Confined spaces are dangerous places.
Several gases such as carbon monoxide, carbon dioxide, hydrogen sulfide and methane can accumulate inside a confined space. Carbon monoxide is a colorless, odorless gas that displaces oxygen in the blood stream - even when there is plenty of oxygen available in the air. It can lead to cardiac arrest. Carbon dioxide displaces oxygen in the air and causes suffocation. Hydrogen sulfide is a poisonous gas with a high concentration that causes almost immediate death.