Carbon monoxide in a tent: how to keep the smoke out and the air clean

It is half past ten on an evening in February. The stove has been heating the tent for three hours, and now everyone is warm, full and tired. Someone puts in two large logs and turns down the air supply so the embers will last until morning. The vent in the roof has been snowed over, but you cannot tell from inside. Shortly after midnight, the ten-year-old wakes up with a headache and feels sick. It is easy to think it is just too warm or that dinner was too big.

That is exactly how carbon monoxide works in a tent. Nothing smells, nothing can be seen, and the symptoms are like everything else you might feel after a long day in the cold. The good news is that the risks can be listed and that almost all of them come down to the same three things.

This guide is built on three questions to ask before you fall asleep: the pipe, the air and the alarm. Where does the smoke go? Where does fresh air come in? And who will wake you if something goes wrong anyway?

If it is your first time sleeping outdoors in winter, start with the overview in winter camping: camping and sleeping outdoors in winter.

What carbon monoxide is and why it is so treacherous

Carbon monoxide is a gas that forms when something burns with too little oxygen. That goes for wood, charcoal, gas, paraffin and petrol. It is colourless and odourless, so your nose will not help you.

When you breathe in carbon monoxide, it binds to the haemoglobin in your red blood cells, which is what otherwise carries oxygen around your body. According to the CDC, carbon monoxide binds 200 to 250 times more strongly than oxygen does. The blood then carries less oxygen, and the body becomes starved of oxygen even though there is plenty of air to breathe.

In a tent it is especially serious for two reasons. The space is small, so the concentration rises quickly. And you are asleep. The CDC writes that people who are asleep can die from carbon monoxide before they even have time to get symptoms.

The symptoms and why they are missed

The Swedish Poisons Information Centre (Giftinformationscentralen) lists headache, dizziness, tiredness, confusion, nausea and vomiting. At higher concentrations, unconsciousness follows. The Swedish Medical Products Agency (Läkemedelsverket) also mentions palpitations in mild poisoning.

The problem is that almost all of the symptoms have another, natural explanation after a day outdoors in winter:

• Headache gets blamed on too little water or the tent being too warm.
• Tiredness is to be expected after a day of skiing or sledging.
• Nausea gets blamed on the food or the heat.
• Dizziness goes unnoticed when you are already lying down.

The NHS in the UK describes a pattern worth knowing: the symptoms come and go, and they get better outside and worse when you go back in. The Camping and Caravanning Club in the UK points out that it resembles flu or food poisoning, but without a high temperature.

Tip: Ask yourself whether more than one person is feeling unwell at the same time. One person with a headache could be down to anything. Two or three people with a headache and nausea in the same tent means: everyone out now, and think about it afterwards.

Children and dogs

The CDC writes that infants tolerate carbon monoxide less well than others, as do older people and people with heart disease, anaemia or breathing problems. Small children can also rarely say that they have a headache. They get whiny, tired or vomit, and it is easy to interpret that as them being overtired. That is why the same rule of thumb applies there: if a child becomes unwell in the middle of the night in a tent with a fire, think carbon monoxide first.

The dog breathes the same air and is affected too. It cannot say anything either, so always take it out with you. There is more about how the whole family sleeps outdoors for the first time in winter camping with kids.

The pipe: what is burning in the tent

This is the most important part of the guide. Every heat source gets a clear answer.

Heat source	In the tent?	Why
Wood stove with a stove pipe out through the fabric	Yes, with conditions	The smoke is led outside. The risks are a leaking pipe, a choked air supply and blocked vents.
Gas stove or spirit stove	Preferably not	The authorities advise against it. If you have to: only in an open vestibule, awake and briefly.
Gas heaters and paraffin heaters	No	They have no stove pipe, and the exhaust fumes stay in the tent.
Charcoal barbecue, disposable barbecue and embers	Never	Smouldering charcoal gives off a lot of carbon monoxide, even when the barbecue looks like it has gone out.
An idling car as a warming hut	No	The exhaust fumes contain carbon monoxide. The CDC has investigated poisonings in cars where snow blocked the exhaust pipe and the gas got into the passenger compartment.

