Final answer:
When conducting in-shelter refueling with shelter doors completely closed, crew members should have at least 30 minutes of low or no fuel vapor exposure between operations to minimize health risks.
Step-by-step explanation:
When conducting in-shelter refueling with shelter doors completely closed, crew members should have at least 30 minutes of low or no fuel vapor exposure between operations. This allows them to minimize the risk of inhaling excessive amounts of potentially harmful fuel vapors.
By having this time gap, crew members can reduce the chances of adverse health effects associated with fuel vapor exposure, such as respiratory irritation or central nervous system effects.