Recently in Chennai, six workers died after inhaling toxic gas exuded from the septic tank. When a worker tried to probe the sump, succumbed into the septic tank due to asphyxiation in the private apartment. Inorder to save the victim, the other five spectators tried and fell into the same trap subsequently like dominoes. All six people died predominantly by inhaling the poisonous gas.

Mistakes lead to Fatalities

The fatality in the drainage occurs mainly as a result of improper planning and evaluation of work space hazards. So as to get the job faster, workers will skip or ignore the safety procedure and this will results in fatalities.  Prior to the work, proper risk assessment should be made based on the work, environment, availability of equipment etc…

“Ignorance and negligence on safety will lead to fatalities”

The improper planning, inadequate assessment of risk, lack of Personal Protective Equipment (PPE) will creates the hazardous environment and leads to multiple deaths. In crucial situations, the rescue should be made only with the trained personnel with perfect protective equipment’s. Because inorder to help victim, co – workers instinctively enter the drainage without analysing the hazards, will also succumbed into gas poisoning.

Hazardous Gases and Lethality

Naturally, hazardous gases will be present in the drainage system, due to the decomposition of organic matters. As drainage is the enclosed system, the hazardous gas will accumulate and the concentration of the toxic gas will increase over time. Toxic gases such as Hydrogen Sulphide, Carbon Monoxide & Methane will be preferably available in the drainage. In many instances hazardous gas exceeds then the exposure limit, if a worker inhales this poisonous gas it will affect the olfactory nerve, cause suffocation, confusion, fainting and finally leads to death. Furthermore, the depletion of oxygen below 21 % will make the workers to loss the co –ordination and unable to work strenuously.

Prevention of Gas Poisoning

Working inside the drainage system should be avoided as far as possible. If it is not feasible to carry out the work without entering the drain, then the competent person should be engaged to do the work with necessary safety precautions. Before the work schedule, proper risk assessment should be conducted, to evaluate the potential safety and health hazards. Air monitoring should be done before entering and while doing work. In certain circumstances, the hazardous gases may not present initially, but the gases may release while progressing the work. Hence the work should be carried out with proper Personal Protective Equipment (PPE).

Control Measures to avoid fatalities

To avoid injuries and fatalities, control measures can be provided before performing the task;

  • Instead of involving workers, use alternate work method wherever practicable
  • To prevent the influx of hazardous material, blank off pipes or supply line can be provided
  • Inorder to avoid manual scavenging mechanical tool like vacuum / jet cleaning instruments can be to clean the drain
  • To avoid the hazardous gas accumulation and further to dilute the concentration of air contaminants, use mechanical ventilation
  • Personal Protective Equipment (PPE) like breathing apparatus with the suitable harness belt would be provided
  • To maintain the communication with workers, standby worker should be stationed outside the drain
  • To ensure the Health and Safety of the workers, permit to work system should be carried out

Hence the Hazard analyzed, Risk assessed environment and competent skilled worker can prevent any fatalities in the unsafe environment.


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