Hydrogen sulphide (H₂S)

Hydrogen sulfide (H₂S)

Hydrogen sulphide is a colourless, malodorous and highly toxic gas that is flammable and highly combustible. It has the typical smell of rotten eggs and is produced when proteins from sulphur-containing amino acids are decomposed by putrefactive and sulphur bacteria.

Can be measured with:

✓ measurable with air-Q pro as well as air-Q science


Hydrogen sulphide can be detected even in very small quantities due to its rotten egg smell. This typical smell arises due to the decomposition process of proteins from sulphur-containing amino acids by sulphur or putrefactive bacteria. It is also used to extract sulphur from crude oil.

Hydrogen sulphide is corrosive and forms a weak acid. As an aqueous solution, it reacts with several different heavy metal salts to form insoluble sulphides. In this way, H₂S can be bound to iron sulphide - thus cleaning bio and digester gas plants of H₂S. This is necessary because the corrosive properties of hydrogen sulphide could otherwise cause significant problems in gas engines during the biogas combustion process.

H₂S is a gasotransmitter that can be produced in the human body and functions as a messenger substance that serves intercellular communication and has a vasodilatory effect. The substance is also said to have a healing effect. It can be found in some spas, where it is contained in low and not harmful concentrations in the healing water and is said to have a positive influence on skin diseases, among other things.

On the other hand, H₂S is a very toxic gas, which in high concentrations can cause death within a short time.

Hydrogen sulphide collects on the ground due to its higher density than air.

Limits of hydrogen sulphide:

Hydrogen sulfide forms a highly flammable gas-air mixture. The lower explosion limit (LEL) of the substance is 4.3% by volume (approx. 43,000 ppm / 60 g/m³) and the upper explosion limit (UEL) is 45.5% by volume (approx. 450,000 ppm / 650 g/m³).

Currently, the occupational exposure limit (OEL) for H₂S is 5 ppm and the maximum occupational exposure limit (MAC) is 10 ppm. Thus, according to current knowledge, at a concentration of 10 ppm, health is not endangered even by prolonged inhalation. However, this value must not be exceeded at any time, even for a short time. Asthmatics react with bronchoconstriction (increase of breathing resistance) already at a concentration of 2 ppm.

Designationning Sulphur limit valueshydrogen
Workplacelimit value (AGW) 5 ppm (corresponds to approx. 7 mg/m³)
MAK value (maximum workplaceconcentration) 10 ppm (corresponds to approx. 14 mg/m³)

Consequences of too high a concentration:

Exposure to the substance in low doses over a longer period of time can lead to symptoms such as fatigue, headaches, impaired memory and concentration, irritability and loss of appetite.

Above approx. 200 ppm, the gas numbs the olfactory receptors by gradually dulling them. As a result, an increased hydrogen sulphide concentration is usually hardly noticed via the sense of smell.

H₂S attacks the mucous membranes and tissue fluid in the eyes, nose, throat and lungs on contact, causing severe irritation. It can also lead to water retention in the lungs.

The destruction of the red blood pigment haemoglobin impairs respiration. Thus, hydrogen sulphide also has a toxic effect on the central and peripheral nervous system as well as the heart.

The following effects arise from the above values:

Concentration Impact
up to 10 ppm no signs of poisoning or other health hazards.
> 20 ppm Damage to the cornea of the eyes with prolonged exposure.
> 100 ppm Irritation of the mucous membranes of the eyes and respiratory tract, coughing irritation, increased salivation.
Life-threatening after several hours.
> 200 ppm Headache, breathing difficulties, anaesthesia of the olfactory receptors.
> 300 ppm Nausea and nausea, fatigue, drowsiness and dizziness.
> 500 ppm Cramps, fainting.
Life-threatening within 30 minutes.
> 700 ppm Sudden loss of consciousness up to respiratory arrest and death.
Life-threatening within a few minutes.
from approx. 5,000 ppm fatal within a few seconds.

Emergence of H₂S:

Hydrogen sulphide occurs in nature in many raw materials, e.g. as a component of both crude oil and natural gas in the form of volcanic gas and in dissolved form in spring water. In addition, it is formed during decay or decomposition processes in any form of biomass decomposition (for example in landfills, sewage systems, sewage treatment plants or slurry pits) or during digestion in the intestine.

Sensor used:

Hydrogen sulfide is measured in the air-Q by means of an electrochemical sensor. H₂S molecules "dock" on the surface of the sensor and cause a measurable current. The sensor used has high accuracy and a particularly long service life. The disadvantage of all electrochemical sensors is cross-sensitivity. Thus, the sensor also reacts slightly to ozone and chlorine and then shows a deflection to negative values as well as slightly to SO₂ and NO with a deflection to positive values.

Measure hydrogen sulphide:

Measure hydrogen sulphide and other gases and pollutants in indoor air in real time with the air-Q air analyser. The hydrogen sulphide sensor can be ordered in the shop.

air-Qs, which use the sensor for

Hydrogen sulfide (H₂S)


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