Measurements · Gases & VOCs
Hydrogen Sulfide (H₂S)
Also known as hydrogen sulphide, sewer gas
Hydrogen sulfide: a toxic, corrosive gas with a rotten-egg odor, common in wastewater and oil & gas.
What it is
What is hydrogen sulfide (H₂S)?
Hydrogen sulfide is a colorless, highly toxic, and flammable gas with the characteristic smell of rotten eggs at low concentrations. It is produced wherever organic matter decays without oxygen and wherever "sour" hydrocarbons are handled: sewers and wastewater plants, oil and gas operations, landfills, tanneries, pulp mills, and manure pits and other agricultural spaces. Its most treacherous property is that at higher concentrations it rapidly deadens the sense of smell, so the very warning people instinctively rely on disappears exactly when the danger is greatest.
That combination (acutely toxic, potentially explosive, and able to dull the sense of smell) makes H₂S one of the most closely monitored gases in industrial and confined-space safety.
Health and operational effects
At low concentrations H₂S irritates the eyes and respiratory tract; as levels rise it causes headache, dizziness, and nausea, and at high concentrations it can cause near-instant collapse and death by disrupting cellular respiration. Because olfactory fatigue removes the smell warning, workers cannot gauge exposure by nose: a rising concentration can feel like the smell is fading. It is a leading cause of workplace gas fatalities, frequently claiming would-be rescuers as well.
For oil and gas, water and wastewater, agriculture, and any confined-space work, continuous H₂S detection is a core life-safety requirement backed by strict exposure and confined-space limits.
Limits
Hydrogen Sulfide (H₂S) Limit Values
The published values, by averaging period; each links to the standard that sets it.
8-hour TWA
8-hour TWA (PEL)
1-hour, notification threshold
Common alarm setpoint
- OSHA construction 10 ppm: general industry sets a 20 ppm ceiling instead
- NIOSH REL 10 ppm: 10-minute
- OSHA confined space 10 ppm: not set by 1910.146, which defers to the OSHA limit (a 20 ppm ceiling); 10 ppm is a common gas-detector alarm setpoint
H₂S is reported in ppm. Occupational and confined-space frameworks (OSHA PEL, ACGIH TLV, confined-space limits) set time-weighted-average, short-term, and ceiling values, and life-safety monitors alarm on instantaneous concentration because H₂S harm can be acute. Because the gas pools and stratifies, a single reading at head height can miss a lethal concentration at the bottom of a space, which is why depth-profiled testing and continuous monitoring, not a single spot check, are the rule.
How it is measured
How Hydrogen Sulfide (H₂S) Is Measured
The standard technology is the electrochemical sensor, which produces a current proportional to H₂S concentration and gives fast, selective, real-time readings suited to personal, portable, and fixed monitors. H₂S is one of the gases in the standard confined-space multi-gas set. For fence-line and area monitoring around facilities, fixed electrochemical or metal-oxide sensors track ambient levels, often with wind data to locate sources. Sensors require regular bump-testing and calibration, and have a finite life, so maintenance discipline is essential to trust the reading.
Aethair PRO cartridge1
A pre-calibrated cartridge in one of Aethair PRO's sockets: Aethair H₂S.
An instrument on Thiamis5
A third-party instrument connected to a Thiamis gateway, reporting into the same Environet account.
Placing H₂S monitoring
For personal safety, the monitor sits in the worker's breathing zone with alarms set to the exposure and short-term limits. In confined-space entry, H₂S is tested at multiple depths before entry (it is denser than air and pools in low points such as pits, sumps, and tank bottoms) and monitored continuously while people are inside. For facility fence-line and odor work, fixed monitors are placed at the boundary and downwind of likely sources, with wind speed and direction to attribute detections.
Every device and option that measures Hydrogen Sulfide (H₂S) 6
| Device / option | Type | Base platform | Measures |
|---|---|---|---|
 Aethair H₂S 0d65 | Gas sensor cartridge | Aethair PRO | Hydrogen Sulfide (H₂S)Dew PointHeat IndexRelative HumidityIlluminance / LightParticle Count (by size)PM1 |
 TSI · GM460 | Gas Detectors | Thiamis | |
 RKI Instruments · GX6000 | Gas Detectors | Thiamis | |
 AMETEK Brookfield · Jerome-631X, Jerome-431X | Specialty Air Analyzers | Thiamis | Hydrogen Sulfide (H₂S)Mercury (Hg) |
 RAE · MultiRAE Lite, MultiRAE, MultiRAE Pro… | Gas Detectors | Thiamis | |
 Trolex · Sentro X (TX6310) | Gas Detectors | Thiamis |
Where it is monitored
Solutions That Monitor Hydrogen Sulfide (H₂S)
Each one links to the solution page showing what that industry measures it for.
Landfill, Biogas & Odor
Core parameterLandfills and anaerobic digesters generate hydrogen sulfide as organic matter decays, making H₂S both a toxic-gas safety hazard and the primary driver of odor complaints around these sites.
Occupational Safety & Industrial Hygiene
Core parameterHydrogen sulfide is among the most dangerous gases in industrial and confined-space work: toxic at low concentrations, and treacherous because it deadens the sense of smell so workers cannot rely on its characteristic odor as a warning.
Oil & Gas / Petrochemical
Core parameterHydrogen sulfide is the defining acute hazard of sour oil and gas operations, toxic at low concentrations and treacherous because it quickly deadens the sense of smell.
Article Library
Reading on Hydrogen Sulfide (H₂S)
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.
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.
Fenceline Air Quality Monitoring: Equipment and Approaches
Compare fenceline air quality monitoring approaches: standalone stations, pelican-case kits, and connected 4G sensor networks.
Data Center Air Quality Monitoring, Inside and Out
Data center air quality monitoring for operators: ISO 14644 cleanliness in the white space, construction dust, generator emissions, and perimeter noise.
How to Choose an Air Quality Monitor: PRO, IAQ, or Thiamis
Compare Aethair PRO, IAQ, and Thiamis to match the right device to your site, from commercial interiors to industrial and fenceline monitoring.
Industrial Perimeter Air Quality Monitoring: Action Levels
What industrial perimeter monitoring requires at fenceline and construction sites: DER-10 CAMP action levels, EPA fenceline rules, and continuous records.
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Questions
Hydrogen Sulfide (H₂S) FAQ
Why can't I rely on the smell of H₂S?
Hydrogen sulfide rapidly deadens the sense of smell at higher concentrations, so the rotten-egg odor fades exactly as the danger increases. Workers who trust their nose can believe the hazard is passing when it is actually worsening, which is why continuous instrumental monitoring, not smell, is the safeguard.
Where does hydrogen sulfide come from?
From the anaerobic decay of organic matter and from sour hydrocarbons: sewers and wastewater plants, oil and gas operations, landfills, manure pits, tanneries, and pulp mills. Because it is denser than air, it accumulates in low, enclosed spaces such as pits, sumps, and tank bottoms.
What H₂S level is dangerous?
Effects range from irritation at low ppm to rapid collapse and death at high concentrations, and harm depends on both level and duration. Occupational limits (OSHA PEL, ACGIH TLV) and confined-space thresholds define the values; life-safety monitors alarm on acute concentrations. The limit table on this page lists the applicable values.
How do I monitor for hydrogen sulfide?
For worker safety, use a multi-gas monitor covering H₂S alongside oxygen, LEL, and CO in the breathing zone; for facility odor and fence-line work, pair a Thiamis gateway with fixed H₂S sensing and wind data. Use the configurator to build a confined-space or fence-line monitoring configuration.
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