Exam Question

### (a) Risks Associated with Opening a Biological Sewage Unit (6 Marks)
Opening a biological sewage treatment plant for repair is a high-risk operation due to the hazardous environment it contains. The primary risks are categorized as atmospheric, biological, chemical, physical, and environmental.
1. **Atmospheric Hazards (Asphyxiation and Toxicity):** The decomposition of organic waste generates several dangerous gases which can accumulate in the confined space of the tank.
* **Hydrogen Sulphide (H₂S):** A highly toxic and flammable gas. At low concentrations, it has a characteristic rotten egg smell, but at higher, lethal concentrations, it paralyzes the olfactory nerves, rendering it odourless. It is a chemical asphyxiant that inhibits cellular respiration and can cause immediate loss of consciousness and death.