Which one is the answer? How do you know that? Occupancy type is a surrogate measure for Fire Load Ventilation Combustibility ToxicityA. Fire LoadB. VentilationC. CombustibilityD. Toxicity Solution Occupancy type is a surrogate measure for ventilation. Surrogate measures of human occupancy and activity in the 10 patient rooms using both indoor CO2 concentrations and infrared (IR) beam-break counters installed at the patient room doorways. Outdoor air fractions in the HVAC systems serving the two floors..