The ventilation design requirements of the laboratory ventilation and comfort air conditioning system are different. The main purpose is to provide safe and comfortable working environment and reduce the possibility of personnel exposure to dangerous air. Ventilation is mainly concerned with the physical health and labor protection of the laboratory personnel.
The ventilation requirements of the laboratory are all from the outside, and then 100% of the exhaust is outside. The exhaust of the fume hood is not in the indoor circulation. The ventilation requirement of the chemical laboratory is greater than 10 times per hour, and the physical laboratory is more than 10 times per hour, and the ventilation can be reduced to 6 times in the laboratory. The design quantity of the laboratory fume hood shall be sufficient, and shall not be used as the only indoor air exhaust device, the instrument room or the instruments that produce hazardous substances shall be equipped with a local exhaust system.
The air supply of the laboratory is directly from the air conditioning system to the new wind in the laboratory, and the new wind changes according to the change of the air volume of the laboratory. The other part passes through the air conditioning system into the corridor of the non-laboratory area and the room is resupplied by the door of the laboratory. The negative pressure of the laboratory is carried out by means of delivery, exhaust air volume and the arrangement of the air outlet, and the air flow organization is from the office, the management room, the inner corridor, and the laboratory room that produces dangerous substances. The position of the fume hood is located far away from the air flow and turbulence, away from the walking area and the fresh air zone. The new wind is introduced from the side of the ventilation cabinet, and the air flow path is far away from the fume hood.
Main function of fume hood.
Is the most main in the function of the fume hood exhaust function, in the chemical laboratory, experimental operation produce a variety of harmful gases, odor, moisture and inflammable, explosive, corrosive substances, in order to protect the users safety, prevent pollution to the laboratory diffusion in the experiment, in the vicinity of pollution sources to use the fume hood.
In the past, ventilation cabinets have been used in a relatively small number of stations, only in particularly hazardous and dangerous gases and in experiments that produce a lot of heat. The fume hood only undertakes the auxiliary function of the experiment station. Considered to improve the experimental environment in recent years, in the experimental stage in experiments gradually transferred to the ventilation cabinet, this requires that in the use of 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: the harmful gas produced in the fume hood should be equipped with the external gas absorption tank, so that it can be diluted back to the outdoor mechanism.
(2) no backflow function: the air flow generated by the exhaust fan inside the fume hood should be used to remove the harmful gas from the interior of the fume hood. 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 limited to the same tree room can be parallel, fan installed at the end of the pipe as far as possible (or roof).
(3) isolation function: the ventilation cabinet shall be separated by a non-sliding glass window in front of the fume hood.
(4) supplemental function: it shall have a passage or an alternative device that draws air out of the fume hood when harmful gases are discharged.
(5) control the wind speed function: to prevent the harmful gas escaping from the ventilation cabinet, it needs to have certain inhalation speed. The factors that determine the intake speed of the ventilation cabinet are: the heat generated by the experiment and the relationship with the number of ventilation. The main ones are the content of the experiment and the nature of the pests. Generally, it is stipulated that generally non-toxic pollutants are 0.25 -- 0.38m/s, toxic or dangerous harmful substances are 0.4 -- 0.5m/s, highly toxic or a small amount of radioactivity is 0.5 -- 0.6m/s, and the gas is 0.5m/s, and the particulate matter is 1m/s. In order to ensure such wind speed, the exhaust fan should have the necessary static pressure, that is, the friction resistance of the 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 the noise of the laboratory (indoor background noise level) limit is 70 db (A), 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.
(6) heat resistance and acid and alkali corrosion function: in the ventilation cabinet, there are some electric furnaces to be installed, and some experiments produce a lot of poisonous and harmful gases, such as acid and alkali, which are highly corrosive. The countertop of the fume hood, the lining board, the side board and the selected water mouth, the gas mouth and so on should have the antiseptic function.
