The most common compounds in arc welding fume when welding on mild or carbon steel are complex oxides of iron, silicon and manganese.
Arc welding fume contains very small particles from the consumables, base metal and base metal coating. The substances in the fume particles vary depending upon the constituents of the electrode and the chemistry of the base metal being welded, including any coatings, paint or plating. The most common compounds in arc welding fume when welding on mild or carbon steel are complex oxides of iron, silicon and manganese, although many other compounds may also be in welding fume.
Welders who are overexposed to substances in welding fume may potentially be at risk for various short-term (acute) or long-term (chronic) health issues.
The two most common U.S. exposure limits are established by OSHA in the form of Permissible Exposure Limits (PEL) and by the American Conference of Governmental Industrial Hygienists (ACGIH) in the form of Threshold Limit Values (TLV). Employers are required by OSHA to keep exposures below the PEL and may choose voluntarily to keep exposures below the TLV.
The new TLV for manganese
A change by the ACGIH was published in the 2013 Edition of its TLVs and Biological Exposure Indices (BEIs) publication. The new TLV of 0.02 mg/m3 for respirable manganese, which is applicable to welding fumes, represents a ten-fold reduction from the previous 0.2 mg/m3 TLV. The new TLV for manganese includes a 0.1 mg/m3 limit for inhalable manganese particulate.
The Permissible Exposure Limit (PEL) of 5.0 mg/m3, ceiling, remains the U.S. exposure limit for manganese enforced by OSHA.
Methods for controlling exposure
To thoroughly explore your welding fume control options, you should identify and assess your actual needs and operating conditions. Start by having an industrial hygienist take and analyze the appropriate number of samples of the air in the workers’ breathing zone to provide a baseline relative to any exposure level.
This is particularly important if you are welding with stainless or hardfacing products, which contain greater amounts of substances that have low exposure limits, for example, manganese and chromium. Be sure to check the safety data sheet for the products you use. Fumes are not exclusive to the welder’s work area as they may migrate to areas where other workers may be exposed. When measuring to a TLV limit, the measurements should be averaged throughout the worker’s shift, which is typically eight hours. Where exposures are assessed to be over the TLV, many approaches can be considered to reduce exposures to acceptable levels.
If there is any potential employee exposure to manganese or other compounds above their respective PELs, OSHA requires that engineering and work practice controls be installed first. The various types of control options for arc welding fumes are described below. The control options listed below should be used before considering a respirator. The use of ventilation/exhaust is often the most feasible method for controlling exposures. Respirators can further reduce exposures and can only do so to those who wear them.
- Substitution – Review your current welding process, consumable, gas, welding procedure and equipment technology to determine if it’s feasible and practical to replace it to generate less welding fume.
- Isolation – Review your welding operation to determine if it’s feasible and practical to isolate and separate the operation by moving it to a regulated area, by automating/ventilating the welding process and/or placing a barrier between the worker(s) and the source.
- Ventilation/Exhaust – Review the welding fume path to determine if it’s feasible and practical to control the path between the source and the worker through source, local, general shop ventilation equipment.
Work practice controls
This involves adjusting the way a task is performed and periodic inspection and maintenance of engineering control equipment.
Work practice controls should complement engineering controls in providing employee protection. These practices include safe welding habits as well as housekeeping, maintenance and general administrative procedures, such as scheduling operations/tasks at a time to minimize potential exposure.
If adequate ventilation is not feasible, it may be necessary to protect employees with the use of personal protective equipment.
Frequently asked questions
Why did the ACGIH make a change that lowers TLV for respirable and inhalable manganese?
The ACGIH’s change is based on reports of pre-clinical neurobehavioral and neuropsychological changes in workers exposed to chronic low levels of manganese. Some reviewers have pointed out methodological flaws in these studies and that they have demonstrated notably inconsistent findings after several decades of research. Nevertheless, the ACGIH decided to move forward with the reduction.
Does the new Threshold Limit Value (TLV) distinguish manganese in welding fume from other types of manganese?
No, the new TLV does not distinguish between the two.
What is the ACGIH and is it part of the government?
The ACGIH is a non-profit, non-governmental corporation dedicated to promoting worker health and reducing exposures to environmental health stressors in the workplace.
What exactly is the TLV?
According to the ACGIH, its TLVs represent conditions under which nearly every worker repeatedly can be exposed without adverse health effects. They also caution that TLVs are not intended to represent fine lines between safe and unsafe exposure levels.
Is the TLV a regulatory exposure limit?
No, the TLV is not a regulatory limit such as OSHA’s Permissible Exposure Limit (PEL). Some governmental entities utilize its TLVs in adopting standards.
Should we follow the new TLV?
The ACGIH is a long-standing body that is comprised of professional industrial hygienists that review applicable health studies, monitor reports related to the health effects and risks of exposure to compounds encountered in the workplace, and advice regarding safe exposure levels.
Do countries outside the U.S. adopt the ACGIH TLV as their legal regulatory exposure limit?
In short, yes. For example, many countries, and the State of California, adopt exposure limits that are equal to the ACGIH TLV. Countries with exposure limit standards equivalent to TLVs include most Canadian provinces, many European countries, Japan, Malaysia, Mexico and much of South America.
How do I know if a welder’s exposure is below the TLV?
As an initial observation, the welder’s breathing zone and general area should be clear of any visible fume or particulate. The most effective means for confirming that exposures are below the TLV is to have a qualified individual such as a professional industrial hygienist conduct an exposure assessment in your workplace.
If any exposures are over the TLV, how can they be reduced to acceptable levels?
Many approaches should be considered to control exposure to welding fume constituents for the workplace. These might include a change in the welding process or procedure to reduce the rate of fume production where consistent with application requirements, the use of engineering controls such as local exhaust ventilation, work practice improvements and work process design changes. More than one of these may be implemented.
The same solution(s) will not work for everyone because many factors can affect exposure levels; however, you should confirm that welding fume exposures in your work area are well controlled by providing enough ventilation and to keep the worker’s exposure to hazardous substances in welding fumes and gases below the applicable exposure level.
Original Source : Canadian Metalworking