We are currently designing a behavioral health inpatient facility in the Seattle area. Per local codes, demand control ventilation is required and is allowed in the return air ductwork for spaces. This is the desired installation method because of the facility requirements, which include that all fixtures meet liagture requirements, temperature/humidity and similar sensors (such as CO2) are inaccessble and vandal resistant. Are there any interpretations existing that allow return air CO2 monitoring for unique situations like this one? Any guidance would be helpful. Thanks!