Every year thousands of people lose their lives during work in confined spaces. Most accidents are caused during work in vessels, tanks, manholes, sewage sumps, sewers, trenches, borewells, etc. The reason behind accidents is allowing individuals to enter confined spaces without carrying out atmospheric tests or lack of awareness about the Hazards it can lead to.
When it comes to defining something as confined space, it should be based on more than the volume of space. Factors like limited opening for Entry or Exit (usually only one opening), the space not being designed for humans to work in for extended periods of time, as well as the space causing risk to human life due to oxygen deficiency, availability of flammable gases, toxic gases, or electrical hazards.