Electric welding, also known as arc welding, is the arc heat effect generated by the welding equipment, which causes the cross section of the welded metal to be locally heated and melted to a liquid state, so that the originally separated metal is combined into a firm and non-removable joint process. According to the welding process, arc welding can be divided into automatic welding, semi-automatic welding and manual welding. Automatic welding and semi-automatic welding are mainly used for the manufacture of large-scale mechanical equipment. The equipment is installed in the workshop and the working place is relatively fixed. The manual welding is not limited by the conditions of the working place, and has good flexibility. It is currently used for outdoor open-air construction. There are more homework. Due to the large difference in workplaces, the work is accompanied by the generation of electricity, light, heat and open flames, so there are various hazards in the welding work.
Main hazards of welding operations
First, it is easy to cause electric shock
1. During the welding process, the welder should frequently change the welding rod and adjust the welding current. The operation should directly contact the electrode and the plate, and the welding power source is usually 220V/380V. When the electrical safety protection device is faulty, the labor protection products are unqualified. When the operator violates the regulations, it may cause an electric shock. If soldered in a metal container, on a pipe, or in a wet location, the risk of electric shock is greater.
2. When the welding machine is unloaded, the secondary winding voltage is generally 60~90V. Because the voltage is not high, it is easily ignored by the welder, but its voltage exceeds the specified safe voltage of 36V, there is still some danger. Assume that the no-load voltage of the welding machine is 70V, and people work in high temperature and humid environment. At this time, the human body resistance R is about 1600Ω. If the welder touches the jaw, the current I through the human body is: I=V/R=70/1600=44Ma Under the action of this current, the welder's hand will be paralyzed, which may cause an electric shock accident.
3. Because welding work is mostly in the open air, the welding machine, welding wire and power line are mostly in high temperature, humidity (construction site) and dust environment, and the stove is often overloaded, which makes the power line and electrical circuit insulation aging The insulation performance is reduced, which is easy to cause leakage accidents.
Second, it is easy to cause fire and explosion accidents
Due to arcing or open flame during welding, it is very easy to cause fire when working in places with flammable materials. Especially in the area of flammable and explosive devices (including pits, trenches, troughs, etc.), it is more dangerous to weld on containers, towers, tanks and pipes that have stored flammable and explosive media. There are still many accident cases on this side. For example, the "12·25" catastrophic fire accident in Luoyang in 2000 was due to the illegal welding work in the commercial buildings. The poor management caused the surrounding flammable objects to catch fire, which caused a total of 309 deaths. On May 26, 2003, the Beijing Dongfang Chemical Plant arranged for the welder to weld the manhole cover pin nut of the train tanker who had stored and transported the methyl acrylate. Since the tanker was not cleaned and replaced beforehand, before the fire No analysis of the combustible gas in the tank truck, without any measures, resulted in the tanker flashing, the manhole cover was opened, and the welder was killed.
Third, easy to cause burns
If arcing or metal slag is generated during the welding process, if the welder is not wearing protective protective overalls, gloves and shoes for welding, especially when welding at high places, due to spark splashing, if no protective isolation measures are taken, It is easy to cause skin burns on the welder or the construction personnel under the work surface.
Fourth, easy to cause electro-optic ophthalmia
Due to the strong visible light and a large amount of invisible ultraviolet rays during welding, it has a strong stimulating effect on human eyes. Long-term direct irradiation can cause eye pain, photophobia, tearing, fear of wind, etc., which may lead to conjunctiva and Corneal inflammation (commonly known as electro-optic ophthalmia).
Fifth, with the role of light radiation
The arc light generated during welding contains infrared rays, ultraviolet rays and visible light, and has a radiation effect on the human body. Infrared rays have the function of heat radiation. When welding in high temperature environment, it is easy to cause heat stroke for workers. Ultraviolet light has photochemical action and damages human skin. At the same time, exposure to exposed skin for a long time will also cause skin peeling, and long-term exposure to visible light will cause Eyesight is declining.
Sixth, easy to produce harmful gases and smoke
Since the arc temperature generated during the welding process reaches 4200 ° C or above, gasification, evaporation and condensation occur after the welding of the electrode core, the coating and the metal weldment, and a large amount of manganese chromium oxide and harmful smoke are generated; The high temperature of light and strong radiation also cause the surrounding air to generate toxic gases such as ozone and nitrogen oxides. Engaged in electric welding for a long time under poor ventilation conditions. These toxic gases and fumes are inhaled by the human body and have a certain impact on human health.
Seventh, there is a risk of falling when working at height
Due to the construction needs, the welder should always climb the welding operation. If the anti-air fall control measures are not done well, the scaffolding is not standardized, and it will not be used after acceptance; the work will be taken against the object to prevent the object; the welder's personal safety protection awareness is not strong. If you don't wear a safety helmet or a seat belt when you climb the work, you may cause a high fall accident if you encounter accidental walking or unexpected objects.
Eighth, easy to cause poisoning, suffocation
Welders often need to enter the closed or semi-closed places of metal containers, equipment, pipes, towers, storage tanks, etc. If the toxic and harmful medium and inert gas are stored, transported or produced, once the work is poorly managed, the protective measures are not in place. It is easy to cause poisoning or lack of oxygen in the workers. This phenomenon occurs mostly in refining and chemical industries.
