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Negative Pressure Room

When operating for patients with infectious diseases, a negative pressure clean operating room should be established. Effective measures such as adding exhaust fan should be taken to adjust the exhaust air volume so as to change the positive pressure into negative pressure in the clean operating room. The negative pressure difference of air was used to control the air flow, absorb harmful gases and clean the indoor air. Negative pressure operating room can fundamentally control and solve the problem of air pollution in operating room.


A negative pressure room usually includes a ventilation system so that air can flow into the negative pressure room from the corridor or any adjacent area, and at the same time, ensure that the polluted air cannot escape from the negative pressure room and flow into other areas of the hospital and health institutions.

Under natural conditions, air flows from the high-pressure zone to the low-pressure zone. If the room is in a negative pressure state, the outside air will flow into the room from under the door continuously, and at the same time, the gaseous pollution particles generated in the room will be prevented from escaping into the outside corridor. To give an example of a common negative pressure room, a bathroom with an exhaust fan is a negative pressure room. After the negative pressure condition is formed, close the bathroom door, and the fan will prevent the bad smell and moisture from escaping from the bathroom.


In order to generate negative pressure state, it can be realized by balancing the ventilation system of the room so that the air discharged automatically is more than the air provided automatically. In this way, the ventilation is unbalanced, and the room ventilation system constantly absorbs air from the outside of the room to supplement. In a well-designed negative pressure chamber, air flows completely through a gap (generally about half an inch high) under the door. In addition to the gap, the negative pressure chamber should be sealed as much as possible to prevent air from entering through various other cracks and gaps, such as all kinds of gaps around the windows, wall lighting equipment and sockets. Even if the room has achieved the negative pressure condition, the air leakage in these places may still offset or eliminate the negative pressure state of the room.


The minimum pressure difference required to achieve and maintain room negative pressure to allow air to flow into the room is very small (0.001 inch of the water gauge). The actual negative pressure value depends on the difference between the air consumption and supply of the ventilation system as well as the structure and size of the room, including the air flow path and flow opening. If the room is well sealed, it is easy to achieve a negative pressure value higher than the 0.001 inch water gauge. However, if the room is not well sealed, as the actual situation of many health institutions (especially the old ones), to achieve a large negative pressure value, the difference between the discharge and supply may need to be greater than the capacity of the ventilation system.


To achieve a negative pressure environment under the normal operation of a ventilation system, first adjust the air flow supply and emission of the room, so that the emission is 10% higher than the supply or 50 CFM higher (depending on the higher value). In most cases, this standard can achieve a negative pressure value of at least 0.001 inch water level gauge. If the negative pressure value of the 0.001 inch water level gauge cannot be achieved, nor can it be achieved by increasing the flow difference (within the allowable range of the ventilation system), the room shall be carefully checked for cracks (such as door cracks, window cracks, water pipe devices and various devices embedded in the wall), and then remedial measures shall be taken to seal these cracks.


The negative pressure value in the room can be changed by changing the operation of the ventilation system or opening and closing the door, corridor door or window of the room. If an operating structure has been established, ensure that all doors and windows of the negative pressure chamber and other areas (such as corridor doors that affect air pressure) are properly closed, except when personnel need to enter or leave the room or area.


Smoke test is a very simple procedure to determine whether the room has been in a negative pressure state. Place a section of fire pipe under the negative pressure chamber door and keep a distance of about 2 inches from the door. Gently squeeze the bulb of the fire pipe to produce a small amount of smoke. Hold the fire pipe in parallel with the door, and the smoke will be slowly discharged from the pipe to ensure that the smoke discharge speed is lower than the air speed. If the room is already under negative pressure, smoke will flow into the room from below the door. If the room is in a non-negative pressure condition, smoke will blow out of the door or remain stationary.


The test must be carried out with the door closed and all windows in the room closed. If the air purifier in the room is already in operation (including ventilation cabinet or biosafety cabinet), it must be kept in operation. If the room has a reception room, test the pressure difference from the corridor to the reception room and from the reception room to the room.

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