H2S

Hydrogen Sulphide (H2S)

Hydrogen Sulphide (H²S) is a highly toxic colourless transparent gas, heavier than air, that has a molecular weight of 38 vapour density 1.189 (air = 1). Hydrogen Sulphide (H²S) is a poison that can paralyse your breathing system and can kill you in minutes. Even small amounts are dangerous to your health. Small amounts of H²S will have an offensive odour similar to rotten eggs. At slightly higher concentration H²S may have a sickly sweet odour. At high concentrations no smell can be detected as H²S paralysing the sense of smell therefore H²S cannot be detected by sense of smell at higher concentrations.

H²S is formed by decomposition of organic materials in landfill sites. H²S means that each molecule of gas is made up of two hydrogen atoms and one sulphur atom.

H²S can be found in large amounts in some landfill sites. Workers involved are at risk from exposure to H²S which, is accelerated by heat or hot weather. On still, foggy days, H²S tends to accumulate in low places in dangerous concentrations if it is warmer than the surrounding air will tend to rise. Readily dispersed by wind movements and air currents.

H²S is a by-product of landfill and is best disposed of by burning in a flare. H²S burns with a blue flame producing SO² that is also a toxic gas.

Possible sources of exposure to H²S in landfill sites

Migration of gas from landfill sites

Uncapped landfill sites

Leachate collection chambers

Drains

Open wells

Vents

Open flares

Low lying area (i.e. ditches and trenches)

Confined spaces

Stagnant water

H²S is more deadly than carbon monoxide (CO) and almost as toxic as hydrogen cyanide (HCN) gas, that was used in some States of America for criminal executions.

H²S is flammable and forms explosive mixtures with oxygen or air, explosive limits 44-46% by volume in air.

Toxicity

0.13 PPM Minimal perceptible odour

4.60 PPM Moderate odour easily detectable

10 PPM Eye irritation

28 PPM Strong unpleasant odour but tolerable

100 PPM Loss of sense of smell after few minutes coughing, eye irritation

200-300 PPM Respiratory tract irritation after one hour of exposure

500-700 PPM Loss of consciousness and possible death in 20-30 minutes

700-1000 PPM Rapid unconsciousness and death

1000-2000 PPM Unconsciousness at once, death in minutes

Death may occur even if individual is removed to fresh air at once.

There are many ways to be alerted to the presence of H²S gas. Your nose is usually the first but unfortunately can be the last. You can smell as little as one part (ppm) of H²S in a million parts of air. If the concentration of gas is say, 100-200 ppm the sense of smell is lost very quickly, giving a false sense of security. The only way is to use gas detectors that will detect H²S gas.

Note: Some detectors do not read above 50 PPM.

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Useful Info

Hydrogen Sulphide (H2S)

Enclosed Vs. Open flare systems