--- title: "ACGIH TLV Limits: CO, H₂S, SO₂, NO₂ | Aethair" description: "ACGIH Threshold Limit Values (TLV) limit values for Carbon Monoxide, Hydrogen Sulfide, Sulfur Dioxide, Nitrogen Dioxide, and more: every value and…" url: https://aethair.io/standards/acgih_tlv/ --- Compliance · ACGIH # ACGIH Threshold Limit Values (TLV) Occupational: recommended guideline, 8-hour TWA unless noted Threshold Limit Values (TLVs) are occupational exposure guidelines published each year by the American Conference of Governmental Industrial Hygienists (ACGIH). They express the airborne concentration of a substance to which nearly all workers may be repeatedly exposed, day after day, without adverse health effects. Like the enforceable legal limits, TLVs come in three forms: an **8-hour time-weighted average (TLV-TWA)**, a 15-minute **short-term exposure limit (TLV-STEL)**, and a **ceiling (TLV-C)** that should not be exceeded at any time. Some substances also carry a "skin" notation warning that dermal absorption contributes to the dose. [Schedule a call](https://calendly.com/d/ctdd-mkr-v9v/aethair-demo-website) [Configure ACGIH TLV Monitoring](https://aethair.io/build/?params=co,h2s,so2,no2,nh3,o3,co2) At a glance **ACGIH** Occupational: recommended guideline, 8-hour TWA unless noted 7 parameters · 9 limit values [Carbon Monoxide (CO)](https://aethair.io/parameters/co/) [Hydrogen Sulfide (H₂S)](https://aethair.io/parameters/h2s/) [Sulfur Dioxide (SO₂)](https://aethair.io/parameters/so2/) [Nitrogen Dioxide (NO₂)](https://aethair.io/parameters/no2/) [Ammonia (NH₃)](https://aethair.io/parameters/nh3/) [Ozone (O₃)](https://aethair.io/parameters/o3/) [Carbon Dioxide (CO₂)](https://aethair.io/parameters/co2/) 2 devices measure them all - **Aethair PRO** Aethair O₃+NO₂ · Aethair CO (electrochemical) · Custom MultiSense - **Thiamis** RAE Gas Detectors [Official text from ACGIH](https://www.acgih.org/science/tlv-bei-guidelines/) The standard ## What ACGIH Threshold Limit Values Are TLVs are **not regulations**. The ACGIH is a scientific body, and its values are recommendations, reviewed and updated far more frequently than statutory limits. Because they track current toxicology, TLVs are often stricter than the corresponding legal limit and are widely treated as best practice. The specific values are given in the limit table on this page. Limit values ## ACGIH TLV Limit Values Every value ACGIH publishes for the 7 parameters below, with its averaging period, as the standard states it. [**Carbon Monoxide (CO)** Gases & VOCs](https://aethair.io/parameters/co/) **25 ppm** *8-hour TWA* [**Hydrogen Sulfide (H₂S)** Gases & VOCs](https://aethair.io/parameters/h2s/) **1 ppm** *8-hour TWA* **5 ppm** *STEL* [**Sulfur Dioxide (SO₂)** Gases & VOCs](https://aethair.io/parameters/so2/) **0.25 ppm** *STEL* [**Nitrogen Dioxide (NO₂)** Gases & VOCs](https://aethair.io/parameters/no2/) **0.2 ppm** *8-hour TWA* [**Ammonia (NH₃)** Gases & VOCs](https://aethair.io/parameters/nh3/) **25 ppm** *8-hour TWA* **35 ppm** *STEL* [**Ozone (O₃)** Gases & VOCs](https://aethair.io/parameters/o3/) **0.1 ppm** *8-hour TWA* light work; lower for heavier work [**Carbon Dioxide (CO₂)** Gases & VOCs](https://aethair.io/parameters/co2/) **5000 ppm** *8-hour TWA* Who it applies to ## Who Uses It Industrial hygienists, occupational-health professionals, and safety managers use TLVs as the benchmark for protecting workers, particularly where the enforceable limit is dated or absent. Many organizations adopt TLVs voluntarily as an internal exposure ceiling, and regulators, insurers, and courts in various jurisdictions reference them as the recognized state of the science. They apply across the same industries as legal limits (manufacturing, chemicals, construction, mining, laboratories, and beyond), wherever airborne hazards are managed to a health-based rather than merely a legal standard. Monitoring ## How Monitoring Demonstrates Compliance Because TLVs share the TWA, STEL, and ceiling framework of enforceable limits, they are assessed with the same measurement approach: **personal sampling in the breathing zone** over the relevant averaging period, compared against the values in the limit table on this page. Real-time gas monitors capture the concentration profile of vapors and gases through a shift, while dust and mist exposures are measured with size-selective samplers or direct-reading aerosol monitors. As with any occupational panel, no single device covers every substance, so instruments are combined to match the hazards present, and area monitors supplement personal sampling to locate sources. [Customize this configuration](https://aethair.io/build/?params=co,h2s,so2,no2,nh3,o3,co2) ### Who measures each parameter | Parameter | Aethair PRO | Aethair IAQ | External | | - | - | - | - | | [Carbon Monoxide (CO)](https://aethair.io/parameters/co/) | CO (electrochemical), MultiGas+ +1 cartridges | — | [3 instruments](https://aethair.io/parameters/co/) via Thiamis | | [Hydrogen Sulfide (H₂S)](https://aethair.io/parameters/h2s/) | H₂S cartridge | — | [4 instruments](https://aethair.io/parameters/h2s/) via Thiamis | | [Sulfur Dioxide (SO₂)](https://aethair.io/parameters/so2/) | MultiSense, SO₂ cartridges | — | [1 instrument](https://aethair.io/parameters/so2/) via Thiamis | | [Nitrogen Dioxide (NO₂)](https://aethair.io/parameters/no2/) | NO₂, MultiSense +1 cartridges | — | [1 instrument](https://aethair.io/parameters/no2/) via Thiamis | | [Ammonia (NH₃)](https://aethair.io/parameters/nh3/) | — | — | [1 instrument](https://aethair.io/parameters/nh3/) via Thiamis | | [Ozone (O₃)](https://aethair.io/parameters/o3/) | O₃+NO₂ cartridge | — | [1 instrument](https://aethair.io/parameters/o3/) via Thiamis | | [Carbon Dioxide (CO₂)](https://aethair.io/parameters/co2/) | CO₂ (dual NDIR), CO₂ (self-calibrating NDIR) cartridges | Built in | [2 instruments](https://aethair.io/parameters/co2/) via Thiamis | Devices ## Devices That Cover ACGIH TLV How much of this standard one Aethair monitor covers, followed by the third-party instruments in the sensor catalog that measure its parameters. Each connects to Environet through a Thiamis gateway, which adds whatever the monitor leaves out. Aethair monitors [**Aethair PRO** Built in + Aethair O₃+NO₂, Aethair CO (electrochemical), Custom MultiSense (H₂S, SO₂, CO₂) 6 of 7: CO, H₂S, SO₂, NO₂, O₃, CO₂](https://aethair.io/products/pro/) Covers part of it (combine on one Thiamis) [**RAE** Gas Detectors 6 of 7: CO, CO₂, H₂S, NH₃, NO₂, SO₂](https://aethair.io/sensors/rae-gas-detectors/) [**TSI GM460** Gas Detectors 2 of 7: CO, H₂S](https://aethair.io/sensors/tsi-gas-detectors/) [**RKI Instruments GX6000** Gas Detectors 2 of 7: CO, H₂S](https://aethair.io/sensors/rki-instruments-gas-detectors/) [**AMETEK Brookfield Jerome** Specialty Air Analyzers 1 of 7: H₂S](https://aethair.io/sensors/ametek-brookfield-specialty-air-analyzers/) [**Particles Plus** Particulate & Dust Monitors 1 of 7: CO₂](https://aethair.io/sensors/particles-plus-particulate-dust-monitors/) [**2B Technologies POM** Specialty Air Analyzers 1 of 7: O₃](https://aethair.io/sensors/2b-technologies-specialty-air-analyzers/) Solutions ## Solutions Judged Against ACGIH TLV ### [Occupational Safety & Industrial Hygiene](https://aethair.io/solutions/occupational-safety/) Worker exposure, confined space, and heat stress ### [Oil & Gas / Petrochemical](https://aethair.io/solutions/oil-gas/) Fence-line VOC, H₂S, and methane leak detection [All solutions](https://aethair.io/solutions/) Article Library ## Articles on ACGIH TLV ### [Ozone Exposure Limits and Monitoring: OSHA and NAAQS](https://aethair.io/resources/ozone-monitoring-exposure-limits/) OSHA's ozone PEL is 0.1 ppm as an 8-hour TWA. How NIOSH, ACGIH, and the 70 ppb NAAQS compare, and why ozone needs short-interval monitoring. ### [How to Choose an Air Quality Monitor: PRO, IAQ, or Thiamis](https://aethair.io/resources/choosing-aethair-monitoring-device/) Compare Aethair PRO, IAQ, and Thiamis to match the right device to your site, from commercial interiors to industrial and fenceline monitoring. ### [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. [All articles](https://aethair.io/resources/) Questions ## ACGIH TLV FAQ Are TLVs legally enforceable? No. TLVs are health-based guidelines from the ACGIH, a scientific association rather than a government agency. They carry no direct legal force, but because they are current and health-based they are widely adopted as best practice and often referenced where a jurisdiction's own limits are outdated. Why are TLVs often stricter than legal limits? The ACGIH reviews and updates TLVs annually as new toxicology emerges, whereas statutory limits such as OSHA's PELs change slowly and many remain as first set decades ago. As a result the health-based TLV frequently sits below the enforceable limit for the same substance. What do the "skin" and "sensitizer" notations mean? A skin notation warns that a substance can be absorbed through the skin or eyes in amounts that add meaningfully to the inhaled dose, so air monitoring alone may understate exposure. A sensitizer notation flags substances that can provoke allergic respiratory or skin responses at low concentrations. How do I monitor against a TLV? Use the same breathing-zone approach as for any exposure limit: real-time gas monitors for vapors and size-selective samplers for dusts, matched to the substances present. Use the configurator to build a personal or area monitoring configuration and compare results against the values listed on this page.