Taken from Backpacking Equipment Buyer's Guide by William Kemsley & the editors of Backpacker Magazine. Copyright © 1978 by Backpacker, Inc Reproduced courtesy of Backpacker Magazine New Research Proves Backpacking Stoves More Deadly Than Suspected Lethal levels of carbon monoxide given off by backpacking stoves in normal use While backpacking in New Hampshire's White Mountains last winter, four members of our party of 12 complained of dizziness and nausea after supper. The symptoms were the same as as those associated with altitude sickness, but we were camped at only 3400 feet. All four men felt fine the next morning, and the incident passed without explanation. Several months later we found a small winter-stove and cook-kit combination at a low price at a local hardware store. We bought a stove and decided to try it out by cooking lunch in an office at work. Afterr 30 minutes, we noticed we felt dizzy and were experiencing mild headaches. We smelled combustion odors and decided to test for carbon monoxide. Our suspicions were confirmed when we found carbon monoxide levels of more than 100 parts per million (ppm) near the stove. We recalled the complaints of the four men during our winter trip. Unlike the rest of the group, they had cooked supper inside their tent because of severe winds and a low temperature. We decided their discomfort probably had resulted from exposure to a high level of carbon monoxide produced by their mountain stove. Why Carbon Monoxide Is Dangerous Carbon monoxide (CO) is a colorless, almost odorless gas that results from incomplete combustion of hydrocarbons. In the body some of the blood’s hemoglobin that ordinarily would pick up oxygen in the lungs picks up CO instead, so the amount of oxygen in the blood is reduced. The CO reacts with the hemoglobin to form carboxyhemoglobin. The amount of carboxyhemoglobin formed depends on the concentration of CO and the duration of exposure. Low amounts cause headache, dizziness and nausea; high amounts cause coma and death. An increase in altitude increases the severity of the effects because of the low oxygen saturation in one’s blood. We decided to investigate the concentrations of CO produced in a standard mountaineering tent by backpackers’ and mountaineers’ stoves. We used an uncoated nylon tent of A-frame construction, the Crestline from Recreational Equipment, Inc. We tested eight stoves: Bleuet (butane), Gerry Mini (liquid propane gas), Gerry Mini Mark II (1p gas), Primus Grasshopper (propane), Optimus 77A (methanol), Svea 123 (Coleman fuel), Optimus 111B (Coleman fuel) and MSR (Coleman fuel). The Svea 123 was tested with the Sigg Tourist Cook Kit, the Gerry Mini stoves in the Gerry Tourist Cookset and alone, and the Optimus 77A in the cookset sold with the stove, All stoves were clean and in excellent operating condition. How the Stoves Were Tested An identical procedure was followed in all experiments. Stoves were centered 18 inches from the front entrance of the tent. Sampling probes were held by a ringstand placed 28 inches from the center of the front entrance at a height of 24 inches, representative of the head level of a person cooking. Tygon tubing connected the probes to two CO analyzers (Ecolyzer, Energetics Science) capable of measuring CO concentrations from 0 to 100 ppm. Measurement of levels greater than 100 ppm was made possible by using a metering pump (Masterflex, Cole Parmer) to bleed in an equal volume of dilution air. Both analyzers were calibrated and checked against each other at levels below 100 ppm. Preliminary tests were conducted outdoors on a calm, 60º F. day; extensive testing was done in a well-ventilated laboratory at 60º F. The tent was pitched normally, without its fly. The nine-inch circular vent in the rear was kept fully open, and the front flap was zipped partly closed to form, a triangular opening measuring 10 x 10 x 12 inches at the tent’s apex. Clamps were placed on the zipper to ensure closing to the same position in each experiment. Prior to each experiment, the analyzers were zeroed and calibrated, and background levels of CO were recorded. They measured a maximum of 5 ppm at the beginning of each test and never exceeded 8 ppm. Three pints of water at 60º F. were placed in a 2½-quart aluminum pan (Sigg). Each stove was started outside the tent. As soon as it reached stable operating conditions it was placed inside the tent in the position indicated. The pot was centered on the burner, the door was quickly zipped shut as far as the clamp stops, and a stop-watch was started. Concentrations of CO were recorded at one-half or one minute intervals until the levels stabilized, The stoves were run for 15 minutes. What the Tests Showed The CO concentrations produced