Which term refers to the combined effects of operating exhaust appliances and air handling equipment in a CAZ?

The term "Worst Case Depressurization" refers to the scenario where operating exhaust appliances and air handling equipment within a combustion appliance zone (CAZ) create a negative pressure that can potentially lead to hazardous conditions, such as backdrafting of combustion gases. This situation arises when the sum of all exhaust effects exceeds the available make-up air, resulting in a significant drop in pressure within the zone.

In a CAZ, it's critical to understand how the operation of various appliances affects air pressure. When exhaust systems, for example, fans or kitchen hoods, operate, they remove air from the space. If the air cannot be adequately replaced—either through intentional ventilation or unintended leaks—it can lead to a scenario where the pressure in the CAZ is significantly lower than the surrounding areas. During such a worst-case scenario, it's essential to measure the airflow and pressure to ensure that combustion appliances operate safely and efficiently.

Recognizing the implications of worst-case depressurization is vital for preventing dangerous backdrafting, which can introduce carbon monoxide or other harmful gases into living spaces. It emphasizes the importance of maintaining proper ventilation strategies and ensuring that air replacement is sufficient to mitigate these risks.