Welding work protection measures
First, anti-shock measures
The general principle is to take safety measures such as insulation, shielding, insulation, leakage protection and personal protection to prevent the human body from touching the charged body. The specific methods are:
1. Improve the insulation performance of electric welding equipment and wiring. The welding equipment and power cable used must be qualified. The electrical insulation performance should be compatible with the voltage level, surrounding environment and operating conditions. The welding machine should be equipped with special personnel for daily maintenance and maintenance to prevent sun and rain. The welder's electrical insulation performance is reduced.
2. When the welder fails to repair, move the work place, change the joint or replace the safety device, the power must be cut off before operation.
3. When installing the power supply to the welder, don't forget to install the leakage protector at the same time to ensure that the person will automatically power off once the electric shock occurs. When welding on wet or metal containers, equipment and components, it is necessary to select a leakage protector with a rated operating current of not more than 15 mA and a rated operating time of less than 0.1 second.
4. The protective earthing or zeroing measures should be taken for the ends of the welding machine housing and the secondary winding lead wires. When the power supply is a three-phase three-wire system or a single-phase system, the protective grounding wire should be installed, and its resistance value should not exceed 4 Ω. When the power supply is a three-phase four-wire neutral grounding system, the protective neutral wire should be installed.
5. Strengthen the education of workers' electricity safety knowledge and self-protection awareness. It is necessary to wear insulated shoes and special insulating gloves when welding work. It is forbidden to apply welding in the open air on rainy days; in special humid places, people must stand on dry wood or rubber insulation sheets.
6. It is forbidden to use metal structures, pipes, rails and other metal connections for wire. Soldering in metal containers or particularly wet locations, the street light supply must use a safe voltage of less than 12V.
Second, fire and explosion prevention measures
1. Welding in inflammable and explosive places, beforehand, the fire operation permit must be handled in advance according to the regulations, and approved by the relevant departments.
After agreeing to work, we must strictly implement the "three no fires."
2. Whether there are flammable or explosive materials under and around the inspection before the formal welding, whether there are anti-corrosion substances such as paint on the working surface, if any, should be properly handled in advance. For welding operations in the adjacent production area and oil tank area, a firewall must be built; if there is high-altitude welding, it should be isolated with asbestos or iron to prevent Mars from splashing.
3. If welding is carried out on containers, equipment or pipelines that produce, store and transport flammable and explosive medium, it is necessary to check whether the equipment and pipeline connected with it are closed or sealed with blind plates before welding; Purge, clean, replace, sample and test, after welding, can be welded.
Third, anti-burn measures
1. Welders must wear the protective overalls, insulated gloves and insulated shoes for welders when welding. When using high current welding, the welding tongs should be equipped with a protective cover.
2. The parts to be welded should be covered with asbestos board in time to prevent direct contact between the feet and the body and cause burns.
3. The electrode heads to be replaced during high-altitude welding should be stacked in a centralized manner, and should not be thrown away to avoid scalding the workers below.
4. Wear protective goggles when cleaning the welding slag; when performing overhead welding or horizontal welding at high altitude, due to serious splashes of Mars, isolation protection measures should be taken.
Fourth, measures to prevent electro-optic ophthalmia
Depending on the size of the welding current, suitable mask goggles filters should be used at the right time. Other personnel in the welding industry should wear colored protective eyes when welding.
Fifth, radiation prevention measures
Welders and surrounding workers should wear protective equipment when welding. It is forbidden to wear electric welding mask without direct observation of arc light without wearing colored mirror; to minimize skin exposure, it is forbidden to wear shorts and short squats for electric welding in summer; and to apply UV protection cream to exposed skin.
Sixth, measures to prevent harmful gases and smoke
1. Reasonably design the welding process, try to use the single-sided welding double-sided forming process to reduce the amount of welding in the metal container.
2. If welding work is carried out in a small or closed container, forced ventilation measures must be taken to reduce the concentration of harmful gases and soot in the working space.
3. Use automatic welding and semi-automatic welding instead of manual welding as much as possible to reduce the chance of welding personnel exposure to harmful gases and smoke.
4. Use low-dust, low-toxic welding rods to reduce the harmful dust content in the working space.
5. When welding, the welder and other people around should wear dust-proof masks to reduce the inhalation of smoke and dust.
Seventh, anti-high fall measures
Welders must perform regular physical examinations. Anyone with a history of hypertension, heart disease, epilepsy, etc. is prohibited from climbing. When the welder climbs up, he must properly fasten the seat belt and wear a safety helmet. Before welding, check the climbing operation point and the surrounding environment, check whether the foothold is stable, secure*, and whether the safety protection facilities such as scaffolding meet the safety requirements. If necessary, pull a safety net under and around the work. Isolation protection measures should be taken when it comes to handing in and off.
Eighth, anti-poisoning, suffocation measures
1. Where welding is carried out in closed or semi-closed places such as containers, equipment, pipelines, towers, tanks, etc., which are stored, transported or produced with toxic and harmful medium or inert gas, all process equipment connected to it must be cut off before operation. Cleaning, purging, replacement, and in accordance with the provisions of the equipment operation permit, after sampling and analysis, qualified to enter the operation.
2. Under normal circumstances, it should be analyzed once every 4 times. If the conditions change, it should be sampled and analyzed at any time. At the same time, the site should also be equipped with an appropriate amount of air (oxygen) gas respirator for emergency use.
3. The operation process should be carried out by special person safety monitoring, and the welder should rotate the work at regular intervals. For equipment with strong airtightness and easy to lack oxygen, use forced ventilation to supplement oxygen (no direct oxygen is allowed) to prevent hypoxia and suffocation.
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