--- title: "Mercury (Hg) Sensors, Monitors & Limit Values | Aethair" description: "Mercury (Hg) vapor is invisible, odorless, and neurotoxic. OSHA, NIOSH, and Cal/OSHA limits, CVAAS and gold-film analyzers, and monitor placement." url: https://aethair.io/parameters/hg/ --- Measurements · Gases & VOCs # Mercury (Hg) Also known as mercury vapor, mercury vapour Mercury vapor: a neurotoxic heavy-metal vapor. [Schedule a call](https://calendly.com/d/ctdd-mkr-v9v/aethair-demo-website) [Configure Mercury (Hg) Monitoring](https://aethair.io/build/?params=hg) At a glance mg/m³ Gases & VOCs 1 way to measure it - **Thiamis** 1 external instrument 4 standards set limits - [OSHA OSHA PEL](https://aethair.io/resources/osha-air-quality-standards-compliance/) - [NIOSH NIOSH REL](https://aethair.io/standards/niosh_rel/) - [OSHA OSHA construction](https://aethair.io/standards/osha_construction_pel/) - [CAL Cal/OSHA PEL](https://aethair.io/standards/cal_osha_pel/) What it is ## What is mercury vapor (Hg)? Mercury is the only metal that is liquid at room temperature, and it evaporates slowly into the air as an invisible, odorless vapor. It is this elemental mercury vapor, rather than the liquid itself, that poses the airborne monitoring challenge, because it is readily inhaled and absorbed through the lungs. Sources include chlor-alkali and other chemical plants, coal combustion, cement and metal production, waste incineration, gold mining and amalgamation, dental and laboratory work, and the breakage or spillage of mercury-containing equipment. Once released, mercury persists in the environment and bioaccumulates up the food chain, which is why it is tightly controlled under international agreement. Its combination of invisibility, lack of odor, and serious toxicity means mercury vapor cannot be sensed; only instruments reveal it. ### Health and operational effects Mercury is a potent neurotoxin. Chronic inhalation of the vapor damages the nervous system, kidneys, and cognitive and behavioral function (the tremor and personality change historically known as "mad hatter" syndrome), and it has no beneficial role in the body. Because it accumulates rather than clearing quickly, low-level exposure over time is a genuine concern, not only acute high exposure. Its environmental persistence and bioaccumulation extend the harm well beyond the workplace. For chlor-alkali, mining, metals, cement, and remediation operations, and for laboratories and clinics, mercury vapor is a worker-protection and emissions parameter backed by strict occupational limits. Limits ## Mercury (Hg) Limit Values The published values, by averaging period; each links to the standard that sets it. 8-hour TWA [**0.1 mg/m³** OSHA construction](https://aethair.io/standards/osha_construction_pel/ "mercury vapor; skin") 8-hour TWA (PEL) [**0.025 mg/m³** Cal/OSHA PEL](https://aethair.io/standards/cal_osha_pel/ "metallic and inorganic mercury") Ceiling [**0.1 mg/m³** OSHA PEL](https://aethair.io/resources/osha-air-quality-standards-compliance/) [**0.1 mg/m³** Cal/OSHA PEL](https://aethair.io/standards/cal_osha_pel/ "metallic and inorganic mercury") TWA [**0.05 mg/m³** NIOSH REL](https://aethair.io/standards/niosh_rel/ "mercury vapor; skin") - **OSHA construction** 0.1 mg/m³: mercury vapor; skin - **Cal/OSHA PEL** 0.025 mg/m³: metallic and inorganic mercury - **Cal/OSHA PEL** 0.1 mg/m³: metallic and inorganic mercury - **NIOSH REL** 0.05 mg/m³: mercury vapor; skin Mercury vapor is reported as a mass concentration, typically in mg/m³ for occupational exposure and in µg/m³ or ng/m³ for the much lower ambient and emissions levels. Occupational limits apply: the OSHA PEL as a ceiling and the [ACGIH TLV](https://aethair.io/standards/acgih_tlv/) as a time-weighted average. Separate ambient and emissions limits apply near sources. The applicable values appear in the limit table on this page. Because mercury accumulates in the body, keeping the time-averaged exposure low is the central goal. How it is measured ## How Mercury (Hg) Is Measured **Cold-vapor atomic absorption (CVAAS)** and atomic fluorescence spectrometry are the reference methods, exploiting mercury's strong absorption of ultraviolet light to achieve very low detection levels