CO Poisoning in a Tent

On the afternoon of March 14th, 1999, a 51-year-old man, his 10-year-old son, a 9-year-old boy, and a 7-year-old girl were found dead in their zipped-up 2-room, 10 ft x 14 ft tent. A propane gas stove which was brought inside for warmth was still burning. The victims had died during the night, succumbing to the poisonous gas as they slept.

Their postmortem blood COHb concentrations were 50%, 63%, 69%, and 63% respectively. To understand these numbers, CO binds to haemoglobin in the body (COHb) with an affinity 200-250 times that of oxygen. The toxic effects are due to hypoxia – oxygen is no longer transported to the tissues and brain. At levels above 50%, this poisonous gas causes seizures, heart attacks, and death. The 7-year-old girl had the highest level at 69%. She never had a chance.

The symptoms of poisonous gas exposure follow a predictable pattern:

• Below 10% COHb: No symptoms
• 20-30% COHb: Slight headache, nausea
• 30-40% COHb: Drowsiness, headache, dizziness, increased respiratory rate
• 40-50% COHb: Confusion, blurred vision, chest pain, memory loss
• Above 50% COHb: Seizure, heart attack, death

The family in this tent likely fell asleep with mild symptoms and never woke up.

There are 2 phases of CO production in poorly ventilated environments. Initially, there is a slow linear phase as oxygen is slowly depleted. This is followed by an exponential, rapidly rising increase of the poisonous gas until the flame is extinguished. Partial ventilation – such as a small window opening – can actually increase CO production compared to no ventilation. This is because the low-flame production of this poisonous gas is prolonged, creating a dangerous feedback loop.

A blue flame indicates little CO production, whereas an orange-yellow flame (which I think is more cheerful) produces far more of this poisonous gas. Many campers prefer the warmer, more cheerful orange flame – not realizing it is a warning sign.

The better a tent is at sealing out storms and water, the more airtight it becomes, trapping poisonous gas inside. CO can also build up if the tent’s fabric has condensation, or if snow has built up outside on the walls. CO will also increase inside the tent under zero wind conditions. The family’s zipped-up tent was designed to keep out the cold – but it also kept in the poisonous gas that killed them.

Opening tent flaps, doors, or windows is insufficient to prevent build-up of CO concentrations from fuel-burning devices. According to Wheeler et al. (1999), the risk factors for CO poisoning in a tent include:

Cooking practices:

• Avoid prolonged simmering
• Keep stove highly pressurized
• Use a maximum blue flame and avoid low flames
• Use small-diameter pans
• Use white, pure fuels

Ventilation issues:

• Inadequate ventilation lowers O₂ and causes incomplete combustion
• CO₂ buildup exacerbates incomplete combustion
• Ventilation area should be at least 50 cm²
• CO egress port should be as high as possible
• O₂ ingress port should be sited low
• Avoid minimal ventilation paradoxically elevating CO concentration

Other factors:

• Higher CO risk in tents in zero-wind conditions
• Insidious onset if sedentary – beware headache and tachycardia
• Duration of CO exposure – regular trips outside to unmask symptoms
• Stale air in tents – ventilate at regular intervals
• Dehydration – good hydration is essential
• Snow holes worse than tents – pay attention to ventilation
• Tent icing and snow cover – keep tent fabric porous by regular clearing

Every one of these factors contributed to the family’s deaths. The poisonous gas built up silently, and by the time anyone noticed, it was too late.

Wheeler et al. (1999) conclude:

“To avoid hazardous CO exposures, fuel-burning equipment such as camping stoves, camping heaters, lanterns, and charcoal grills should never be used inside a tent, camper, or other enclosed shelter. Opening tent flaps, doors, or windows is insufficient to prevent build-up of CO concentrations from these devices.”

My advice would be to always have a CO detector when you are inside a tent. This simple device can detect the poisonous gas long before it reaches dangerous levels. A CO detector costs less than $50. It could save your life or the lives of your loved ones.

The wilderness is beautiful. But the poisonous gas we bring with us – from stoves, heaters, and lanterns – can turn a camping trip into a tragedy. Don’t let it happen to you.

References: 

• Leigh-Smith, S., “Carbon Monoxide Poisoning in Tents- A Review”, Wilderness and Environmental Medicine, 15: 157-163, 2004
• Wheeler, R., Koppen, M.A., Johnson, A.B., et al., “Carbon Monoxide Poisoning Deaths Associated with Camping- Georgia, March 1999”, MMWR, 48: 705-706, 1999