sitting on hands waiting for teleoperated equipment to provide a miracle was an error. An entry should have been made somewhere around 24 hours post blast to get in and quickly asertain the situation. All, I’m afraid, a moot point now.

  12. Deborah Blum says:

    Thanks so much for writing. I did oversimplify; certainly all coal mines are not alike. I really was trying to make a simple point: that coal mines of this type need to be managed extremely carefully, that they contain all the right ingredients for an explosion if this isn’t done. I used the standard definition of afterdamp (there’s a link to all the sources) but probably semantics are not the real issue here. As you noticed, I listed six gas explosions in mines around the world this year. Obviously, that means that mines don’t blow up on a daily basis, that they can be run safely. But people in charge do have to remember everyday that these are structures that can explode – go off like a bomb, in my analogy – and work every day to prevent that from happening. The real tragedy here is one of human error.

  13. Deborah Blum says:

    Thanks so much for writing. Best wishes to you all.

  14. Ngarongoa Poaneki-Temomo says:

    Our hearts go out to our minors and there families with all our love.

  15. Calli says:

    Ever since the first explosion the temperature in that mine has been exceedingly high and it appears there is a fire – announced following today’s 4th explosion where fire set alight bush to the sides of the top of the ventilation shaft. Gas levels taken from the site clearly indicates that it would have been improper to enter the mine and the Mine Rescue unit was there within the so-called ” window of opportunity” which simply did not exist. In at least one other mine disaster, rescuers have died going into the mine straight after an explosion. The Brunner coal seam is fraught with methane difficulties and it is my belief that the men were possibly dead before the first explosion and most miners in Greymouth believe nobody could have survived the first explosion. Remember this is a horizontal mine leading uphill at about 1 in 11 and the two miners who staggered out following the first explosion were nearly overcome with various toxic gases. Given the amount of soot around the place I can’t understand why the whole place hasn’t gone up.

  16. Deborah Blum says:

    Thanks, Calli. You’ve given an excellent explanation of the risks involved and I believe one that should offer real comfort to the family and friends of those lost.

  17. Lyn says:

    The uplifting comparisons to the Chilean rescue were unrealistic – and ultimately cruel.

    I think this is an excellent point, and your article really pinpointed the problem with that false analogy. I had not realised how different the conditions were in the two mines. The media constantly (and implicitly) reinforced that comparison when they referred to the “trapped miners,” rather than, say, the “missing miners.”

  18. Grant says:

    Just to add to your story, it has now be decided to cease efforts to retrieve the miners remains.

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