The constant threat of fire in Last One Out is rooted in the real-world environmental hazard of spontaneous combustion in coal-mining waste. Coal can self-ignite when exposed to oxygen: The oxidation process generates heat, and if that heat can’t dissipate, the temperature rises until it reaches the coal’s ignition point. Coal is classified by rank according to how much heat and pressure it has undergone over geological time, and lower-rank varieties, such as lignite and brown coal, retain more moisture and are more porous, making them especially prone to spontaneous heating.

Underground coal-seam fires can occur naturally. Australia’s Burning Mountain in New South Wales, a naturally ignited coal-seam fire estimated to be over 5,500 years old, is the oldest known example on Earth. However, mining dramatically accelerates and multiplies this phenomenon. The crucial difference is that mining operations freshly expose vast quantities of coal and carbonaceous waste material to oxygen, creating conditions far more conducive to self-heating than a slowly weathering natural outcrop. Open-cut mines, in particular, generate enormous spoil piles of reactive carbonaceous shale, low-quality coal, and pyrite-rich waste, precisely the kind of material most susceptible to self-heating. Overall, the number of coal fires worldwide has increased dramatically since the Industrial Revolution as a direct result of mining, land clearing, and related human activity.

The consequences can be devastating. In 2014, a bushfire spread into the Hazelwood open-cut brown coal mine in Victoria’s Latrobe Valley, igniting exposed coal faces that burned for 45 days and blanketed the nearby town of Morwell in toxic smoke (“Hazelwood Open Cut Mine Fire, Victoria 2014.” Australian Disaster Resilience Knowledge Hub). Internationally, the most infamous case is Centralia, Pennsylvania, where a 1962 landfill burn spread through an unsealed opening into abandoned coal mines beneath the town. The fire still burns today and forced the relocation of nearly all 1,500 residents at a cost of over $42 million (Guss, Jon. “Inferno: The Centralia Mine Fire.” Pennsylvania Center for the Book, 2007). In India’s Jharia coalfield, the first recorded fire broke out in 1916, and roughly 70 fires now burn across more than 100 square miles of mined land, with government relocation costs forecast to reach $1 billion (Ferris, Robert. “India’s Jharia Coal Field Has Been Burning for 100 Years.” CNBC, 3 Dec. 2015).

In Last One Out, Harper channels this scientific reality through both setting and character. The novel’s “washery rejects,” the waste material left after coal processing, and the “spot flares that constantly threaten[] to break out” are direct consequences of the Lentzer mine’s operations (19). Griff’s job patrolling for these fires underscores the tangible, daily danger that mining imposes on the landscape, turning Carralon Ridge into a volatile environment that threatens to erupt at any moment.