For an appliance containing 10 pounds of CFC-500 manufactured before November 15, 1993, to what level must it be evacuated before disposal?

The correct answer indicates that the appliance containing CFC-500 must be evacuated to 4 inches of mercury (Hg) before disposal. This level of evacuation is part of environmental regulations designed to minimize the release of refrigerants into the atmosphere, especially substances that deplete the ozone layer like CFCs.

Regulatory guidelines often define specific vacuum levels that must be reached to ensure that the refrigerants are fully removed from the system. Evacuating to 4 inches of Hg means that the internal pressure of the appliance is reduced significantly, allowing for effective removal of refrigerants.

Achieving this specific vacuum level is crucial because it signifies that there is little to no refrigerant remaining in the system, which helps prevent potential environmental damage and complies with safe disposal practices. Reaching this level of evacuation helps ensure that any remaining refrigerant does not escape during transportation or disposal, as escaping refrigerant can contribute to global warming and ozone layer depletion.

Other options present higher vacuum levels that exceed the requirements for safe disposal of the refrigerant. Though these higher levels might seem like they would be better for the environment, they are not necessary according to the regulations applicable to appliances manufactured before the specified date.