for compliance and emissions monitoring. **Gold-film sensors** work by amalgamating mercury onto a thin gold film and detecting the resulting change in electrical resistance; they are portable and real time, and are the practical choice for spill detection, workplace surveys, and locating contamination. Mercury is not part of the Aethair PRO cartridge set, so it is measured with an external professional analyzer on a Thiamis gateway. An instrument on Thiamis 1 A third-party instrument connected to a Thiamis gateway, reporting into the same Environet account. ### Placing mercury monitoring Position monitors in the worker's breathing zone near sources such as cells, furnaces, retorts, and laboratory benches, and over spills or contaminated areas during cleanup. Mercury vapor is very dense and tends to accumulate low down, pooling in floor cracks, drains, and traps, so surveys should include floor level and low points rather than only head height. For emissions, monitor the stack; for ambient assessment, monitor at the boundary. ### Every device and option that measures Mercury (Hg) 1 | Device / option | Type | Base platform | Measures | | - | - | - | - | | [AMETEK Brookfield](https://aethair.io/sensors/ametek-brookfield-specialty-air-analyzers/) · Jerome-631X, Jerome-431X | Specialty Air Analyzers | Thiamis | Mercury (Hg) [Hydrogen Sulfide (H₂S)](https://aethair.io/parameters/h2s/) | [Configure Mercury (Hg) Monitoring](https://aethair.io/build/?params=hg) Where it is monitored ## Solutions That Monitor Mercury (Hg) Each one links to the solution page showing what that industry measures it for. ### [Occupational Safety & Industrial Hygiene](https://aethair.io/solutions/occupational-safety/) Often added Worker exposure, confined space, and heat stress Article Library ## Reading on Mercury (Hg) ### [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/) Related ## More in Gases & VOCs [Carbon Dioxide (CO₂)](https://aethair.io/parameters/co2/) [VOC (Total)](https://aethair.io/parameters/voc/) [Hydrogen Sulfide (H₂S)](https://aethair.io/parameters/h2s/) [Carbon Monoxide (CO)](https://aethair.io/parameters/co/) [Methane (CH₄)](https://aethair.io/parameters/ch4/) [Oxygen (O₂)](https://aethair.io/parameters/o2/) [Sulfur Dioxide (SO₂)](https://aethair.io/parameters/so2/) [Nitric Oxide (NO)](https://aethair.io/parameters/no/) [Nitrogen Dioxide (NO₂)](https://aethair.io/parameters/no2/) [Ammonia (NH₃)](https://aethair.io/parameters/nh3/) [Combustible (LEL)](https://aethair.io/parameters/lel/) [Chlorine (Cl₂)](https://aethair.io/parameters/cl2/) Questions ## Mercury (Hg) FAQ Why is mercury vapor dangerous if you cannot see or smell it? Elemental mercury evaporates into a colorless, odorless vapor that gives no sensory warning, yet it is readily inhaled and is a potent neurotoxin that accumulates in the body. People can be exposed for long periods without realizing it, which is why continuous or survey monitoring is needed wherever mercury is present. The absence of warning signs makes instrumentation essential. Where does mercury vapor come from? Industrial sources include chlor-alkali plants, coal burning, cement and metal production, and waste incineration, while gold mining and amalgamation are major sources elsewhere. On a smaller scale, dental and laboratory work and broken mercury equipment release vapor. In each case the invisible vapor, not the liquid, is what is monitored. How is mercury vapor measured: gold film or CVAAS? Both have their place. Cold-vapor atomic absorption and atomic fluorescence are the sensitive reference methods for compliance and emissions, giving very low detection limits. Gold-film sensors are portable and real time, ideal for surveys, spill detection, and finding contamination, though generally less sensitive than laboratory-grade analyzers. How do I monitor mercury? Mercury is a specialist measurement outside the Aethair PRO cartridge set, so it is measured by connecting an external CVAAS or gold-film mercury analyzer to a Thiamis gateway. This suits workplace surveys, spill response, and emissions monitoring around industrial and mining operations. Use the configurator to combine mercury monitoring with the other parameters your site requires.