What is a critical safety measure when transporting propane in a vehicle?

When transporting propane, a critical safety measure is ensuring that the container is upright. This is essential because propane is stored as a liquid under pressure, and when it is stored in a vertical position, it allows for safe vaporization and prevents the liquid propane from leaking. If the container were to be transported in a horizontal position, there is a risk that the valve or connection could become damaged, potentially leading to a leak or even a dangerous release of gas. Keeping the propane container upright also helps to minimize the risk of accidents and spills during transit, as the liquid is less likely to escape in this position.

The other options, while they may have some relevance to safety, do not directly address the critical aspect of maintaining the integrity of the propane container in transport. For example, while opening windows may provide ventilation, it does not affect the primary concern related to how the propane container is positioned. Similarly, while keeping the container tightly sealed is important, the primary safety measure during transport revolves around its upright positioning to prevent leaks and potential hazards.