Is Carbon Monoxide Flammable? (A 5 point guide)   

This article will answer the following question: “Is Carbon Monoxide Flammable?”, and other important safety manners regarding the chemical compound.

Is Carbon Monoxide Flammable?

Yes, it is. Any carbon monoxide leaking is a huge fire hazard. If there’s any source of ignition like flames, intense heat, sparks, lit cigarettes, etc., the substance can even explode.

What is carbon monoxide?

Carbon monoxide (CO) is a gas that comes from the incomplete combustion of a source of fuel. There are also numerous environmental and biological processes that can emit CO into the atmosphere.

Any fire has some percentage of incomplete combustion and can produce carbon monoxide, hence why it’s so important to have a good exhaustion system in any place where a fire is needed.

Carbon monoxide has no color, taste, or odor, and is a little heavier than air. It is best known as a poisonous gas that rises from the incomplete combustion of coal.


There is evidence that point to the fact that controlled fires happened as far as 800 thousand years ago. 

It is accepted that these primitive cavemen someday brought fire into their dwellings, eventually discovering the dangers of carbon monoxide. 

It’s conceivable that Native Americans had experienced CO psychoactive effects during fireside rituals, around 20.000 years ago.

The earliest documentation of where carbon dioxide appears is around 350 BCE (before the common era/ before Christ). Aristotle wrote that “coal fumes lead to heavy head and death”.

The oldest report of CO poisoning occurred in Nuceia, where Romans suffocated in bathhouses due to leaks in the hypocaust heating technology. Romans also executed prisoners during the second Punic War using fumes containing CO.

During the Julius Cesar era, fumes were used as a capital punishment method performed by leveraging “the greenest-possible wood capable of producing the most smoke”, by Emperor Lucius Verus.

Evidence suggests that Cleopatra died due to accidental poisoning by CO, in 30 BCE. The same could have happened with Princess Diana, in 1997.

Physical properties of carbon monoxide

Physical properties:

  • Molecular weight: 28.0
  • Boiling Point: -313ºF
  • Melting Point: -337ºF
  • Solubility: 2%
  • Vapor pressure: >35atm
  • Ionization Potencial:14.01eV
  • Flashpoint: N/A. It is a gas.
  • Upper explosive limit: 74%
  • Lower explosive limit: 12.5%
  • Relative gas density: 0.97

Carbon Monoxide Hazards

These are common pictograms for carbon monoxide hazards. 

Carbon monoxide is an extremely flammable gas. It presents acute toxicity and is toxic if inhaled. The compound can damage organs through prolonged exposure and even harm unborn children.

Carbon monoxide is a big problem because it doesn’t present any colors and is odorless. Leaking may not be detected through smell and vision alone.

Maximum Airborne Concentration:

  • Below 200ppm (230mg/m3), individuals exposed for up to 1h hour wouldn’t experience anything rather than mild health effects.
  • Between 200 and 350 ppm (230 – 402.50mg/m3), individuals exposed for up to 1h wouldn’t experience irreversible effects.
  • At a maximum of 500ppm (575mg/m3), individuals exposed for up to 1h wouldn’t experience or develop life-threatening health effects.
  • Above 500ppm, humans can experience life-threatening health effects.

Inhalation can cause headache, dizziness, confusion, nausea, limbs can get weakened. People can turn unconscious at a considerably low concentration of CO, and eventually, it will lead to death.

Direct skin contact with carbon monoxide can cause severe burns, injuries, and frostbite. Carbon monoxide is the most common cause of chemical asphyxia. 

This happens because carbon monoxide has a big affinity with the red blood cells. These cells are specialized in transporting oxygen from one place to another through our circulatory system, they harvest this oxygen in our lungs.

Oxygen binds to them, but not so firmly. As a result, once the cell reaches its destination after traveling in our blood, it can release the oxygen gas that will be used by the other cells in our bodies.

CO binds with these oxygen receptors, but can’t let go easily. Carbon monoxide is a much more reactive molecule because it is not stable. If there’s enough of it in our blood, there’s not going to be enough cells to transport oxygen, and we die from asphyxia.

The most common organs targeted by carbon monoxide are the cardiovascular system, lungs, blood, and central nervous system.

