Which portion of a cargo tank must be painted a reflecting color?

The correct portion of a cargo tank that must be painted a reflecting color is the upper two-thirds. This requirement is primarily aimed at enhancing the safety and visibility of the cargo tank, particularly in conditions where it may be exposed to direct sunlight. By painting the upper two-thirds with a reflective color, heat absorption by the tank is minimized, which helps to prevent pressure buildup within the tank due to rising temperatures.

The reflective color serves to deflect sunlight, thereby maintaining the integrity of the liquefied petroleum gas stored within. This is crucial in preventing potential hazards such as vaporization of the LPG, which can lead to overpressure and increase the risk of explosions or leaks.

Other options, such as painting only the lower one-third or every section equally, do not adequately address the need to manage heat absorption effectively. Painting the entire tank would also not conform to the specific regulation, as it doesn't focus on the critical upper portion that is most affected by sunlight and heat. Therefore, the requirement highlights the importance of targeting the specific area that balances safety and regulatory compliance.