Which of the following methods can be used to protect common exhaust ducts?

The correct answer involves the simultaneous operation of all independent systems as a method to protect common exhaust ducts. This approach ensures that all connected systems are active and can effectively work together to mitigate fire hazards. By having all systems operational at the same time, it's possible to enhance the overall protection of the exhaust duct, preventing potential fire spread.

This method promotes coordinated response from multiple fire suppression systems, creating a comprehensive barrier against fire propagation within the ductwork. It ensures that if a fire occurs, various extinguishing agents can be deployed simultaneously, maximizing their effectiveness in controlling and extinguishing the fire at its source.

Other methods, while they may offer certain benefits, do not provide the same level of comprehensive protection. For instance, relying solely on individual duct protections might leave some areas vulnerable if one system fails. Similarly, periodic manual checks can help identify issues, but they do not actively suppress a fire when it occurs. The use of thermal blankets could add insulation to the ducts but wouldn't offer real-time fire suppression capability like the simultaneous activation of all systems would.