What is Negative Pressure?
Negative pressure is when a room inside the building is held at a lower pressure than the surrounding rooms. Or to put it another way, negative pressure occurs when more airflow is drawn out of a room then airflow pumped in. This ensures any air leaks in the room will flow from outside the room to the outside. This is most commonly used in hospital isolation rooms to prevent airborne viruses or bacteria from escaping the room into other rooms.
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, potentia
Pressure is said to be negative when it is less than the local barometric or atmospheric pressure. What is relative and absolute pressure? A pressure measurement that is absolute is not related to any other. The atmospheric pressure at sea level is 14.7 psia (pounds per square inch absolute), that is, 14.7 psi above zero absolute. Relative pressure is always related to the local atmospheric pressure. For example, 10 psig (pound per square inch gauge) is 10 psi above the local atmospheric pressure. Most pressure measurements are taken in psig which is relative to the local pressure. Pressure measurements do not normally have to be corrected for altitude since all the measurements you might do on a system are relative to the same atmospheric pressure therefore the effect of elevation is not a factor. An important exception to this is when taking a pressure measurement at the pump suction to determine the N.P.S.H. available. This pressure measurements is converted to absolute pressure whi
Ok, I’m no expert in biology – but I got 2 degrees, so I’m gonna chance it! Every living organism lives in a pressurised environment – either atmospheric pressure or water pressure. Pressure of biological system – atmospheric pressure = NEGATIVE pressure. Hence, it is really the atmospheric pressure that is driving (pushing) the system. The fluid flows because the system is trying to establish an equilibrium between the two pressures, i.e. Pressure of biological system = atmospheric pressure So long as this equilibrium is NOT established; fluid flow will occur. Its like a plane! The plane flies because nature is trying to establish an equilibrium between the forces on either side of the wing. Basically: Nature Loves an Equilibrium – Acky’s Law! (since the entropy of the universe is always increasing – but that’s another story!
By OSHA’s definition, “negative pressure” means the relative air pressure difference between two areas. A room that is under negative pressure has a lower pressure than adjacent areas, which keeps air from flowing out of the room and into adjacent room or areas”. Simply put, the environment in a negative pressure room is somewhat like a vacuum. When doors are opened in negatively pressured rooms, air only rushes into the room, not out.
