To determine a specific “settle time” for a specific room, the number of Air Changes per Hour (ACH) must be evaluated as each room can be different (size, temperature, humidity, ventilation capacity, etc.). The higher the ACH, the less time is required for settle time. If the number of ACH for the patient room is known, a specific “settle time” can be calculated using the tool above Then staff will know how long they must wear an N95 respirator or how long before Housekeeping can enter the room to clean. Please note: the number of ACH does not reflect the direction of air flow (i.e., negative pressure vs positive pressure). If the number of ACH is unknown, the “settle time” for a patient room has been determined to be 2 hours or 120 minutes.