Regarding the negative pressure isolation ward laboratory, there is still a lack of comprehensive unified design and construction specifications in China. Only in the DB11//663-2009 "Basic Requirements for the Construction and Configuration of Negative Pressure Isolation Wards", a series of basics are proposed for the construction and configuration of negative pressure isolation wards. The requirements involve various aspects such as process layout, air flow control, pressure control, and purification system settings. They have played a benchmark role in the construction of isolation wards in various regions, and have been used for reference by relevant departments in various regions. Recently, CEIDI received a project to transform the negative pressure laboratory in Shanghai, so we have compiled this detailed introduction for the design of laboratory negative pressure.

I.Positive and negative pressure laboratory

Common classifications of wards are: S-level (zero pressure), N-level (negative pressure), A-level (pressure switching), and P-level (positive pressure). The so-called "positive and negative pressure" is a relative value of air pressure. The area with lower air pressure is the negative pressure zone, and the area with higher air pressure is the positive pressure zone. Through the setting of positive and negative pressure in the construction of the hospital, the air and pollutants in the negative pressure area are prevented from flowing to the positive pressure area, thereby effectively controlling the diffusion of pollutants. Airtightness and air pressure classification are usually important means to prevent the spread of viruses in hospital design, which can effectively isolate indoor air from spreading to the outside.

For the highly contagious new type of coronary pneumonia, the isolation ward is the most important line of defense in the hospital. The uses of isolation wards are mainly divided into two categories:

1.For patients with low resistance. Since the patient's own resistance is low and it is more susceptible to infection by pathogens, this type of isolation ward must isolate the patient from the outside world as much as possible, and the air supply must also be kept clean to reduce the possibility of pathogen invading the patient.

2.Negative pressure isolation ward for highly infectious patients. For patients infected with diseases such as new coronary pneumonia, measles, tuberculosis and SARS, in order to prevent the virus from spreading to others and polluting the environment, when designing and building negative pressure isolation wards, special attention should be paid to positive and negative pressure, air tightness, airflow direction, and ventilation. Rate, sewage system, building materials, etc.

II.International standards for negative pressure isolation wards

The United States, the United Kingdom, Australia and other countries have different standards for negative pressure isolation wards, but the principles are the same-strictly control the flow of polluted air, let the polluted air flow to the preset safe place, and reduce the impact on the surrounding environment and people . HTM is a guide for the design, construction, acceptance, and maintenance of electromechanical systems for medical projects prepared by the British Ministry of Health and Social Security. It is a basic requirement for the construction standards of Hong Kong and Commonwealth National Hospitals.

According to HTM, the negative pressure isolation ward has its own bathroom and front room. The front room and the isolation ward are equipped with air supply and exhaust, and the bathroom is equipped with exhaust. The exhaust equipment adopts High efficiency particulate air Filter (HEPA) filter (filters that meet the HEPA standard, with an effective efficiency of 99.7% for 0.1 micron and 0.3 micron. The characteristic of the HEPA filter is that air can pass, but fine particles cannot pass. ), after cleaning the polluted air, an independent exhaust system will discharge the filtered air to a pre-designed place. The pressure difference between the front room and the corridor is -5Pa, and the pressure difference between the isolation ward and the front room is also -5Pa. The air flow direction is: corridor → front room → isolation ward → bathroom → ventilation system.

Since the front room and the corridor also have a pressure difference of -5Pa, when the door is opened, air will flow from the corridor to the front room. This design allows the front room to act as a barrier to prevent the dirty air from the negative pressure isolation ward from flowing into the corridor. In addition, the door between the front room and the corridor is also designed as an interlock switch to prevent the two doors from being opened at the same time, which will cause the dirty air in the isolation area to flow to the clean area in the case of loss of pressure.

III,the key points of the design and decoration of the negative pressure ward laboratory

1.Air tightness

The main purpose of the negative pressure isolation ward is to separate the patient from the surrounding environment and people, avoid direct contact with the body or air exchange, and prevent cross-infection. The main building of the negative pressure isolation ward must reach the airtight level, and the electromechanical system must carefully handle the gap between the structure and the structure through the room. The negative pressure isolation ward is generally installed with airtight ceilings to provide airtight protection. During maintenance, if the ceiling is opened, the effectiveness of the airtightness may be reduced. The airtightness test must be performed again according to the American ASTM E779-1 standard. Because the airtightness of the negative pressure isolation ward is extremely important.

2.Airflow direction

The design of the negative pressure isolation ward can generally effectively control the outflow of pollutants. However, since the source of infection is in the isolation ward, the airflow design in the ward should also consider avoiding the accumulation of viruses in the room and protect the medical staff working in the ward. In the negative pressure isolation ward, the principle of airflow design is to flow from the clean area to the polluted area, and minimize the distance between the polluted area and the exhaust port.

Among them, a more effective method is to design the air supply port at the end of the bed at the ceiling, and place the ventilation near the patient's head. In addition, it is also ideal to place the air supply outlet on the other side of the doctors' regular work, and keep the place where the doctors and nurses often work in the room relatively clean. The airflow should also be designed as a unidirectional flow as much as possible to keep the airflow stable and low speed to avoid the accumulation of pollutants due to short-circuit and stagnation of the airflow.

Based on the principle of airflow design, due to different limitations in the real situation, the specific layout will be different. For complex situations, computer-assisted virtual airflow analysis is required.

3.HEPA filter

The air quality entering the negative pressure isolation ward from the outside can be in accordance with the standard of ordinary wards, and the G4 level filter can meet the corresponding requirements. On the contrary, because the source of infection is in the isolation ward, the contaminated air must be handled carefully before being discharged outside to avoid leaking the virus and polluting the surrounding environment.

When necessary, the dirty air in the negative pressure isolation ward must be cleaned by a filter before being discharged. For the negative pressure isolation ward that admits highly infectious patients, it is recommended that the outdoor air exhausted should be cleaned with a H13-level filter. Based on the H13 cleaning efficiency rate of 99.95% (% Efficiency at most penetrating particle size MPPS), it can provide an excellent cleaning effect. In order to avoid cross-infection, the exhaust of the negative pressure isolation ward must be separated from other exhaust systems.