The term “negative pressure” is used in physics and engineering to refer to a situation in which an enclosed area has lower pressure than the area around it. Any compromise in the divide between the area of negative pressure and the more highly pressurized area around it would cause substances to flow into the area of negative pressure. Negative pressure is useful for a number of applications, including the prevention of oil spills, quarantine of highly contagious patients, and in the household vacuum cleaner.
Pipelines commonly have areas of negative pressure. Usually this is an intentional choice. For example, undersea pipelines used for oil and other materials are kept in a state of negative pressure so that if they rupture, seawater will flood the pipe. If the pipes were positively pressurized, their contents would explode into the ocean, potentially creating a hazardous spill. Negative pressure can also be dangerous, as is the case when municipal waterlines lose pressure, potentially sucking contaminated groundwater up into the water supply. In pipes, pressure is carefully monitored with the use of gauges, and is controlled with valves.
In quarantine situations, a room with negative pressure will suck air into it when doors or windows are opened. This prevents contagions from escaping through opened doors and windows, and makes it safer for medical personnel to care for the patient. Most research labs have rooms with negative pressure for studying dangerous diseases, preceded by a series of checkpoints to ensure that only authorized individuals enter the room. Negative pressure pipelines and vent hoods are also used in laboratory situations, to vent dangerous substances away from scientists.
Many homeowners interact with negative pressure on a fairly frequent basis, when they use a vacuum cleaner. When a vacuum is switched on, an area of negative pressure is formed in the bag or canister of the vacuum, which sucks air in as it tries to even out its internal pressure. Along with the air, the vacuum picks up particulate matter, leaving the floors cleaner. The basic vacuum principle is also used in a great deal of electronics and industrial applications.
The understanding and control of negative pressure have greatly contributed to many scientific and technological advances. The opposite principal, positive pressure, or an area of higher pressure than the surrounding regions, is also used to help control environments. Many manufacturing facilities, for example, use positively pressurized “clean rooms” for handling delicate substances such as computer chips.