The stove

A wood stove in a tent made for it is the only way to heat the air in the tent that keeps the smoke out, because the smoke is led out through the pipe. It works as long as the pipe is tight and the draught is unobstructed. How to choose a tent and stove, where it should stand and how to run the pipe out is covered in the hub guide tents with a stove. If you want to understand the idea itself first, the basics are in what a hot tent is.

These are the stove's carbon monoxide traps:

1. A leaking pipe. In our test of a tent stove, the pipe came rolled up and had to be formed into a round pipe before use. It ended up dented, and luckily the leak was outside the tent. Form the pipe around something round at home, and check the joints before you light the stove.
2. The lid on the hotplate. The same test shows another detail. If the stove has a hole with a lid for the pot, smoke can come into the tent when the lid is removed and the draught is not perfect. Only open it when the fire is burning well.
3. A choked air supply with embers. Läkemedelsverket and Giftinformationscentralen say the damper should be open. A fire inspector in Ostrobothnia, Finland, puts it simply: do not close the damper too early, let the embers go out first. Embers with too little air are exactly the kind of combustion that produces the most carbon monoxide.
4. Burning the stove while everyone is asleep. The advice from MCF (Myndigheten för civilt försvar, the Swedish Civil Defence Agency, formerly MSB) for the home is not to use a stove while you are asleep. In a tent, this means the fire should be allowed to burn down while someone is awake. If the stove is to burn all night, the adults take turns staying awake and tending it, as Metsähallitus (Forststyrelsen) in Finland describes it for tents with stoves. Do not add large logs or choke the air supply just before everyone falls asleep. It is the sleeping bag that should keep you warm for the rest of the night, see staying warm in a tent in winter.

The stove also needs fire protection, and that is a separate issue from carbon monoxide. Here is our test of a stove mat.

The gas stove in the vestibule

The gas stove is the easiest thing to bring into the tent when it is windy. MCF writes that gas produces carbon monoxide when there is not enough ventilation, and both the NHS and the Camping and Caravanning Club say that camping stoves should not be used inside tents. So cook outdoors whenever you can.

If the weather forces you into the vestibule:

• Open the vestibule fully or almost fully. No zip should be closed.
• Sit up and stay awake. Never cook lying down in your sleeping bag, and never fall asleep with the stove on.
• Never in the sleeping area. The stove stands in the vestibule and the inner tent is open on the other side, or closed.
• The right pot. Use the size specified in the stove's instructions.
• Look at the flame. MCF describes a clean gas flame as blue-green. Yellow in the flame means poor combustion.
• Change canisters outside and turn off the stove as soon as the water boils.

Gas works less well in the cold, and it is tempting to keep the stove close to your body and the tent. How to cook safely without electricity, with both spirit and gas, is covered in cooking without electricity. The advice on where the stove should stand applies just as much in the tent as at home.

Gas heaters, barbecues and embers

Here the answer is simple: never in the tent. Gas and paraffin heaters made for outdoor use, porches or building sites have no flue. The exhaust fumes stay where you sleep. Läkemedelsverket says that products for outdoor use must never be used indoors.

The barbecue is the most dangerous because it looks harmless once it has gone out. The Camping and Caravanning Club points out that even a barbecue that is cooling down gives off a lot of carbon monoxide, and Giftinformationscentralen warns against bringing in a charcoal barbecue that has just been used. The CDC's investigation from 1999 describes two incidents in which six people died in closed tents, four of them children. In one case a lit gas stove stood in the tent for warmth, in the other a charcoal barbecue that had first been used outside for cooking. Let the barbecue cool down completely outside, well away from the tent.

The air: vents and ventilation

A tent with a wood stove needs air in and smoke out. The smoke goes through the pipe, but the stove needs fresh air to burn well, and you need air to breathe. That is why tents made for stoves have vents. Keep them open even when it is cold.

