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Going beyond OSHA regulations for manganese exposure

Oregon OSHA helps fab shop reduce welding fumes

Figure 1
A welder is gas metal arc welding brackets onto I-beams with standard metal-core wire. No local ventilation is used, resulting in the welder being engulfed in welding fumes.

Understanding Occupational Safety and Health Administration (OSHA) requirements and protecting their workers from injuries is a complex task for fabrication shop managers.

Unfortunately, some OSHA requirements do not adequately protect workers. Consider OSHA’s permissible exposure limits (PEL) for air contaminants—particularly manganese, which is present in most welding operations (see Figure 1).

As Dr. David Michaels, assistant secretary of labor for occupational safety and health, said in October 2013, “American workers use thousands of chemicals every day, and every year tens of thousands of workers are made sick or die from occupational exposures to hazardous chemicals. While many chemicals are known or suspected to be harmful, only a small proportion is regulated by OSHA, and for many of those chemicals that are covered by our regulations, our workplace exposure limits are dangerously out of date.”

In 2013 the American Conference of Governmental Industrial Hygienists (ACGIH®) reduced the manganese threshold limit value (TLV) of 0.2 milligram per cubic meter (mg/m3) to 0.02 mg/m3 over an eight-hour work period. Under the lowered TLV, an employee should not breathe in more than 0.02 mg/m3 of air contaminated with manganese. The current OSHA PEL for manganese is 5 mg/m3, which is 250 times higher than the TLV.

The ACGIH TLV is based on the respirable fraction of a substance that can enter the deep lung. Welding fumes are very small particles in the respirable fraction of less than 5 µm. According to the Centers for Disease Control, “Inhaled manganese is of concern because it bypasses the body’s normal defense mechanisms. This can lead to manganese accumulation and adverse health effects, including damage to the lungs, liver, kidney, and central nervous system. Male workers exposed to manganese also have a higher risk of fertility problems. Prolonged exposure to high manganese concentrations may lead to a Parkinson’s syndrome known as ‘manganism.’”

The ACGIH TLV for manganese is not an OSHA air contaminant requirement. However, OSHA has issued “General Duty” citations for other air contaminant exposures above recommended guidelines. Additionally, workers’ compensation carriers may require their clients to comply with the ACGIH TLV to reduce risk.

Working to Reduce Employees’ Exposure

One company that stepped forward to explore further protection of its workers was Unobtanium Inc., a small fabrication job shop in Oregon City, Ore. In 2014 it voluntarily requested Oregon OSHA Consultative Services to evaluate its employees’ exposure to welding fumes at its facility, focusing on exposure to manganese.

The preliminary sampling of the shop environment was the first step. The sampling included air monitoring of four employees performing gas metal arc welding while using a standard metal-core wire (AWS E70C-6M H4). Employees were welding rebar onto angle iron to be used for earthquake reinforcement (see Figure 2).

For ventilation, the shop used two articulating-arm ventilation exhaust systems, as well as general dilution ventilation, which was done by opening the shop’s bay doors.

Air monitoring was completed beneath the employees’ welding helmets to evaluate contaminants in their breathing zones. The time-weighted average manganese exposure ranged from 0.134 mg/m3 to 0.871 mg/m3 during the four-hour sample period. The highest manganese concentration was 1.35 mg/m3. The exposures ranged from 6.7 to 67.5 times the ACGIH TLV.

Figure 2
A welder uses GMAW to attach rebar on angle iron with standard metal-core wire. Local exhaust is poorly placed over the employee’s head. Manganese exposure is 1.35 mg/m3, 67 times higher than the ACGIH TLV.

By comparison, the highest exposure reading was 3.7 times lower than the OSHA PEL. The workers were not using any respiratory protection and were at risk of chronic illness based on the ACGIH TLVs.

The high level of manganese exposures presented another problem. An N95 filtering facepiece (dust mask) and half-mask respirator provide protection up to 10 times above the OSHA PEL. Consequently, employees wearing a respirator could have a false sense of security and be at risk of exposure to manganese. Unobtanium did not want to require employees to wear respirators because of the discomfort and the regulatory burden of a respiratory protection program.

A Move to Improve Consumables and Work Practices

To resolve the problem, the Oregon OSHA consultant suggested that Unobtanium use less hazardous welding materials and better work practice controls to reduce employees’ manganese exposure. The company substituted standard metal-core wire with a new low-manganese wire (AWS E71T-1C/

-9C H8). This low-manganese wire is reported by the manufacturer to “reduce welding fume by 60 percent to 80 percent over the standard E71T-1C product.” Unobtanium also trained employees to properly position the fume extractor for maximum efficiency and provided forced-air ventilation to clear smoke out of the shop.

With the new welding consumables in place and work practices underway in December 2014, follow-up air monitoring was completed for three employees welding under similar production conditions. The time-weighted average manganese exposure ranged from “under the detection limit” (less than 0.012 mg/m3) to 0.055 mg/m3.

Although two employees were still exposed above the ACGIH TLV, the company was able to achieve a substantial reduction in manganese exposure with low-cost solutions.

As for the new weld wire, one employee welding under the same conditions with no local exhaust ventilation for both tests had a 65 percent reduction in manganese exposure (see Figure 3). The manganese concentration in the employee’s breathing zones was 2.85 times lower, compared to the concentration with the standard metal-core wire.

Properly positioning the ventilation hood (see Figure 4) and using low-manganese wire reduced exposures by 87 percent to 99 percent for two of the employees (see Figure 5).

In moderate- to heavy-welding environments with high arc-on times, it is likely that low-manganese welding wire will not reduce employee exposures below the ACGIH TLV. However, low-manganese welding wire may reduce exposures enough that supplemental, proper use of respirator protection will be effective.

Metal fabricators that are interested in exploring a reduction in manganese exposure for their employees or that have questions on safety can contact their local OSHA office to determine the availability of free safety and health consultation services: www.osha.gov/dcsp/smallbusiness/consult.html.