The Hex

WHAT IS HEXAVALENT CHROMIUM? Chromium is found in nature as part of chromite ore (FeCr₂O₄). This ore is processed to produce pure chromium metal. Chromium easily bonds with other elements to form different compounds. This bonding usually occurs when chromium (Cr) accepts electrons from other elements, thereby joining together with them. If Chromium accepts three electrons, then it is considered trivalent chromium, or Cr (III), in that compound. If it accepts six electrons it is considered hexavalent chromium, or Cr (VI).

Compounds containing hexavalent chromium are used in electroplating and the production of paint pigments, corrosion inhibitors and many other products. Workers can be exposed in the fumes or spray from operations using these compounds, including in scrap-related operations.

HEALTH RISKS. The most significant health risks result from exposure to hexavalent chromium particles by inhalation and through skin contact. Particles of hexavalent chromium can be in mists, dust or fumes. Mists can come from using molten metal, such as chrome plating baths or painting. Dusts can come from grinding or cutting. Fumes can be generated during torch cutting and welding operations.

When hexavalent chromium particles are inhaled, large particles may be trapped in the mucous membranes of the mouth and nose. Smaller particles may travel farther and deposit in the throat, trachea or the left and right bronchi. These particles are likely to be coughed up and swallowed.

The smallest particles will travel beyond the bronchi and deposit, ultimately, in the blood stream and be carried to the rest of the body.

The health risks from hexavalent chromium particles can include respiratory tract tumors.

Inhalation exposure to soluble hexavalent chromium can lead to nasal irritation, nasal ulcerations and perforations, asthma and bronchitis. Direct skin contact can lead to dermatitis and skin ulceration. Direct eye contact may lead to conjunctivitis.

WELDING AND TORCH CUTTING EXPOSURE. Welding or torch cutting uses intense heat from either a gas fired flame or an electric arc. This heat can bring a metal to above its boiling point. This superheating converts small metal particles into metal vapor. Visible or invisible fumes form when the vapor cools and condenses back into particles. Welding smoke is an example of visible fumes. But particles can still be present even when fumes cannot be seen.

Metal particles in welding fumes can come from several sources and can vary in size from 0.00 µm to 20 µm. These sources include the base metal, coatings, residues or paint, electrode material, flux material and filler metal.

The boiling point for chromium is 4,841 degrees Fahrenheit. Since the heat of welding or cutting can exceed 5,432 degrees Fahrenheit, chromium particles can easily vaporize and then condense into fumes. Chromium particles generated in welding fumes can undergo a chemical reaction to become hexavalent chromium particles. Variables include electrical current, voltage, droplet size, surface temperature, evaporation rate, shielding gas, arc length and ultraviolet radiation.

OSHA REGULATIONS. There is a specific standard for general industry, shipyards and construction.

All industries must comply with the new permissible exposure limit of 5 micrograms of hexavalent chromium per cubic meter of air (5 µg/m3) for an 8-hour TWA. Exposure that falls below the action level (2.5 µg/m3) has no compliance requirements. Each of the regulations has requirements for:

For companies with 20 or more employees, all requirements of this standard, except for engineering controls, are effective Nov. 27, 2006. For businesses with 19 or fewer employees, the standard’s requirements are in effect, except for engineering controls, on May 20, 2007.

THE COMPLIANCE CONCERNS. Monitoring for exposure from welding fumes is accomplished by drawing air from a worker’s breathing zone through a filter. The filter is then processed in a lab to determine the amount of hexavalent chromium and other metals, such as lead and cadmium, to which the employee was exposed. This is expressed as an 8-hour TWA. While important, this monitoring alone will not provide information on the origin of the hexavalent chromium.