Further discussion on the harm and prevention of steel drum coating production

Further discussion on the harm and prevention of steel drum coating production

Xin Qiaojuan

In July, a barrel factory in East China called and said that they were very uncomfortable recently. The paint drying room was on fire when the honey barrels were painted inside. The fire was big. The local government was involved in the rescue operation. The company could not be normal for more than half a month. produce. In the peak season of honey barrel sales, their own enterprises can not produce, very anxious, the current repair work is nearing the end, but their companies have been unable to find the cause of the fire.

I remember that a few years ago I had analyzed the safety hazards of the steel drum drying room. Now I will analyze the dangers and harmful factors in the painting process of the spray drying room.

First, the risk factors of steel drum spraying drying room

At present, when we paint domestic steel drums, we usually use medium temperature baking varnish. The baking temperature is between 135 and 150 °C, and the baking time is about 18 minutes. When the inner coated honey bucket is produced, the baking temperature of the inner coating is about 200 ° C or higher than 200 ° C, and some inner coatings such as PVF, the baking temperature is 280 ° C ± 10 ° C. If the specified temperature is not reached, the coating has no adhesion because the baking process is actually a polymerization process in which the coating is exposed to high temperatures. If the temperature does not meet the process requirements, the fluoride (toxic) in the PVF coating cannot be completely reacted, and toxic and harmful substances are generated, and the adhesion is almost no (large pieces can be detached), and the overall quality of the steel drum cannot meet the customer's requirements. However, if it is produced at high temperature, the drying room of most manufacturers will not meet the requirements, and some will not reach the high temperature of 300 °C when it is built. Some manufacturers require the maximum temperature of the drying room to be 350 °C, but because of the long years Working at around 150 °C, the interior of the drying room produces soot, oil, etc. Once it reaches the honey barrel production season, it is found that the furnace temperature is difficult to rise above 250 °C. At this time, many people in the workshop will start to show their talents. Various operations that violate the operating procedures, such as closing the air intake device, are employed, resulting in different levels of insecurity. Below we specifically analyze the possible risk factors for doing so:

1. Risk factors for fire and explosion in steel barrel drying room

At present, domestic steel drum spraying is divided into electrostatic spraying and high-pressure airless spraying, and drying has three kinds of gas, coal and fuel.

(1) A large number of electrical equipment (such as lighting fixtures, motors, switches and wiring boards, etc.) used in the steel drum spray drying workshop, if improperly selected (not explosion-proof) or not repaired in time after damage, or considered in the structure explosion-proof grade Insufficient, did not solve the overall explosion-proof problems of the electrical system.

2) During the electrostatic spraying process, the operator does not follow the operating procedures, and is prone to discharge sparks, which may cause a coating fire accident and a mixture of solvent volatilized gas and air, natural gas and the like to explode.

(3) Waste paint, paint mist, paint, and waste rags that have been wiped with solvents are not well stored, and they are easily ignited and ignited when stacked together.

(4) The operator lacks fire awareness, does not comply with the fire prevention rules, and uses an open flame (smoking) in the spray drying room to cause a fire.

(5) If the spray booth is not sufficiently ventilated and the safety air volume is insufficient, the concentration of gas such as paint mist and solvent volatile gas is easy to reach the combustion and explosion limit; in the coating leveling and drying process, the coating leveling area and the tunnel drying Poor indoor ventilation, solvent volatilization gas concentration may also accumulate excessively, reaching the explosion limit and encountering open flames (Mars, sparks) may cause burning and explosion accidents.

(6) Facilities and equipment such as paint storage, paint mixing room, painting equipment, paint conveying pipeline, paint distribution system, etc. all have flammable solvents in different degrees, and there are environmental conditions that are prone to explosion and fire.

(7) The grounding of the metal equipment in the spray drying workshop is poor or the resistance is too large, causing static electricity to accumulate, and even the electrostatic discharge reaches the ignition energy level.

(8) Lightning strikes occur during the thunderstorm season. Lightning power destroys buildings or personal injury or death, and even causes fire and explosion in the spray drying workshop. If the exhaust outlet of the spray drying workshop encounters lightning strikes, it is easy to cause burning and explosion accidents.

