Each fuel gas appliance shall be provided with a shutoff valve located not further than how many feet upstream of the union it serves?

The correct answer is 6 feet because it is the established standard that each fuel gas appliance must have an accessible shutoff valve located no more than 6 feet upstream of the union it serves. This regulation is crucial for safety, as it ensures that a gas supply can be quickly and easily shut off in case of an emergency or maintenance requirement. Following this guideline minimizes potential hazards associated with gas leaks and enhances the safety and efficiency of gas systems.

Other distances such as 4 feet, 8 feet, and 10 feet do not meet this specific requirement or standard. Either they fall short of the necessary accessibility provided by a 6-foot distance or they exceed practicality in emergency situations where rapid access to the shutoff valve is imperative.