Where must a fusible link be located in a common duct fire extinguishing system?

In a common duct fire extinguishing system, the fusible link must be located at each branch duct-to-common duct connection. This placement is critical because it ensures that if a fire occurs down any branch of the duct system, the fusible link will melt at the specified temperature, activating the extinguishing system in response to the heat. By positioning the link at each connection, it allows for a targeted response, meaning that the system can effectively suppress flames localized to that specific branch duct, rather than relying on detection further up in the system which might not respond in time.

Additionally, having the fusible links at these points allows for proper coverage of the entire duct system, ensuring that all areas susceptible to fire are adequately protected. This strategic placement is in line with the standards set forth by NFPA, which emphasizes the need for effective and timely activation of fire suppression systems in high-risk environments such as commercial kitchens.

While fusible links may also be present at other locations, such as the exhaust hood or the main duct junction, the primary concern is ensuring rapid response in areas where fires are most likely to originate. Therefore, focus on the branch duct-to-common duct connections is essential for effective fire suppression.