by the Optimus 77A, the Gerry Mini (with and without the Gerry Tourist Cookset), the Optimus 111B and the MSR rose rapidly during the first few minutes, then stabilized when the rate of CO escaping from the tent became equal to rate of CO produced by the stoves. The final concentrations produced by these stoves ranged from 70 to 130 ppm. (The Gerry Mini in the Tourist Cookset might have produced higher levels, but the stove ran out of fuel). The CO concentrations produced by the Bleuet, the Primus Grasshopper and the Svea 123 with the Sigg Tourist Cook Kit rose at a slower rate and stabilized at much lower levels – 20 to 25 ppm. The CO level produced by the Gerry Mini Mark II had not stabilized when the run was terminated. What caused the high concentrations? Clearly, the greater the rate of production of CO, the higher the final concentration in the tent. The rate of CO production depended on two factors: the amount of fuel and oxygen combusted by the stove (the output of the stove) and the degree of incomplete combustion (the amount of CO produced by the amount of fuel burned). The output was determined easily by by the output of energy: the Optimus 111B and MSR had high outputs; the Gerry Minis, the Optimus 77A and the Svea 123 had moderate outputs; and the Bleuet and Primus Grasshopper had lower outputs. We determined the degree of incomplete combustion by measuring the CO concentration very near each stove – by placing the probe from the ecolyzer close to the burner while the stove was operating without pans on its supports. We found that the Optimus 111B and 77A, MSR and Gerry Minis did not produce a CO concentration as high as that at head level inside the tent. Then we repeated the tests for incomplete combustion, this time with pans of water placed on the stoves, and got quite different results. The concentrations of CO near the bottom of the pan were more than 200 ppm in every case except for the Svea 123 with the Sigg Cook Kit, which produced 30 ppm exactly as it had before when no pan was used. The reason for high production by the other stoves was apparent: the flame impinged on the pan, We decided the cold pan surface caused quenching (cooling) of the flame, which resulted in incomplete combustion and CO production. The flame of the Svea 123, however, did not impinge on the pan. We raised the pans on several stoves. When flames no longer impinged on the pans, CO concentrations dropped. Next we modified several stoves to prevent flame impingement and lower the amount of CO produced. The Optimus 111B was modified by replacing the pan supports with supports one inch longer. The pan support for the MSR stove was first raised three-fourths of an inch, then one inch. The short windscreen on the Gerry Tourist Cookset was replaced by the windscreen from the Sigg Cook Kit, which was 1¼ inches taller. The original experiments were repeated using the modified stoves. The CO levels produced by both 'Gerry'Minis with the modified cookset and the modified Optimus 111B were dramatically reduced and. were well within safe limits. The CO concentration produced by the MSR with the pot raised three-quarters of an inch was reduced, but still high; with the pot raised one inch, the level was very low. Conclusions It is apparent from our tests that several of the high-output stoves used by winter mountaineers produce high levels of carbon monoxide in a partially vented, breathable nylon tent as a result of incomplete combustion caused by flame quenching. It is likely most other high-output stoves produce similar levels and that even low-output stoves could produce high levels in a coated nylon tent. Exposure to such levels of carbon monoxide probably is not dangerous at low altitudes although it may lead to discomfort. At altitudes above 10,000 feet, however, carbon monoxide poses a potentially dangerous hazard by reducing the already low oxygen saturation of the blood. The effects would depend also on the performance of the particular stove, the ventilation of the tent and the duration of cooking time. Tables of Deadly Doses Here's How Much Carbon Dioxide The Stoves Gave Off The curves on the chart indicate incremental levels of carbon monoxide in the tent produced by the burning stoves. The authors took carbon monoxide measurements at one minute intervals. Curves were plotted from these measurements. The horizontal dotted line indicates the maximum level of carbon monoxide considered "safe" by the Amended Air Quality Act of 1970. 