It is a truism that the tent always has to be open while cooking - and one that is often ignored. When it is too cold or windy, mountaineers pull the zipper of the tent completely closed. They ignore the risk of carbon monoxide poisoning. We show what you should pay attention to.

An article by Franziska Haack - first published in the specialist journal bergundstieg

It comes unnoticed and inconspicuous and is precisely why it is so dangerous: carbon monoxide (CO), a colorless, odorless and tasteless gas. It occurs when carbon-containing substances burn incompletely if the oxygen supply is insufficient. For example when cooking in poorly ventilated tents or snow caves.

March 2020 on the Taschachferner in Pitztal. Two men die of carbon monoxide poisoning in the tent. There are three more tents just a few meters away, but nobody notices anything. Almost as imperceptibly as the toxic gas spreads, it also works in the body.

A lower opening for O supply and a higher opening for CO discharge is ideal.
A lower opening for O supply and a higher opening for CO discharge is ideal.

Carbon monoxide (also called carbon monoxide) enters the blood through the lungs and binds there to hemoglobin, the iron-containing protein complex in the red blood cells that is responsible for transporting oxygen. Since the hemoglobin affinity of carbon monoxide is two to three hundred times that of oxygen, it is preferentially taken up by the red blood cells. As a result, there is less hemoglobin available for oxygen transport and there is a lack of oxygen in organs and tissues. The victims are suffocating internally - often quietly, without gasping or gasping for breath.

Cooking in a tent can be dangerous because suffocation is slow.
Cooking in a tent can be dangerous because suffocation is slow.

The two deceased were participants in a course to prepare for expedition mountaineering and had already spent the third night on the Taschachferner. The program ranged from safety techniques on the glacier to the question of what goes into the sleeping bag at night to how to use the gas stove correctly. "I showed the participants how to operate the stove and told them that they were only allowed to cook in the apse and only when the entrance was open," explains course instructor and mountain guide Hansjörg Pfaundler.

"I showed the participants how to operate the cooker and told them that they were only allowed to cook in the apse and only when the entrance was open"

Hansjörg Pfaundler

During the first two nights he made patrols. “Because everyone followed the instructions well, I didn't do it on the third evening and only communicated with the group by shouting from my tent,” says Pfaundler. Everything seemed fine.

What happened in the night

That night it is quite cold, -6 ° C is measured in one of the other tents. This may lead the two men to keep the zipper of the tent entrance closed, contrary to instructions, while the snow is melting. It also snows lightly. When two members of the group noticed the accident the next morning, a thin layer of snow covered the tent and the zips of all entrances were completely closed. When opening, a gas odor escapes. The gas cartridge is empty, the stove valve is open.

Snow, ice and condensation really seal a tent roof and prevent the exchange of air. When cooking in such a small, enclosed space, the open flame consumes the limited amount of oxygen available and produces carbon dioxide that displaces the oxygen. In addition, there is the consumption of oxygen through breathing.

The gas burns increasingly incompletely, the flame now also produces carbon monoxide - with the effect described above. If at some point there is no longer enough oxygen available, the flame goes out and the gas continues to escape until the cartridge is empty. Studies suggest that a poorly ventilated room can be even more dangerous than one that is not at all ventilated. Since in the latter the flame starves to death faster without oxygen and does not continue to produce CO. An extinguished flame is - like a yellow flame - a warning sign that the oxygen content in the tent is too low.


Avoid carbon monoxide poisoning

  • Ensure sufficient ventilation, suggested opening of at least 50 cm², ideal is a lower opening for O supply and a higher one for CO discharge
  • if the stove is used continuously, ventilate the stove from time to time
  • low air supply can be more harmful than no ventilation at all (the flame then simply goes out)
  • cook only with maximum and blue flame; if the flame is yellow, ensure more air supply
  • Avoid long simmering
  • Use pots with a small diameter
  • Regularly clear the tent of ice and snow
  • pay attention to symptoms, go outside when entering
  • Remain attentive as possible, do not sleep when the stove is in operation

At the time of the forensic examinations, the dead both had pulmonary edema and COHb (carbon monoxide-bound hemoglobin) of 48 and 59 percent. This means that just under or over half of the hemoglobin was occupied with carbon monoxide and was no longer available for oxygen transport. Values ​​in the highly toxic to comatose range. "The carbon monoxide displaces the oxygen and the increasing lack of oxygen leads to changes in shock, including pulmonary edema," explains forensic doctor Professor Walter Rabl from the Medical University of Innsbruck, who autopsied the corpses. “The pure lack of oxygen leads to euphoria and feelings of happiness in the body. There is no feeling of suffocation because the carbon dioxide content in the blood does not rise, as carbon dioxide can be exhaled normally. "

When the flame on their stove goes out, the men have been unconscious or at least asleep for a while. This is indicated by charred leftovers in the pot. In addition to the closed entrance, another flaw with serious consequences. “By burning the food, the carbon monoxide poisoning process is likely to have been accelerated,” the police report said. The improper preparation of the expedition food - simmering the food in the saucepan over the flame instead of pouring hot water into the bag - has likely increased the cooking time and thus increased CO production. And: Small flames (as is necessary for simmering) produce more carbon monoxide than operating the stove with maximum flame.

The next morning it remained quiet in the fourth tent of the small camp for an unusually long time. Two other participants want to wake the supposed late riser, open the tent and see a comrade in a sitting position tipped over to one side, with his feet still in the recess in the apse. The second is in the inner tent in the sleeping bag. The participants are frightened, they call the mountain guide for help, together they pull a body out of the tent, but Hansjörg Pfaundler immediately notices, despite the rosy complexion of the corpses, that all help is too late. He takes care of the rest of the group, gives consolation, and then climbs up to Mittelbergjoch, where there is cell phone reception to call 140.


