I. Comparative analysis of the standard exhaust ventilation and actual conditions It can be seen from the above regulations that the original production workshop only installs exhaust fans on the top of the building to reduce the concentration of combustible gas, which cannot meet the production needs. It is also necessary to install the exhaust fan in the lower part to assist it according to the above requirements. After consultation with the Design Institute, they have used more than 14 times of ventilation. At the same time, the scientific design of the comprehensive, local exhaust mode, scientific calculation of exhaust air volume is also an important factor to ensure the ventilation effect, only The installation position of the exhaust system, the air exhaust mode, and the air volume of the exhaust air are all scientifically implemented, so as to better eliminate the inflammable and explosive toxic chemicals that are permeated throughout the production workshop, and to ensure the safety of the production process. □ Floorstanding Bathtub Faucet,Floor Stand Faucet,Bathtub Faucet Tap,Bathtub Faucet Brass kaiping aida sanitary ware technology co.,ltd , https://www.kpfaucets.com
From the above analysis, it can be seen that the ventilation effect of the production workshop is very important. It must be scientifically designed, installed and installed, and ensure the normal opening of ventilation facilities, eliminating or reducing the dangers caused by flammable and explosive toxic chemicals. harm. 
Speaking of the thought of chatting with my classmates some time ago, I talked about the methanol concentration of the flammable and explosive chemicals in the workshop that he was responsible for in his work unit. The online flammable gas detector always alarmed. He knew that I was engaged in safety work. I took it to the scene and saw that the exhaust fan was only installed in the upper part, and the ventilation effect was not satisfactory. The problem of ventilation and exhausting was discussed below. 
With the above problems, the relevant standards have been sorted out. The relevant standards have the following requirements:  "Code for Fire Protection of Building Design" (GB 50016-2006) 10.1.5 When the mixture containing flammable gas and air lighter than air is excluded, The full length of the exhaust horizontal pipe should be laid up in the direction of the airflow. 10.1.6 Combustible gas pipelines and liquid pipelines of Class A, B and C shall not pass through the ventilation room and ventilation ducts, and shall not be laid close to the outer wall of the ventilation ducts. It can be seen from the standard that ventilation should be provided with ventilation ducts, which requires scientific analysis. Where there is a release source, a collection port is opened in the ventilation duct to reduce the volatilization of the release source (flammable and explosive toxic chemicals) in the production workshop. 
So, why do some production workshops have exhaust fans on the firewall? After consultation with the Chemical Design Institute and personal analysis, its exhaust fan plays a role in auxiliary ventilation and ventilation in today's large production. The workshop and ventilation facilities designed according to the old standards of the past were small in production and flammable. Explosive toxic chemicals are used in a small amount, and the fan can be used to meet the production gas exchange needs. However, as the production scale continues to expand, the previous design and installation cannot meet the needs of such large-scale production. When the situation does not match the specification standards, the following methods are recommended to meet the safety production needs.
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"Safety Evaluation" (3rd edition, the first volume, edited by the State Administration of Work Safety, 2005 edition, Coal Industry Press) 5.2.2 Countermeasures for fire prevention and explosion protection It is clearly stated that the ventilation mode of mechanical ventilation should meet the following requirements :
1. When the flammable gas that is released is lighter than air, it should be discharged from the upper part. 
2. When the flammable gas that is released is heavier than air, it should be discharged simultaneously from the upper and lower parts. However, when the gas temperature is high or the airflow rises due to the heat dissipation, it should be discharged from the upper part. 
3. When volatile substances evaporate, they are cooled down by the surrounding air or when volatile substances are often spilled on the ground, they should be discharged simultaneously from the upper and lower parts. In the production workshop with flammable gas, an accidental exhaust device should be provided. 
"Safety Regulations for Explosive Hazardous Locations" (Labor Fa [1995] No. 56) Article 16 Explosive hazardous areas must have good ventilation facilities to prevent the accumulation of explosive atmospheres. As far as possible, the production equipment should be arranged in the open air and semi-open air. The ventilation should be arranged indoors. The ventilation and ventilation facilities should be determined according to the specific gravity of the gas. For the local leaky parts, mechanical exhausting facilities that meet the explosion-proof requirements should be installed. 
