Hydrogen sulfide (H₂S)
air-Q with a hydrogen sulfide sensor
Description:
Hydrogen sulfide can be detected even in very small quantities because of its rotten-egg smell. This characteristic odor is caused by the decomposition of sulfur-containing amino acids by sulfur-oxidizing or putrefactive bacteria. It is also used to extract sulfur from petroleum.
Hydrogen sulfide is corrosive and forms a weak acid. As an aqueous solution, it reacts with various heavy metal salts to form insoluble sulfides. In this way, H₂S can be precipitated as iron sulfide; this is how biogas and digestion plants are purified of H₂S. This is necessary because the corrosive properties of hydrogen sulfide could otherwise cause significant problems in gas engines during the biogas combustion process.
H₂S is a gas signaling molecule that can be produced in the human body; it acts as a messenger, facilitating intercellular communication and exerting a vasodilatory effect. It is also said to have healing properties. As such, it is found in some spas, where it is present in low concentrations—harmless to health—in the thermal water, and is believed, among other things, to have a positive effect on skin conditions.
On the other hand, H₂S is a highly toxic gas that, in high concentrations, can cause death within a short time.
Hydrogen sulfide accumulates in the soil because it is denser than air.
Hydrogen sulfide limit values:
Hydrogen sulfide forms a highly flammable gas-air mixture. The lower explosive limit (LEL) of the substance is 4.3% by volume (approx. 43,000 ppm / 60 g/m³), and the upper explosive limit (UEL) is 45.5% by volume (approx. 450,000 ppm / 650 g/m³).
Currently, the occupational exposure limit (AGW) for H₂S is 5 ppm, and the maximum workplace concentration (MAK) is 10 ppm. Thus, based on current scientific knowledge, a concentration of 10 ppm does not pose a health risk, even with prolonged inhalation. However, this limit must not be exceeded at any time, not even briefly. People with asthma experience bronchoconstriction (increased respiratory resistance) even at concentrations as low as 2 ppm.
| Denomination | Hydrogen Sulfide Limit Values |
| Occupational Exposure Limit (AGW) | 5 ppm (equivalent to approximately 7 mg/m³) |
| MAK (maximum workplace concentration) | 10 ppm (equivalent to approximately 14 mg/m³) |
Consequences of a concentration that is too high:
If you are exposed to the substance in low doses over a prolonged period, symptoms such as fatigue, headaches, memory and concentration problems, irritability, and loss of appetite may occur, among others.
Starting at approximately 200 ppm, the gas numbs the olfactory receptors through a gradual dulling of the sense of smell. For this reason, a high concentration of hydrogen sulfide is usually no longer detectable by the sense of smell.
H₂S attacks the mucous membranes and tissue fluid in the eyes, nose, throat, and lungs upon contact, causing severe irritation. It can also cause fluid buildup in the lungs.
When hemoglobin, the red pigment in the blood, is destroyed, respiration is impaired. Thus, hydrogen sulfide also has a toxic effect on the central and peripheral nervous systems, as well as on the heart.
Based on the values mentioned above, the following effects occur:
| Concentration | Effects |
| up to 10 ppm | There are no signs of intoxication or other indications of a health risk. |
| > 20 ppm | Corneal damage from prolonged exposure. |
| > 100 ppm | Irritation of the mucous membranes of the eyes and respiratory tract, coughing, increased salivation. Life-threatening within several hours. |
| > 200 ppm | headaches, difficulty breathing, numbness in the olfactory receptors |
| > 300 ppm | nausea and the urge to vomit, exhaustion, lightheadedness, and dizziness |
| > 500 ppm | Seizures, fainting. Life-threatening within 30 minutes. |
| > 700 ppm | Sudden loss of consciousness, leading to respiratory arrest and death. Life-threatening within minutes. |
| starting at approximately 5,000 ppm | fatal within a few seconds. |
Source of H₂S:
Hydrogen sulfide occurs naturally in numerous raw materials; for example, it is a component of both petroleum and natural gas in the form of volcanic gas, as well as dissolved in spring water. In addition, it is formed during putrefaction or decomposition in any process involving the breakdown of biomass (for example, in landfills, sewers, wastewater treatment plants, or manure pits) or during intestinal digestion.
Sensor used:
Hydrogen sulfide is measured in the air-Q using an electrochemical sensor. H₂S molecules “adhere” to the sensor’s surface and generate a measurable current. The sensor used is highly accurate and has an exceptionally long service life. The disadvantage of all electrochemical sensors is cross-sensitivity. Thus, the sensor also reacts slightly to ozone and chlorine, resulting in a deviation toward negative values, and slightly to SO₂ and NO, resulting in a deviation toward positive values.
Measure hydrogen sulfide:
Use the air-Q air analyzer to measure hydrogen sulfide, as well as other gases and pollutants in indoor air, in real time. The hydrogen sulfide sensor is available for purchase in the store.
More measured values / sensors
