--- title: "Carbon Monoxide (CO) Sensors & Limit Values | Aethair" description: "Carbon monoxide (CO) is a colorless, odorless gas from incomplete combustion. See EPA, OSHA, and NIOSH limit values and the monitors that measure CO." url: https://aethair.io/parameters/co/ --- 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. [Schedule a call](https://calendly.com/d/ctdd-mkr-v9v/aethair-demo-website) [Configure Carbon Monoxide (CO) Monitoring](https://aethair.io/build/?params=co) At a glance ppm Gases & VOCs 2 ways to measure it - **Aethair PRO** 3 cartridges - **Thiamis** 4 external instruments 10 standards set limits - [EPA EPA NAAQS](https://aethair.io/standards/epa_naaqs/) - [WHO WHO 2021](https://aethair.io/standards/who_aqg_2021/) - [OSHA OSHA PEL](https://aethair.io/resources/osha-air-quality-standards-compliance/) - [ACGIH ACGIH TLV](https://aethair.io/standards/acgih_tlv/) - [OSHA OSHA confined space](https://aethair.io/standards/confined_space/) - [WELL WELL v2](https://aethair.io/resources/well-building-standard-air-quality/) - [NIOSH NIOSH REL](https://aethair.io/standards/niosh_rel/) - [OSHA OSHA construction](https://aethair.io/standards/osha_construction_pel/) - [CAL Cal/OSHA PEL](https://aethair.io/standards/cal_osha_pel/) - [LEED LEED v5](https://aethair.io/standards/leed_v5/) 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 [**4 mg/m³** WHO 2021](https://aethair.io/standards/who_aqg_2021/) 8-hour [**9 ppm** EPA NAAQS](https://aethair.io/standards/epa_naaqs/) 8-hour TWA [**50 ppm** OSHA PEL](https://aethair.io/resources/osha-air-quality-standards-compliance/) [**25 ppm** ACGIH TLV](https://aethair.io/standards/acgih_tlv/) [**50 ppm** OSHA construction](https://aethair.io/standards/osha_construction_pel/) 8-hour TWA (PEL) [**25 ppm** Cal/OSHA PEL](https://aethair.io/standards/cal_osha_pel/) 1-hour [**35 ppm** EPA NAAQS](https://aethair.io/standards/epa_naaqs/) Common alarm setpoint [**35 ppm** OSHA confined space](https://aethair.io/standards/confined_space/ "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") A01 Air Quality [**9 ppm** WELL v2](https://aethair.io/resources/well-building-standard-air-quality/) TWA [**35 ppm** NIOSH REL](https://aethair.io/standards/niosh_rel/) Ceiling [**200 ppm** NIOSH REL](https://aethair.io/standards/niosh_rel/) [**200 ppm** Cal/OSHA PEL](https://aethair.io/standards/cal_osha_pel/) One-time test [**9 ppm** LEED v5](https://aethair.io/standards/leed_v5/ "and no more than 2 ppm above outdoor") - **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 cartridges 3 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 Thiamis 4 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 | Carbon Monoxide (CO) [Dew Point](https://aethair.io/parameters/dew_point/) [Heat Index](https://aethair.io/parameters/heat_index/) [Relative Humidity](https://aethair.io/parameters/humidity/) [Illuminance / Light](https://aethair.io/parameters/light/) [Particle Count (by size)](https://aethair.io/parameters/particle_count/) [PM1](https://aethair.io/parameters/pm1/) | | **Aethair MultiGas+** `0d16` | Gas sensor cartridge | Aethair PRO | Carbon Monoxide (CO) [Methane (CH₄)](https://aethair.io/parameters/ch4/) [VOC (Total)](https://aethair.io/parameters/voc/) [Dew Point](https://aethair.io/parameters/dew_point/) [Heat Index](https://aethair.io/parameters/heat_index/) [Relative Humidity](https://aethair.io/parameters/humidity/) [Illuminance / Light](https://aethair.io/parameters/light/) | | [TSI](https://aethair.io/sensors/tsi-gas-detectors/) · GM460 | Gas Detectors | Thiamis | Carbon Monoxide (CO) [Analog Input (generic)](https://aethair.io/parameters/analog_input/) [Methane (CH₄)](https://aethair.io/parameters/ch4/) [Hydrogen Sulfide (H₂S)](https://aethair.io/parameters/h2s/) [Oxygen (O₂)](https://aethair.io/parameters/o2/) | | [RKI Instruments](https://aethair.io/sensors/rki-instruments-gas-detectors/) · GX6000 | Gas Detectors | Thiamis | Carbon Monoxide (CO) [Analog Input (generic)](https://aethair.io/parameters/analog_input/) [Methane (CH₄)](https://aethair.io/parameters/ch4/) [Hydrogen Sulfide (H₂S)](https://aethair.io/parameters/h2s/) [Oxygen (O₂)](https://aethair.io/parameters/o2/) | | [RAE](https://aethair.io/sensors/rae-gas-detectors/) · MultiRAE Lite, MultiRAE, MultiRAE Pro… | Gas Detectors | Thiamis | Carbon Monoxide (CO) [Methane (CH₄)](https://aethair.io/parameters/ch4/) [Chlorine (Cl₂)](https://aethair.io/parameters/cl2/) [Carbon Dioxide (CO₂)](https://aethair.io/parameters/co2/) [Hydrogen Sulfide (H₂S)](https://aethair.io/parameters/h2s/) [Combustible (LEL)](https://aethair.io/parameters/lel/) [Ammonia (NH₃)](https://aethair.io/parameters/nh3/) | | [Trolex](https://aethair.io/sensors/trolex-gas-detectors/) · Sentro X (TX6310) | Gas Detectors | Thiamis | Carbon Monoxide (CO) [Methane (CH₄)](https://aethair.io/parameters/ch4/) [Carbon Dioxide (CO₂)](https://aethair.io/parameters/co2/) [Hydrogen (H₂)](https://aethair.io/parameters/h2/) [Hydrogen Sulfide (H₂S)](https://aethair.io/parameters/h2s/) [Ammonia (NH₃)](https://aethair.io/parameters/nh3/) [Nitric Oxide (NO)](https://aethair.io/parameters/no/) | [Configure Carbon Monoxide (CO) Monitoring](https://aethair.io/build/?params=co) 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](https://aethair.io/solutions/occupational-safety/#measure-co) Core parameter Carbon 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](https://aethair.io/solutions/outdoor-monitoring/#measure-co) Core parameter In 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](https://aethair.io/solutions/wildfires/#measure-co) Core parameter Close 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](https://aethair.io/solutions/cabin-air/) Often added Respirable dust, gases, and blast monitoring ### [Healthcare Air Monitoring](https://aethair.io/solutions/healthcare/) Often added Clinical air quality, pressurization, and patient safety ### [Indoor Air Quality](https://aethair.io/solutions/iaq-monitoring/) Often added Offices, schools, homes, and public buildings ### [Oil & Gas / Petrochemical](https://aethair.io/solutions/oil-gas/) Often added Fence-line VOC, H₂S, and methane leak detection ### [School Air Monitoring](https://aethair.io/solutions/education/) Often added Classroom CO₂, particulates, and campus IAQ Article Library ## Reading on Carbon Monoxide (CO) ### [OSHA Air Quality Standards 2026: PELs & 29 CFR 1910.1000](https://aethair.io/resources/osha-air-quality-standards-compliance/) 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](https://aethair.io/resources/indoor-air-quality-monitoring-parameters/) 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](https://aethair.io/resources/wildfire-smoke-air-quality-monitoring/) 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](https://aethair.io/resources/ambient-air-quality-monitoring/) 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](https://aethair.io/resources/building-certifications-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](https://aethair.io/resources/fenceline-air-quality-monitoring/) Compare fenceline air quality monitoring approaches: standalone stations, pelican-case kits, and connected 4G sensor networks. [All articles](https://aethair.io/resources/) Related ## More in Gases & VOCs [Carbon Dioxide (CO₂)](https://aethair.io/parameters/co2/) [VOC (Total)](https://aethair.io/parameters/voc/) [Hydrogen Sulfide (H₂S)](https://aethair.io/parameters/h2s/) [Methane (CH₄)](https://aethair.io/parameters/ch4/) [Oxygen (O₂)](https://aethair.io/parameters/o2/) [Sulfur Dioxide (SO₂)](https://aethair.io/parameters/so2/) [Nitric Oxide (NO)](https://aethair.io/parameters/no/) [Nitrogen Dioxide (NO₂)](https://aethair.io/parameters/no2/) [Ammonia (NH₃)](https://aethair.io/parameters/nh3/) [Combustible (LEL)](https://aethair.io/parameters/lel/) [Chlorine (Cl₂)](https://aethair.io/parameters/cl2/) [BTEX / speciated VOC](https://aethair.io/parameters/btex/) 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.