【 Weak current College 】 spraying fire risk analysis---Power By 【 China power house network 】

In recent years, the domestic electronics manufacturing brought a rapid development, and related parts spraying industry, spraying industry, increasing the size of production, only in Suzhou region in the last two years the scale of production capacity will expand a 2-3 times, technology and equipment changes rapidly, in fire protection technology is also facing new issues and tasks. In my view, relative to the traditional spraying technique and technology, new technology performance is highly automated and large-scale flow, plant structure, scale to large steel structure development, fire equipment and technically more advanced, therefore, need to fire design, fire technical approval, timely response to these new changes, and the response basis based on the characteristics of the spraying process and fire risk analysis for scientific research, it is clear that the spraying fire hazard analysis is necessary, are combined with the production instance, make a few observations.

I. spraying workshop fire risk classification and its importance

The architectural design fire protection standard (GBJ16-87, hereinafter referred to as buildings》) stipulates that "the production of fire risk is used by the production process or processing of goods of the fire risk categories", spraying workshop with different production processes, has a different fire risk. Paint spray booth and provisioned storage room use or storage, category b flammable or explosive chemicals such as organic solvents, paint, etc., to the fire risk categories a, b. Total shop area ratio larger before processing, and other processes, the fire risk is small, usually c. Ding, "production. Therefore, spraying workshop plant design, there will be workshops overall production fire hazard as a, b, or set it to c, d, r. Categories for different production, fire-fighting system and facility size, configuration requirements vary greatly, both plant fire rating, structural fire protection, fire prevention Division and the process partition area material choice will have a significant impact. For example, will the overall fire hazard workshop as a, b, according to buildings》 requirements, fire-resistant grade must be one, two, and now spraying workshop the light steel structure workshop fire resistance is low, in accordance with the present specification requirements, more difficult to achieve a higher fire resistance rating. Therefore, reasonable to determine the overall production of painting shop, have a bearing on the workshop on economic, security application and production problems.

2. spraying workshop to determine fire hazard

According to the characteristics of the spraying process, their fire risk in the use of paint itself has a fire hazard. In the existing safety code for painting and coating process safety "(GB6514-95) will contain a variety of organic solvents in paints is divided into class a, powder coating as category b, water-based coatings, latex paint for the CPI. Reference to the fire risk of paint itself, the different processes of fire risk characterization. But how to determine the overall production of painting shop categories, you should reference buildings》 relevant requirements.

In buildings》, depending on the nature of production, operating conditions, protective measures and other factors affecting the existing production plant of fire risk according to the a, b, c, d and e are classified into five categories in the order in which a plant fire danger, "to a minimum.

From spraying of Group b substances used, the use of organic solvents and paints area restricted to building local, it is not possible in general terms as a whole, CPI. Buildings》 provisions in section 3.1.1: Ding, "workshop of the paint section," when using closed painting process, closed spraying Chamber maintain negative pressure between, and the paint section sets the concentration of combustible gas alarm system or an explosion suppression systems, fire-retardant paint section covers an area of the partition where the ratio should not exceed 20 per cent. " That requirement is closed painting technology area, currently new spraying workshop, the majority adopted a special spray equipment, such as waterfall, water jet and venturi spray booth, are steel closure device, send the complete exhaust system, you can adjust the room remains negative, electrical equipment and lighting, and so are explosion-proof requirements set, and are equipped with the concentration of combustible gas alarm system with a closed painting process, this section covers an area of the fire prevention Division ratio should not exceed 20 per cent. So for Ding "plant as a whole, including painting, closed leveling (dry), closed drying equipment and paint the provisioning of storage rooms, the sum of the area should not exceed a total of 20 per cent of workshop area. Otherwise, the production category should not be characterized as Ding "production.

At the same time, from the use of spraying type b the number of items, not the use of organic solvents and coating processes are part of a category b production. Buildings》 section 3.1.1 article provides: "in the production process, such as use or produce flammable substances is less, the amount is not sufficient to constitute a risk of explosion or fire, you can determine the actual situation of the fire risk categories." In practice, you should consider in extreme conditions, a small amount of use in flammable or explosive (a) dangerous goods constitutes a danger of explosion or fire. For flammable liquids, should consider all volatile after the shop is filled with air volume mixing ratio is below the lower explosion limit, reached the lower explosion limit, there is a danger of explosion, fire risk in accordance with a category b, if below the lower explosion limit, you should also consider a reasonable safety factor, that is, just below the lower explosion limit, are clearly insufficient to fully exclude the risk of fire and explosion, you should clear a suitable risk "scale", to minimize the probability of fire and explosion. Buildings》 that article also stipulates that "a workshop or fire zones have different properties of production, which category should follow the fire risk in large part determine, but the fire risk large part covers the layer or the proportion of the area of fire protection district is less than 5% (Ding," production of paint section is less than 10%), and in the event of an accident is not enough to spread to other parts of the body, or to take measures to prevent the spread of fire, according to the fire risk smaller determine ". Reference to the provisions of the safety factor of 5% is more appropriate, i.e. with the air volume mixing ratio should be at least below the lower explosion limit of 5%,Before you can follow the smaller fire hazard. In this way, we can use flammable substances of number to determine the production category.

To the domestic present painting process most commonly used solvent xylene, for example, its flash point below 28 degrees centigrade, the fire danger for the CPI, steam explosion limit of 1 per cent, steam density 3.68kg/m3. According to calculations, reached the lower explosion limit of 5%, the air quality of xylene gas concentration 1840mg/m3. That is, under the above conditions, only when the plant in the xylene in air concentrations lower than 1840mg/m3, the plant's fire danger is not in accordance with the determination of CPI.

3. fire risk analysis applied in production

Located in the Suzhou high-tech development zone of a painting enterprise is a professional manufacturer of surface treatment, the No.1 and no.2 plant originally r workshop, using water-based coatings, then business development needs, the use of coating category, in spray paint mix rooms and limited use of oily coatings and organic solvents, their closed mixing room and paint the area between the provisioning and the proportion of the total of the workshop are in 5% (robot painting line original 6.6% improvement after reached 5%), the use of specialized spray equipment, such as water curtain Cabinet and dry spraying room, are all closed equipment, steel exhaust air system is complete, you can adjust the room remains negative, electrical equipment and lighting are explosion-proof requirements set, all equipped with a combustible gas concentration alarm device. The main ingredients of organic solvent to xylene, butyl acetate, isopropanol. A category b liquid solvent production usage according to data provided by the company are as follows:

No.1 plant: deliverability 69000 pieces/day, paints and thinners for maximum dosage 40L/day; 2 production plant: 8000 pieces/day, paints and thinners for maximum dosage 35L/day.

By calculation: 1 plant in accordance with the painting line takes up plant volume 23000 cubic meters, consider all volatile solvent of Group b, the volume of solvent per cubic metre plant is 0.0017 litres/cubic metre page〈 0.002 litres/M3 rated requirements (the numerical reference xylene, its relative density is 870mg/ml); 2, a workshop by spraying line up of plant capacity to 20000 cubic volume of solvent per cubic metre plant is 0.0018 litres/cubic metre page〈 0.002 litres/M3 rated requirements, the main component of the production quantity in line with the "all volatile and air mixture ratio is below the lower explosion limit of xylene 5%" requirement, therefore, in the strict limits of use of CPI coatings and organic solvents, production of the plant remains as a class c fire hazard.

Fire risk analysis is a dynamic process of analysis, not to simply apply the fire technical specification, can not be separated from the specific production process in general terms, the authors on this issue made some personal perspectives, hope fire technology colleagues humour.