What is required where a grease duct serving a Type I hood penetrates a ceiling?

When a grease duct serving a Type I hood penetrates a ceiling, it is essential to enclose the duct. This is primarily to minimize the risk of fire spread, contain grease-laden vapors, and protect the surrounding structure. Enclosures help maintain the integrity of the fire-resistance-rated assembly through which the duct passes, especially considering that grease ducts convey combustible materials.

The enclosure serves multiple purposes: it protects the duct from physical damage, aids in temperature control, and ensures that any grease buildup is contained, reducing the likelihood of fire hazards associated with grease accumulation. Local codes may specify the materials and construction standards for such enclosures to ensure they effectively manage the associated risks.

The other options, while they might be relevant in certain contexts, do not provide the necessary level of protection and function as an enclosure in this specific scenario. Therefore, the requirement for an enclosure is both a practical and a code-driven necessity in the context of mechanical systems serving commercial kitchens.