How Do Firefighters Check for Carbon Monoxide (CO)?

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What exactly is Carbon Monoxide? Why is it dangerous? Is it flammable? Can you smell it? Does the fire department check for Carbon Dioxide? How do firefighters check for it?

Firefighters check for Carbon Monoxide using gas detecting meters called CGI’s (Combustible Gas Indicator). These tools can measure the levels of certain dangerous gases including: CO, Oxygen, Propane, Natural Gas, Hydrogen Cyanide, and Hydrogen Sulfide.

Responding to check for Carbon Monoxide and other potentially dangerous gases is one of the many things that firefighters are responsible for these days. Below we will discuss what Carbon Monoxide is, why it is dangerous, and how firefighters work to protect people from it.

Your # 1 priority is keeping your family safe. As a firefighter, I recommend everyone has updated smoke detectors that don’t require battery changes, like these ones from Kidde, a fire extinguisher, like this one from Amerex, and a fire escape ladder if you have bedrooms above the first floor, I recommend this one from Hausse.

Also read: Is It Safe To Sleep In A House After A Small Fire?

What is Carbon Monoxide?

Most people have heard of Carbon Monoxide but may not understand what it is and why it is dangerous.

Carbon Monoxide (CO), not to be confused with Carbon Dioxide (CO2), is a gas containing one oxygen molecule and one carbon molecule. It is produced by incomplete combustion of carbon-containing compounds.

What does that mean? Basically, when something burns and there is not enough oxygen (in an enclosed space) to create CO2 (one carbon and two oxygen molecules), CO is the byproduct.

Carbon Monoxide is colorless and odorless, which makes it even more dangerous, because you don’t know when it is present.

Flash Point:  The lowest temperature at which the vapors of a combustible or flammable substance will ignite in air when exposed to flame.

Flammable Range: The flammable range of a combustible gas is the range of concentration (% of the air) at which it will burn. The range is between the LEL (Lower Explosive Limit) and the UEL (Upper Explosive Limit) Below this range, the substance is too lean (not enough) to burn, and above it is too rich (too much) to burn.

CO is flammable with a low flash point (-311.8 Degrees F) and wide flammable range (12.5 – 74.2%). These basically mean that it can burn even at low temperatures and low or high concentrations in the air. This means that the flammability hazard is significant, but that isn’t the biggest hazard with Carbon Monoxide.

Toxicity! Carbon Monoxide is very dangerous to your (or most any animals) health when inhaled. To understand how Carbon Monoxide is toxic, we must first understand a little about the biology of the human body. Don’t worry, we won’t be getting too sciency.

Humans have a red-colored protein in their blood called hemoglobin. Hemoglobin is responsible for carrying oxygen through the body. When you take a breath, oxygen is filtered out of the air by your lungs and attaches to the hemoglobin in your blood (then called oxyhemoglobin). Your heart will then pump the blood throughout your body and deliver oxygen (as well as other things) to the tissues that need it.

FUN FACT: Hemoglobin in your blood is what makes it red. The Iron in the hemoglobin reacts with the oxygen giving it it’s red color. Depending on how much oxygen is in the blood (and therefore the shape of the hemoglobin) will determine if it’s a darker or brighter shade of red.

Carbon Monoxide disrupts this vital oxygen delivery process in the body. When you breathe in CO, it binds to the hemoglobin instead of the oxygen (creating carboxyhemoglobin). The CO has a stronger bond then oxygen and that means that your blood can now transport less oxygen to your body.

Depending on how much CO is in the air and how long you are breathing will determine how much CO is bonded to your blood cells and therefore how severe the symptoms.

Here is a video from the Center for Disease Control (CDC) about the dangers of Carbon Monoxide:

To learn more about Carbon Monoxide see this:

Also read: Is Carbon Monoxide Flammable? Should You Be Worried?

Combustible Gas Indicators (CGI’s)

A CGI or Combustible Gas Indicator/Detector is one of the tools that firefighters use to measure if there are dangerous (combustible/flammable, toxic, or oxygen displacing) levels of Carbon Monoxide or other gases.

They are also used regularly in certain industries. Some can only detect one specific gas, others are able to sense for a variety (usually about 4-5) specific gases.

These tools usually have a display that shows the amounts of the specific gases that are detected in the area. They also have audible and visual alarms (lights and sounds) to alert the firefighters of potentially dangerous levels.

When you call 911 for a suspected CO or gas leak, the fire department will respond. Sometimes they will send a special Hazardous Materials team with all the necessary detection tools, but a lot of times they will send the closest engine or truck that has a gas detector (CGI).

Most importantly, they will make sure everyone is out of the space where there is a potential gas exposure (if not already out).

They will then make sure their detection tool/s are calibrated for the area (quick test to make sure it performs as it should). Then they will go into the affected area, usually while wearing safety gear and air tanks (SCBA’s)(so they don’t breathe the harmful gases), and get a reading of what and how much is present.

They will assess the danger, find potential sources of the gas and do whatever is necessary to make the space safe again.

This can be as simple as stopping the source of the leak and ventilating the area (opening doors and windows, possibly using high powered fans) or calling for special resources (HazMat Team, Gas or Utility company, Police, etc.) which may take a very long time to get the area totally safe. This all depends on what gas is present, how much, and what is required to remove it.

How Do You Check for Carbon Monoxide in Your Home?

white smoke in valley of mountains

So how can you check for Carbon Monoxide in your home? Because there is no way to see or smell CO, the only way to detect if it’s present is with a gas detection tool. While you probably don’t have a multi-gas CGI at home, you very well may (and DEFINITELY SHOULD) have one or more Carbon Monoxide Detector as well as Smoke Detectors.

While this type of CO detector is not as fancy as the gas detectors used by the fire department, it is just as capable of detecting harmful levels of CO in your home. The law for requiring these detectors varies by state (you need to check the laws where you live), but everyone should have one or more Carbon Monoxide Detectors in their home, as they can save lives.

CO Detectors/Alarms are recommended to be installed on every floor and near each sleeping area at a minimum. Here is a multi-pack of CO Detectors from Kidde.

Smoke Detectors should be installed on every floor, near each sleeping area and common area, and in laundry rooms and kitchens, where fires can start. Here is a multi-pack of 10-year battery Smoke Alarms from Kidde, so you can install them throughout your home.

For more recommendations on how and where to install Carbon Monoxide Detectors, see this article on

For more recommendations on how and where to install Smoke Detectors, see this article on

What Gives off Carbon Monoxide in Your Home?

There are many things that produce Carbon Monoxide, but if all your appliances are working properly, there should be little, if any produced. It is usually caused by faulty appliances or doing something that’s a bad idea (like running a heater designed only for outdoor use, indoors).

Carbon Monoxide is produced by incomplete combustion, so possible sources in your home include:

  • gas fireplaces
  • central heaters
  • water heaters
  • boilers
  • cookers
  • open flames with oil, gas, wood, or coal-burning
  • running a car in an enclosed space can create CO.

According to an article on,

“If household appliances are well serviced and used safely, they should produce negligible quantities of CO gas. Using old appliances, and not servicing them frequently, leads to a higher risk of CO emission.”


Related Questions

Can You Smell Carbon Monoxide?

No, you can not smell Carbon Monoxide as it is an odorless, colorless, tasteless gas. The only way to know if it is present is with gas detecting tools.

Does the Gas Company Check for Carbon Monoxide?

No, the gas company does not check for Carbon Monoxide. For all suspected Carbon Monoxide leaks, 9-1-1 should be called and firefighters and other necessary emergency personnel will respond to assist.

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