When must all sources of heat to appliances be turned off in systems using a common exhaust duct?

In systems using a common exhaust duct, all sources of heat to appliances must be turned off upon actuation of any protection system to ensure safety and prevent the risk of fire or explosion. This requirement is critical for the effective functioning of the dry chemical extinguishing systems as it helps to eliminate any additional heat sources that could reignite a fire after it has been suppressed.

The actuation of the protection system signifies that a fire hazard is present, and by turning off the heat sources immediately, the system can achieve a more effective suppression of flames and mitigate the risk of a rekindle. This protocol is part of the safety measures established in NFPA 17 to protect both property and human life from the dangers of fire.

This practice is not limited to maintenance checks, regular operational hours, or emergency situations, but rather is a necessary action every time the protection system is activated. The emphasis on immediate action helps ensure that any potential fire scenario is managed promptly and effectively.