Detect carbon monoxide poisoning

From 10 percent COHb (for non-smokers) it is a mild poisoning. The carbon monoxide tolerance can vary from person to person; smokers generally have an increased COHb content. The first symptoms of up to 20 percent COHb occur in the form of a slight headache, followed by fatigue, rapid heartbeat, visual disturbances and, with increasing concentration, drowsiness, dizziness, ringing in the ears and muscle weakness and finally nausea, vomiting, concentration disorders, circulatory collapse and loss of consciousness. Further signs of poisoning are pink skin and cherry-red mucous membranes; the dead have pink corpse marks. If the COHb content exceeds 50 percent, the victims fall into deep unconsciousness, can get convulsions and breathing disorders, and their life is in acute danger. At this concentration, death is likely to occur within two hours.


"To see immediately that a small stove has such a big effect was a clap of thunder," says mountain guide Hansjörg Pfaundler. Due to his special duty to protect the course participants (guarantor position), the public prosecutor initiated proceedings against Pfaundler, which they soon closed. Both the stove and the tent were of high quality, flawless and corresponded to the standard and the mountain guide had repeatedly explained the handling, as he and the participants testified to the police. But the incident concerns Hansjörg Pfaundler for a long time.

“I've been sleeping - and cooking - in tents for 20 or 30 years, admittedly not always under optimal conditions. Like so many. "

Hansjörg Pfaundler

He wonders how often mountaineers just barely escape carbon monoxide poisoning without realizing it. How often he confused the first signs of poisoning with mild altitude sickness even on expeditions. “I've been sleeping - and cooking - in tents for 20 or 30 years, admittedly not always under optimal conditions. Like so many. "

What to look out for?

"[A poisoning with] carbon monoxide mimics the symptoms of altitude sickness excellently, with unspecific, flu-like symptoms that are familiar to anyone who has ever been at high altitude: headache, nausea, weakness and dizziness," it says in the literature.

With severe impaired consciousness and movement, and ultimately unconsciousness, the symptoms of severe CO poisoning are similar to those of high altitude cerebral edema. But: "Despite the similar symptoms, carbon monoxide poisoning is actually quite easy to distinguish from altitude sickness - unless the climbers have only recently ascended," says Ken Zafren, professor of emergency medicine at Stanford University and former vice-president of the International Commission for alpines Rescue services.

It is safest to cook in front of the tent. Photo: Eric Larsen
It is safest to cook in front of the tent. Photo: Eric Larsen

The previous history and the circumstances are usually very informative. "If several people develop similar symptoms within a tent that is being cooked in, i.e. headache, nausea, vomiting, CO poisoning is the most likely diagnosis."

Then quick action is the order of the day. The person concerned must immediately (be brought) out of the closed room into the open air. If it really is a question of CO poisoning, the symptoms disappear on their own after a while in the fresh air - in contrast to those of altitude sickness. In severe cases, it makes sense to give pure oxygen, which accelerates the breakdown of COHb in the body.

The problem with this is that in order to be able to act, the mountaineers have to notice their symptoms of poisoning in good time, before consciousness and mobility are restricted.

The carbon monoxide content in the air increases slowly at first, but then exponentially. "Even 0,1 percent carbon monoxide in the ambient air can cause death," says coroner Rabl. Laboratory experiments have shown that in tents a critical concentration can be reached after half an hour of cooking.

A blue flame is a good sign.
A blue flame is a good sign.

Jelle Staleman, a mountain guide from the Netherlands, who gave Hansjörg Pfaundler the group and who was on site the day after the accident, reports on a lucky case in which a climber noticed CO poisoning just in time. Years ago, Staleman was on an expedition in the Karakoram with other mountain guides. “Two colleagues were already a camp further up at 6000 meters, a storm was raging. With a wind speed of 80 to 100 km / h it was simply impossible to cook with the tent open, ”he explains. When one climber passed out, the other with presence of mind turned off the stove and tore open the tent entrance. "I found it remarkable that the second alpinist was still reacting and always really paying attention," says Staleman.

While the accident on the Taschachferner was one of the rare cases of carbon monoxide poisoning among mountaineers in Austria, the problem is more common in other parts of the world. Ken Zafren estimates that many alpinists are affected by mild poisoning. That must have something to do with the infrastructure - where there are no huts, people cook more often in tents - and with the fact that carbon monoxide is more dangerous at high altitudes. Due to the lower oxygen partial pressure, there is less oxygen in a tent in the high altitude camp, which increases the breathing rate. The alpinists take in more carbon monoxide. The half-life of COHb in the body, which is four to six hours at sea level, also increases with increasing altitude. And last but not least, high-altitude climbers spend several hours a day melting snow - in suboptimal conditions, as the stoves burn worse when it is cold and there is less oxygen in the air and produce more carbon monoxide. 

“Actually everyone knows how to cook properly in a tent. But many underestimate how quickly carbon monoxide can become dangerous. "

Hansjörg Pfaundler

And that people probably only learn from tragedy. Although he has not been on an expedition himself since the accident, he has since “made sure that the tent remains open, no matter how uncomfortable it is”. Above all, however, he wants to sensitize other mountaineers and colleagues to the subject. 


About the magazine bergundstieg

Bergundstieg is an international magazine for safety and risk in mountain sports and illuminates the topics of equipment, mountain rescue, rope technology, accident and avalanche knowledge. Bergundstieg is published by the Alpine Associations of Austria (PES), Germany (DAV), South Tyrol (AVS) and Switzerland (SAC).


+ + +
Credits: This article first appeared in the journal mountaineering.