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CO Gas and its Sensor

Intro to Carbon Monoxide

Carbon monoxide is a chemical compound with the formula CO. Carbon monoxide gas is colorless, odorless, and tasteless, making it very difficult to detect without gas detectors specifically configured for CO. It is very toxic and results in more poisoning fatalities than any other kind of poisoning. The risk of carbon monoxide poisoning increases at lower temperatures. CO poisoning is often misdiagnosed as the Flu, due to similar symptoms being present.

Having a device that can detect CO is often very important in the workplace, otherwise you may unknowingly face prolonged exposure. This is a particularly dangerous scenario for those working in confined spaces, as a lack of ventilation could lead to a fatal accumulation of CO in the body. Carbon monoxide, along with other harmful gases, is frequently present in confined spaces, and should always be tested for prior to entry. 

Gas Characteristics

  • "Silent Killer" 
  • Poisonous 
  • Colorless
  • Odorless 
  • Tasteless 
  • Extremely flammable 
  • Compressed gas 
  • Extremely toxic 
  • Lighter than air 
  • Can explode if heated 
  • Bonds to hemoglobin ~250X greater than O2
  • Often mixed with other gases that do have an odor 
  • Non-irritating 
  • More people die from carbon monoxide than ANY other type of gas exposure
  • CAS 630-08-0
GHS WHMIS Flammable Symbol
GHS WHMIS Toxic Icon
GHS WHMIS Compressed Gas Icon
GHS WHMIS Harmful Icon

Industrial CO hazards and sources

  • Boiler rooms  
  • Blast furnaces
  • Warehouses  
  • Petroleum refineries  
  • Pulp/paper production  
  • Steel and production of other metals
  • Manufacturing of other chemicals  
  • Construction workers using fuel-burning tools/equipment 

Annually, 400+ people in the United States die from CO poisoning, and about 50,000 more are treated at an emergency care center.

(Centers for Disease Control and Prevention)

High Risk Scenarios

  • Proximity to any internal combustion engine without proper ventilation.
  • Confined spaces pose considerable risk for CO exposure.
  • Running fuel-burning equipment without proper ventilation can lead to a dangerous accumulation of the gas.
  • Vehicle exhaust contains CO and can build-up in indoor spaces.
  • Workers are more likely to be exposed to CO in cold weather due to the use of heating appliances (furnaces, water heaters, portable non-electric space heaters, etc.).
  • Exhaust from gas powered generators, tools and equipment give off CO and can accumulate if not properly ventilated.
  • As carbon monoxide is lighter than air, there is greater risk of exposure higher up than at ground level in areas without complete ventilation.
  • Repeated exposure to low concentrations may not cause immediate symptoms, but can create long-term issues. The oxygen carrying capacity of blood can be hindered, leading to physiological issues. 

CO Sensor Info

Type: Electrochemical
Range: 0-500 ppm (1 ppm resolution)
High range CO: 0-2000 ppm (5 ppm resolution)
Hydrogen resistant (CO-H): 0-500 ppm (1 ppm resolution)
Carbon monoxide and hydrogen sulfide (COSH): CO: 0-500 ppm (1 ppm resolution), H2S: 0-100 ppm (0.1 ppm resolution)

Default Alarm Levels

Low Alarm: 35 ppm
High Alarm: 200 ppm
STEL — 15 minute — Short Term Exposure Limit: 50 ppm 
TWA  — 8 hour time weighted average: 35 ppm 

Questions about the detection of CO?


Special Applications and Considerations

  • Workers using fuel-burning tools are even more at risk to CO poisoning when they are using these tools in a confined space.  
  • The most common toxic gases found in confined spaces are carbon monoxide (CO) and hydrogen sulfide (H2S). 
  • Carbon monoxide can be generated by hot work that involves combustion, operating internal combustion engines within a confined space, or introduced into the space by improper use of ventilation equipment. 
  • The gas can collect in CSEs and cause workers harm without them knowing due to its lack of distinguishable characteristics.
  • When an incident involving carbon monoxide occurs, would-be rescuers are also commonly at risk. 
  • Confined space exposures to CO are most prevalent during winter, when indoor areas are sealed to prevent cold temperatures and heating equipment is used. 
  • Workers should avoid using gas-powered equipment in confined spaces, or ensure that CO sensors and proper ventilation are in place if gas-powered equipment must be used. 

Health Risks and Handling of CO

0 - 34 ppm
Typical background concentrations, unlikely to cause harm
35 - 69 ppm
Physical symptoms including nausea, headache, dizziness, & fatigue will begin after 6-8 hours of exposure
70 - 149 ppm
1-4 hour alarm, physical symptoms will likely be present after 2-3 hours of exposure
150 - 399 ppm
Physical symptoms will be present after 1-2 hours of exposure, after 3 hours it is life-threatening
400 - 799 ppm
Physical symptoms as soon as 45 minutes of exposure. Will be knocked unconscious after 2 hours, often fatal after 2-3 hours
800 - 1599 ppm
Physical symptoms after only 20 minutes of exposure. Will likely be fatal after 60 minutes
1600 - 6399 ppm
Physical symptoms in 5 - 10 minutes of exposure. Death is probable after just 25-30 minutes
6400 - 12799 ppm
1-2 minutes of exposure will cause physical symptoms. Death after 10 - 15 minutes
12800 ppm +
Almost certainly fatal within 1-3 minutes of exposure
Carbon Monoxide First Aid Icon
  • Urgent treatment required  
  • Call 911, poison control/doctor, or go to the hospital  
  • If you are helping the victim, use a gas detector to see if CO hazard is still present and wear SCBA gear if it is prior to a recue attempt. 
  • Move the victim to fresh air (see above)
  • If breathing is difficult for victim, trained personnel can administer oxygen
  • If the victim has stopped breathing, trained personnel should administer CPR or AED
Carbon Monoxide (CO) gas dangers
  • Evacuate the area immediately and isolate the area to protect other workers
  • Eliminate heat and ignition sources such as sparks, open flames, hot surfaces and static discharge. 
  • Wear SCBA equipment to stop or reduce leak or source. 
  • Knock down gas with fine water spray. 
  • Immediately report leaks, spills or failures of the safety equipment (e.g. ventilation system)


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