Final answer:
Houses built after 1999 are required to have AFCIs on circuits serving bedrooms to prevent electrical fires, as mandated by the National Electrical Code (NEC).
Step-by-step explanation:
The question is asking about the requirements for Arc-Fault Circuit Interrupters (AFCIs) in residential buildings. In houses built after 1999, AFCIs have been required by the National Electrical Code (NEC) on circuits serving bedrooms to prevent electrical fires. This requirement was enforced to improve home safety as AFCIs are designed to detect a wide range of arcing electrical faults, which could otherwise lead to electrical fires. The implementation of this safety measure has contributed significantly to reducing the risk of fire hazards in modern homes.