Question 32 QMED05 - Machinist-Pump Technician

The Correct Answer is D **Why option D ("Oxidation") is correct:** Spontaneous ignition (or spontaneous combustion) occurs when a material reaches its ignition temperature solely through internally generated heat, without an external spark or flame. This internal heat generation is primarily caused by **oxidation**. Oxidation is a chemical reaction involving the loss of electrons, often resulting in the combination of a substance with oxygen. When this reaction happens at a rate that releases significant thermal energy (it is an exothermic reaction), and if the heat produced cannot escape quickly enough (due to insulation or poor ventilation, especially in materials like hay, coal piles, or oily rags), the internal temperature of the material rises rapidly until it reaches the substance's fire point, causing it to spontaneously ignite. **Why each of the other options is incorrect:** **A) Putrefaction:** Putrefaction is the decomposition of organic matter, primarily proteins, by microorganisms (bacteria and fungi), often resulting in foul-smelling gases. While it is an exothermic process and produces some heat, the rate of heat production is generally too slow and insufficient in magnitude to reliably cause the high temperatures required for spontaneous ignition, especially compared to rapid chemical oxidation reactions. **B) Anaerobic decomposition:** This is decomposition that occurs in the absence of oxygen (e.g., in landfills or manure pits). The primary product is often methane gas. While anaerobic decomposition releases heat, the overall energy yield and rate of heat production are typically much lower than aerobic processes (like oxidation) or specific chemical reactions necessary to push the temperature up to the ignition point. **C) Aeration:** Aeration is the process of exposing a substance to air (oxygen), often used deliberately to cool or dry materials (e.g., grain or compost). By increasing airflow, aeration facilitates the removal of heat, actively preventing temperature buildup and thus counteracting the conditions necessary for spontaneous ignition.