In the event of a leak of LNG, which portion is at risk of catching fire?

The correct answer highlights the fact that the invisible vapor portion of LNG (liquefied natural gas) poses the most significant fire risk in the event of a leak. When LNG is stored, it is in a liquid state at extremely low temperatures. When it spills or leaks, the liquid begins to evaporate rapidly, producing vapor that is lighter than air. This vapor is highly flammable and can ignite easily if it comes into contact with an ignition source.

While the liquid portion is cold and can cause frostbite, it does not ignite; rather, it is the vapor that escapes into the atmosphere that creates a fire hazard. The visible portion may refer to any condensation or mist created as the cold LNG evaporates, but visibility does not directly relate to flammability. The solid residue portion is not a concern in this scenario, as LNG does not leave behind a solid residue when it vaporizes.

Understanding the behavior of LNG and its molecular properties helps emphasize the importance of monitoring for vapors and implementing safety measures in areas where LNG is present. Proper training and knowledge of these risks are critical for safety in the handling and transport of LNG.