There are significant concerns about potential neurological effects associated with exposure to manganese in welding fumes.   Welding fumes are composed of metals and most fumes contain a small percentage of manganese.  Manganese may be found in carbon steel shielded metal arc welding (SMAW or stick) electrodes as part of the flux coating on the welding rod, as a flux in carbon steel flux core arc welding (FCAW) and as a filler metal in gas metal arc welding (GMAW or MIG) wire.   It is present in recycled carbon steel and used in abrasion resistant applications such as ball mills or earth moving equipment.   Manganese has a substantially lower boiling point than iron, therefore, it will vapourize more easily than iron leading to a higher presence on a percentage basis in welding fumes than in the original wire.

Current research on the effects of manganese in welding on health.

Recent studies indicate neurological and neurobehavioral deficits may occur when workers are exposed to low levels of manganese (<0.2 mg/m³) in welding fumes. These effects include changes in mood and short-term memory, altered reaction time, and reduced hand-eye coordination. Affected workers frequently show abnormal accumulations of manganese in a region of the brain known as the globus pallidus. The globus pallidus plays an important role in movement regulation[1].

The onset of motor fluctuations and dyskinesia among welders occurred at a mean age of 46 compared to a mean age of 63 among non-welder controls. Dyskinesia refers to a category of movement disorders that are characterized by involuntary muscle movements, including movements similar to tics or chorea and diminished voluntary movements.   Also observed were decrements in verbal learning, working memory, cognitive flexibility, visuomotor processing speed and motor efficiency[2].   Five measures of eye-hand coordination (precision, percent precision, imprecision, percent imprecision, and uncertainty) reflected more erratic control of fine hand-forearm movement in a manganese-exposed group than the control group.

Regulations are not keeping up with the science.

In February 2013, the American Conference of Governmental Industrial Hygienists (ACGIH) recommended a decrease in the time weighted average (TWA) (measured over an eight hour shift) threshold limit value (TLV) for respirable manganese particulate of 0.2 mg/m³ to 0.02 mg/m³ which represents a tenfold reduction[3].    The respirable fraction is the smallest particulate fraction sampled and is less than 4 µm mass median aerodynamic diameter, which covers the particulates typically found in welding fumes.

The ACGIH also issued a guidance of 0.1 mg/m³ TWA inhalable manganese particulate that can be inhaled into the nose and mouth but not likely to be inhaled into the deep lungs because of size. These larger particulates are normally associated with grinding operations instead of welding.

The problem is that five years later, provincial regulatory limits have not kept pace with the current science.   These regulations do not account for the higher toxicity of ultrafine manganese particulates found in welding fumes, which can deposit deep in the lung alveoli and are capable of passing directly into the blood stream.  Ontario Regulation 833 currently limits manganese exposure to 0.1 mg/m³ TWA total particulate.  Similarly, Quebec Regulation respecting occupational health and safety (Chapter S-2.1, s.223) limits manganese exposure to 0.2 mg/m³ TWA total particulates and is not protective enough for manganese.  Alberta Regulation 87/2009 amended June 1, 2018 also limits manganese exposure to 0.2 mg/m³  TWA total particulate.

What is the bottom line for manganese?

As this article shows, current provincial limits do not provide sufficient protection, so it is wise for employers to take measures to protect worker above and beyond the regulatory limit. Here are some steps you can take:

• Welders should use portable or fixed local exhaust ventilation (LEV).
• Welders should wear respiratory protection (half face air purifying respirator with P100 filter)
• Employers should substitute for Hobart low manganese GMAW wire. Mn is reduced about 1/3 from regular wire
• Employers should assess worker airborne exposure to manganese in welding
• Occupational exposures should be controlled to meet more protective ACGIH OELs
• A manganese control program should be developed for welding processes.
• Annual air exposure monitoring should be performed to verify controls are effective.
• A regular review of LEV should be conducted to ensure engineering controls are effective

T. Harris Environmental Management Inc. has experienced occupational hygienists and occupational hygiene technicians to help you assess your welding shop to ensure that you practice ‘due diligence’ to safeguard the health and safety of your welding personnel.

References:

[1] https://www.cdc.gov/niosh/topics/welding/default.html

[2] AIHA Fall Conference 2015, PDF 3: Welding: Identifying Exposures and Controls, Orlando Oct. 26-27, 2015

[3] https://www.thefabricator.com/article/arcwelding/new-guideline-reduces-manganese-exposure-limit-dramatically