Question 45 TK01 - Tank Vessel Assistant - Dangerous Liquids

The Correct Answer is D **Explanation of why option D is correct:** Combustible gas indicators (CGIs), also known as explosimeters, typically rely on a catalytic filament (often a Wheatstone bridge circuit) to detect the presence of flammable gases or vapors. For the gas to combust (oxidize) on the filament and generate a measurable change in resistance, **oxygen must be present**. If the air sample contains insufficient oxygen (i.e., it is oxygen-deficient or inerted), the gas will not combust properly, and the instrument will provide an inaccurately low or zero reading, failing to detect the true concentration of flammable gas. Therefore, they do not work properly where there is a lack of oxygen. **Explanation of why the other options are incorrect:** A) **They are calibrated to read the percentage chance of explosion.** This is incorrect. CGIs are calibrated to read the concentration of flammable gas as a percentage of the Lower Explosive Limit (LEL). For example, a reading of "50% LEL" means the atmosphere contains 50% of the minimum concentration required for a flame to propagate. They do not measure the "chance" or probability of an explosion. B) **They will detect a lack of oxygen.** This is incorrect. CGIs are designed specifically to detect combustible gases. Detecting a lack of oxygen requires a separate specialized instrument, such as an oxygen sensor (O2 monitor). C) **One sample of air is adequate to test a tank.** This is incorrect, especially when dealing with confined spaces like tanks. Flammable gases can stratify (layer) in different areas of a tank due to differences in density or ventilation. Proper testing requires sampling at multiple levels (top, middle, and bottom) to ensure all potential hazards are identified.