Fume hood function and safety
Function and safety of the fume hood Building a modern biochemical laboratory is a comprehensive system engineering. While equipped with various instruments and equipment and its supporting facilities, it is necessary to consider the requirements of power supply, water supply, drainage, air supply, exhaust air purification and sewage discharge, and also consider the safety, noise and odor of people, objects and surrounding environment. The comfort of the visual environment, the operability and functionality of the equipment, and the convenience of information processing. Therefore, modern biochemical laboratories must have the best design and high quality equipment to meet.
In the modern laboratory equipment, there are fume hoods, central test benches, side tables, medicine cabinets, utensil cabinets, gas cylinder cabinets, etc., among which the fume hood is a vital function in the biochemical laboratory equipment and is an indispensable equipment. . Therefore, the selection of the fume hood is an important issue in the construction of the laboratory and must be given sufficient attention.
The main function of the fume hood :
The most important function of the fume hood is the exhaust function. In the chemical laboratory, all kinds of harmful gases, odors, moisture and flammable, explosive and corrosive substances are generated during the experimental operation, in order to protect the safety of users. To prevent the spread of pollutants in the laboratory to the laboratory, use a fume hood near the source of pollution. In the past, the number of fume hoods used was small, and it was only used in experiments with particularly harmful and dangerous gases and large amounts of heat. The fume hood is only responsible for the auxiliary functions of the test bench. In recent years, considering the improvement of the experimental environment, the experiments carried out on the test bench have gradually shifted to the fume hood, which requires the function of the most suitable equipment for use in the fume hood. In particular, most newly built laboratories require air conditioning, so the number of fume hoods to be used in the initial design phase of the building is included in the air conditioning system plan. Since the fume hood occupies a very important position in the biochemical laboratory, the number of fume hoods has increased dramatically in terms of improving the laboratory environment, improving the sanitary conditions, and improving work efficiency. It is followed by ventilation ducts, piping, wiring, and exhausting, which have become important topics in laboratory construction. The main purpose of using the fume hood is to remove the harmful gases generated in the experiment and protect the health of the experimenter, that is to say, to have a high degree of safety and superior operability, which requires the fume hood to have the following special functions:
(1) Release function: The mechanism for absorbing the harmful gas generated inside the fume hood to absorb the gas outside the cabinet should be diluted to exclude the outdoor unit.
(2) Non-backflow function: It should have the function of the airflow generated by the exhaust fan inside the fume hood to prevent harmful gas from flowing into the room from the inside of the fume hood. In order to ensure the realization of this function, a single fume hood and a ventilator are connected by a single pipe. It is the best method. It cannot be connected by a single pipe. It is also limited to the same room in the same floor. Install at the end of the pipe (or at the top of the floor).
(3) Isolation function: The inside of the fume hood should be separated by a non-sliding glass window.
(4) Supplementary function: There shall be a passage or alternative means for drawing in air from outside the fume hood when harmful gases are exhausted.
(5) Control wind speed function: In order to prevent the harmful gas in the fume hood from escaping, a certain suction speed is required. The factors that determine the suction speed of the air inlet of the fume hood are: the heat generated by the experimental content and the relationship with the number of air changes. The main ones are the experimental content and the nature of the harmful substances. Generally, the generally non-toxic pollutants are 0.25-0.38 m/s, the toxic or dangerous pollutants are 0.4-0.5 m/s, highly toxic or a small amount of radioactivity is 0.5-0.6 m/s, and the gas is 0.5m/s, granules are 1m/s. In order to ensure such a wind speed, the exhaust fan should have the necessary static pressure, that is, the frictional resistance of the air as it passes through the ventilation duct. When determining the wind speed, you must also pay attention to the noise problem. When the air flows through the pipeline, it is limited to 7-10m. If it exceeds 10m, noise will be generated. Generally, the noise limit of the laboratory (indoor background noise level) is 70dBA, and the pipe cut area will be increased. Reducing the wind speed also reduces noise. Considering the cost of the pipeline and construction problems, the power of the pipeline and the exhaust fan must be carefully selected.
(6) Heat-resistance and acid-alkali corrosion resistance: There are some electric furnaces in the fume hood, and some experiments produce a large amount of toxic and harmful gases such as acid and alkali, which are extremely corrosive. The countertops, linings, side panels and selected water nozzles and air nozzles of the fume hood should have anti-corrosion function. In the semiconductor industry or corrosive experiments using strong acid such as sulfuric acid, nitric acid, hydrofluoric acid, etc., the overall material of the fume hood must be resistant to acid and alkali, and must be made of stainless steel or PVC material.
