Measurements · Gases & VOCs
Carbon Monoxide (CO)
Also known as CO gas
Carbon monoxide: a toxic, odorless combustion gas that binds to hemoglobin. An ambient and occupational hazard.
What it is
What is carbon monoxide (CO)?
Carbon monoxide is a colorless, odorless, tasteless gas produced by incomplete combustion of carbon-containing fuels. Wherever something burns without enough oxygen (vehicle engines, gas appliances, furnaces, generators, fires, industrial processes), CO is generated. Its lack of any sensory warning is what makes it so dangerous: people cannot detect it until symptoms appear. Indoors it accumulates from faulty or unvented appliances and from vehicles running in attached garages; outdoors it is largely a traffic and combustion marker.
CO spans two monitoring worlds: an ambient criteria pollutant at low concentrations and an acute life-safety hazard at high ones.
Health and operational effects
Carbon monoxide binds to hemoglobin far more readily than oxygen, starving the body's tissues of oxygen. Low-level exposure causes headache, dizziness, nausea, and confusion (often mistaken for flu), while high concentrations cause loss of consciousness and death within minutes. It is a leading cause of fatal poisoning worldwide. Because the effect is dose-and-time dependent, both the concentration and how long someone is exposed matter.
For confined-space work, industrial settings, parking garages, and buildings with combustion appliances, CO monitoring is a core life-safety and compliance requirement, not merely an air-quality nicety.
Limits
Carbon Monoxide (CO) Limit Values
The published values, by averaging period; each links to the standard that sets it.
24-hour
8-hour
8-hour TWA (PEL)
1-hour
Common alarm setpoint
A01 Air Quality
One-time test
- OSHA confined space 35 ppm: not set by 1910.146, which defers to the OSHA PEL (50 ppm, 8-hour TWA); 35 ppm is the NIOSH REL and a common gas-detector alarm setpoint
- LEED v5 9 ppm: and no more than 2 ppm above outdoor
CO is reported in ppm. Its limits reflect the dual nature of the hazard: ambient standards such as the US EPA NAAQS use 1-hour and 8-hour averages for community health, while occupational and confined-space limits (OSHA PEL, ACGIH TLV, confined-space thresholds) protect workers over a shift and trigger alarms for acute risk. Because CO poisoning depends on cumulative dose, an 8-hour average within limits can still hide a dangerous short peak, so life-safety monitors alarm on instantaneous concentration as well as time-weighted exposure.
How it is measured
How Carbon Monoxide (CO) Is Measured
The workhorse for both safety and ambient monitoring is the electrochemical sensor, which generates a current proportional to CO concentration; it is selective, real-time, and well suited to personal, fixed, and portable instruments. Regulatory ambient networks may use non-dispersive infrared or gas-filter correlation analyzers for low concentrations. For life-safety applications the important properties are fast response and reliable alarming; for ambient air quality, sensitivity at low ppm and stability matter more.
Aethair PRO cartridges3
A pre-calibrated cartridge in one of Aethair PRO's sockets: Aethair CO (electrochemical), Aethair MultiGas+, and Aethair CO (ppb, four-electrode).
An instrument on Thiamis4
A third-party instrument connected to a Thiamis gateway, reporting into the same Environet account.
Placing CO sensors
For life-safety, place CO monitors where people work or sleep and near (but not directly on) potential sources such as appliances and vehicle bays, following the relevant standard for mounting height. In confined-space entry, CO is one of the atmospheric gases tested continuously in the breathing zone before and during entry. For ambient monitoring, roadside and urban sites at breathing height capture traffic-related CO.
Every device and option that measures Carbon Monoxide (CO) 6
| Device / option | Type | Base platform | Measures |
|---|---|---|---|
 Aethair CO (electrochemical) 0d01 0d35 | Gas sensor cartridge | Aethair PRO | |
 Aethair MultiGas+ 0d16 | Gas sensor cartridge | Aethair PRO | |
 TSI · GM460 | Gas Detectors | Thiamis | |
 RKI Instruments · GX6000 | Gas Detectors | Thiamis | |
 RAE · MultiRAE Lite, MultiRAE, MultiRAE Pro… | Gas Detectors | Thiamis | |
 Trolex · Sentro X (TX6310) | Gas Detectors | Thiamis |
Where it is monitored
Solutions That Monitor Carbon Monoxide (CO)
Each one links to the solution page showing what that industry measures it for.
