Several years ago, I took a WEA course on Islam for no other reason that I wanted to understand more about the faith and particularly about the faith in daily practice. How, for example, do surgeons and any other profession cope with fasting where concentration and safety are key?
This is how is works:
Starting the Fast: Workers must begin the day with the intention to fast. You cannot pre-emptively decide to skip a fast at dawn simply because you have a hard shift ahead, unless you are already chronically ill or facing unavoidable severe conditions.
Real-time Hardship: If during the workday a worker experiences dangerous exhaustion, severe dehydration, dizziness, or a severe drop in concentration that threatens safety (such as operating heavy machinery, driving public transport, or performing surgery), Islamic rulings permit breaking the fast.
Making Up Fasts: Any fast broken due to occupational danger or necessity must be made up (qada') day-for-day later in the year when conditions are easier, such as during shorter winter days.