"Industrial Enterprise Design Hygiene Standards" (GBZ1-2010) 6.1.5.1 Ventilation, dust removal, detoxification design should follow the corresponding dustproof, anti-virus technical specifications and procedures. d) The air volume at the air inlet shall be determined by calculation according to the principle of preventing dust or harmful gases from escaping into the room. When conditions permit, actual adjustments should be made with measured data or empirical values ​​before being put into operation. h) Local mechanical exhaust system All types of exhaust hoods should refer to the requirements of GB/T 16758, follow the design principles of appropriate form, correct position, moderate air volume, sufficient strength and convenient maintenance. The wind speed of the hood or the wind speed of the control point should be sufficient. The dust and poison generated by the source are sucked into the hood to ensure high collection efficiency. When the partial exhaust hood cannot be sealed, the appropriate umbrella-shaped exhaust device should be selected according to different process operation requirements and technical and economic conditions. 6.1 6.1.5.2 In the indoor working place where a large amount of harmful substances or chemicals that may cause acute poisoning or flammable or explosive substances may suddenly escape during production, an accident ventilation device and a leakage alarm device interlocked with the accident exhaust system shall be provided. . a) Accident ventilation should be ensured by the frequently used ventilation system and the accident ventilation system, but in the event of an accident, it must be ensured that sufficient ventilation is provided. The air volume of the accident ventilation should be determined by calculation according to the process design requirements, but the number of air changes should not be <12 times/h. 
Second, the exhaust method and air volume calculation
It is also recommended in the design to consider comprehensive ventilation and local ventilation. The principle of transformation must be economical and reasonable, and reduce expenditure.
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1. Determination of the overall ventilation volume  The so-called comprehensive ventilation volume refers to the amount of ventilation required to change the indoor temperature, humidity or dilute the harmful substances emitted into the room to the maximum allowable concentration specified by the sanitary standard. Generally, the following methods are used. Calculation.计算 Calculation formula for ventilation required to dilute harmful substances: L=kx(yp-ys)(1) In the formula: L——full ventilation, m^3/s; k—— The safety factor is generally used in the range of 1 to 3; x——the amount of harmful substances emitted, g/s; yp——the maximum allowable concentration of harmful substances in indoor air, g/m^3; Ys - the concentration of this harmful substance contained in the air supply, g/m^3. 
2. Determination of local ventilation  Local ventilation is the delivery and distribution of air to the local working area, suitable for the production of hazardous materials, as shown in Figure 1. Partial air supply directly delivers fresh air to the work site, which improves the environmental conditions of the work area and saves energy.  Local exhaust is to remove harmful substances in situ at the place where they are produced, and not to contact the staff before they are excluded. Compared with general ventilation, local exhaust can not only effectively prevent harmful substances from harming the human body, but also greatly reduce the amount of ventilation, as shown in Figure 2. The local exhaust system consists of an exhaust hood, a duct, a purification device, and a fan. The exhaust hood is the starting device for the removal of harmful substances, and its performance has a direct impact on the technical and economic effects of the local exhaust system. The selected exhaust hood should effectively and quickly eliminate the harmful substances at the working place with the minimum air volume. The common local exhaust hoods are: a closed cover, an external suction hood, a suction suction hood and a receiving cover, as shown in Fig. 3. Figure 4 shows.  Fig.1 Schematic diagram of local air supply systemFig.2 Schematic diagram of local exhaust systemFig.3 Closed exhaust hoodFig.4 External suction hood
3. Calculation of ventilation and ventilation volume The ventilation ventilation required to exclude air pollutants generated in buildings is calculated by the following formula: L=ZCp-C0(2) In the formula: L—— Ventilation capacity of buildings (m^3/h); Z——distribution of air pollutants in buildings (mg/h); Cp——concentration of exhaust air pollutants (mg/m) ^3), take the highest allowable concentration in the workshop hygiene standard; C0——the concentration of airborne air pollutants (mg/m^3). 
Clean air is the life of every individual, and people cannot survive without oxygen. In chemical enterprises, especially those that produce and use dangerous chemicals, the air in the production site contains inflammable and explosive toxic substances exceeding the national allowable limit, which brings danger and harm to the workers in chemical production sites, and is flammable. After the explosive substances exceed the standard, it may cause a fire and explosion accident, causing serious economic losses and negative impacts on the enterprise, and bringing occupational diseases and Other hazards to the operators. 