Measurements · Gases & VOCs
Hydrogen Chloride (HCl)
Also known as hydrochloric acid gas
Hydrogen chloride (HCl), a corrosive acid gas from industrial processes and incineration, and a toxic respiratory irritant.
What it is
What is hydrogen chloride (HCl)?
Hydrogen chloride is a colorless gas with a sharp, irritating odor that fumes visibly on contact with moist air, forming a mist of hydrochloric acid. It is a corrosive acid gas produced by burning chlorine-containing materials (waste incineration and coal combustion are major sources) and by many industrial operations, including metal pickling, chemical manufacturing, and semiconductor processing. It is also released whenever hydrochloric acid is used, heated, or spilled. Because it is so soluble, hydrogen chloride dissolves readily into the moisture of the eyes and airways to form acid, which is what makes even brief exposure sharply irritating.
As an acid gas it is monitored both for worker safety and, in incineration, as a regulated emission that scrubbers are designed to remove.
Health and operational effects
Hydrogen chloride is a corrosive irritant to the eyes, skin, and respiratory tract. Low concentrations sting the eyes and throat, while higher ones cause airway burns and, in severe exposure, pulmonary edema. The same corrosivity attacks equipment and structures, so leaks damage plant as well as people. Its solubility means it acts quickly on moist tissue, giving the acute irritation that acts as a warning but also the immediate hazard. In incineration and combustion, uncontrolled HCl in the flue gas is an environmental as well as an occupational concern.
For incinerators, metal-treatment lines, chemical plants, and semiconductor fabs, hydrogen chloride is a combined safety and emissions parameter.
Limits
Hydrogen Chloride (HCl) Limit Values
The published values, by averaging period; each links to the standard that sets it.
8-hour TWA (PEL)
Hydrogen chloride is reported in ppm for ambient and workplace air and in mg/m³ for stack emissions. Occupational exposure is judged against limits such as the OSHA PEL, often a ceiling value, and the ACGIH TLV, while incinerators are held to acid-gas emission limits at the stack; the applicable values appear in the limit table on this page. Because HCl is acutely irritating, a ceiling or short-term value is often the governing figure rather than a long average.
How it is measured
How Hydrogen Chloride (HCl) Is Measured
Electrochemical sensors provide ppm-level detection and alarming around processes and acid handling, producing a current proportional to concentration. For stack and emissions monitoring, Fourier-transform infrared (FTIR) and tunable-laser analyzers measure HCl continuously and specifically among other combustion gases, and ion-selective or colorimetric methods give time-averaged results. Hydrogen chloride is extremely soluble and adsorbs onto surfaces, so heated, inert, and short sample lines are essential to avoid losing the gas before it reaches the detector. It is measured with the Aethair HCl cartridge in Aethair PRO, or with an external professional analyzer connected through Thiamis.
Aethair PRO cartridge1
A pre-calibrated cartridge in one of Aethair PRO's sockets: Aethair HCl.
Placing hydrogen chloride monitoring
For worker protection, place detectors near acid-handling stations, pickling baths, and process points where a release is credible, in the breathing zone. For emissions, monitor in the stack or after the scrubber to demonstrate acid-gas removal. Because HCl is slightly denser than air and adsorbs readily onto surfaces, both the mounting position and the design of the sample path (kept short, heated, and inert) strongly affect the reading.
Every device and option that measures Hydrogen Chloride (HCl) 1
| Device / option | Type | Base platform | Measures |
|---|---|---|---|
 Aethair HCl 0d75 | Gas sensor cartridge | Aethair PRO | Hydrogen Chloride (HCl)Dew PointHeat IndexRelative HumidityIlluminance / LightParticle Count (by size)PM1 |
Where it is monitored
Solutions That Monitor Hydrogen Chloride (HCl)
Each one links to the solution page showing what that industry measures it for.
Occupational Safety & Industrial Hygiene
Often addedWorker exposure, confined space, and heat stress
Article Library
Reading on Hydrogen Chloride (HCl)
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.
Related
More in Gases & VOCs
Questions
Hydrogen Chloride (HCl) FAQ
Why does hydrogen chloride fume in air?
Hydrogen chloride is extremely soluble in water, so on contact with the moisture in humid air it condenses into a fine mist of hydrochloric acid droplets: the visible white fuming. The same solubility makes it dissolve instantly into the moist surfaces of the eyes and airways, which is why it is so immediately irritating. The fuming is a visual sign of an acid-gas release.
Where is hydrogen chloride a hazard?
It is generated by burning chlorine-containing materials, so waste incineration and coal combustion are major sources, and it is handled directly in metal pickling, chemical manufacturing, and semiconductor processing. Any use, heating, or spillage of hydrochloric acid can release it. These are the settings where HCl detection and emissions monitoring are applied.
Why is hydrogen chloride difficult to sample accurately?
Because it is so soluble and reactive, HCl readily adsorbs onto surfaces and dissolves into any moisture in the sampling system, so gas can be lost before it reaches the sensor. Accurate measurement requires short, heated, inert sample lines and careful instrument choice. This "stickiness" is a defining practical challenge with acid gases.
How do I monitor hydrogen chloride?
Aethair PRO can measure hydrogen chloride with an Aethair HCl cartridge (an electrochemical sensor for area and safety monitoring), and for stack emissions, Thiamis can connect an FTIR or tunable-laser analyzer configured with heated, inert sampling. This suits incineration, acid handling, and semiconductor work. Use the configurator to combine HCl with the other parameters your site needs.
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