How dangerous is coal?

To this simple question, a mischievous mind would answer “certainly not”, otherwise we wouldn’t use it! In the post-Fukushima era, one might even add that it is certainly less dangerous than nuclear energy to produce electricity (the dominant use of coal in the world), since our German neighbors, though considered as the security champions in the world, want to replace partially nuclear by coal, as the Japanese might do.

The same mischievous mind will notice that our favorite paper sees casulaties everywhere as soon as there is the suspicion of an alpha particle somewhere, but turning in operation a new coal fired power plant per week in China does not seem to be such an issue. Therefore coal must not be that dangerous?

Unfortunately, it is not the last time that reality is not exactely similar to what most people think, or to what occupies the most space in our favorite paper or radio. If we look carefully, coal is, by far, the most dangerous of all the energies we use on earth, no matter whether we look at sanitary or environmental impacts.

Let’s go mining

Coal is a rock. A burning rock, indeed, but still a rock. As all rocks, it has to be extracted from the Earth crust. Depending on where it lies in the underground, it wil lbe extracted by one of the following methods :

• when the coal seam is far from the surface, an underground mine is the answer. It is then necessary to dig galleries to get to the coal. These galleries have to be propped up (which means using wood or steel structures to prevent the gallery roof to collapse), drained (mine galleries often cross aquifers or underground rivers, that will pour water into the mine, and this water has to be pumped out), aerated (to prevent miners from suffocating, and to prevent firedamp explosions), lit (otherwise nobody sees anything!), and taken care of in many other ways.

• when coal is close to the surface, it is generally exploited in an open pit mine. The first step in such a case is to remove the layer above the coal (that can be several ten meters thick), and then the coal is removed with giant excavators (photos below).

When coal is close to the surface, it is generally, for geological reasons, “young” coal, that is lignite (see formation of oil and coal). The best quality coal is also, in general, the one burried the deepest. This is why lignite is most commonly obtained with open pit mines, when hard coal – with the highest carbon content – is rather extracted through underground mines.

Lignite open pit mine, in Garzweiler, in the Cologne basin (Germany).

The lignite is removed by a giant excavator, which then puts it on a conveyor belt that goes to a train terminal. The lignite is then brought by train to a power plant (generally not very far).

Another lignite mine in Germany, in Hambach, in the Cologne Bay.

When coal is extracted in an underground mine, a number of unpleasant things can happen :

• Firedamp explosions. Firedamp is nothing else than methane, which was formed along with coal, and has been adsorbed on the coal when it was formed. One tonne of coal contains roughly 4 m3 of methane. When a mine gallery reaches the coal seam, the pressure drops (from the pressure underground to the atmospheric pressure), and the methane is released, and then diffuses into the gallery. Of course, mines are ventilated, among other things to prevent methane accumulations (though mainly to allow miners to breathe!), and incidentally methane is then released into the atmosphere, and contributes to the greenhouse gases emissions. When the ventilation is poor, or when a methane pocket enclosed into the seam is pierced by minig operations, there can be the formation of a detonating mixture (methane+oxygen coming from the air). If this mixture explodes, it is a firedamp explosion, with potentially hundreds of casualties associated, either because of the explosion, or because of suffocation or drowning that follows a gallery collapse. Ukrainian or Chinese mines are regularly subject to such accidents.

• Dust explosions. They happen when coal dust, mixed with air, forms an explosive mixture which is ignited by a spark. Consequences are about the same than with firedamp explosions.

• A gallery collapse for any other reason than an explosion: proping up poorly or not done, flooding, etc. Such accidents can kill miners instantly, or imprison them and then they die from suffocation, cold, drowning, or even hunger or thirst.

• Mine fires. It seems that coal burns, and when underground fires happen then can cause all the consequences of a fire.
• Deaths or injuries can also come from mud slides (in open pit mines), elevator accidents…

All put together, how dangerous is coal extraction? Well, the answer is not that easy to give. What is best known is the consequences of coal mining in occidental countries, with a good focus on accidents that killed more than 5 people. But the country that dominated coal production, in 2011, was China, with almost half of the world total, and roughly 5 million miners. In this country, reliable statistics are hard to obtain, particularly for accidents in small mines (that are mostly not ran by state companies), that cause “just” several deaths, but are by far the most numerous.

The table below, done by your humble servant, gives estimates of deaths per million tonnes, for several zones and several times in history.

On the basis of these figures, we can estimate that for China and India combined, that is 3.8 billion tonnes of coal produced in 2010, there has been about 7000 deaths in mines. Then we can add roughly 100 deaths in OECD countries. Then, depending on what happens in Indonesia, Ukraine, Russia, etc, we can add anything between 100 and 3000 deaths, depending on what way we extrapolate. Overall, accidents in coal mines are probably responsible for something close to 10,000 deaths per year.

As 66% of coal (that is 4.5 billion tonnes) will be burnt to produce 8000 TWh of electricity in the world (one TWh = one billion kWh), it means that each TWh coming from a coal fired power plant has caused 0,8 death from mining, in average.

