Three persons lost their lives inside a boiler while attending maintenance. For entry into confined spaces (a space which is not a regular work place), the area needs monitoring before entry for ensuring safe work atmosphere. The oxygen levels and presence of other pollutants will be checked, the area will be flushed with air before and during work to ensure that the work area is as good as working in open atmosphere anywhere.
http://www.newindianexpress.com/cities/bengaluru/2018/jul/12/bengaluru-toxic-gas-snuffs-out-three-lives-inside-boiler-at-anthem-biosciences-factory-1842047.html