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Cr 6 and metals weld

Welder who welds a piece of metal, hexavalent chromium production

Test and management of air containing welding fumes hexavalent chromium and metals.

It was in 1798 that metallic chromium was isolated by Nicolas Louis Vauquelin. It is naturally found in the environment in small quantities. It is in the form of a steel gray hard metal. Its main assets are to resist tarnishing and corrosion over time. It has several oxidation states ranging from 2 to 6. The hexavalent chromium or chromate (Cr VI) is highly oxidizing and is the sixth state of oxidation of the chromium element.

Its use is mainly recognized in the field of metallurgy. Indeed, it is used for its brighter finish to the material. It gives it at the same time its properties is a resistance to corrosion. It is also used in the manufacture of pigments, the treatment of metal surfaces, tanning of leather and the preservation of wood. It is also found in cement and mortar dust. Its use in the industrial environment ensures that it can be released into the environment.

Hexavalent chromium is a man made. This state of chromium is known to be toxic and to have irritating effects and sensitizing effects (allergic reactions) on the health of individuals who are in contact. It crosses biological membranes easily. Indeed, hexavalent chromium can enter the human body through the respiratory tract, through direct contact with the skin or if an individual eats in a contaminated environment. Irritating effects of chromium include redness or ulcers in the skin and nose, sore throat, redness in the eyes, coughing and breathing difficulties, stomach, gastric and esophageal ulcers. Allergic reactions can lead to nasal discharge, bronchitis, asthma and pulmonary fibrosis. Hexavalent chromium can also give cancer to the lungs and bronchi. People who smoke tobacco can see the risks of increasing chromium. According to the literature, it is estimated that 10% of the hexavalent chromium ingested is absorbed by the gastrointestinal tract. When inhaled, between 12 and 30% of the chromium is absorbed. It is eliminated by the body in the urine when ingested and stool when inhaled. In studies in the chrome plating industry, there has been a correlation between exposure to hexavalent chromium and the development of lung cancer or nasal cancer. It was also concluded that duration of exposure may also be an important factor in the development of this cancer. Other studies in the chromate pigment production sector have also shown an increase in lung cancer among workers. Again, an association was made in relation to the duration and level of exposure.

In workers, the main source of exposure to hexavalent chromium is through inhalation and dermal absorption. The most chromate-exposed workers are those who work in the production of chromate compounds and pigments, in the production of stainless steel, in welding, in chrome plating, in the production of ferrochrome, in the wood processing and in the leather tanning industry. These by the industrial processes in connection with chromium that the exposure of workers to hexavalent chromium toxic substances occurs.

The population may be exposed to hexavalent chromium through food, drinking water and residential air. In fact, individuals living near uncontrolled landfills containing hazardous residues or plants using chromium could be more exposed to hexavalent chromium than the rest of the population. Indeed, it is an industrial waste that can be released into the environment during the production of electricity, finishing of metals and wood treatment.

The major source of workers' exposure to Cr (VI) occurs during "hot work", such as welding of stainless steel or other steel alloys containing metallic chromium. Fumes composed of gases and metal particles, including hexavalent chromium, are emitted as soon as the temperature reaches the melting point (196 ° C) of CrO3; these toxic fumes are then inhaled by workers and by people who are nearby. It is in this context of high-risk work that all preventive measures must be applied to safeguard the health of workers.

The results of the analysis will then guide stakeholders to the type of solutions to consider: mechanical ventilation and / or wearing appropriate protective equipment and in compliance with health and safety regulations in force.

Protective equipment for hexavalent chrome

Welding fumes are a complex mixture of oxide, silicates and metal fluorides. Smoke is formed when a metal is heated to a higher temperature than its boiling point. The vapors that emerge condense to produce very fine solid particles that come from the welded material. Its composition is variable depending on the metals present in the parts to be assembled.

For example, welding smoke from silica or fluoride contains amorphous silica, silicates and metal fluorides. For those that come from the welding of mild steel parts, we find mainly iron and small amounts of added metal particles (chromium, nickel, manganese, molybdenum, vanadium, titanium, cobalt, copper, etc.). Smoke mainly contains chromium or nickel can come from welding stainless steel.

The coating of the parts to be welded can be found in the welding fumes and some can be toxic for the health of the worker. For example:

  • Products used for metalworking such as oils and rust prevention products;
  • The zinc layer found on galvanized steel;
  • Cadmium on cadmium metals;
  • Solvents and paint;
  • Primers that are made from lead oxide;
  • Some plastic coatings.

It is best to remove the coating from the weld faces before welding to reduce welding fumes. This step can be done using appropriate stripping products. Never proceed with sanding as this technique produces dust that may be toxic. Sometimes, when the coating is very toxic, it must be removed wet vacuum.

Inadequate exposure to welding fume can cause irritation of the eyes and respiratory tract since several metal oxides or released gases may be irritating. The welder, when exposed to high concentrations of irritating gases or particles, may develop pulmonary edema. In the literature, it has been reported that welders who have accidentally exposed to high concentrations of irritant gases have developed a bronchial irritation syndrome that has even caused symptoms of gill obstruction. The health risks to exposed individuals depend on several factors: the type of welding process, the composition of the material to be welded, the type of coating present, the concentration and the conditions of exposure to welding smoke (type of ventilation open space or enclosed space). Worker practices can also have an impact on exposure (removing clothes, cleaning surfaces ...).

Workers may be exposed to melting fever. The latter is caused by the inhalation of oxides of certain metals such as magnesium, zinc and copper. In rare cases, aluminum, cadmium, iron, manganese and nickel can cause melting fever. The symptoms observed are: fever, chills, sore throat, muscle aches, stiffness, sweating, metallic taste, nausea, vomiting and thirst. All these symptoms may appear four (4) to eight (8) hours after exposure. They disappear on their own about 24 to 48 hours later.

In the long run, workers can develop more chronic health problems. Generally, the effects observed are rhinitis, chronic bronchitis, lesions in the skin and mucous membranes, an increase in pulmonary infections and pneumoconiosis (fibrosis in the lungs). Cases where workers developed asthma when welding smoke contained zinc were noted in the literature. The metals that are detected in the welding fume analysis are as follows: aluminum (Al), antimony (Sb), beryllium (Be), cadmium (Cd), chromium (Cr), copper (Cu), cobalt (Co), iron (Fe), manganese (Mn), molybdenum (Mo), nickel (Ni), titanium (Ti), vanadium (V) and zinc ( Zn).