Medical-grade negative air machines remove bacteria, viruses, mold allergens, dust, and other small particles from the air in settings such as cleanrooms, medical clinics, and hospitals. They are often used for virus containment and patient-isolation applications. They have higher airflow and clean air more efficiently than air cleaners, but they are also louder than air cleaners. Negative air machines can be placed in a space to filter and recirculate air within that space. They can also be connected to flexible ducting to exhaust contaminated air out of a space, which is known as negative-pressure air cleaning. Each machine consists of a blower that moves air through the machine and multiple filters that trap airborne contaminants as the air passes through them.