How to Control Food Dusts in Your Processing Facility

The most common is explosion venting because it is the most cost effective, but some facilities may also be required to have explosion isolation valves or integrated safety monitoring filters. All of these mitigate incidents and prevent the flame front and pressure from traveling to process areas. The NFPA provides guidelines to design, locate, install, and maintain these explosion protection devices to minimize harm to personnel as well as structural and mechanical damage. It is important to note that if the dust collector is protected properly, an explosion inside the unit is much safer than having it occur in an open facility or around employees.

Q. What does explosion venting do?

A well-designed explosion vent functions as a weak element in the dust collector’s pressure envelope. It relieves internal combustion pressure (back pressure) to keep the collector from blowing up into pieces.

Typically, the collector is located outside so that it vents away from buildings and populated areas to a safe location. If it is properly equipped and located indoors, standards mandate designating a safe area around the collector. While explosion venting will usually save the dust collector from being a total loss, the collector can sustain major internal damage. Nonetheless, if personnel remain safe and facility structural damage is minimized, the explosion venting equipment has done its job.

Q. Which food manufacturing or processing facilities are required to have their dust tested?

NFPA standards require a dust hazard analysis (DHA) for any facilities that generate, handle, or store potentially explosive dust. The burden of proof is on manufacturers to demonstrate that their dust is not combustible, so it is important for them to have their process dust tested by a valid third-party testing lab and keep records on file proving that it is not combustible.

If tests show that the facility has combustible dust, NFPA Standard 652 requires the completion of a DHA of the dust collection system. Operators also need to keep this report on file to show when requested by the local fire marshal or any other authority with jurisdiction. In addition, explosion venting equipment must be inspected at least annually based on the documented operating experience.

Q. How are explosion vents and discharge ducts sized to make sure they are right for a dust collector?

Chapters 7 through 9 of NFPA 68 provide the calculations to use for properly sizing explosion vents, vent discharge ducts (also called vent ducts), and other components. A reputable dust collector supplier will follow the vent sizing equations in chapter 8 (Venting of Deflagrations of Dusts and Hybrid Mixtures). The supplier can also provide a calculations sheet that becomes part of the documentation manufacturers keep on file to demonstrate the plant’s compliance. An experienced dust collector supplier may also have performance-based solutions for this type of equipment, which is also allowed by the NFPA standards.

Q. Is it safe to recirculate the air from your dust collector back into the work environment?

Recirculating heated or cooled air back into the workspace can provide significant energy savings and eliminate the cost of replacing that conditioned air. Containing the air indoors also avoids the time-consuming permitting involved when contaminated air is exhausted outside. Recirculating the air can be done safely, even if the facility handles explosive dust, by outfitting the dust collector with a safety monitoring filter. This helps isolate the downstream equipment from the progression of a flame front during an explosion.

Thomason is the senior applications specialist at Camfil Air Pollution Control and has served in the dust collection industry for 35 years. Reach him at [email protected].