Fume hood category:
The fume hoods are classified according to the exhaust mode: they are divided into the upper exhaust type, the lower exhaust type, and the upper and lower simultaneous exhaust type. In order to ensure uniform wind speed in the working area, the lower air exhaust type should be adopted for the ventilating cabinet of the cold process, and the upper exhaust type for the ventilating cabinet of the thermal process. For the process of unstable heat generation, the air vent can be installed on the upper and lower sides. The change in internal heat regulates the ratio of the upper and lower exhaust air to obtain a uniform wind speed. Ventilation cabinets are classified into three categories according to the air intake method. It is called a full exhaust type by circulating indoor air in the cabinet and then discharging it. This is a very widely used type. When the fume hood is installed in a room with heating or control requirements for temperature and humidity, in order to save heating and air conditioning energy consumption, the method of exhausting air from the outside and circulating it in the cabinet and then discharging it outside is called a supplemental air fume hood. The other is a variable air volume control type fume hood. The ordinary constant air volume system needs to manually adjust the damper of the fixed vane, adjust the exhaust air volume of the fume hood, and achieve the desired surface wind speed when the valve is adjusted to a certain angle. The variable air volume control is to change the air volume by adjusting the sensor of the valve to achieve a given surface wind speed. Of course, the standard type has low cost and high variable air volume cost, and is suitable for occasions requiring high precision. The fume hood can be divided into the whole lower open type, floor type, two-sided type, three-sided glass type, table type, conjoined type according to the state of use, and the radioactive experiment and the synthetic experiment designed according to the needs of different experimental uses. , a dedicated fume hood for perchloric acid experiments.
Safety of the fume hood:
Safety is the biggest mission pursued by fume hoods. The use of fume hoods in the laboratory is to ensure the safety of users and to prevent pollution to the surrounding environment.
Smile is one of the earliest professional companies in China to develop and produce fume hoods. Combining the characteristics of similar products at home and abroad, the company has gradually developed the research and development of laboratory equipment centered on fume hood technology. While pursuing performance and functionality, it is greatly considered for its security. These security features mainly have the following characteristics:
1. Adopt a single-slot exhaust structure to effectively discharge harmful gases.
2. Streamlined handlebars, leaving a gap between the handlebar and the glass. The flow of air on the tabletop is rotated, ensuring effective intake from the surface.
3, set the window anti-drop pin, in case the wire rope off the glass window accidentally falling, with the anti-drop pin will catch, to prevent people from hurting.
4, the glass window is made of tempered glass, even if the glass accidentally crashes or explodes, there will be no accidents.
5. Ventilation holes are provided in the upper part of the fume hood to allow air to enter even if the glass window is closed, to avoid generating a larger negative pressure.
6, the fume hood shell is made of metal material, fireproof and non-combustible. The inner cavity is made of flame retardant or non-combustible materials such as anti-double plate and stainless steel plate. The countertop is made of solid core physical or chemical plate or stainless steel plate to prevent acid and alkali, heat and flame retardant.
7. The effective height of the glass window is 800mm, the inner cavity is 1200mm, and the height of the table is 800mm. It is ergonomic, easy to operate, and has large space for safety.
8. The water nozzle and the air nozzle operate the handle remotely at the peripheral of the cabinet, which is more convenient and safer than direct manual operation.
The fume hood must also be safe when in use. â—† Before the experiment begins, it must be confirmed that the fume hood should be in operation before the experiment can be performed. â—† At least 5 minutes or more before the end of the experiment, the fan can be turned off to discharge the residual gas in the pipeline. It is also conceivable to install an exhaust time delay to ensure that the fan is delayed. â—† During the experiment, do not put any equipment within 150mm from the glass window. Large experimental equipment should have sufficient space and should not affect the flow of air. The front window should be closed as much as possible. Fume hood selection
When constructing the laboratory, selecting the fume hood and determining the installation position of the fume hood, it is necessary to select the type, material, shape, etc. of the fume hood according to the experimental content, which is usually considered. The following: Drugs used: When using organic or other special reagents, consider the control of wind speed. Heat source: When using a device with a heat source, the amount of ventilation required to dissipate heat should be considered to determine the power of the fan when the heat exceeds 2000 kcal/hour. In the case of radioactive materials or perchloric acid: a dedicated fume hood should be used, and the inlet air velocity must be set greater than 0.5 m/s. When experimenting with large equipment: Consider the internal effective size and leave the necessary space for the exhaust. Material: When using special acid experiments, consider the material of the fume hood, such as the semiconductor industry, corrosion industry, etc. must be made of anti-corrosion materials. Dimensions: According to the experimental content, choose its external dimensions, the volume is too large, causing waste, too small to affect the use. Environmental protection: Exhaust harmful gases should be installed if they are required to be below national environmental requirements if they exceed national health standards.
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