Exam Question

### (a) Reasons for Oxygen Deficiency in Enclosed Spaces
Oxygen deficiency, where the oxygen level drops below the normal atmospheric concentration of 20.9%, can occur in certain shipboard spaces for several reasons. A space is considered oxygen-deficient if the level falls below 19.5%.
1. **Oxidation (Corrosion):** The process of rusting is the oxidation of steel, a chemical reaction that consumes oxygen from the atmosphere. In enclosed, damp spaces with large exposed steel surfaces, such as ballast tanks, chain lockers, and void spaces, this process can significantly deplete oxygen over time. The chemical reaction is: $$ 4Fe + 3O_2 \rightarrow 2Fe_2O_3 $$ (Iron + Oxygen → Iron Oxide).
2. **Microbial Activity (Decomposition):** Aerobic bacteria consume oxygen during the decomposition of organic materials. This can occur with certain cargoes like grains, wood chips, fishmeal, or in spaces like sewage tanks. This biological process can also produce other gases like carbon dioxide (CO2), methane (CH4), and hydrogen sulphide (H2S), which are either asphyxiants or toxic.