Those who are evaluating export proposals might do well to examine one little-talked-about peculiarity of Powder River Basin (PRB) coal: it has an unfortunate tendency to spontaneously combust, even in rail cars and stockpiles.

To be clear, it’s not as if coal trains will be delivering blazing cargoes. The threat is likely to be more insidious—slowly smoldering coal that is perhaps emitting noxious gases into neighboring communities. Yet the severity and toxicity of these gases are largely unkown.

Does self-ignited coal pose a genuine pubic health risk or is it little more than a handling annoyance for coal shippers? We don’t know. But we do know that even the coal industry says self-ignition is a problem:

Operators familiar with the unique requirements of burning PRB coal will tell you that it’s not a case of “if” you will have a PRB coal fire, it’s “when.”

In fact, one technical analysis—demonstrating that “PRB represents the extremes of handling problems”—found that:

Spontaneous combustion of coal is a well-known phenomenon, especially with PRB coal. This high-moisture, highly volatile sub-bituminous coal will not only smolder and catch fire while in storage piles at power plants and coal terminals, but has been known to be delivered to a power plant with the rail car or barge partially on fire…

Needless to say, even low intensity fires are potentially troublesome for communities near stockpiles or along rail corridors. Yet it’s hard to evaluate the magnitude of the problem.

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I’m not aware of any scientific study that has looked at the health risks of spontaneously combusted Powder River Basin coal. (There is ample occupational safety literature for coal facility operators.) That said, there is reason to worry that smoldering coal emits harmful pollutants:

A study in Israel that evaluated oxidizing coal found that stockpiles emit concentrations of carbon monoxide and hydrogen, as well as hydrocarbons like propane and methane. (This study looked at US coal, but of a higher sulfur variety than PRB coal.)

A study of spontaneous combustion in coal fields in South Africa found that the coal fires emitted a range of gases, including toxic substances, carcinogens, and heavy metals. (This study focused on coal mining sites, which can have rather different characteristics than stockpiles.)

Though Powder River Basin coal does not spontaneously explode or burst into full flame (at least not outside of confined environments) it is clear that under the wrong conditions it can self-ignite and burn slowly while traveling in a rail car, standing in a stockpile, or moving along a conveyor system.

We don’t know enough to understand the risk of hazardous emissions from smoldering coal. But the problem is worrisome enough that Northwest officials should carefully evaluate the health and safety risks to ensure that large coal shipments would not threaten local communities with spontaneous combustion problems.

Thanks to Kathy Washienko who provided invaluable research assistance.