Question 29 3AE02 - Third Assistant Engineer (Alt)

The Correct Answer is B **Explanation for B (phosgene gas):** Chlorinated fluorocarbon refrigerants (CFCs), such as R-12, and hydrochlorofluorocarbon refrigerants (HCFCs), such as R-22, contain chlorine and fluorine atoms. When these refrigerants are exposed to extremely high temperatures from an open flame or very hot surfaces (like a soldering iron or a furnace heat exchanger), they thermally decompose. This decomposition process typically involves the chlorine atoms reacting with moisture in the air to form highly toxic byproducts. The primary and most dangerous byproduct formed is **phosgene gas** ($\text{COCl}_2$), a colorless, highly poisonous chemical warfare agent that can cause severe respiratory damage and death. **Why the other options are incorrect:** * **A) water vapor:** Water vapor ($\text{H}_2\text{O}$) is a product of typical combustion involving hydrocarbons, but it is not the hazardous decomposition product formed when CFCs or HCFCs encounter high heat. Water vapor is generally harmless. * **C) carbon monoxide:** Carbon monoxide ($\text{CO}$) is a toxic gas formed by the incomplete combustion of carbon-containing fuels (like wood, oil, or natural gas). While the refrigerant decomposition does release carbon, phosgene gas is the primary toxic product of concern, rather than carbon monoxide. * **D) petroleum crystals:** This term is not a standard chemical decomposition product. Refrigerants decompose into gases, not solid crystalline substances derived from petroleum.