Septic tanks are enclosed area made for an accumulation of decomposed domestic wastes, sewerage and its resultant gases. Sewer gases can be both toxic and non-toxic. Its major component is Methane, which can be extremely toxic in high concentrations. Sewer gas is a mixture of Hydrogen Sulphide, Ammonia, Carbon-dioxide, Nitrogen dioxide, Sulphur dioxide and sometimes, even carbon monoxide. The concentration of these components differs with the time, sewage composition, and temperature. Hydrogen sulphide can be poisonous even in small concentrations leading to irritation of the eyes, shortness of breath and incessant cough. Exposure to higher concentrations can be fatal.

I hereby present a fatal case of septic tank gas poisoning to a young man.


There was a 20 years old male who jumped into a septic tank to save a child, who accidentally fell into the septic tank while playing near the tank. Before he could bring out the child, he became unconscious and was trapped inside the septic tank for nearly fifteen to twenty minutes, until the neighbours helped to evacuate him.

The young man succumbed to septic tank gas poisoning and developed cardiorespiratory arrest, which could not be revived.


Septic Tanks are quite common in residential and industrial areas to maintain sewage wastes. Natural decomposition and mixture of sewage lead to the production of sewage gases. These gases can be toxic if inhaled in high concentrations for a prolonged period of time. Septic tank gases contain methane, hydrogen sulphide, carbon dioxide, sulphur dioxide, ammonia, nitrogen dioxide and traces of carbon monoxide.

Hydrogen sulphide has a characteristic smell of rotten eggs, which is easily identifiable by human olfactory organs and serving as a warning signal for sewer gas leakage. It is a colourless gas, heavier than air, further corrosive and flammable. Exposure to even low concentrations of hydrogen sulphide can cause irritation of the eyes, sore throat, dyspnoea and cough. Prolonged exposure can even cause pulmonary edema, headache and dizziness.

Exposure to 0.032-0.02 PPM (Parts per Million) leads to Olfactory threshold (begin to smell),

Exposure to less than 5 PPM start the dose-response curve in short-term exposure, Increase in anxiety symptoms in single exposure and Metabolic changes observed in exercising individuals, but not clinically significant.

Exposure to > 5-10 PPM leads to Relatively minor metabolic changes in exercising individuals during short-term exposures,

Exposure to 5-30 PPM leads to Moderate irritation of the eyes, Exposure to > 100 PPM lead to Dangerous circumstance to Life and Health (IDLH concentration),

Exposure to > 150-200 PPM leads to Olfactory fatigue (sense of smell is significantly impaired),

Exposure to > 100-1,000 PPM leads to Serious respiratory, central nervous, and cardiovascular system effects and

Exposure to > 1,000-2,000 PPM leads to loss of consciousness and possible death. Source of this information is ACGIH and NIOSH.

 Exposure to high concentrations of methane can also be dangerous as it reduces the percentage of oxygen in the air and causes hypoxia. Further Methane gas inhalation can cause asphyxia, loss of consciousness and pneumonitis.


 The Young man had entered the septic tank to save a child accidentally trapped inside it. After evacuating the child, the young man became unconscious probably due to exposure to high concentrations of sewer gases for nearly fifteen to twenty minutes, before he was evacuated by neighbours. He was brought in a comatose state to the Emergency where he was managed according to the standard protocol of the hospital; and given all supportive treatments. The young man would have already suffered brain injury. There is no specific antidote to septic tank gas poisoning. Injury to the brain and other organs is usually irreversible and hence the young man could not be saved.


There are no standard guidelines or protocols for designing, construction, cleaning and maintenance of septic tanks. Casualties occurring due to septic tanks may not even be reported, which may be responsible for the lack of accurate statistical data on the health hazards caused by them. All septic tanks should have a display board highlighting the do’s and don’ts as well as the possible hazards due to sewer gases. Only authorized and trained personnel wearing personal protective equipment should be allowed inside the septic tanks. All necessary precautions should be taken by the septic tank workers to prevent themselves and others from getting trapped inside the septic tanks. The government agencies should formulate special rules and regulations for safe use and maintenance of septic tanks, and Non-Profit Organizations should conduct awareness Training Programs. Measures for Quick Evacuation must be ensured in the event of any accident. First Aider aim must be to provide adequate ventilation and oxygenation, to prevent secondary brain injury, multi-organ damage and to maintain stability.


Septic Tanks continue to be a health hazard as that produce sewer gases which can be toxic to human beings and also cause greenhouse effects. Septic tank Gas Poisoning can be fatal if inhaled in high concentration or for prolonged periods. Proper precautions should be taken before entering into septic tanks; people must be educated about the health hazards of sewer gases. Damage to the vital body organs can be extremely difficult to treat and the desired outcome may not be possible.

request-call-back-02 24.07.2018