2. Electrical hazards in steel drum drying room

The main problems of electrical hazards in steel drum spray drying workshops are inseparable from fire and explosion hazards, because electrical accidents are often related to burning and discharging phenomena. Because the spray drying workshop is a typical flammable and explosive dangerous place, most of the space in the workshop may contain flammable and explosive mixed gas and flammable and flammable medium, which can get ignition energy and easily cause fire and explosion. Among various electrical hazards, electrostatic hazards in the spray drying workshop are the most common problems. Table 1 shows examples of common electrostatic hazards.

Table 1 Examples of common electrostatic hazards

Static electricity is produced by the contact, separation and friction of two or more different substances. The high-speed flow of organic coatings and organic solvents in the production process of steel drums may accumulate electrostatic charges in pipes and containers. At the same time, the electrostatic spraying is used in the steel barrel spraying production, and the application of the coating by the electrostatic principle is more likely to cause accidental release of the electrostatic charge, causing harm.

Once the spark of electrostatic discharge reaches the ignition energy, it may cause an explosion and fire.

Many accident cases have confirmed that the energy generated during electrostatic discharge is likely to reach the ignition level, which can cause the combustion of solvent-based coatings and powder coatings. The cause of electrostatic discharge in spray production is mainly caused by the breakdown of air between the two electrodes. There is obvious discharge concentration point on the electrode. In an instant, the energy concentrates to release the paint mist, solvent and other flammable suspended matter space formed by electrostatic spraying and electrostatic powder spraying, which is easy to generate spark discharge, ignite and detonate flammable and explosive. substance.

Second, the toxic and harmful factors in the steel drum spray drying room

In recent years, with the enhancement of people's awareness of environmental protection and the implementation of enterprise safety production standardization, steel drum enterprises have exerted great efforts to improve the occupational health and working environment of employees. Many companies reduce environmental pollution and improve the working environment of employees by improving coating equipment and using environmentally friendly coatings (water-based paints). However, benzene, toluene, xylene, carbon monoxide and other gases in traditional paints are not sprayed and dried in steel drums. Avoiding will seriously affect the personal health of employees. Let's analyze the toxic and harmful factors produced by the spray drying room.

1. Degree of xylene contamination during steel drum spraying operation

In the process of steel drum spraying production, the most serious poisoning hazard is air pollution in air painting and electrostatic painting workplaces. In the range of painting operations, the results show that the content of xylene is 1600-2400 mg/m3. Especially in workplaces where there is no closed spray booth and exhaust air, operators often use air or electrostatic spray guns to spray directly on the steel drum at the workplace, resulting in the accumulation of organic solvents in the workplace, which is the most harmful. In this case, the xylene content often exceeds 10 to 20 times the national standard limit. In the painting operation, occupational hazards such as benzene poisoning are common.

2, benzene poisoning hazards

The steel barrel painting process, especially the painting operation, is a typical position for exposure to toxic substances. The toxic substances are mainly from organic solvents such as paints and thinners. If the steel drum is treated with a variety of organic solvents, it will also be exposed to toxic substances. The most harmful of these are benzene, toluene and xylene. If you operate for a long period of time in the absence of anti-virus safety measures, it may cause benzene poisoning.

3. The harm of lead poisoning

Long-term exposure to organic solvent coatings in steel drum spraying operations may also cause lead poisoning by operators. The presence of lead in the coating is caused by the following various substances.

The lead tetraoxide (also known as red dan) used in the anti-rust primer has a high alkalinity. Yellow, green oil paint, lead chromate in lead chrome used in enamel, including a small amount of lead sulfate. Lead white used in the manufacture of white paint is an ancient white pigment. Its main component is basic lead carbonate. It is easily soluble in gastric juice and can reach 59.8%~77.9%. It is easy to absorb and has high toxicity. In the paint, the yellow dan can be used as a drier and lead soap is formed from oil, and the composition is lead oxide.

Red Dan is an excellent anti-rust pigment widely used in anti-rust paints, but it is a highly toxic lead-containing pigment. Therefore, red Dan cannot be used in food-related coatings.

