Negative room pressure is an isolation

Solitary confinement

Solitary confinement is a special form of imprisonment in which a prisoner is isolated from any human contact, though often with the exception of members of prison staff. It is sometimes employed as a form of punishment beyond incarceration for a prisoner, and has been cited as an additional...

 technique used in hospital

Hospital

A hospital is a health care institution providing patient treatment by specialized staff and equipment. Hospitals often, but not always, provide for inpatient care or longer-term patient stays....

s and medical centres to prevent cross-contaminations from room to room. It includes a ventilation

Ventilation (physiology)

In respiratory physiology, ventilation is the rate at which gas enters or leaves the lung. It is categorized under the following definitions:-Sample values:...

 system that generates negative pressure to allow air to flow into the isolation room but not escape from the room, as air will naturally flow from areas with higher pressure to areas with lower pressure, thereby preventing contaminated air from escaping the room. This technique to used for isolation of patients with airborne contagious disease

Contagious disease

A contagious disease is a subset category of infectious diseases , which are easily transmitted by physical contact with the person suffering the disease, or by their secretions or objects touched by them....

s such as tuberculosis

Tuberculosis

Tuberculosis, MTB, or TB is a common, and in many cases lethal, infectious disease caused by various strains of mycobacteria, usually Mycobacterium tuberculosis. Tuberculosis usually attacks the lungs but can also affect other parts of the body...

, measles, or chickenpox.

Mechanism

Negative pressure

Vacuum

In everyday usage, vacuum is a volume of space that is essentially empty of matter, such that its gaseous pressure is much less than atmospheric pressure. The word comes from the Latin term for "empty". A perfect vacuum would be one with no particles in it at all, which is impossible to achieve in...

 is generated and maintained by a ventilation system that removes more exhaust air from the room than air is allowed into the room. Air is allowed into the room through a gap under the door (typically about one half-inch high). Except for this gap, the room should be as airtight as possible, allowing no air in through cracks and gaps, such as those around windows, light fixtures, and electrical outlets. Leakage from these sources can compromise or eliminate room negative pressure.

Smoke test

A smoke test can help determine whether a room is under negative pressure. A tube containing smoke is held near the bottom of the negative pressure room door, about 2 inches in front of the door. The smoke tube is held parallel to the door, and a small amount of smoke is then generated by gently squeezing the bulb. Care is taken to release the smoke from the tube slowly to ensure the velocity of the smoke from the tube does not overpower the air velocity. If the room is at negative pressure, the smoke will travel under the door and into the room. If the room is not a negative pressure, the smoke will be blown outward or will stay stationary.