--- title: "OSHA Construction Limits: CO, CO₂, H₂S, SO₂ | Aethair" description: "OSHA Construction Exposure Limits (29 CFR 1926.55) limit values for Carbon Monoxide, Carbon Dioxide, Hydrogen Sulfide, Sulfur Dioxide, and more: every…" url: https://aethair.io/standards/osha_construction_pel/ --- Compliance · US OSHA 1926.55 # OSHA Construction Exposure Limits (29 CFR 1926.55) Occupational: construction (USA), 8-hour TWA unless noted OSHA regulates airborne contaminants in construction under **29 CFR 1926.55**, whose Appendix A lists the permissible exposure limits for gases, vapors, fumes, and dusts on construction sites, generally as **8-hour time-weighted averages**. The values date from the 1970 ACGIH threshold limit values and differ in places from the general industry Table Z-1: **hydrogen sulfide is 10 ppm as an 8-hour TWA** in construction against a 20 ppm ceiling in general industry, **chlorine 1 ppm as a TWA** rather than a ceiling, and **mercury vapor 0.1 mg/m³ as a TWA**. Carbon monoxide is 50 ppm, nitrogen dioxide a 5 ppm ceiling, sulfur dioxide 5 ppm, and ozone 0.1 ppm, as in general industry. [Schedule a call](https://calendly.com/d/ctdd-mkr-v9v/aethair-demo-website) [Configure OSHA construction Monitoring](https://aethair.io/build/?params=co,co2,h2s,so2,no,no2,o3,nh3,cl2,hg,hcl,hf) At a glance **US OSHA 1926.55** Occupational: construction (USA), 8-hour TWA unless noted 12 parameters · 12 limit values [Carbon Monoxide (CO)](https://aethair.io/parameters/co/) [Carbon Dioxide (CO₂)](https://aethair.io/parameters/co2/) [Hydrogen Sulfide (H₂S)](https://aethair.io/parameters/h2s/) [Sulfur Dioxide (SO₂)](https://aethair.io/parameters/so2/) [Nitric Oxide (NO)](https://aethair.io/parameters/no/) [Nitrogen Dioxide (NO₂)](https://aethair.io/parameters/no2/) [Ozone (O₃)](https://aethair.io/parameters/o3/) [Ammonia (NH₃)](https://aethair.io/parameters/nh3/) [Chlorine (Cl₂)](https://aethair.io/parameters/cl2/) [Mercury (Hg)](https://aethair.io/parameters/hg/) [Hydrogen Chloride (HCl)](https://aethair.io/parameters/hcl/) [Hydrogen Fluoride (HF)](https://aethair.io/parameters/hf/) 2 devices measure them all - **Aethair PRO** Aethair O₃+NO₂ · Aethair CO (electrochemical) · Custom MultiSense - **Thiamis** RAE Gas Detectors · AMETEK Brookfield Specialty Air Analyzers [Official text from US OSHA 1926.55](https://www.osha.gov/laws-regs/regulations/standardnumber/1926/1926.55) Limit values ## OSHA construction Limit Values Every value US OSHA 1926.55 publishes for the 12 parameters below, with its averaging period, as the standard states it. [**Carbon Monoxide (CO)** Gases & VOCs](https://aethair.io/parameters/co/) **50 ppm** *8-hour TWA* [**Carbon Dioxide (CO₂)** Gases & VOCs](https://aethair.io/parameters/co2/) **5000 ppm** *8-hour TWA* [**Hydrogen Sulfide (H₂S)** Gases & VOCs](https://aethair.io/parameters/h2s/) **10 ppm** *8-hour TWA* general industry sets a 20 ppm ceiling instead [**Sulfur Dioxide (SO₂)** Gases & VOCs](https://aethair.io/parameters/so2/) **5 ppm** *8-hour TWA* [**Nitric Oxide (NO)** Gases & VOCs](https://aethair.io/parameters/no/) **25 ppm** *8-hour TWA* [**Nitrogen Dioxide (NO₂)** Gases & VOCs](https://aethair.io/parameters/no2/) **5 ppm** *Ceiling* [**Ozone (O₃)** Gases & VOCs](https://aethair.io/parameters/o3/) **0.1 ppm** *8-hour TWA* [**Ammonia (NH₃)** Gases & VOCs](https://aethair.io/parameters/nh3/) **50 ppm** *8-hour TWA* [**Chlorine (Cl₂)** Gases & VOCs](https://aethair.io/parameters/cl2/) **1 ppm** *8-hour TWA* general industry sets it as a ceiling [**Mercury (Hg)** Gases & VOCs](https://aethair.io/parameters/hg/) **0.1 mg/m³** *8-hour TWA* mercury vapor; skin [**Hydrogen Chloride (HCl)** Gases & VOCs](https://aethair.io/parameters/hcl/) **5 ppm** *Ceiling* [**Hydrogen Fluoride (HF)** Gases & VOCs](https://aethair.io/parameters/hf/) **3 ppm** *8-hour TWA* Who it applies to ## Who Must Comply Employers performing construction work: building, renovation, demolition, excavation, utilities, and