What is the definition of worst case depressurization?

Worst case depressurization refers to the specific scenario in which a building or a designated space, such as a combustion appliance zone (CAZ), experiences the most significant negative pressure compared to the outside environment. This condition is crucial for assessing how various factors, such as ventilation, air leakage, and combustion appliance operation, affect indoor air quality and appliance safety.

When evaluating a building's performance, worst case depressurization helps identify the potential for backdrafting, where combustion gases are drawn into the living space rather than vented outside. This situation can lead to dangerous conditions, such as the accumulation of harmful gases like carbon monoxide, which can pose serious health risks.

Choosing the option related to the greatest CAZ pressure relative to the outside makes sense, as it directly addresses the essential concept of measuring the maximum level of depressurization that can occur during specific operational scenarios or system failures, impacting overall safety and indoor air quality.