What does make-up air refer to in the context of negative ventilation?

Make-up air in the context of negative ventilation refers to fresh air that is introduced into a space to replace other air that has been exhausted. This is particularly important in situations where negative pressure is created, such as in buildings where exhaust systems (like fume hoods or bathroom fans) are used. When air is removed from a space, it can cause a drop in pressure, creating a vacuum that can lead to the infiltration of outside air, potentially bringing in contaminants or affecting indoor air quality.

In this scenario, the term "make-up air" specifically highlights its role in replenishing the atmosphere within a building, especially following events such as smoke removal, which involves the exhaust of interior air filled with contaminants. The introduction of fresh air helps maintain indoor air quality while ensuring the overall ventilation system operates effectively.

Other options focus on different aspects of air handling, such as recirculation, heating, or filtration, which do not directly align with the primary function of make-up air in negative ventilation scenarios.