There were three common factors in these accidents:

• recent modification of plant, equipment or the production process.
• product storage for longer than normal in a confined space such as a pit or tank.
• liquids or sludges present in each confined space. This enabled micro-organisms to grow and the gases formed were retained below the liquid surface. When these surfaces were later disturbed the gas clouds were released into the upper levels of the confined space.

These three factors are believed to have contributed significantly to the levels of gas generated. One reason for this is the action of micro-organisms on a variety of waste products which can cause toxic gas to form in confined storage areas.

People may not be aware that toxic gas is formed in these conditions and that high concentrations may be fatal to humans.

It is important to note that the pungent smell of hydrogen sulphide, or rotten egg gas, did not act as a warning to the people who died. The stench of rotten egg gas is obvious at lower concentrations but it cannot be smelt at higher, more dangerous levels because the sense of smell can quickly be overcome.

Workers required to work in confirmed spaces need to comply with the provisions of Chapter 4, Part 4.3, Division 9 Working in confined spaces of the Occupational Health and Safety Regulation 2001.

The Regulation outlines entry protection methods, training, record keeping, entry permits, controls, equipment, risk control measures, atmospheric testing and limits, purging, penalties, emergency measures and stand-by assistance.

Clause 51 (Division 5 – Atmosphere) of the Regulation also states that the employer must ensure that no person at a place of work is exposed to an airborne concentration of an atmospheric contaminant that exceeds or breaches a standard a standard referred to in the Worksafe Australia publication Exposure Standards for Atmospheric Contaminants in the Occupational Environment.