1: Svea 123 in Sigg Tourist Cook Kit 2: Primus Grasshopper 3: Bleuet 4: Gerry Mini Mark II 5: MSR 6: Optimus 111B 7: Optimus 77A 8: Gerry Mini 9: Gerry Mini in Gerry Tourist Cookset When Pot Supports Were Raised The authors found that carbon monoxide dangers of stoves were reduced by raising stove pot supports one inch, high enough so the flame did not touch the pot bottom. While it took longer to boil a quart of water, the carbon monoxide emission was lowered to safer levels. Some Little-Known Effects of Carbon Monoxide Poisoning Carbon monoxide (CO) combines with hemoglobin in the blood to form carboxyhemoglobin (HbCO). This reduces the ability of the blood to transport oxygen as oxyhemoglobin (HbO2). At sea level 97%of the hemoglobin in the blood is bound with oxygen as HbO2. Carbon monoxide reduces this amount by tying up hemoglobin. The resulting condition is termed hypoxia. Hypoxia can also be caused by low oxygen pressure at high altitudes or by certain diseases. The amount of HbCO formed depends on the concentration of CO, the duration of exposure and the rate of breathing. The physiological effects of hypoxia increase progressively as the level of HbCO increases and the level of HbO2 decreases. The first symptoms appear at HbO2 levels between 95% and 92% saturation, when an individual may begin to experience improvement in time interval discrimination, visual acuity and other psychomotor responses. The symptoms become more noticeable as the HbO2 level drops to 90% saturation. The individual may experience drowsiness, lassitude and mental fatigue. At 85% saturation, headache, occasional nausea and euphoria may experienced. The symptoms intensify and are dominated by a throbbing headache as the concentration of HbO2 drops to 80% saturation. Vomit and collapse occur at 70% saturation, coma at 60% and death at 40%. The ambient air quality standards as legislated by the 1970 Amended Air Quality Act limit the maximum average concentration of CO for a one-hour exposure to 35 ppm, or an HbO2 saturation level of 95.25%. As an example, consider two winter mountaineers camped at a low elevation in an A-frame tent. Let’s say they spend two hours melting snow, boiling water and cooking. This would expose them to approximately 100 ppm CO from the stove. This would result in HbCO levels of 5%, The HbO2 level in their blood would be 92% (the normal 97% minus the 5% tied up as HbCO). The mountaineers might feel unpleasant and experience some impairment in visual acuity and other psychomotor responses but would be in no danger. The effects of breathing CO increase dramatically at higher altitudes. As altitude increases, atmospheric pressure decreases and oxygen saturation in the blood decreases. The following table shows the oxygen saturation at various altitudes for a person breathing pure air. Since both altitude and carbon monoxide reduce the oxygen saturation of the blood, their effects are approximately additive. Suppose our winter mountaineers cook in their tent at an elevation of 5,000 feet, instead. The HbO2 saturation in their blood would be 95% (the normal amount at 5,000 feet) minus the 5% reduction caused by the stove, or 90%. They would experience drowsiness, lassitude and mental fatigue. At 10,000 feet the mountaineers’ HbO2 levels would be 85% saturation. Headache, nausea and euphoria could ensue, and they could be in some danger. At altitudes higher than 10,000 feet, exposure to levels of CO becomes very dangerous. At altitudes of 17,000 feet, the mountaineers could vomit and collapse. These effects represent what typical mountaineers might experience under the conditions indicated. But they might vary considerably from one individual to another depending on physical condition, acclimatization to altitude and amount of exercise.
Very interesting article. Seems familiar, but all new again. The MSR stove in 1976, the date of this article, would be the MF, correct? The MSR model G & GK started in 1977. Unless the MSR model 9 or 9A was still available or used for this test. I believe a few years later the MSR model XGK pot supports were raised and the efficiency of the stove was reduced, but the safety, inside a tent, was improved. I wonder why that is. Ken in NC
Ken, I am GUESSING it might be related to the velocity of the gas through the vents/jets and the better mixing of the fuel with air on the gassies. Or, it might be magic.
Oh it's definitely just magic. It is surprising that MSR didn't raise the pot stands (reduce the efficiency of the stoves) until after REI had bought them. This article is written in 1976. I would bet that most mountaineers at the time would have said they wanted efficiency first and foremost. Ken in NC
If the flame is cooled down you get incomplete combustion and CO. When lifting the pot you get more complete combustion and less CO. A pot with heat sinks, like the Primus ETA pots, the flame is more effective cooled down (better heat transfer) and less complete combustion and more CO as a result.