Third, the safety precautions for the steel drum spray drying room

1. The steel drum spraying operation personnel must pass the education and training of fireproof and explosion-proof safety knowledge, and after being qualified, they can engage in steel drum spraying operation.

2, steel drum painting workshop must have strict safety operation procedures and fire and explosion prevention system, and check the implementation status at any time, can not be paralyzed.

3. During the spraying operation of the steel drum, it should be noted that the solvent gas concentration in the workplace should not exceed the specified range, the barrels for storing paints and solvents should be tightly sealed to avoid solvent evaporation; the painting work place should be equipped with exhaust and exhaust equipment. To reduce the concentration of solvent gases. When constructing in a limited space, in addition to strengthening ventilation, it is also necessary to prevent the indoor temperature from being too high.

4. Smoking should be strictly prohibited at the production work site. It is not allowed to bring matches, lighters and other fires into the work site (paint drying room). If you must use fire, use blowtorch, soldering iron, welding, you must go through the fire safety approval procedures in accordance with the safety production regulations, there is a special person on-site supervision during the fire.

5. During the painting operation, the wiping paint and waste materials contaminated with organic solvents, cotton cloth, cotton yarn, protective clothing, etc. should be stored in a centralized manner and properly disposed of, especially some wastes should be stored in a closed bucket containing clean water. Avoid fires near hot stoves or near heating pipes and drying rooms.

6, all kinds of electrical equipment, such as lighting, electric motors, electrical switches, etc., should have explosion-proof devices. It is necessary to regularly check the circuit and equipment, whether the insulation is damaged, whether the motor is overloaded, and whether the electrical equipment is reliably grounded.

7. During the painting operation, try to avoid knocking, collision, impact, friction iron and other actions to avoid sparks and cause burning. It is strictly forbidden to wear people with nail shoes to enter the work site, and do not need iron bars to open metal paint buckets.

8, to prevent sparks caused by electrostatic discharge, electrostatic spray gun can not be too close to the workpiece, eliminating static accumulation in equipment, containers and pipes. Wear anti-static clothing, etc. when producing and painting in a limited space.

9. Prevent the rapid heat release when the two-component paint is mixed. Stir the paint continuously and place it in a ventilated place. Aluminum powder paint should be packaged in cans to prevent spontaneous combustion of hydrogen due to moisture. When preheating the paint, the temperature should not be too high, and the container should not be sealed and cannot be heated by an open flame.

10. The maximum content of flammable gas in the drying room should not exceed 25% of the lower limit of the explosion. The maximum content of dust in the air should not exceed 50% of the lower limit of the explosion. The drying room should be ventilated, and the position of the exhaust vent should be set at the highest concentration of flammable gas. The heater surface temperature should not exceed 80% of the workpiece coating ignition temperature.

11. The internal height of the large spray booth should not be less than 2.5m, and the indoor outlet should be unobstructed and the width should be no less than 0.9m. The indoor equipment is made of flame retardant materials, and various metal parts need to be reliably grounded. The spray booth should be equipped with a multi-point flammable gas detection alarm. The lower limit of the alarm content should be controlled at 25% of the lower limit of the detected flammable gas explosion.

12. A sufficient number of fire extinguishing equipment, asbestos felt, yellow sand box and other fireproofing tools must be provided in the spray drying room. The construction personnel should be skilled in using various fire extinguishing equipment.

13. In the event of a fire, do not use water to extinguish the fire. At the same time, reduce the amount of ventilation. Use asbestos felt, yellow sand, fire extinguisher (carbon dioxide or dry powder) to extinguish the fire. If the overalls are on fire, don't pat with your hands and roll them off on the spot.

14. A fire damper should be installed on the exhaust pipe of the large drying room. If there is a fire in the drying room, the valve should be automatically closed, and the circulating fan and the exhaust fan should be automatically stopped.

15. A large number of flammable materials should be stored in the safe area of ​​the warehouse. The paint drying room should be stored in the paint room to avoid storing a large amount of flammable and explosive materials such as paint and solvent.

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