Problems and suggestions during the operation of the clean safety cabinet

Application field of clean safety cabinet


1. The safety cabinet brands currently on the market have limited alarms for the opening height of the window. This setting can avoid the phenomenon that the opening height of the window is too high and the wind speed of the window is reduced, and the polluted air in the experimental area overflows. At the same time, because the safety cabinet protects the operator mainly by the window to form a directional wind speed, with the use of the equipment, the resistance of the high efficiency filter will gradually increase, which will cause the window wind speed to deviate from the set value, and there is a safety hazard for personnel protection. Therefore, there should be an audible and visual alarm when the wind speed of the window deviates from a certain range of the set value.
2. The airflow direction is an intuitive embodiment of the effect of the vertical wind speed and the working window inlet wind speed. It is also an intuitive means to verify the protection effect of the safety cabinet on the operator, the protection ability of the product, and the effect of preventing cross-contamination of the product. It is relevant at home and abroad. The standards have the same requirements for the direction of air flow. Therefore, it is a necessary verification item in the safety cabinet test.
Third, the noise statistics results show that if the sound level A in the room where the safety cabinet is located, the noise level should not exceed 68dB for evaluation, and the pass rate can reach 83.9%. Since the environment of the safety cabinet is mainly located in the laboratory, considering the superimposition effect of other noise sources in the laboratory, if the sound level noise value of the safety cabinet A is set to not exceed 68dB, the noise in the laboratory will not be able to guarantee the requirements of the laboratory specification . Therefore, it is recommended to appropriately adjust the noise upper limit requirements in order to meet the relevant requirements of the current laboratory.
4. For the Class Ⅱ B2 safety cabinet, the vertical air flow and window air intake are provided by different power fans. After the exhaust air volume is insufficient or the exhaust fan is damaged, if the air blower keeps running all the time, the safety cabinet will appear normal. Pressure, causing a large amount of airflow to overflow, which poses a great safety risk. Therefore, the air blower of the safety cabinet should be interlocked with the exhaust fan. When the air volume of the exhaust fan is insufficient or the exhaust fan stops due to failure, the air blower of the safety cabinet should be interlocked to stop, and the operator should be notified through an alarm.
5. When the vertical wind speed is too high, it will increase the load of the fan, which may cause excessive noise, and at the same time increase the risk of airflow overflow from the working window. It is found that the vertical airflow speed is between 0.25 and 0.5m/s by sorting out the sample book. Intervals accounted for 91.1% of the total number of samples, and there was no unqualified airflow organization. Therefore, it is recommended that the upper limit of wind speed be specified in accordance with the above requirements under the premise of ensuring that other parameters are qualified.
6. The verification of the integrity of the air supply HEPA filter above the operating surface can only show that the HEPA filter element and frame have not leaked, and cannot eliminate the problem of polluted air entering the experimental area due to excessively high window wind speed or low vertical wind speed. This phenomenon may lead to external contamination of the experimental operation area. Even if the equipment is tested for product protection performance during the factory and type inspection, the impact of uncontrollable factors during the transportation of the equipment on the performance cannot be completely avoided. Therefore, it is very necessary to test the cleanliness of the experimental operation area during the field test.
7. When the inlet wind speed of the working window is too high, it is easy to affect the cleanliness of the working surface near the exhaust orifice plate close to the window. According to the statistical results, 3.7% of the sample windows have an average inlet wind speed of more than 0.7m/s. In some samples within the interval, the cleanliness of the working surface near the exhaust orifice plate of the window is not up to standard or the airflow passes through the working area. Therefore, we should not only consider the requirement of the lower limit of the wind speed of the working window, but ignore the requirement of the upper limit of the wind speed.
8. For the vertical air supply of the safety cabinet, the air flow should be laminar. However, due to the structure of the air supply system, the wind speed of each section of the high-efficiency filter is inevitably different. When the speed difference is too large, There will be shear stress between the fluid layers, and then the vortex will be formed. If the vortex phenomenon occurs near the working window, polluted air will be drawn into the experimental operation area, thereby destroying the clean environment of the operation area. Therefore, in order to reduce the occurrence of the vortex phenomenon, the wind speeds at all points of the vertical airflow are required to be consistent, and the verification of the uniformity of the vertical wind speed is particularly important.