You should not fly within 24 hours after which circumstance?

• A. Running a marathon
• B. Eating a large meal
• C. Scuba diving or getting a new cast
• D. Standing in line for hours

Answer: (C)

The situation tested is the risk from rapid changes in air pressure on the body after certain activities. Flying reduces cabin pressure, and after scuba diving the body has more dissolved nitrogen. If you board a plane soon after diving, that nitrogen can come out of solution and form bubbles in your blood and tissues, potentially causing decompression sickness, which can be serious. Waiting at least 24 hours allows some of that excess dissolved nitrogen to be safely expelled and reduces the risk of bubble formation during the flight.

The other scenarios don’t involve this same gas-related risk from pressure changes, so they don’t carry the same precaution. A large meal or standing in line for a long time may cause discomfort or fatigue, and running a marathon is taxing, but they don’t create the hazardous gas bubble risk that diving followed by flight does. The mention of a new cast adds a separate medical consideration (swelling or discomfort from a fresh injury) but the well-known, time-sensitive risk that's commonly advised against is diving before flying.