Article: Recirculating Air From Dust Collectors

When deciding on a dust collection system, one of the top concerns is recirculating the return air from a dust collector back into the facility.  An article by dust collection expert Lee Morgan will give you information needed to make the right decision that is best for your application.  The article  "Recirculating Air From Dust Collectors" explores the benefits, safety issues, media, filter monitoring, fire safety and explosions, as well as the recirculation process.

By containing the air totally inside a building, the plant engineer deals with OSHA instead of the EPA  who has strict environmental standards, permit appllications, testing and regulatory paperwork.  When a dust collector is designed to recirculate heated or cooled air back through the plant, the cost to replace that conditioned air is eliminated which can lead to higher energy savings. Dust collecting systems for welding shops with high ceilings can often improve the efficiency of a heating system by taking hot air off the ceiling and delivering it at ground level where employees are working.  

Another critical concern is to ensure that the dust collection system is adequately removed dust to protect the workers' health.   OSHA has set an indoor limit of 5 mg of nonspecific or nuisance dust (< 10 microns in size) per cubic meter of air. Toxic dusts, such as silica, carry an indoor limit of only 0.05 mg per cubic meter - 100 times stricter than the allowable threshold for nuisance dust. A crucial concern with any recirculating dust collector is to ensure the system has adequately removed the dust to protect workers' health.  Meeting OSHA standards and following guidelines published by the American Conference of Governmenlal Industrial Hygienists (ACGlH) can ensure regulatory compliance.

Dust testing is strongly recommended, especially when toxic dusts are involved. A qualified test laboratory can perform a series of bench tests on a representative dust sample to determine its characteristics - which can influence collector design.  Selecting the right filter media is critical to meeting emission requirements.  With a wide variety of filter media available.  It is critical to have the correct media for the application.

To prevent contamination from filters rupturing and releasing dust back inside the plant, the use of a safety monitoring system is recommended.  The systems typically include a side-access housing, prefilter, and high efficiency ASHRAE filter, which form a backup system to keep emissions at acceptable levels in the event of a dust collector failure.

When the captured dust is explosive or flammable, special safety concerns must be addressed.  Some combustible dust can prevent recirculating air back into a facility.  Others can be recirculated inside as long as adequate safety precautions are followed.  Explosions and fire are a big concern.  Collectors requiring explosion vents should be located outside and vent away from buildings and populated areas.

You can explore more detailed information regarding this article by following the links  below.

Full article:  Recirculating Air From Dust Collectors
OSHA website
EPA website
American Conference of Governmenlal Industrial Hygienists (ACGlH)