Under ASHRAE standard 62.1, ventilation is required when which condition applies?

• A. When space is occupied
• B. During construction only
• C. Only when CO2 exceeds 1000 ppm
• D. Unoccupied times only

Answer: (A)

Ventilation is required when a space is occupied because the purpose of ASHRAE 62.1 is to provide enough outdoor air to dilute contaminants generated by occupants and by materials in that space during use. When people are present, they emit CO2, moisture, odors, and other pollutants, and the standard specifies minimum outdoor air delivery rates to keep indoor air quality acceptable. CO2 exceeding a threshold is not the trigger for the requirement; it’s an indicator that ventilation may be inadequate, but the rule is to supply outdoor air during occupancy. Ventilation during construction or only during unoccupied times do not meet the standard’s intent, since the primary aim is to protect occupants and maintain IAQ when the space is in use.