The general air cleaning method must create enough air changes per hour to overcome the amount of contaminant being generated. Depending on the type of welding being done, 10 to 25 or more air changes per hour may be required to maintain desired levels of contaminant removal. The advantages of this method over source capture methods include the elimination of a need for source capture hoods, ductwork, and the associated effect on the gas shielding and weld integrity. Conversely, a larger amount of air movement and air cleaners is required and this method does not directly remove the contaminant out of the welders breathing zone.
As mentioned earlier, source capture of welding fumes is the best method of removal. Connecting a source capture hood to a flexible duct which is suspended over the welding source allows for direct removal. Attaching this duct to air cleaning equipment (either stationary or mobile) then allows for removal of contaminants and recirculation of this air. Downdraft or sidedraft welding tables also offer direct removal of fumes with somewhat less mobility.
Mechanical Filter Removal Equipment:
Mechanical filtration removal equipment describes those devices using fiber and/or fabric filters that, because of their high efficiency on particles, remove particulate contaminants to acceptable levels. Progressive filtration describes the use of several filters in a system, each having a higher efficiency than the one previous to it. This allows larger particles to be removed by lesser priced filters, thus providing longer life to those filters with the highest efficiencies.
Single pass progressive filtration commonly uses spark arrestor deflectors to prevent fire hazards in the first part of the system. The first-stage disposable filter should be a minimum MERV 6 to remove the largest of particles.
This filtration device uses a multiple stage process to clean the air for re-circulation into the environment. Electrostatic precipitation describes the use of an ionizing section that creates a highly charged corona of air that imparts a charge to the incoming particles, and a collector section with oppositely charged plates that capture the particle by positive/negative attraction.Intermediate stages of filtration should utilize MERV 15 filters unless welding specific metals containing chromium, nickel, or other regulated compounds. In these instances the use of a HEPA filter must be used as a final filter.
Molecular Filtration filters such as activated carbon may be included to remove specific molecular contaminants determined with the welding process. Standard activated carbon filters are most commonly used, but there may be instances where a treated carbon or other specialty media should be used to remove specific molecular contaminants. This is determined by the welding process. For proper molecular filtration selection please contact a NAFA Certified Air Filter Specialist (CAFS).