If you are soon to empty, clean and inspect effluent pits, sumps, storage tankers or tanker-out lagoon effluent-be careful. The partial microbial breakdown of wastes during anaerobic (without oxygen) storage produces toxic gases such as ammonia, carbon dioxide and hydrogen sulphide.

These gases mostly remain dissolved while the effluent is undisturbed but are rapidly released during any pumping, agitation or mixing. The hazards are increased in pit-ends, tanks and tankers because carbon dioxide and hydrogen sulphide, being heavier than air, can concentrate to very high levels with possibly fatal results.

Hydrogen sulphide (H2S) is potentially the most lethal of the manure gases. It is colorless, has a characteristic 'rotten-egg' smell (when dilute) and is slightly heavier than air. At high concentration it is a rapid and powerful systemic poison and is instantly lethal. Above 1,000 ppm our sense of smell is paralysed so its warning odour is not detected.