Pressure is the force exerted by a fluid on a surface area, and negative pressure refers to a lower pressure in an enclosed volume. Negative pressure is used in oil spill prevention, quarantine rooms, and wound therapy. It can also be dangerous, such as in water lines losing pressure. Positive pressure is used in clean rooms for delicate materials. Vacuum cleaners use negative pressure to suck up particles.
Pressure is defined as force per unit area and usually refers to the force exerted by a fluid, such as air or water, on a uniform surface area. As such, it is always positive, but the term negative pressure is often used in physics and engineering to refer to a situation where an enclosed volume has a lower pressure than its surroundings. Any compromise in the gap between this area and the more pressurized area around it would cause substances to flow inward. It is useful for a number of applications including oil spill prevention, quarantine of highly infectious patients, and household vacuum cleaners.
Conducts
Fluids, such as oil, commonly flow through sections of pipeline where the pressure is lower than the surrounding environment; usually this is an intentional choice. For example, underwater pipelines used for oil and other materials are kept in a state of negative pressure so that if they break, seawater will flood the pipe. If the pipes were positively pressurized, their contents would explode in the ocean, potentially creating a dangerous spill. Negative pressure can also be dangerous, as is the case with municipal water lines losing pressure, potentially sucking contaminated groundwater into the water supply if there are cracks in the pipe. In the pipes, the pressure is carefully monitored with the use of pressure gauges and is controlled with valves.
Medical, laboratory and industrial uses
In quarantine situations, a negative pressure room will suck air into it when doors or windows are opened. This prevents microorganisms and contaminated material from escaping through open doors and windows and makes it safer for medical personnel to care for the patient. Most research laboratories have rooms of this type for the study of dangerous diseases, preceded by a series of checkpoints to ensure that only authorized people enter the room. Negative pressure ducting and fume hoods are also used in laboratory situations, to expel dangerous gases and fumes away from scientists.
The opposite principle, maintaining a greater pressure area than its surroundings, is also used to help control environments. Many manufacturing plants, for example, use positive pressure “clean rooms” for handling delicate materials such as computer chips. It is essential that these do not collect dust particles and the positive pressure ensures that air leaves the area, rather than dust laden air entering, when a door is opened.
Wound therapy
Negative pressure wound therapy is a fairly new technique, aimed at accelerating the healing of severe wounds, which has been used for post-operative care, burns and chronic wounds. A sealed dressing is applied to the wound, then a vacuum pump is connected, in order to reduce the pressure around the wound to below one atmosphere. This sucks fluid, and possibly infected material, from the area and increases blood flow. It is said to be quite effective, but, apparently, it is not without risk. Numerous adverse effects, including deaths, have been reported, usually resulting from blood loss or infection.
Vacuum
Many people use a negative pressure device on a fairly frequent basis, when using a vacuum cleaner. When a vacuum is turned on, an area of negative pressure forms in the bag or container, sucking in air as it tries to level things out. Together with the air, the vacuum cleaner sucks up the particles, leaving the floors cleaner. The basic principle of vacuum is also used in many electronic and industrial applications.
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