What should be checked when safe during an event of decompression?

In an event of decompression, the most critical aspect to check is the oxygen supply. During decompression, oxygen levels in the cabin can drop significantly, compromising the safety and health of passengers and crew. Ensuring that there is an adequate supply of oxygen is vital to prevent hypoxia and maintain adequate breathing capability for all on board.

While other options may have their importance in different contexts, they do not directly address the immediate needs and risks associated with decompression. For instance, cabin temperature can affect comfort but is not a priority during a rapid decompression scenario. Lavatories are important for the comfort of passengers but do not influence immediate safety factors. Life jackets, although crucial in water evacuation scenarios, are unnecessary in the context of dealing with decompression issues. The focus must remain on securing the availability of oxygen to ensure the well-being of everyone in the cabin during such an emergency.