Incomplete combustion of carbon-based fuels such as wood, charcoal, gasoline, kerosene, alcohol, and methane produces carbon monoxide. Carbon monoxide (CO) is lighter than air, and inhaling it can lead to poisoning. Carbon dioxide (CO2) is heavier than air; while humans inhale oxygen and exhale carbon dioxide, high concentrations of carbon dioxide are also harmful to health.
The most common cause of carbon monoxide poisoning is idling in a car with the air conditioning on. When the car is stationary, the engine takes in less oxygen, which leads to incomplete combustion of gasoline and the production of carbon monoxide. If a person is resting or sleeping in the car, they are very likely to suffer from carbon monoxide poisoning. There have been many news reports of such poisoning incidents, and the consequences are very serious.
The February 2019 issue of *Health and Life* magazine reported on a case of Ms. Li, a resident of Liuyang, who suffered carbon monoxide poisoning after using a closed room for heating. At the time, Ms. Li only experienced mild symptoms such as dizziness and nausea, so she did not seek any treatment. Unexpectedly, two weeks later, Ms. Li suddenly developed symptoms including incontinence, inability to speak, impaired limb movement, and slowed reflexes. She was taken to the hospital and diagnosed with delayed encephalopathy due to carbon monoxide poisoning. In fact, similar cases are common, so even if mild symptoms of carbon monoxide poisoning occur, it is necessary to immediately stop your travel and seek medical attention at a hospital. However, if you are heating yourself in a confined space without proper ventilation, the concentration of carbon monoxide gas can rise, posing a danger.
If a fire is lit for warmth in a poorly ventilated environment, carbon dioxide levels will slowly rise. Symptoms in this environment mainly include headaches, dizziness, difficulty concentrating, and memory loss. During the day, when a person is awake, they will feel uncomfortable and naturally go outside to breathe fresh air, so there shouldn’t be a problem. However, it’s important to note that if a person uses a heater at night while sleeping, excessively high carbon dioxide levels can be life-threatening.
A carbon monoxide concentration below 50 PPM is considered safe. If it exceeds this level, it can have adverse effects on health, and immediate ventilation is necessary. To better monitor carbon monoxide levels, it is strongly recommended that people carry a carbon monoxide detector. Of course, a combined carbon monoxide and carbon dioxide detector would be even better.
While there are many carbon monoxide alarms on the market, they are mainly used in kitchens. Carbon monoxide sensors are divided into two types: electrochemical sensors and semiconductor sensors. Electrochemical sensors are more expensive but offer higher accuracy and better real-time performance; semiconductor sensors are cheaper but less accurate. Therefore, carbon monoxide alarms used for outdoor camping etc. should ideally employ high-precision electrochemical sensors for better sensitivity. However, most current carbon monoxide alarms use semiconductor sensors, with electrochemical sensors being less common.
Electrochemical sensors can be further divided into solid-state electrochemical sensors and liquid-state electrochemical sensors. Liquid-state electrochemical sensors have a wider range of applications, mainly detecting carbon monoxide concentration by reacting chemical materials with oxygen and carbon monoxide in the air. They are cheaper than solid-state electrochemical sensors, but have three major problems:
Carbon Monoxide Detector
First, the chemical materials inside react very easily with oxygen in the air and oxidize, so the accuracy will drop rapidly after a period of use, causing the alarm threshold to increase. It may be able to alarm at 150PPM at the beginning, but after a period of time it will become 200PPM.
Secondly, liquid electrochemical sensors require an internal liquid to react chemically with carbon monoxide in the air, necessitating sufficient contact with air. This can lead to problems such as internal liquid leakage and evaporation. Higher external temperatures accelerate evaporation, and the liquid itself is harmful to humans. As shown in Figure 1-3 above, some reputable manufacturers use larger liquid electrochemical sensors containing more chemical reagents, resulting in a longer lifespan.
Third, liquid electrochemical sensors are designed for use in areas like kitchens. In harsh outdoor temperatures, the liquid easily freezes, losing its ability to detect carbon monoxide.
Therefore, high-end carbon monoxide detectors mainly use solid-state electrochemical sensors. This effectively avoids the three problems mentioned above.
Many vendors misleadingly include descriptions of gas, natural gas, and carbon monoxide alarms in their product descriptions. In reality, natural gas and carbon monoxide have completely different compositions. A natural gas alarm cannot be used to detect carbon monoxide. If a carbon monoxide alarm is purchased and fails to sound in a real emergency, it can cause serious personal injury. Furthermore, the gas we commonly refer to as “coal gas” is not actually carbon monoxide; it is methane and its mixtures. Gas companies also add an odorous gas to prevent explosions from leaks, but these do not cause poisoning.
Most carbon monoxide alarms have a threshold of 150 PPM. While a carbon monoxide concentration of 50 PPM may not pose an immediate threat to life, it is already above the legal limit. In a tent where a kerosene stove or similar appliance is burning, the carbon monoxide concentration may not rise rapidly, but it could take several hours to reach the alarm threshold of 150 PPM. Prolonged exposure to an environment with 50 PPM will almost certainly result in carbon monoxide poisoning.
Furthermore, many carbon monoxide alarms are used in environments where carbon monoxide poisoning doesn’t actually occur, such as company cafeteria kitchens, which are often poorly ventilated. Therefore, manufacturers engage in price wars to gain market share, constantly lowering prices and cutting costs. They remove all functions, including screen displays, and users lack the environment and methods to test the alarms. If a real carbon monoxide poisoning occurs, tragedy ensues.
Most carbon monoxide alarms on the market do not immediately sound an alarm when the concentration exceeds the limit. The alarm is triggered over a period of time, which could be a few minutes or even tens of minutes, depending on the algorithm of the alarm’s timer. The main reason for this is to save power, so many alarms are advertised as having a ten-year lifespan. In reality, the battery life in a discharged environment is also less than 10 years. By adjusting the algorithm and extending the time interval for detecting gas concentration, such as checking carbon monoxide concentration every 10-60 minutes, the alarm can achieve a longer operating time, but this can easily lead to danger in actual use.