road work, including the gases from welding and cutting, combustion engines and generators, and work in trenches and below-grade spaces. Silica ([1926.1153](https://aethair.io/standards/osha_silica/)), formaldehyde ([1926.1148](https://aethair.io/standards/osha_formaldehyde/)), and benzene ([1926.1128](https://aethair.io/standards/osha_benzene/)) have their own standards and follow those instead. Monitoring ## How Monitoring Demonstrates Compliance The employer must keep exposures below the limits, shown by representative exposure sampling. On a changing construction site, continuous monitoring of carbon monoxide, hydrogen sulfide, and nitrogen dioxide where engines run or gases can collect gives warning before a limit is reached; personal sampling documents each worker's exposure. [Customize this configuration](https://aethair.io/build/?params=co,co2,h2s,so2,no,no2,o3,nh3,cl2,hg,hcl,hf) ### 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 | | [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 | | [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 | | [Nitric Oxide (NO)](https://aethair.io/parameters/no/) | NO cartridge | — | [1 instrument](https://aethair.io/parameters/no/) via Thiamis | | [Nitrogen Dioxide (NO₂)](https://aethair.io/parameters/no2/) | NO₂, MultiSense +1 cartridges | — | [1 instrument](https://aethair.io/parameters/no2/) via Thiamis | | [Ozone (O₃)](https://aethair.io/parameters/o3/) | O₃+NO₂ cartridge | — | [1 instrument](https://aethair.io/parameters/o3/) via Thiamis | | [Ammonia (NH₃)](https://aethair.io/parameters/nh3/) | — | — | [1 instrument](https://aethair.io/parameters/nh3/) via Thiamis | | [Chlorine (Cl₂)](https://aethair.io/parameters/cl2/) | — | — | [1 instrument](https://aethair.io/parameters/cl2/) via Thiamis | | [Mercury (Hg)](https://aethair.io/parameters/hg/) | — | — | [1 instrument](https://aethair.io/parameters/hg/) via Thiamis | | [Hydrogen Chloride (HCl)](https://aethair.io/parameters/hcl/) | HCl cartridge | — | — | | [Hydrogen Fluoride (HF)](https://aethair.io/parameters/hf/) | HF cartridge | — | — | Devices ## Devices That Cover OSHA construction 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 (CO₂, H₂S, SO₂) 6 of 12: CO, CO₂, H₂S, SO₂, NO₂, O₃](https://aethair.io/products/pro/) Covers part of it (combine on one Thiamis) [**RAE** Gas Detectors 8 of 12: Cl₂, CO, CO₂, H₂S, NH₃, NO, NO₂, SO₂](https://aethair.io/sensors/rae-gas-detectors/) [**TSI GM460** Gas Detectors 2 of 12: CO, H₂S](https://aethair.io/sensors/tsi-gas-detectors/) [**RKI Instruments GX6000** Gas Detectors 2 of 12: CO, H₂S](https://aethair.io/sensors/rki-instruments-gas-detectors/) [**AMETEK Brookfield Jerome** Specialty Air Analyzers 2 of 12: H₂S, Mercury](https://aethair.io/sensors/ametek-brookfield-specialty-air-analyzers/) [**Particles Plus** Particulate & Dust Monitors 1 of 12: CO₂](https://aethair.io/sensors/particles-plus-particulate-dust-monitors/) [**2B Technologies POM** Specialty Air Analyzers 1 of 12: O₃](https://aethair.io/sensors/2b-technologies-specialty-air-analyzers/) Solutions ## Solutions Judged Against OSHA construction ### [Perimeter Monitoring](https://aethair.io/solutions/perimeter-monitoring/) Site boundary dust, silica, and noise compliance [All solutions](https://aethair.io/solutions/) Article Library ## Articles on OSHA construction ### [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. ### [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 ## OSHA construction FAQ What is the OSHA construction limit for hydrogen sulfide? 10 ppm as an 8-hour time-weighted average under 29 CFR 1926.55, while general industry has a 20 ppm ceiling. Where are OSHA's construction exposure limits? In Appendix A to 29 CFR 1926.55, the construction counterpart of the general industry Table Z-1. Do the construction limits cover silica? No. Respirable crystalline silica in construction falls under its own standard, 29 CFR 1926.1153.