February 1st, 2013 the American Conference of Governmental Industrial Hygienists (ACGIH®) announced a revision to its good practice recommended Threshold Limit Value (TLV®) for manganese.(1) This action changed the TLV® from an 8-hour time weighted average (TLV-TWA) of 0.2 mg/m3 for total manganese (i.e. all particle sizes) to 0.02 mg/m3 for respirable size manganese particles.
Respirable particles are generally less than 4 micrometers (µm) in diameter, which includes welding fume. These particles can penetrate and be retained deep in the lungs. In addition, a TLV-TWA of 0.1 mg/m3 was added for inhalable manganese (particles less than 100 µm in diameter).