In the Sigg cooker with a 123, the flame contacts nothing but air. So less CO. Just another reaon to love the 123/Sigg combination. And as CO in any concentration is unhealthful, and as I'm a coward about cooking in my tent in any event and don't do it, I've never had a problem with CO. In Western WA, any time one camps more than fifty feet from an occupied dwelling he is in bear country. Bears can smell food of any sort a long way off and are worse threats than any stove to one's continued well being, cooking in a tent, any tent, with any stove is a bad idea. That said, I do brew coffee and tea in my wall tent at Mt. Man Rendezvous' and have done it in the vestibules of sundry packtents over the years. No food though. Any time a bear expresses a desire for a cup of coffee or tea, I just pour him one and ask if he'd like sugar. Just because he might tear my camp apart is no reason to be inhospitable. Gerry
Given the date of the article, it's likely the risk of carbon monoxide was not so well known as it is now amongst the masses. Awareness of this 'silent' killer has increased substantially, and carbon monoxide detectors a staple in most people's homes, cottages, etc. Yet it's still the cause (non-suicides) of numerous, preventable deaths a year - many from the use of propane powered heaters and stoves in poorly ventilated areas. They were not testing the stoves directly in the tents, just a foot or so outside of them. Not sure if a vestibule was involved, which would have increased the concentration, but by the looks of the image they did it in open air. Like Gerry I never run any combustible fuel or gas powered device (minus human exhaust, lol) in a tent, regardless of the precautions taken. I wouldn't classify that as 'cowardly', it's a smart move and not just for the carbon monoxide risk. Wood burning is different, as it has a chimney that vents the majority of the exhaust outside (and most tents designed to support wood stove are constructed differently in both design and material than your typical 2, 3 or 4 season tent). Like most I love the 123, great little powerful stove and glad to see her near the top of this list too, even though I'd never use it under the scenario envisioned.
I have to tell you....Here in Norway when I was a young man we had to go to the army for one year. We used the Optimus 111 roarer and with silentburners. We were 8 men in each tent and used the Optimus when sleeping, making food and so on. They taught us to be careful to keep the flame blue, except for that no problem. We used to watch the stove 2 hours each when the others slept, no one I have heard about got any problems from carbon monoxyd.
Jeez, you must have been exhausted, then - they're just about the noisiest stove of all! I'm surprised you haven't heard of deaths from carbon monoxide when camping etc. It happens several times each year in this country when people leave the stove burning overnight for warmth, having made sure the tent was as draught-free as possible. Others do the same with a portable barbeque, for instance. Sadly, some folk are extremely resistant to education and they suffer the consequences...
CO kills far to many people here as well. From a family heating there house with an outdoor patio heater to Doc workers (who should know better) cooking in a tent on a gas stove with no trivet.
I have used the Optimus 111 to keep warm in both tents and a tiny hunting cabin we use . And for cooking. I have used the stove for hours , and we haven't had any problems. But I / we have rules when we do this. We never let it burn when we are in our sleeping bags, even if we don't plan to sleep just yet. And we are aware of the problem with CO. But the stove produced most CO when it is used for cooking , and a cold pot is put on top of it. All combustion produces CO. A paraffin lamp that burns for hours to produce light, will also produce CO. And paraffin lamps has caused deaths too. The only safe combustion that will not produce CO in a room/ space , is where a chimney vent the CO out of the room.
Venting, in addition to getting rid of combustion products, does something just as important -- it draws fresh air into the room. Stoves and lamps contribute to the depletion of O2. A small reduction in O2 concentration would be of little consequence to us, except that it reduces the efficiency of combustion such that the ratio of CO to CO2 increases from those stoves or lamps. In a roomy tent or drafty small cabin there is generally enough fresh air so that O2 levels remain adequate. The focus on stove testing and pot vs no pot, IMO, is less important than the need for fresh air when using any such equipment.
Yes, and so do the people in the tent - a factor often overlooked. I agree, absolutely... The great danger with CO is that it's insidious - people may have every intention of putting out the stove or lamp or whatever before they turn in but they fall asleep due to the effects of CO and simply never wake up again...
I have heard about deaths from CO but not in the army. The noise was no problem, we got used to that. I am sure in here have to be somemore Scandinavians with army service behind them that can confirm my story The stove wasn't the worst tho, we had these storm lamps made in Germany. We called them flaggermuslykter in Norwegian...Bat lamps I think it's in English. If we forgot to adjust those properly, or forgot to blow them out before sleeping, we woke up with black soot in the nose sometimes. As a soldier in the Norwegian army we have slept in tent with the Optimus 111 in - 35dgr Celsius several times, the most important was to keep the eyes open when on fireguard and not fall to sleep. If you did that and the pressure in the stove fell it could get ugly
Sounds like 'Fledermaus lights' which is approximately German and English for Bat Lamps - not that we have many of them over here in the UK...
