Little space, lack of oxygen and hazardous substances: Workers in the water treatment industry who enter the confined spaces of ducts, manholes and vaults need to trust that they can also get back out again safely.
Although the definition of a confined space varies between jurisdictions, which leads to numerous local regulations, it is generally recognised as;
- A space that is mostly covered by permanent walls.
- A space with typically little air exchange.
- A space where hazards due to substances, contamination or compounds which exceed the normal danger level can occur.
Confined spaces include, but are not limited to, tanks, vessels, silos, storage bins, hoppers, vaults, pits, manholes, tunnels, equipment housings, ductwork, and pipelines.
The International Labour Organization (ILO) of the UN and the Occupational Safety and Health Administration (OSHA), USA, estimates that worldwide around 200 people die each year due to accidents in confined spaces in industry, agriculture, and private households. Approximately two thirds of these accidents were caused by toxic atmospheres, which in 70 percent of the cases had prevailed there even before entering the spaces.
Official national statistics rarely contain all accidents and the precise extent of its consequences (type of injury, severity of the injury, deaths). According to a study performed by the University of Berkeley, California/USA, the situations with the highest accident rates are: Repair and maintenance work (24 percent of recorded cases), followed by cleaning work (12 percent) and inspections (11 percent).
What are the most common causes of accidents?
The causes of accidents which occur during confined space entry work in the wastewater treatment industry vary: They include a lack of, or insufficient assessment of the danger, underestimating the danger, or the use of personnel who don’t have training for confined space entry work, despite all of the regulations. Other potential causes include underestimating the concentration of gases inside the canal or structure (oxygen content – OX, explosion risk – EX, toxicity – TOX) or unexpected biological processes such as rotting and fermenting processes.
Workers and/or supervisors may have received training on how to behave in confined spaces, but they may have insufficient knowledge of how to use gas measurement and breathing protection equipment.
Knowledge, skill and experience are often lacking even when it comes to checking the atmosphere inside a space immediately before the start of work. Errors in judgement often result because the measurement is taken at the wrong location: During entry into a shaft, it is possible for CO2 or digester gas (a mixture including CH4, CO2, H2S, O2, and H2) to have formed and settled at different heights. This means that the atmosphere can appear safe when measuring from a safe position, while dangerous gas concentrations are present when the person bends down into the shaft.
So it is important for workers in these areas to always carry a mobile gas measurement device and emergency escape equipment directly on their bodies. In addition to digester gases, the gases which are flammable and/or poisonous at certain concentrations and are typically found in wastewater treatment facilities include CH4, CO2, H2S, O3, CL2, NH3 and VOC’s. The formation of digester gas can also result in a lack of oxygen. An elevated oxygen concentration, for example due to leaking lines on welding equipment, can lead to the spontaneous combustion of oils and fats and also explosions. To ensure that the workers are protected when gases are present whilst working in confined space, they should use breathing protection.