Laboratory ventilation is an indispensable part of laboratory design. In order for laboratory staff not to inhale or swallow toxic, pathogenic or unknown chemicals and organisms, the laboratory should be well ventilated. To prevent the absorption of some steam, gas, and particulates (smoke, soot, dust and air suspension), the pollutant must be removed by ventilation, ventilation, or local ventilation.

Structure
The structure of fume hood is up and down type, its top has air vent, can install fan.There is a guide plate in the upper cabinet, the circuit controls the touch switch, the power outlet, etc., the perspective window adopts toughened glass, which can be moved or left or right. For operation.The lower cabinet USES the experiment side table style, the top is countertop, below is the cabinet body. Table can be installed small water cup and bibcock.The material of fume hood is various, all steel, steel wood, whole wood, aluminium wood, plastic steel, PVC structure, etc., its mesa is the place that directly and operator contact, by solid core physical and chemical board, stainless steel board, PVC, ceramic and other material composition.The old style fume hood is made of wood, but modern is mostly made of steel with epoxy resin. The common cabinets are 1000, 1200, 1500,
1800 and 2000 mm specifications, which are 700-900 mm deep and 1,900-2400 mm high. Available for 1-3 people at the same time. The fume hood is generally installed on the wall.The front center is a transparent door that can be moved up and down (mostly glass), and the height is usually 100 to 600 mm. After the door, the working face for the experiment, water pipe, sewer, power supply, vacuum pump, gas pipeline and other experimental needs of the connection, the lamp lighting with protective cover. The air is removed by a fan at the top of the cabinet, or through a pipe to be used elsewhere (known as a fully ventilated), or through filtration to reuse (to be unventilated).

Most fume hoods will alert the operator when they are overblown and when the glass door opens too large. The internal exhaust fan speed and light have a switch adjustable.

When used, people will stand or sit in front of the cabinet, keep the glass door low, and carry out the experiment through the door under the door. Since the exhaust fan is pumped through the open door, harmful gases in normal conditions do not overflow.

Classification method
Sorted by wind
It is divided into the upper exhaust type, the lower exhaust air type and the upper and lower air lines. Uniform wind speed, in order to ensure the work area for the cooling process of fume hood should use the lower exhaust type, for thermal process of the fume hood adopt upper exhaust type, the calorific value is not stable, the process of air outlet can be set in both up and down along with the change of calorific value contained in the adjust the ratio of upper and lower exhaust air volume, and uniform wind speed is obtained.

Categorize by wind
All exhaust ventilation cabinet: through indoor air inlet in the inner circle of the inner circle is called the whole exhaust type, which is a very broad type of application.Fill the wind ventilation cabinet: when the fume hood set in heating or is required to control the temperature and humidity room, to save on heating, air conditioning energy consumption, use the back from the outdoor supplies wind circulation inside ark out way called wind type
fume hood.Variable air volume ventilators: the normal air conditioning system needs to manually adjust the wind valve of the fixed blade, adjust the exhaust volume of the fume cupboard, and achieve the desired surface wind speed when adjusting the valve to a certain Angle. The variable air volume control is to change the air volume to the given surface wind speed by adjusting the valve’s sensor. Of course, the standard type cost is low and the variable air volume is high, which is applicable to the occasion where the precision is high.

Classification by use state
Can be divided into the integral lower open, floor, two, three sides of glass, the table type, even the asana and designed according to the needs of different experimental use of radioactive experiment, synthetic experiment, across chlorate experiment of special fume hood.

Main function of fume hood
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, only in particularly harmful and dangerous gas and produce a large amount of heat used in the experiment. The ventilation cabinet is
only for the auxiliary function of the test bench. In recent years, considering the improvement of the experimental environment, the experiment carried out on the experimental stage has been gradually transferred to the ventilation cabinet, which requires the most suitable function for the equipment to be used in the fume hood. In particular, most new laboratories require air conditioning, so the use of ventilation cabinets should be incorporated into the air-conditioning system in the preliminary design phase of the building. Because of the fume hood
occupies very important position in the biochemical laboratory, from the improvement of laboratory environment, improve the labor hygiene conditions, improve the work efficiency into consideration, such as the use of the fume hood number by leaps and bounds.

The following is the ventilation ducts, piping, wiring, exhaust and so on become the important project of the laboratory construction.Using the fume hood is the biggest purpose discharge harmful gases generated in the experiment, protect the health of the researchers, that is to say, want to have a high security and excellent operability, which requires the fume hood should have the following features:
(1) release function: it shall have the means to absorb the harmful gas from the fume hood inside the cabinet, so as to eliminate the outdoor mechanism after dilution.
(2) no reverse flow function: the air flow generated by the exhaust fan in the fume hood shall be the function of the harmful air flow from the inside of the fume hood into the interior. In order to ensure the implementation of this function, a hood and a fan with a single pipe connection is the best way, cannot use a single pipe connection, also
only can be provided the same room and even, fan installed at the end of the pipe as far as possible (or roof).
(3) isolation function: in front of the fume hood, the ventilation cabinet shall be separated by an unsliding glass window.
(4) supplementary function: a passage or an alternative device that takes air out of a fume hood when discharging harmful gases.
(5) control the wind speed function: to prevent the harmful gas escaping from the ventilation cabinet, it needs to have a certain speed of inhalation. The factors that determine the intake speed of air inlet are: the heat and the relationship with the number of ventilation. The main one is the content of the experiment and the nature of the harm.

Generally, it is stated that the non-toxic pollutants are 0.25%-0.38m/s, toxic or dangerous substances are 0.4-0.5 m/s, and the poisonous or small amount of radioactivity is 0.5-0.6 m/s, the gas is 0.5m/s and the particle is 1m/s. In order to ensure the wind speed, the exhaust fan should have the necessary static pressure, namely the friction resistance of air through the ventilation ducts. 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 reduce noise, considering the funding and pipeline construction question, must choose carefully pipeline and exhaust fan power.