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.
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.
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), formaldehyde (1926.1148), and benzene (1926.1128) 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.
Recommended
best match-
Industrial monitor for indoor and outdoor sites. Built-in sensors cover the essentials, and hot-swappable gas sensor cartridges and a differential-pressure option add more.
Gas 1
Aethair O₃+NO₂
Nitrogen Dioxide (NO₂)Ozone (O₃)Four-electrode electrochemical sensing measures oxidizing gases (ozone plus nitrogen dioxide) and reports one…
Gas 2
Aethair CO (electrochemical)
Carbon Monoxide (CO)An amperometric electrochemical CO cell with a solid, non-aqueous electrolyte (the long-life, low-power…
Also fits: Aethair MultiGas+, Aethair CO (ppb, four-electrode)
MultiSense
Custom MultiSense built to order
Carbon Dioxide (CO₂)Hydrogen Sulfide (H₂S)Sulfur Dioxide (SO₂)Built to order for the MultiSense socket with the Aethair CO₂ (dual NDIR) cartridge's sensor (0-5000 ppm, 1 ppm resolution), the Aethair H₂S cartridge's sensor (0-50 ppm, 5 ppb resolution), and the Aethair SO₂ cartridge's sensor (0-100 ppm, 5 ppb resolution).
Expansion
Free: differential pressure
Also measures 13 more
Dew PointHeat IndexRelative HumidityIlluminance / LightParticle Count (by size)PM1PM10PM2.5Total PM / Mass Conc.Barometric PressureEquivalent Continuous Level (Leq)Sound Pressure Level (SPL)Air Temperature -
Thiamis connects 2 instruments
A gateway that connects the third-party instruments you choose to the Aethair Platform.
-
Chlorine (Cl₂)Ammonia (NH₃)Nitric Oxide (NO)RAE Systems (Honeywell) portable gas detectors.
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AMETEK Brookfield Specialty Air Analyzers
Mercury (Hg)Jerome portable single-gas analyzers by AMETEK Brookfield (formerly AMETEK Arizona Instrument).
Also measures 4 more
Methane (CH₄)Combustible (LEL)Oxygen (O₂)VOC (Total) -
Not coveredHydrogen Chloride (HCl)Hydrogen Fluoride (HF)no supported configuration measures these yet
Who measures each parameter
| Parameter | Aethair PRO |  Aethair IAQ | External |
|---|---|---|---|
| Carbon Monoxide (CO) | CO (electrochemical), MultiGas+ +1 cartridges | — | 3 instruments via Thiamis |
| Carbon Dioxide (CO₂) | CO₂ (dual NDIR), CO₂ (self-calibrating NDIR) cartridges | Built in | 2 instruments via Thiamis |
| Hydrogen Sulfide (H₂S) | H₂S cartridge | — | 4 instruments via Thiamis |
| Sulfur Dioxide (SO₂) | MultiSense, SO₂ cartridges | — | 1 instrument via Thiamis |
| Nitric Oxide (NO) | NO cartridge | — | 1 instrument via Thiamis |
| Nitrogen Dioxide (NO₂) | NO₂, MultiSense +1 cartridges | — | 1 instrument via Thiamis |
| Ozone (O₃) | O₃+NO₂ cartridge | — | 1 instrument via Thiamis |
| Ammonia (NH₃) | — | — | 1 instrument via Thiamis |
| Chlorine (Cl₂) | — | — | 1 instrument via Thiamis |
| Mercury (Hg) | — | — | 1 instrument via Thiamis |
| Hydrogen Chloride (HCl) | HCl cartridge | — | — |
| Hydrogen Fluoride (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
Covers part of it (combine on one Thiamis)
RAE Gas Detectors8 of 12: Cl₂, CO, CO₂, H₂S, NH₃, NO, NO₂, SO₂
TSI GM460 Gas Detectors2 of 12: CO, H₂S
RKI Instruments GX6000 Gas Detectors2 of 12: CO, H₂SAMETEK Brookfield Jerome Specialty Air Analyzers2 of 12: H₂S, Mercury
Particles Plus Particulate & Dust Monitors1 of 12: CO₂
2B Technologies POM Specialty Air Analyzers1 of 12: O₃Solutions
Solutions Judged Against OSHA construction
Perimeter Monitoring
Site boundary dust, silica, and noise compliance
Article Library
Articles on OSHA construction
Ozone Exposure Limits and Monitoring: OSHA and NAAQS
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
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.
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.
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