What Is Lab Fume Hood
Lab Fume Hood Specifications:
Lab fume hood is an indispensable part of laboratory design. In order to prevent lab staff from inhaling or swallowing some toxic, pathogenic or toxic chemicals and organisms, there should be good ventilation in the laboratory. To prevent the absorption of some vapors, GASES AND particulATES (smoke, soot, dust AND AIR suspensions), contaminants MUST be removed by means of fume hoods, hoods or local ventilation.
Lab fume hood is the most commonly used local exhaust equipment in the laboratory. There are many kinds of fume hood. Because of its different structure, different conditions of use, its exhaust effect is not the same. The performance of the fume hood is mainly determined by the speed of air movement through the fume hood.
Classification method of lab fume hood
The fume hood is classified according to the exhaust mode:
It is divided into upper exhaust type, lower exhaust type and upper and lower exhaust type at the same time. In order to ensure uniform wind speed in the working area, the lower exhaust type should be used for the ventilation cabinet of cold process, and the upper exhaust type should be used for the ventilation cabinet of hot process. For the process of unstable heat, the ratio of the upper and lower exhaust air volume can be adjusted with the change of heat in the cabinet, so as to obtain uniform wind speed.
The fume hood is classified according to the air intake mode:
Full exhaust fume hood: through the indoor air intake in the cabinet circulation after the outdoor is called full exhaust, which is a very widely used type.
Replenishment ventilation cabinet: When the ventilation cabinet is set in the room with heating or temperature and humidity control requirements, in order to save energy consumption of heating and air conditioning, it is called replenishment ventilation cabinet by taking supply air from outdoor and circulating inside the cabinet before leaving the outdoor.
Variable air volume fume hood: the ordinary fixed air volume system needs to manually adjust the air valve of the fixed blade, 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. Variable air volume control is by adjusting the valve sensor to change the air volume to reach a given surface wind speed, of course, the standard low cost, high variable air volume cost, suitable for occasions requiring high precision.
The fume hood is classified according to the use state:
It can be divided into open lower part of the whole, floor type, two-side type, three-side glass type, table type, integrated type and special ventilation cabinet designed according to different experimental use needs for radioactive experiment, synthetic experiment and perchloric acid experiment.
Fold edit this section main function
The function of the fume hood exhaust function, is the most major in in the chemical laboratory, experimental operation produce a variety of harmful gases, odor, moisture and inflammable, explosive, corrosive substances, in order to protect the safety of the user, to prevent the spread of pollutants to the laboratory, in the vicinity of pollution sources to use fume hood, fume hood before using the Numbers is less, Use only in particularly harmful and dangerous gases and in experiments where a large amount of heat is produced. The fume hood only bears the auxiliary function of the experimental table. Considering the improvement of the experimental environment, the experiments carried out on the experimental bench are gradually transferred to the fume hood, which requires that there should be the most suitable function for the use of equipment in the fume hood. In particular, most newly built laboratories require air conditioning, so in the preliminary design stage of the building, the number of fume hoods used should be included in the air conditioning system plan. Because the fume hood occupies a very important position in the biochemical laboratory, the number of fume hood use has increased by leaps and bounds from the aspects of improving the laboratory environment, improving labor health conditions, improving work efficiency and so on. Followed by the ventilation pipeline, piping, wiring, exhaust and so on have become an important subject of laboratory construction.
The biggest purpose of using the fume hood is to discharge the harmful gas produced in the experiment and protect the health of the experimental personnel, that is to say, to have a high degree of safety and superior operation, which requires the fume hood should have the following functions:
(1) Release function: the harmful gas generated inside the fume hood should be absorbed by the gas outside the fume hood, so that it can be diluted and excluded from the outdoor mechanism.
(2) Non-backflow function: It should have the function that the air flow generated by the exhaust fan in the fume hood will not reverse flow into the room from the inside of the fume hood. In order to ensure the realization of this function, a fume hood and a fan with a single pipe connection is the best method, can not be connected with a single pipe, also limited to the same floor and the same room can be connected, the fan as far as possible installed in the end of the pipe (or the top of the layer).
