Which of the following is the required distance from operable openings into buildings for ducts conveying flammable vapors?

The required distance from operable openings into buildings for ducts conveying flammable vapors is ten feet. This specification is crucial for ensuring safety in environments where flammable vapors are present.

Maintaining this distance helps to mitigate the risks of flammable vapors entering living or workspace areas, which could pose serious fire hazards. By placing ducts that convey flammable vapors at least ten feet away from any operable openings, such as windows or doors, the likelihood of vapor intrusion is significantly reduced, thus enhancing overall safety for building occupants.

This requirement also supports effective ventilation by ensuring that any dangerous vapors are carried away from occupied spaces, further preventing any accidental ignition or exposure. Proper adherence to this regulation helps to establish a safe operational environment, which is a fundamental principle of the mechanical code.