Hydrogen sulphide is a poisonous, flammable gas that occurs naturally, is released from sewage sludge and sulphur hot springs, and is formed in the petroleum refining process and through paper pulping. Heavier than air, it collects in low-lying areas such as basements, tunnels and sewer lines.
Smelling of rotten eggs, hydrogen sulphide is primarily absorbed via inhalation. Due to 'olfactory fatigue' – at continuous low-level exposure or high concentrations – the ability to smell the gas is quickly lost.
In several occupational exposure incidents, hydrogen sulphide has caused unconsciousness and even death. As exposure increases, symptoms escalate from irritation of the eyes and respiratory tract to pulmonary oedema and then loss of consciousness. There is also the risk of the gas being ignited.
Air monitoring equipment such as a sulphide detector or a multi-gas meter should be used to check an area for hydrogen sulphide, while providing ventilation is the key to managing the gas. If it is still present, personal protective equipment and respiratory protection is required.
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Forced ventilation is used to prevent hydrogen sulphide from leaking into the work area. For work in a tunnel, air is channelled from one end to the other, to dilute the gas to a safe level.