Many workplaces have areas that are considered "confined spaces" such as sewers, manholes, wastewater tanks, pit wells, towers, etc. Because they are non-recurrent places for working inside, workers usually neglect the hazards easily. Once occupational accident happens, it is difficult to rescue and may result in many deaths and injuries, including employers, employees, contractors, and even rescuers, due to the restrictions on entry and the characteristics of harmful environment. The major hazards of confined spaces are lacking of oxygen or existing of toxic gases, workers cannot rely on their own sense of smell or taste to identify these hazardous substances and may lower the awareness of hazards that lead to measures such as ventilation and environmental monitoring have not been implemented.
Common hazards of confined space
- Lack of oxygen in the air:
The normal oxygen content in the air is 20%-21%. When the concentration of oxygen is less than 18%, it is called oxygen-deficient air. If the oxygen content is insufficient for a short period of time, it will cause breathing difficulties, dizziness, and even fatal.
- Hydrogen sulfide poisoning:
The concentration of hydrogen sulfide in the workplace shall not exceed 10 ppm. Hydrogen sulfide is mainly produced from organic waste liquid, generally dissolved in aqueous solution and accumulated in muddy substances. It is a type of gas that is colorless and smells like rotten eggs. It is heavier than air and often exists at the bottom, which increases the difficult of ventilation and may easily cause harm.
- Carbon monoxide poisoning:
The concentration of carbon monoxide in the workplace must not exceed 35 ppm. Carbon monoxide is colorless and tasteless gas usually exhausted under an uncompleted combustion. Inhaling excess carbon monoxide may cause people to feel headache, nausea and weakness of the limbs, and be unable to escape from the hazardous environment.
- Flammable gases:
Confined spaces with existing flammable gases (g., methane, vapor of organic solvent) must not exceed 30% of the lower combustion limit, otherwise an explosion or fire may be caused if there is ignition source.
The number of cases and deaths of major occupational disasters in confined space from 2011 to 2021 in Taiwan are shown below. Although the number of occurrences has gradually declined in recent years, it is difficult to completely eliminate disasters.