Discussion on whether circulating air can be used in high-level biosafety laboratories

The biosafety laboratory is an important venue for conducting biosafety related research such as infectious disease prevention and control, biological invasion, etc. It also provides important safety guarantees for laboratory personnel to prevent pathogen infection and prevent pathogen leakage. According to the degree of biological harm to the object being processed and the protective measures taken, it can be divided into four levels, with the highest level being level four. When carrying out high-risk biological experiments, high-level biosafety laboratories need to ensure the safety and stability of the indoor environment. Ventilation and air conditioning systems are important technical means and safeguards to ensure the stable operation of high-level biosafety laboratories. The ventilation and air conditioning system of a highlevel biosafety laboratory not only ensures the internal air quality and biosafety of the laboratory, but also provides clean and stable environmental conditions to ensure the accuracy and success of the experiment. At the same time, it reduces the risk of leakage and transmission of pathogenic microorganisms and protects the safety of laboratory staff and the environment. In order to avoid cross contamination, ventilation and air conditioning systems generally require the use of fresh air conditioning systems. In order to reduce energy consumption and operating costs, high-level biosafety laboratories in China have adopted energy-saving technology measures such as variable air volume operation and heat recovery devices, which have achieved certain energy-saving effects, but are not very significant. In recent years, the use of circulating air in the ventilation and air conditioning system of high-level biosafety laboratories has become one of the most concerned issues for designers and maintenance managers. With the application of high-precision instruments and equipment with high temperature requirements for the surrounding environment (such as cryomicroscopes) in high-level biosafety laboratories, the issue of whether to use circulating air has become more prominent. This paper discusses the problem of using recycled air in high-level biosafety laboratories, including comparative analysis of domestic and foreign standards, characteristics and challenges of fresh air systems, systemic risk and countermeasures of recycled air systems, biosafety risk management of recycled air systems, etc. Through relevant research and practice analysis, it aims to provide ideas and suggestions for the optimization of ventilation and air conditioning systems in high-level biosafety laboratories. The results of this study show that in order to minimize the risk of cross contamination caused by the spread of pathogenic microorganisms through the ventilation and air conditioning system, the fresh air system should be preferentially used in high-level biosafety laboratories. When the process equipment in the core workspace has high requirements for the stability and uniformity of the surrounding temperature field, and it is necessary to use a circulating air system, the return air should be efficiently filtered and only circulated within the core workspace. Additionally, biosafety risk management of the circulating air system should be strengthened.