Workers in sewers are especially exposed to the risks of inhaling toxic gases that are emitted from the drains because of various chemical and biological processes, resulting from the decomposition of wastage. Usually sewers have a high concentration of hydrogen sulfide that is liberated when organic materials are decomposed by bacteria. In high concentrations, exposure to hydrogen sulfide can cause suffocation, paralysis of the olfactory system (that is responsible for our sense of smell), failure of the respiratory system, loss of consciousness and in some cases even death.
Although hydrogen sulfide has a rotten egg smell, people can lose awareness of it because of its ability to affect the olfactory system. Apart from that, other toxic gases like oxides of nitrogen, ozone and carbon monoxide may also be present in sewers. Toxic gases like phosgene and carbon monoxide are odorless and colorless, so most people are not aware of their presence in the atmosphere until it is too late. In addition to hydrogen sulfide, toxic gases that can cause death include carbon monoxide, arsine, oxides of nitrogen, hydrogen cyanide, chlorine.
Use of acids to clean sewers may result in the evolution of toxic gases. The reaction of hydrochloric acid (which is commonly used for cleaning purposes), for example, with iron sulfide which is found in rusty places results in the expulsion of hydrogen sulfide.
More than 5,000 serious injuries and 50 casualties take place in confined spaces every year. OSHA (Occupational Safety and Health Administration) issued a rule on Permit Required Confined Spaces in January 1993. This was intended to save workers from the dangers of serious injuries and possibly death. A place with an oxygen concentration of 19.5 percent is considered an oxygen deficient area. Concentration below this level can seriously affect the workers’ health. In any area that has an oxygen concentration of less than 19.5 percent, the workers are required to wear self-contained breathing apparatus (SCBA) as per the OSHA regulations.
Moreover, according to OSHA, if hydrogen sulfide is present in any area, the workers must wear a special apparatus to aid the breathing and the area must be continuously ventilated. As sewers are considered as hazardous, the employers are required to ensure that the concentration of toxic gases is not dangerous and the workers adopt adequate safety measures. For safety, the workers entering a confined space are required to wear tracking equipment so that their activity may be monitored from the outside. Atmospheric readings are also taken before workers are sent into the confined spaces. Levels of oxygen, carbon monoxide, explosive gases and hydrogen sulfide are checked on the meter.
Hazards of confined spaces, such as sewers, can be prevented by educating employees about the dangers they face and by making them aware of the safety measures they can take to prevent any possible accident.