Which of the following is an example of an active fire protection system?

An active fire protection system is designed to take action when a fire occurs, actively working to extinguish the fire or suppress its effects. Sprinkler systems are a prime example of this category, as they automatically activate to deliver water when heat from a fire is detected, thus helping to control or extinguish the flames and protect property and lives.

In contrast, the other options represent passive fire protection measures. Fire-resistive construction materials are used to slow the spread of fire, allowing more time for occupants to evacuate and for emergency services to respond. Fire-rated doors serve a similar purpose by blocking smoke and flames from traveling through doorways, while smoke barriers are structures designed to contain smoke during a fire event. Although they are crucial for enhancing safety, none of these options actively engage in fighting a fire, which is the defining characteristic of active fire protection systems.