Life and death after the mine

Once back on the ground, miners are not necessarily done with problems, alas. In the course of their work they breathe all kind of unpleasant substances, that cause – sometimes after retirement – various lung diseases that are often deadly.

• The first of these diseases is silicosis, which is caused by the inhalation of fine particles of silicia, a very common mineral in the Earth crust. Mining operations put such particles in suspension in the air in mines galleries. Miners where very frequently exposed to this pathology in Europe a couple of decades ago, and it is still the case in a large number of countries in the present world. Pouring water on the coal seam can prevent a dusty air in the galleries, but it slows down production, so this process is not used in countries where going fast is the main objective and human health a secondary thought.

• In mines one can also breathe – what a surprise! – fine particuls if coal, leading to a similar lung disease called anthracosis. The consequences on health for the patient, and number of casualties are about the same than for silicosis.

• Coal miners are also exposed, like all miners, to radon, a radioactive gas that is found is poorly aerated underground places (including basements). A frequent inhalation of this gas causes lung cancer.

To a greater extent than for mine accidents, it is difficult to obtain a reliable estimation of the numer of casualties that happen worldwide for these diseases, because we deal with delayed effects, that happen for a part of them when people are not working in mines any more. It would require repeated cohort studies in a large number of countries to get the answer, and obviously it is not the case.

For example, a systematic autopsy performed on a cohort of miners deceased in the US between 1972 and 1996 showed that 23% had lung silicosis (even though they had died from something else), and more than 50% a silicosis of the lymphatic kidneys. But systematic autopsies are not the rule everywhere! In France, 34 000 deaths through silicosis have been registered between 1946 and 1987, and if we compare them to the coal production from 1926 to 1967 (to take into account the delay between cause and consequence) it means roughly 60 deaths per million tonnes of coal produced.

As mining conditions in many emerging countries are close to what Occidental countries had at the beginning of the 20th century, we can assume that professional diseases (mostly anthracosis and silicosis) are in a bracket of 50 to 100 deaths per million tonnes of coal produced, with a time lag of roughly 20 years. The 2011 coal production in the world – 7 billion tonnes – will therefore cause 250,000 to 500,000 prematurate deaths “later”, in a population of miners that amounted to 10 million people that year.

If we bring this figure against the electricity produced with the coal extracted, it means that one electrical TWh produced with coal will cause, on a world average, 20 deaths through delayed lung diseases.

Breathe !

Be it for producing electricity, heating, producing steel, using coal is basically burning it. During this combustion, various coumpounds, either already present in coal, or formed through combustion, will be emitted in the air. Some of them are not propper to coal, but are not avoided either with this fuel!

• As coal contains sulfur, burning it produces SO2 (sulfur dioxide), just as for heavy fuel oil. SO2 aggravates cardiovascular and lung diseases. It also combines with atmospheric water to form sulfuric acid, that acidifies water then soils, and can hinder the development of plants,

• As for any combustion in the air, we will get nitrous oxides (NOx), that – among other things – lead to ozone formation when they are mixed with organic compounds (such as unburnt gasoline or molecules alike). Ozone is toxic and irritating,

• A combustion is never complete: it then frees unburnt molecules, among which methane, and aromatic hydrocarbons (that poorly justify their name, since they designate molecules with a benzene cycle, and not at all the main component of a good perfume!), that are known carcinogen,

• If a hydrocarbon is burnt without enough oxygen, which often happens in domestic stoves using coal or wood, then you end up with carbon monoxide,which is a poweful poison that can kill the inhabitants (in Europe deaths happen every year like this).

Burning coal will also free more “exotic” elements, like arsenic, fluor, thallium, selenium, lead, cadmium, mercury, and other things still, including… uranium. These elements can form chemically toxic compounds, that can induce damage to the bones, teeth, nervous system, skin…

When coal is used in domestic stoves, most of the consequences come from direct breathing of the fumes, or the contamination of food dryed or heated over the stove. As the photographs below show, coal can induce malformations… that some little joker could very well attribute to nuclear! (if I had written that the two right malformations below were consequences of the Chernobyl accident, 99% of the French press would have taken it for granted without asking any question).

Hyperkeratosis due to arsenic poisoning in China.

Arsenic is disseminated in food and indoor air through coal combustion in domestic stoves.

Source : Health Impacts of Coal, Robert B. Finkelman, US Geological Survey, 2003

Bone deformation due to chronic poisoning by fluorine – coming from coal – in China.

Source : Health Impacts of Coal, Robert B. Finkelman, US Geological Survey, 2003

Combined effect of a lack of vitamin D and chronic poisoning by fluorine – coming from coal – on a Chinese child.

