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On the night of June 6, 2018, a snowstorm hit the climbers’ camp at 14,200 feet on Denali. Overnight lows hovered near 0°F that week. At around 9 P.M., a climber who had been feeling “funny” stepped outside for some air, and returned to find his tentmate in the midst of a seizure. Carbon monoxide from a stove in the tent had accumulated to near-lethal levels. If the ill climber hadn’t gone outside when he started feeling out-of-sorts, both would likely have been dead by morning.
Carbon monoxide gas—a deadly, colorless, and odorless product of combustion—kills more than 400 people yearly in the US. Most deaths are household exposures from faulty furnaces or improperly placed heaters, but hikers and climbers who use stoves in confined, poorly ventilated spaces (think your zipped-tight tent in the middle of a blizzard) are at high risk.
When levels reach about 70 parts per million (ppm), exposed individuals report headache, nausea, dizziness, or just feeling unwell. Once levels top 200 ppm for sustained periods, serious outcomes like unconsciousness, confusion, and even death follow. A 2013 study showed that the concentration of the deadly gas depended on both the type of tent and the fuel used. Concentrations rose to more than 150 ppm burning white gas in a four-season tent, and over 200 when unleaded gasoline was used as fuel. In some studies, concentrations reached toxic levels within minutes, although the rate of increase depended on fuel type and degree of ventilation. A stove burning white gas in a three-person, four-person tent topped 100 ppm in just six minutes.
After the incident on Denali, National Park Service rangers used supplemental oxygen and a portable hyperbaric chamber to treat the poisoned climbers. Their most important action, though, was removing their patients from that toxic tent. Both climbers improved and were evacuated to safety when weather conditions cleared.
High-altitude mountaineers aren’t the only ones at risk of carbon monoxide poisoning. In 1999, the CDC reported two separate incidents at Georgia campsites in which two adults and four children died while using a propane gas stove in one case, and a charcoal grill in the other, to warm up on cold nights. The two youngest victims were seven years old.
Carbon monoxide poisoning is avoidable for hardcore climbers and weekend campers alike. Sure, it’s cold out. The risk can be reduced by opting to use a stove in a vestibule rather than within the tent itself, and making sure snow doesn’t block the doors and vents, cutting off airflow. No matter what, ensuring adequate ventilation—or keeping the stove outside the tent altogether—may well save some lives.