Common symptoms after carbon monoxide exposure:

  • Headache 
  • Tachypnea
  • Nausea
  • Weakness 
  • Exhaustion
  • Dizziness
  • Confusion
  • Hallucinations
  • Cyanosis
  • Angina
  • Syncope
  • Depressed S-T Segment Of Electrocardiogram

First-aid measures

If any inhalation, ingestion, or skin contact with a concentrated source of carbon monoxide happens, medical attention should be sought immediately. 

Severe frozen burns may occur during an eventual leaking of compressed carbon monoxide. If the skin or eyes get affected and a burn appears, do not waste any time and go straight look to medical care.

If the region affected didn’t burn, the area must be flushed with abundant water for at least 15 minutes. Medical attention must be sought if any condition like pain, swelling, lacrimation, or photophobia persists. 

If a person eventually breathes large amounts of CO, must be moved to fresh air as soon as possible. If the person stops breathing, mouth-to-mouth resuscitation or artificial respiration and cardiac massage are required.

The affected person must remain warm and rested at all times. Medical attention is required as soon as possible.

Flammability and combustion of carbon monoxide

Carbon monoxide is a very flammable compound. It is the result of the incomplete combustion of organic compounds. It can continue to burn if the right conditions are given to it, especially if it’s under pressure.

Flames from the burning of monoxide carbon have very few colors.

Carbon monoxide as a refrigerated liquid is extremely flammable, it can burn easily if close to a source of ignition such as flames, intense heat, and sparks.

The vapors from the liquefied gas are heavier than air and can stick around for some time if the ventilation is bad. Because of that, there’s a serious risk of explosion when dealing with CO.


Carbon monoxide doesn’t make 4 connections, but 3. Even so, in this case, it is a stable molecule because it can remain that way unless it comes across another reactive specie.

Fire Fighting measures

Leaking gas fires must NOT be extinguished unless the leaking can be stopped. Regular people shouldn’t try to put down fires unless it is small. 

The best thing to do is to evacuate the area, consult an expert and use self-containing breathing apparatus (the ones that have compressed air, designed for dangerous atmospheres. Other masks won’t serve against carbon monoxide.

Always try to stop the flow of gas before extinguishing the fire.

For small fires, water spray, dry chemical, CO2 or alcohol-resistant foam extinguishers can be used. For large fires, water spray, fog, or alcohol-resistant foam.

If the fire involves tanks, it must be fought at the maximum distance possible. The tanks must be cooled with flooding quantities of water until the fire runs out. Water shouldn’t be applied directly to the flames.

Always stay far from tanks engulfed in fire.

If it is not possible to shut down the fuel supply, let the fire burn itself out

Safety Data Sheets

You can always find more specific safety information in Safety Data Sheets. They are documents made by authorities, companies, and labs that evaluate all the relevant risks for substances.

You can find some here, here, and here.

These documents present carbon monoxide as a very flammable, potentially teratogenic, and health-hazardous compound.


Carbon monoxide is a very flammable substance that can catch fire easily if a source of ignition is provided. CO inhalation can lead to asphyxiation, and it’s a byproduct of any combustion. 

Of course, small fires like candles or ovens don’t generate enough CO to be a concern. It will surely not cause any acute health hazard.

Frequently Asked Questions (FAQS): Is Carbon Monoxide Flammable?

Is carbon monoxide a greenhouse gas?

It is a weak greenhouse gas because it’s not an important constituent of our atmosphere.

Carbon dioxide is reactive, so it bonds to something before becoming a greenhouse gas. Although, it can steal hydroxyl (OH) ligands from other compounds in the air, reducing their abundance.

Hydroxyl is important because it can diminish the methane concentration in the atmosphere. Methane is the 2nd most important greenhouse gas, being only behind carbon dioxide.

is carbon monoxide heavier than air?

Yes, it’s slightly heavier than air. 

Carbon monoxide detectors should be put on a wall about 5 feet (1.5meters) above the floor. The detector must not be placed near a fireplace or any fire-producing equipment.

Is carbon monoxide polar?

Yes. Carbon monoxide structures may look symmetric, but the carbon-oxygen bonding is polar, and so is the rest of the molecule. 

Carbon and oxygen have very different electronegativity values. Since oxygen is more electronegative, it attracts the electrons closer to itself, making the molecule polar. But it’s not very polar.


Hopper, C. P., Zambrana, P. N., Goebel, U., & Wollborn, J. (2021). A brief history of carbon monoxide and its therapeutic origins. Nitric Oxide, 111-112, 45–63. doi:10.1016/j.niox.2021.04.001

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