Hydrogen sulphide (H₂S) is a colorless, highly toxic, and flammable gas known for its distinctive odor of rotten eggs. Though it occurs naturally in various environments, it is also produced by human activities. Due to its toxicity and potential environmental impact, hydrogen sulphide is a subject of concern in many industrial and public health contexts.

Chemical Properties

Hydrogen sulphide is composed of two hydrogen atoms and one sulphur atom. It is slightly heavier than air and tends to accumulate in low-lying areas. One of its most distinguishing features is its strong, unpleasant odor at low concentrations, which makes it easy to detect initially. However, prolonged exposure can lead to olfactory fatigue, where the sense of smell becomes dulled, making it more dangerous.

H₂S is highly soluble in water and forms a weak acid known as hydrosulphuric acid when dissolved. It is also combustible and burns in oxygen to form sulphur dioxide (SO₂) and water. Because of these properties, hydrogen sulphide poses significant risks in both open and confined environments.

Natural and Industrial Sources

Hydrogen sulphide is naturally produced through the anaerobic breakdown of organic matter by bacteria. This process often occurs in swamps, sewers, volcanic gases, natural gas, and oil wells. It is commonly associated with the decay of plant and animal matter in oxygen-depleted environments.

In industry, hydrogen sulphide is generated as a byproduct of various processes. It is found in petroleum refining, natural gas processing, wastewater treatment, paper manufacturing, and tanning industries. In oil and gas fields, particularly in sour gas reservoirs, H₂S concentrations can be high, necessitating careful handling and processing to ensure safety.

Health and Safety Risks

Hydrogen sulphide is extremely toxic even at relatively low concentrations. Inhalation is the most common route of exposure. Short-term exposure to concentrations as low as 10 parts per million (ppm) can cause eye irritation, coughing, dizziness, and nausea. At concentrations above 100 ppm, it can lead to respiratory distress, unconsciousness, and even death.

One of the most insidious aspects of hydrogen sulphide exposure is the loss of the ability to smell it after a short period. This can give a false sense of safety while the individual remains exposed to harmful concentrations. As a result, strict safety protocols are necessary wherever H₂S might be present, including gas detection systems, ventilation, and the use of personal protective equipment (PPE).

Environmental Impact

Hydrogen sulphide can also have detrimental effects on the environment. When released into the atmosphere, it contributes to the formation of acid rain and can damage vegetation. In aquatic environments, it is toxic to fish and other marine life. The gas is also corrosive, leading to the degradation of metals, concrete, and other materials over time, especially in sewer systems and industrial equipment.

Detection and Mitigation

Because of its high toxicity, detecting and mitigating hydrogen sulphide is critical in occupational and environmental settings. Portable gas detectors and fixed monitoring systems are commonly used in industries where H₂S exposure is a risk. These devices are calibrated to sound alarms when concentrations exceed safe thresholds.

Mitigation strategies include improving ventilation, using scrubbers and neutralizing agents to remove H₂S from emissions, and isolating high-risk areas. In oil and gas processing, techniques such as gas sweetening are employed to remove hydrogen sulphide from natural gas before it reaches consumers.