According to regulations, which agent cannot be used in an extinguishing system for hoods, vent pipes, flues, or ducts?

The use of hydrogen gas as an extinguishing agent in hoods, vent pipes, flues, or ducts is not permitted due to safety and effectiveness concerns. Hydrogen is highly flammable and poses significant risks when used in fire suppression systems, especially in environments where oil and grease may accumulate, as is often the case in commercial kitchens.

In contrast, carbon dioxide, fine water spray, and steam are commonly accepted extinguishing agents for these applications. Carbon dioxide is effective because it displaces oxygen, which is necessary for combustion, while fine water spray can cool the fire and reduce the temperature. Steam can also be utilized in certain applications to suppress fires. Therefore, hydrogen gas is specifically excluded from use in these fire protection systems to ensure safety and compliance with regulations.