(3) Isolation function: in front of the fume hood, there should be a non-sliding glass window to separate the inside and outside of the fume hood.
(4) Supplementary function: there should be a channel or alternative device for inhaling air from outside the fume hood when discharging harmful gases.
(5) Wind speed control function: in order to prevent harmful gases from escaping from the fume hood, it is necessary to have a certain inhalation speed. The factors that determine the suction speed of the fume hood inlet air are: the heat generated by the experimental content and the relationship with the number of air changes. The main ones are the content of the experiment and the nature of the harmful substances. Generally, it is stipulated that the general non-toxic pollutants are 0.25-0.38m /s, the toxic or dangerous hazardous substances are 0.4-0.5m /s, the highly toxic or a small amount of radioactivity is 0.5-0.6m /s, the gaseous substances are 0.5m/s, and the granular substances are 1m/s. In order to ensure such wind speed, the exhaust fan should have the necessary static pressure, that is, the friction resistance when the air passes through the ventilation duct. Determine the wind speed must also pay attention to the noise problem, through the air in the pipe flow is limited to 7-10 m, more than 10 m will produce noise, usually laboratory (indoor background noise level) noise limit is 70 dba, increase the pipeline laying area can reduce wind speed, also reduces the noise, the funding and construction of pipeline into consideration, must carefully choose the pipe and the exhaust fan Power.
(6) heat resistance and acid and alkali corrosion resistance function: some of the fume hood should be placed in the electric furnace, and some experiments produce a large number of acid and alkali and other toxic and harmful gases with strong corrosion. The mesa, lining board, side board and selected water nozzle and air nozzle of the fume hood should have anti-corrosion function. When sulfuric acid, nitric acid, hydrofluoric acid and other strong acids are used in the semiconductor industry or corrosive experiments, the overall material of the fume hood must be acid-alkali resistant, and must be made of stainless steel or PVC materials.
Collapse edit this section category
According to the classification of the use state, the fume hood can be divided into the open lower part of the whole, the floor type, the two-sided type, the three-sided glass type, the table type, the integrated type and the special fume hood designed for the radioactive experiment, the synthesis experiment and the perchloric acid experiment according to the different experimental use needs.
Safety is the biggest mission of the fume hood. The use of fume hood in the laboratory is to ensure the safety of users and prevent the pollution of the surrounding environment.
These security mainly reflected in
1, the use of single-slit exhaust structure, effectively discharge harmful gases.
2, flow line handle, the gap between the handle and the glass due to the flow of air on the table is rotating, from the surface to ensure effective air intake.
3, set up window anti falling pin, in case of steel wire rope off the glass window accidentally fell, with the anti falling pin will catch, to prevent injuries to personnel.
4, the glass window using toughened glass, even if the glass accidentally crashed or exploded, there will be no injury accident.
5, the ventilation hole is set on the top of the fume hood, even if the glass window is closed, it can enter the air, to avoid greater negative pressure.
6. The fume hood shell is made of metal material, fireproof and non-combustible. The inner cavity is made of anti-times special plate, stainless steel plate and other flame retardant or non-combustible materials, and the table is made of solid core physical and chemical board or stainless steel plate, acid and alkali resistance, heat resistance and flame retardant.
7, the effective height of the glass window is 800mm, the inner cavity is 1200mm, the height of the table is 800mm, which is ergonomic, easy to operate, large space to use, and improve the safety.
8. The water nozzle and air nozzle are equipped with remote handle outside the cabinet, which is more convenient and safe than direct hand operation.
Fume hood in use must also pay attention to safety
◆ Before the start of the experiment, it is necessary to confirm that the fume hood should be in the running state before the experiment operation.
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. An exhaust time delay device can also be considered to ensure delayed operation of the ventilator.
◆ Experiment, in the distance from the glass window 150mm do not put any equipment, large experimental equipment to have enough space, should not affect the flow of air, the front window as far as possible to close the use.