Question 64 RVR04 - Master or Mate of LT 200 GRT

The Correct Answer is B **Explanation for Option B (More protective against re-flash):** Dry chemical agents, particularly ABC (monoammonium phosphate) or BC (sodium bicarbonate/potassium bicarbonate) powders, extinguish fires primarily through chemical interference (breaking the chain reaction of the fire) and, in the case of ABC, by forming a residue that smothers the fuel. This residue forms a physical barrier or crust over the burning material (especially Class A fuels like wood and paper for ABC powder, although its primary effectiveness is on B and C fires). This physical barrier effectively separates the fuel from oxygen and inhibits the release of flammable vapors, providing significant protection against re-flash (reignition) once the primary fire is out. In contrast, carbon dioxide (CO2) extinguishes fire by cooling and, primarily, by displacing oxygen. Once the CO2 gas dissipates (which happens quickly as it is lighter than air and disperses rapidly), the fuel source is immediately exposed to ambient oxygen. If the fuel is still hot enough to vaporize or ignite, re-flash is a serious and immediate danger, making CO2 significantly less protective against re-flash than dry chemical agents. **Explanation for Incorrect Options:** * **A) Compatible with all foam agents:** Dry chemical agents, particularly standard sodium bicarbonate powders, are generally **incompatible** with many protein and film-forming (AFFF) foams. Mixing them can break down the foam blanket, rendering both agents ineffective (this is why specialized "Purple-K" powder was developed to be more compatible, but the general class of dry chemical agents is not universally compatible). CO2, being an inert gas, has no chemical effect on foam agents and is generally considered compatible. Therefore, this option is incorrect. * **C) Cleaner:** Dry chemical is notoriously **dirty**. It is a fine powder that spreads widely, adheres to surfaces, is difficult to clean up, and is corrosive to electronics and machinery. CO2, being a gas that dissipates completely, leaves virtually no residue and is considered the much "cleaner" agent, making this option incorrect. * **D) All of the above:** Since options A and C are incorrect, this option is also incorrect.