What material should be used to seal the annular space where a clothes dryer exhaust duct penetrates a wall or ceiling membrane?

The correct choice is to use a noncombustible material to seal the annular space where a clothes dryer exhaust duct penetrates a wall or ceiling membrane. This requirement is primarily grounded in safety and building code regulations aimed at preventing the risk of fire and ensuring proper ventilation.

Noncombustible materials are essential in this context because they do not ignite or contribute to the fire when exposed to high temperatures, which could occur if there were a malfunction in the dryer or overheating of the exhaust duct. Proper sealing with noncombustible materials helps maintain the integrity of fire-rated assemblies and ensures that the exhaust is effectively vented outside, thus reducing the likelihood of lint buildup that can also pose a fire hazard.

In contrast, materials like wood, plastic caulk, and foam insulation are not suitable for this application. Wood, being combustible, can easily catch fire and compromise the safety of the space. Plastic caulk may not withstand the high temperatures associated with a dryer exhaust, potentially leading to degradation and failure over time. Likewise, foam insulation can be flammable and may not provide a proper seal against heat or fire, which is crucial in this scenario.