Protection of common exhaust ducts shall be achieved by which method?

• A. Simultaneous operation of all independent hoods
• B. Independent operation of each hood and duct
• C. No protection is required
• D. Simultaneous operation of any hood, duct, and appliance protection system and the system protecting the entire common duct exhaust duct

Answer: (D)

Protection of common exhaust ducts requires a coordinated, unified response that covers every part of the shared path. When multiple hoods feed into a single duct, a fire in one hood can travel through the common duct and threaten the others. To prevent that, the protection must act in concert: any hood, duct, or appliance protection system should trigger together with the system that protects the entire common exhaust duct. This simultaneous operation ensures that the fire is contained and extinguished not just locally, but throughout the entire duct network, stopping fire spread along the common path. Relying on independent hood or duct protection alone, or having no protection at all, would leave the shared duct vulnerable to fire propagation.