Source : Health Impacts of Coal, Robert B. Finkelman, US Geological Survey, 2003

In the case of coal fired power plants, that use two thirds of the coal produced on Earth, most pollutants are removed from the exhaust fumes, but there is the apparition of something else: massive amounts of ashes. They can belong to either of these categories :

• ashes that fall to the bottom of the boiler after combustion (bottom ash), and that are composed of particles too massive to be flown away by the fumes,

• ashes that are flown away by the fumes (fumes are composed of hot air before anything else), called fly ashes. Part of these is captured by appropriate filters, but a fraction escapes in the environment (particularly particles smaller than 10 microns). The smaller particles of fly ash contain the higher concentrations of the trace elements mentionned above (mercury, arsenic etc). A modern coal fired power plant rejects roughly 100 grammes of soot and fly ash per MWh, that is100 tonnes per TWh, but old or not state of the art power plants reject much more.

A coal fired power plant with a yield of 33% (which is the world average for these plants) will use roughly 400 kg of coal to produce one electric MWh. If ashes represent 20% of the incoming weight, we will get roughly 80 kg of ashes. 1 TWh électrique (one million MWh, or one billion kWh) means 400,000 tonnes of coal used, and 80,000 tonnes of ashes at the end. A 500 MW plant used for baseload (7000 hours per year, or more), that will produce 3,5 TWh of electricity, will :

• use almost 1.5 million tonnes of coal,

• produce 300,000 tonnes of ashes,

• emit in the air 350 tonnes of soot and fine particles loaded with unpleasant products.

With a 1 GW plant, that is the equivalent of a nuclear reactor, it is the double. Germany, that produces 300 TWh of electricity with coal (before phasing out nuclear), among which part is lignite (that has a higher proportion of ashes and is more “dirty” than hard coal) produces roughly 25 million tonnes of ashes per year (100,000 times the weight of nuclear waste for an equivalent electricity generation!), and sends 30,000 tonnes of fine particles in the air.

Even bottom ashes can be annoying. Before being used as construction material (their most frequent use), these ashes are generally stored near the plant. They can lead, through lixivation (dissolving of soluble elements in water coming from rain or rivers), to local pollutions. In the US, there has even been a dam retaining mud formed by ashes and water that broke, leading to hundreds of deaths!

But it is the fly ashes – those not stopped by filters, measuring less than 10 microns, as a comparison base a hair is several tens of microns thick – that are of most concern for human health. The table below gives an estimate of the sanitary effect of an increase of the fine particles (PM10) on immediate mortality.

However, it is always difficult to guess by how much the life of someone has been shortened by a pollution of some kind (this is an ongoing hot debate among physicists). Did that individual lose one week of life expectancy? Or 20 years? Because the consequence is obviously not the same!

Whatever the case, if we sum up all the sanitary consequences that we have gone through above, coal fired power plants represent the worst possible idea to produce electricity, even in Europe, and even without taking climate change into account.

Number of deaths by electrical TWh (and CO2 emissions per electrical kWh) for power generation in Europe. Future casualties linked to climate change are not taken into account.

Professional diseases of coal miners in Europe are significantly less frequent than in non-OECD countries, where the death toll per TWh is higher.

Source : Electricity generation and health, Anil Markandya & Paul Wilkinson, The Lancet, 2007; 370: 979–90.

The values of the above graph, that are mentionned in the ExternE report of the European Commission, lead to the conclusion that the German coal fired power plants generate about 10,000 prematured deaths per year, because of pollution and fine particles. Without even mentionning climate change, or the dependancy on imports, replacing nuclear energy by gas or coal is clearly choosing to increase the death toll, and not at all to diminish it!

Heat ahead !

And, last but not least, coal is generating a quarter of the world emissions of greenhouse gases, and is therefore a major contributor to the future deaths due to climate change, even if their number is even more difficult to evaluate than for the impacts that have been adressed above.

Breakdown of world greenhouse gas emissions in 2004 by a mixture of energy and use. “Lime calcination” is the process done in cement production (lime is heated over 1000 °C, and calcium carbonate molecules are broken in calcium oxide and CO2).

One will notice that coal fired and gas fired power plants together account for almost a quarter of the world greenhouse gases emissions. Therefore considering that “running on electricity” is pollution free is a debatable conclusion!

Source : Author’s compilation on CDIAC (lime calcination), Houghton et. al 2005 (deforestation), IPCC AR4, International Energy Agency, BP statistical review

And given the lifetime of a coal fired power plant (40 years), when building one of these device we have a lock-in effect which is major. We should think about it before going on building on coal!

The above graph represents the world CO2 emissions that will derive from the use, to their end of life, of infrastructure already built in 2010.

These include boilers of buildings (residential and commercial), industrial boilers, existing vehicles (planes, boats, cars and trucks), and power plants and refineries (the two last are in the category “primary energy”). The decrease of each area corresponds to the decommissioning, each year, of a fraction of the infrastructure existing in 2010.

One can clearly see that the largest part of the emissions “committed for the future” come from the existing power plants. It is therefore in this sector that decisions taken today have the greatest impact for the future.

Source : Davis et al., Science vol 329, 2010

When all that precedes is summed up, coal turns out to be, and by far, the most dirty of all the energies we can use. But it is clearly not the opinion of a number of people that say they care about the environment, since they generally prefer to phase out nuclear to replace it by… coal, as in Germany. Which leads to the following question: is being against nuclear being a sound environment activist, or is it just being… against nuclear?