Occupational Safety & Industrial Hygiene
Core parameterCarbon monoxide is a core industrial-hygiene and confined-space hazard because it is colorless, odorless, and binds to hemoglobin far more readily than oxygen, incapacitating workers before they sense it.
Outdoor Monitoring
Core parameterIn ambient air, carbon monoxide is a low-concentration traffic and combustion marker and one of the six criteria pollutants, distinct from the acute life-safety CO hazard of confined spaces.
Wildfire Air Monitoring
Core parameterClose to an active fire line, carbon monoxide from combustion rises alongside smoke particulate and poses an acute hazard to firefighters and nearby residents.
Cabin Air Quality
Often addedRespirable dust, gases, and blast monitoring
Healthcare Air Monitoring
Often addedClinical air quality, pressurization, and patient safety
Indoor Air Quality
Often addedOffices, schools, homes, and public buildings
Oil & Gas / Petrochemical
Often addedFence-line VOC, H₂S, and methane leak detection
School Air Monitoring
Often addedClassroom CO₂, particulates, and campus IAQ
Article Library
Reading on Carbon Monoxide (CO)
OSHA Air Quality Standards 2026: PELs & 29 CFR 1910.1000
OSHA air quality standards for indoor and outdoor work: permissible exposure limits, Table Z-1, 29 CFR 1910.1000, and the heat and wildfire smoke triggers.
IAQ Monitoring Parameters: PM2.5, CO2, VOCs & Formaldehyde
Indoor air quality monitoring parameters explained: PM2.5, CO2, VOCs, and formaldehyde, plus the sensors, thresholds, and OSHA, ASHRAE 62.1, and WELL limits.
Wildfire Smoke Air Quality Monitoring: Detection & Response
Wildfire smoke monitoring for EHS and public health teams: real-time PM2.5, the AQI 151 respirator trigger, and how to alert workers before smoke arrives.
Ambient Air Quality Monitoring: What Nonattainment Changes
Ambient air quality monitoring explained: how PM2.5 attainment is measured, what a nonattainment designation triggers, and what site-level monitoring adds.
How Building Certifications Use Air Quality Monitoring
How WELL and LEED v5 incorporate air quality monitoring, why both frameworks are moving toward continuous performance, and what that means for building teams.
Fenceline Air Quality Monitoring: Equipment and Approaches
Compare fenceline air quality monitoring approaches: standalone stations, pelican-case kits, and connected 4G sensor networks.
Related
More in Gases & VOCs
Questions
Carbon Monoxide (CO) FAQ
Why is carbon monoxide called the silent killer?
Because it is colorless, odorless, and tasteless, people cannot sense CO before it harms them, and its early symptoms (headache, dizziness, nausea) mimic flu. It binds to hemoglobin and starves tissues of oxygen, and at high concentrations it can cause unconsciousness and death within minutes, which is why continuous detection is essential.
What CO level is dangerous?
Effects depend on both concentration and exposure time. Occupational limits such as the OSHA PEL and ACGIH TLV set shift-average thresholds, confined-space rules set entry limits, and life-safety alarms respond to acute concentrations. The limit table on this page lists the applicable ambient and occupational values with their averaging periods.
Is CO an air pollutant or a safety hazard?
Both. At the low concentrations found in ambient air it is one of the six criteria pollutants tracked for community health; at the high concentrations possible around faulty appliances, engines, and confined spaces it is an acute, potentially fatal safety hazard. The monitoring approach differs accordingly.
How do I monitor carbon monoxide?
The Aethair PRO measures CO with a gas sensor cartridge; for confined-space and industrial safety, pair a Thiamis gateway with a multi-gas monitor. Use the configurator to combine CO with O₂, LEL, and H₂S for confined-space monitoring, or with the criteria pollutants for ambient monitoring.
Monitor Carbon Monoxide (CO) on the Record
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