• Brush off snow from the vents and around the bottom edge of the tent before you go to bed, and again if it snows during the night.
• Condensation dripping from the fabric shows that the air is not moving. Open the vents more.
• Air out the tent after cooking by opening the door fully for a while.

The CDC's report is clear on one point: open tent flaps are not enough to make a gas heater or a barbecue safe. Ventilation helps the stove and the cooker burn cleanly, but it does not make an appliance without a flue safe to sleep next to.

The alarm: the carbon monoxide alarm

A carbon monoxide alarm is the only thing that will warn you while you are asleep. It should be seen as extra protection and not as a reason to bring in something that does not belong in the tent. That is also what the Camping and Caravanning Club writes.

Which type. MCF mentions alarms that meet the EN 50291 standard as a good choice. There is a separate part of the standard, EN 50291-2, for motorhomes, caravans and boats. It is the closest to a tent environment, and the Camping and Caravanning Club recommends one of these. The CDC suggests an alarm with a display, which also shows the highest concentration. Choose a battery-powered alarm.

The cold. This is something many people miss. Alarms are generally made for homes. Manufacturers' operating temperatures often start at minus ten degrees, and for some only at a few degrees above freezing. Once the stove has gone out, the tent can get colder than that. Read the instructions before you buy. Keep the alarm warm between trips, in an inside pocket or in your sleeping bag during the day, and bring spare batteries.

Where it goes. Hang it from a cord on the tent's roof or wall by the sleeping area, roughly where your heads are. Läkemedelsverket advises keeping the alarm close to where the fire is, and the CDC advises keeping it close to where you sleep. In a tent, the two are close to each other. Manufacturers usually specify one to three metres from the source, so do not hang it directly above the stove.

Test it. Press the test button the same evening, before you fall asleep. Läkemedelsverket says the alarm should be tested at least once a month and the batteries replaced regularly. Replace the whole alarm when the manufacturer's stated lifespan has run out.

It does not go off immediately. An alarm to EN 50291 is designed to go off quickly at high concentrations but only after a while at low ones, in one manufacturer's data sheet after 60 to 90 minutes at the lowest alarm level. Headache and nausea in several people are therefore a reason to go outside, even if the alarm is silent.

A smoke alarm and a carbon monoxide alarm are two different things. An ordinary smoke alarm does not detect carbon monoxide, and a carbon monoxide alarm does not detect smoke.

If someone feels unwell

If you suspect carbon monoxide, the order is always the same.

1. Everyone out into the fresh air. Children, adults and the dog. Wake anyone who is asleep.
2. Turn off the source if it takes just a few seconds, for example the gas stove's knob. Do not go back in to put out the stove.
3. Call 112 if anyone is confused, hard to wake, unconscious, having seizures, has chest pain or difficulty breathing.
4. Call Giftinformationscentralen on 010-456 67 00 for milder symptoms. They answer around the clock. Their advice after inhalation is fresh air and rest, and Läkemedelsverket says you should contact a doctor afterwards.
5. Keep warm outside. Take sleeping bags and jackets out with you, so nobody gets chilled while you wait. Children get cold quickly, see how cold is too cold on the slopes.

In the ambulance and at the hospital, oxygen is given and the level of carbon monoxide in the blood is measured. The NHS advises against driving yourself to A&E after poisoning. Do not go back and sleep in the tent until it has been aired out and you know what caused it.

The same rules apply in the cabin and at home

Carbon monoxide is not just a tent problem. The same stove, the same gas cooker and the same barbecue are used during power cuts at home and in the mountain cabin. How to heat your home when the power goes is covered in a warm room, and the damper, the stove and the alarm at the cabin are covered in preparedness at the cabin.

Three questions before you fall asleep

Take a minute in the tent every evening, ideally out loud so the children can hear:

• The pipe. Is something burning in the tent? Is the smoke going out, and have the embers been allowed to die down with the damper open?
• The air. Are the vents open and free of snow?
• The alarm. Is the alarm hanging by your heads, and does it beep when you press the test button?

If you can answer yes to all three, you can crawl into your sleeping bag and listen to the snow against the fabric.