Research On The Technology And Strategy Of Differential Pressure Control In The Airtight Biosafety Laboratory

In recent years, the repeated outbreaks of deadly infectious diseases and thecontinual emergence of new pathogens caused that the countries of the world,including China, began to step up the construction of high-level biosafety laboratories.The high-level biosafety laboratory is not only the important technology platformengaged in of the highly pathogenic microbiological testing and scientific research,but also the containment barrier to protect laboratory workers from being infected andthe outside environment from pollution. Airtight biosafety laboratory (includingABSL-3、ABSL-4and BSL-4) is the high-level biosfety containment laboratory, thepathogenic microorganism operated can causes severe human disease and is a serioushazard to employees, is likely to spread to the community and there is usually noeffective prophylaxis or treatment available. Studies have shown that many laboratoryprocedures may produce harmful bio-aerosols. If bio-aerosols spread to thesurrounding environment, it will lead to serious public health events.Generally, the basic principle to prevent the leakage of the pathogenicmicroorganism from laboratory is isolation. And the specific isolation methods aremechanical seal isolation and air negative pressure isolation. The mechanical sealisolation refers to isolate the infectious biological factors operating environment withreliable tightness building envelope from the external environment, which is the staticcontainment of the laboratory; the negative pressure isolation refers to achieve thedirectional air flow through the control of the air difference pressures of the relativecontaminated area and the relative clean area to prevent effectively the air polluted bythe pathogenic microorganism from diffusing to the area with lower potentialcontaminated and the external environment, which is the dynamic containment of thelaboratory.The BSL-4laboratory has strict requirements to the air tightness of the buildingenvelope and differential pressure control of the laboratory. However, due to the lackof relevant platforms in our country, there is less research on the mechanical sealisolation and air negative pressure isolation of the airtight biosafety laboratory. The BSL-4laboratories in our country are under construction now, which is pressed forthe relevant technical support. Therefore, it is necessary to carry out the systematicresearch on the airtight laboratory isolation techniques. The laboratory of NationalProtection Equipment Center (NPEC) meeting the requirements of the air tightness ofBSL-4laboratory was taken as the experimental subject to carry out the theoreticalanalysis and experiment study on the protection and isolation techniques of airtightlaboratory with the air negative pressure control as the research emphasis.First of all, the research on air permeability of building envelope of airtightlaboratory was carried out. And the specific air permeability equation for airtightlaboratory was established based on the experimental measurement and the datafitting. The value of the flow index b is close to1, which suggests that the air flow ofthe room cracks of this kind of airtight room is closer to the laminar flow. That makesa big difference with that of the ordinary clean room. The computation results of thepressure decay model established on the basis of air permeability equation is inconsistent with the measured pressure decay result of the laboratory, which provesthat the established pressure decay model can estimate accurately the air leakage rateof the laboratory under different pressures. That provides the theoretical basis for thedifferential pressure control of the airtight laboratory.After sealing technology modification the tightness of one large animal room inLanzhou Veterinary Research Institute, the test results show that the air tightness ofthe laboratory can meet the requirements of the Standard for BSL-4laboratory. It isshown that with the strength of the sealing technology and selection of suitableairtight protective equipments, the tightness of containment enclosure of high-levelbiosafety laboratory in our country can completely meet the requirements of standardGB19489-2008.The air leakage of the BSL-4laboratory building envelope is very low, so tinychanges of the air input and output will cause fluctuation of the airtight laboratorydifferential pressure. This feature determines directly the selection of the differentialpressure control method and the control device. Through the establishment of themathematical model of laboratory differential pressure control, the influence of the airtightness of the building envelope and pipeline condition on the differential pressurecontrol was analyzed; the results show that the differential pressure control of theairtight laboratory is not achieved through controlling the differential air volumebetween the air input and output but through changing the volume damper impedance. The constant air volume control method was studied by theoretical analysis andexperiment, the result shows that any kind of volume damper used for constant airvolume control is not suitable for the differential pressure control of the airtightlaboratory. Therefore, the variable air volume (VAV) closed-loop control must beadopted for the differential pressure control of the airtight laboratory. And theclosed-loop control algorithm determines the control effect.The differential pressure control principle of the airtight laboratory was analyzed,and the mathematical model of the VAV differential pressure closed-loop control wasestablished by the Simulink tool of the MATLAB simulation software. Through thesimulation experiment, the control effect of the three parameters Kp, Ki,, Kdofconventional PID on the differential pressure were studied and the influence ofdifferential pressure transducer delay and volume damper operating speed ondifferential pressure control was analyzed, which provide data basis for theclosed-loop control optimization.Due to that the conventional PID only can regulate the differential pressurethrough one pair of parameters, which can hardly guarantee the good stability andrapid responsiveness at the same time. Therefore, the study on the intelligent fuzzyPID control algorithm was carried out. And the fuzzy PID control model wasestablished, and the pressure deviation e and deviation change rate ec were taken asthe input variable and the three control parameters of PID as output variable. Thismodel can set the PID control parameter on line according to the differential pressureoperating conditions and the established fuzzy rule by the real time monitoring overthe differential pressure operating parameter. And the simulation result shows that thefuzzy PID control can further improves the responsiveness and the disturbancerejection performance while making the differential pressure control system havegood stability. Compared with the conventional PID control, it is more suitable for thedifferential pressure control of the airtight laboratory.In order to verify the actual control effect of the conventional PID control andthe fuzzy PID control, the experimental study on differential pressure closed-loopcontrol of the airtight laboratory was carried out. Through the establishment of thedifferential pressure closed-loop system of the Micro environmental laboratory and onthe basis of the conventional PID control, the fuzzy PID differential pressure controlbased on PLC was achieved. The experimental result shows that the fuzzy PID controlhas better stability and robustness and the control quality of which is obviously higher than that of the conventional PID control.There will be various disturbances during the normal operation of the laboratory.In order to handle the disturbances better, the disturbance-resistant control study wascarried out. On the basis of intelligent control, the differential pressure disturbancediagnostic system was established through the disturbances classification, and hybridcontrol strategy was applied to actively deal with the disturbances. The experimentresults prove that this control strategy can control effectively the adverse effectproduced by large disturbances and guarantee the smooth transition of the differentialpressure to improve the stability of differential pressure of the laboratory.The technology strategy of man-made additional air leakage control was putforward and studied. The experimental study shows that under the premise of notreducing the static protection performance of the airtight laboratory, this controlstrategy not only can reduce effectively the sensibility of airtight laboratory towardthe air volume fluctuation, but also can effectively reduce the opening and shuttingdoor’s disturbance toward the differential pressure of airtight laboratory at the sametime and guarantee the directional airflow when open the door. This technologystrategy has important practical application value in terms of differential pressurecontrol of airtight biosafety laboratory and deserves the further study and completion.At the same time, the double control valve with coarse and fine control techniquewas also studied: carry out the composite control by adopting one large and one smallVAV control valves. The study shows that this technique indeed can reduce thedifferential pressure fluctuation in the normal operation of the laboratory. And it canbe applied to the laboratory with high air volume demand. However, the coordinationand regulation of the two valves need to be solved in the practical application of thiscontrol technique.In conclusion, this research conducted a systematic theory analysis andexperiment study on the differential pressure control of airtight laboratory. Theresearch achievement will provide the technical reference for the safe construction ofthe airtight laboratories and fill the gap in the study on differential pressure control ofairtight biosafety laboratory in our country.