A duct serving a type one grease hood that penetrates a ceiling, wall, or floor should be enclosed in a duct enclosure from which point?

The requirement for a duct serving a type one grease hood to be enclosed in a duct enclosure begins at the point of penetration into a ceiling, wall, or floor. This is primarily due to the need to prevent grease-laden vapors, which are highly combustible, from escaping into non-grease areas of a building and to contain potential fire hazards associated with grease accumulation.

By enclosing the duct from the point of penetration, the system is designed to safely manage and contain these vapors as they move through the building structure. The duct enclosure helps ensure that any grease that may be present is kept within a controlled path until it can be exhausted outside, significantly reducing the risk of fire.

The other options focus on different points in the duct system that do not directly address the safety and fire protection needs mandated by codes and standards related to type one grease hoods. Starting from the kitchen does not provide the necessary protective measure needed from the point of entry into building materials, and moving along to the exhaust outlet or always below the hood does not adequately control the risks associated with the transition into more combustible areas of the structure.