Welding Fume Control:
Exhaust System Method and General Air Cleaning Method
Air cleaning for welding operations can be achieved mainly through either exhaust systems or general air cleaning and each may or may not involve source capture.
The source capture method of removal is generally the best method of capture as it removes airborne contaminants at the point of generation, and more effectively removes them from the breathing zone of the operator. Stationary, mobile or portable source capture systems may consist of the following basic elements; capture hood, duct system, air filter, fan and exhaust ductwork. These elements must be specifically engineered for each application, but the distance between the capture hood and the point of fume generation should generally be no more than 1 times the duct diameter of the capture hood. (See Figure 1.)
Exhaust System Method
Exhaust systems involve the removal of air that contains welding fumes and molecular contaminants from a facility directly to the outdoor environment.1 While seemingly inexpensive, this method can pollute the surrounding environment and may violate lo state regulations, can negatively affect the air balance in a building, and creates a need for conditioning (heating or cooling) all air that is brought into the facility to equal the air removed (makeup air). The energy cost of conditioned makeup air can make this metho more costly than either general air cleaning or source-capture air cleaning.
Exhaust systems may be a large exhaust fan pulling air away from the welding operation and out of the facility, a booth or canopy over the work designed to pull fumes upward, a welding table, specially designed to pull air across the welding work surface and exhaust it, or a source capture hose with hood specifically designed to be positioned at the welding spot pull fumes and gases off of the work.
Air Cleaning Method – NAFA – Recommended Best Practice
Recirculated Exhaust Air:
Exhaust air from a welding operation may be re-circulated in a work area under the following conditions:
- The recirculation of air is in compliance with the regulatory authority or the authority having jurisdiction.
- The exhaust air is cleaned by passing it through a highly efficient filter MERV 16 (HEPA filtration efficiency tested to MIL Std. 282 to achieve 99.97% on 0.3 micrometer particles of thermally generated DOP or suitable substitute challenge).
- Gases that cannot be removed by molecular filtration do not exceed acceptable
Components to be welded and materials used in the welding process are not prohibited. challenge). Gases that cannot be removed by molecular filtration do not exceed acceptable limit.