Different lab fume hood classification
- Classified according to the way of exhaust:
It is divided into three types: upper exhaust type, lower exhaust type and simultaneous upper and lower exhaust type.
In order to ensure uniform wind speed in the work area, the lower exhaust type should be adopted for the fume hood in the cold process, and the upper exhaust type should be adopted for the fume hood in the hot process. For the process of unstable heat generation, the upper and lower exhaust outlets can be provided with the cabinet The change of internal heat generation adjusts the ratio of the upper and lower exhaust air volume, so as to obtain a uniform wind speed.
- Classified by the way of air intake
1) Full exhaust type fume hood:
It is called the full exhaust type, which is a type that is widely used.
2) Supplementary air fume hood:
When the fume hood is set in a room with heating or temperature and humidity control requirements, in order to save heating and air conditioning energy consumption, the method of taking the supply air from the outside and circulating it in the cabinet and exhausting it to the outside is called the supplementary air fume hood.
3) Variable air volume fume hood: （VAV Fume Hood）
Ordinary constant air volume systems need to manually adjust the fixed blade air valve, adjust the exhaust air volume of the fume hood, and reach the desired surface wind speed when the valve is adjusted to a certain angle. Variable air volume control is to change the air volume to a given surface wind speed by adjusting the sensor of the valve. Of course, the standard type has low cost and high variable air volume cost, which is suitable for occasions requiring high precision.
- Classified by usage status
It can be divided into integral type, open bottom type, floor type, two-sided type, three-sided glass type, desktop type, conjoined type, as well as radioactive experiments, synthetic experiments, and perchloric acid experiments designed according to different experimental needs. Dedicated fume hood.
- Classified according to the presence or absence of external pipes
It can be divided into external row fume hoods and ductless fume hoods.
The external exhaust type fume hood is to directly extract the toxic and harmful gas generated during the experiment operation out of the outdoor through the external pipe.
The ductless fume hood directly adsorbs the toxic and harmful gases produced by the experimental operation with the activated carbon filter.
The main function of the fume hood is exhaust. In the chemical laboratory, various harmful gases, odors, moisture and flammable, explosive, and corrosive substances are generated during the experiment operation.
- Arrangement principles
In order to protect the safety of users and prevent pollutants in the experiment from spreading to the laboratory, a fume hood should be arranged near the pollution source.
In particular, most newly built laboratories require air-conditioning, so the number of fume hoods used must be included in the air-conditioning system plan in the preliminary design stage of the building.
In terms of improving the laboratory environment, improving labor hygiene conditions, and improving work efficiency, the number of fume hoods will be more and more used, and its auxiliary facilities: ventilation ducts, piping, wiring, exhaust, etc. have become laboratory construction designs Problems in need to be solved.
The biggest function of the fume hood is to discharge harmful gases in the experiment and protect the health of the experimenters. It has a high degree of safety and superior operability. The fume hood should have the following functions:
(1) Release function: It should be equipped to discharge harmful gas generated in the laboratory outside.
(2) Non-reverse flow function: The generated air flow prevents harmful gas from flowing into the room from the inside of the fume hood.
(3) Isolation function: a non-sliding glass window is used to separate the inside and outside of the fume hood.
(4) Wind speed control function: In order to prevent harmful gases from escaping in the fume hood, a certain suction speed is required.
(5) Heat resistance and acid and alkali corrosion resistance: some electric furnaces must be installed 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, lining boards, side panels, and selected water nozzles and gas nozzles of the fume hood should have anti-corrosion functions.
In laboratory operations, safety is the main purpose of using a fume hood, and its function is to ensure the safety of users and prevent pollution to the surrounding environment.
Ventilation usually adopts the following technologies to improve safety:
- Adopt a single-slit exhaust structure to effectively exhaust harmful gases.
- Streamlined handle, there is a gap between the handle and the glass. Because the air flow on the table is rotating, it can ensure effective air intake from the surface.
- Set the window anti-dropping pin, in case the steel wire rope falls off and the glass window accidentally falls, the anti-dropping pin will catch it to prevent people from being injured.
- The glass window adopts toughened glass, even if the glass is accidentally crashed or exploded, there will be no injury accidents.
- Ventilation holes are arranged on the upper part of the fume hood, even if the glass window is closed, the air can be entered to avoid the generation of greater negative pressure.
- The fume hood shell is made of metal material, which is fireproof and non-combustible. The inner cavity is made of fire-retardant or non-combustible materials such as anti-fold special plates and stainless steel plates, and the table tops are made of solid physical and chemical plates or stainless steel plates that are acid-proof, heat-resistant and flame-retardant.
- The effective height of the glass window is 800mm, the inner cavity is 1200mm, and the table height is 800mm. It is ergonomic, easy to operate, and has a large space for use, which improves safety.
- The remote operation of the handle of the faucet and gas nozzle outside the cabinet is more convenient and safer than direct manual operation.
◆Before the start of the experiment, it must be confirmed that the fume hood should be in operation before the experiment can be performed.
◆Before the end of the experiment, continue to run for at least 5 minutes before turning off the ventilator to discharge the residual gas in the pipeline. You can also consider installing an exhaust time delay device to ensure that the ventilator runs delayed.
◆ During the experiment, do not put any equipment within 150mm from the glass window. Large-scale experimental equipment should have enough space and should not affect the air flow. The front window should be closed as much as possible.
Three, the use and maintenance of the fume hood
In addition to correct design, the effectiveness of laboratory fume hoods has a great relationship with reasonable use and maintenance. Therefore, the following points should be noted:
(1) During the experiment, the experimental device that produces harmful substances should be placed in the fume hood where the operation port of the cabinet is greater than 150mm to prevent the overflow of harmful substances;
(2) The experimental device of the fume hood should not block the exhaust slits;
(3) After the experiment is completed, the fan should not be turned off immediately, it must be turned off after 3 to 5 minutes;
(4) The fume hood should not be used as a storage cabinet;
(5) The inside of the fume hood should always be kept smooth and airtight, and it should be cleaned and cleaned regularly and thoroughly. If it is damaged, it should be overhauled in time;
(6) The fans, air ducts and related accessories should be overhauled regularly.
(7) The fume hood must be measured and adjusted at regular intervals; make the fume hood operate under the design conditions;
(8) The temperature in the fume hood, such as the electric furnace with a large wattage, should be cushioned, and it should not be stored for a long time to avoid affecting the use of the fume hood.