As awareness of industrial dust and dust safety grows, so does the need for accurate information. Although it is not possible in this short article to answer every question, we hope the following list of frequently asked questions and answers will be helpful.
What is industrial dust?
In general, industrial dust is any dust created due to the processing of certain materials in the workplace. These processes could include sanding, crushing, conveying, mixing, or any number of activities that create fine particles. Although inhaling dust is often a health concern, some dusts are also combustible. If this dust accumulates, it can cause a fire or explosion, threatening workers and the surrounding community.
According to the NFPA, combustible dust is a solid material composed of distinct particles or pieces less than 500 microns in size that presents a fire or deflagration hazard when suspended in air or some other oxidizing medium over a range of concentrations.
What are the most common combustible dusts?
Following are some common types of combustible dusts:
- Agricultural products: egg whites, powdered milk, soy flour, cornstarch, sugar, tapioca, whey, and wood flour
- Agricultural dusts: alfalfa, apple, cocoa powder, coffee dust, malt and rice flour
- Carbonaceous dusts: charcoal, coal, coke and cellulose
- Chemical dusts: adipic acid, ascorbic acid, calcium acetate, lactose, methylcellulose, sodium ascorbate and sulfur
- Metal dusts: Aluminum, titanium, iron, magnesium and zinc
- Plastic dusts: (poly) acrylamide, (poly) ethylene, epoxy resin, molded melamine, phenolic resin and polyvinyl chloride
- You can download a list of combustible dusts from OSHA here: https://www.osha.gov/Publications/combustibledustposter.pdf
What are the top 5 risk factors for dust combustion?
Many of the materials on OSHA’s list are only combustible when they occur in the right particle size, concentrations and environmental conditions:
- Combustible fuel, such as dust
- Sufficient dispersion of dust particles
- Heat or an ignition spark, whether by friction or static electricity
- The presence of enough oxygen
- Confined dust clouds
Dust explosions can occur in any industrial manufacturing context where these five risk factors are present. Although a solid piece of wood, metal, or plastic does not pose the potential for an explosion, these materials can ignite or explode when dispersed as fine particulates in the presence of an ignition source. Solid, noncombustible items can be turned into combustible dusts during manufacturing processes like machining (sawing, grinding or drilling) or finishing (buffing, polishing and abrasive blasting, etc.).
How do I reduce the risk for dust explosions?
OSHA recommends the following dust control steps to help cut the risk for a fire or explosion:
- Capture: Install a properly designed, approved and maintained dust collection system.
- Contain: Make sure dust is contained within the equipment or system that is built to handle it safely.
- Clean: Regularly clean work areas, surfaces and spaces to remove combustible dusts not captured or contained.
What is an industrial dust collector?
Industrial dust collection is a time-tested method of air quality control. There are two types of industrial dust collectors: dry dust collectors and wet scrubbers.
Dry dust collecting involves capturing and removing industrial particulate from the processing source using a dry dust collector like a pulse clean or reverse air baghouse, cyclone or cartridge collector. Although dust collector designs can vary, typically, dust-laden air enters the collector through a baffled inlet located in the hopper where large, heavy dust collects, and the fine particulate is drawn upward and collected on the filter media. Then, either a large flow of reverse air or regular bursts of compressed air dislodge the dust cake from the filters, and it drops back into the hopper. This continuous cleaning will preventing excessive buildup on the filter media extending its life and maintaining consistent operating conditions. The particulate is continuously discharged out of the hopper and into a container for disposal or conveyed for reintroduction into the process.
Wet scrubbers incorporate devices that use water to remove dust from the air. With these systems, the scrubbing liquid (usually water) is introduced to a gas stream containing the dust particles. Greater contact of the gas and liquid streams yields higher dust removal efficiency. Wet scrubbing options include impingement, venturi, eductor, and packed-tower scrubbers.
Wet scrubbers are an alternative to baghouses or other dust collection approaches for some types of combustible dust. By the nature of the mechanisms applied within a wet scrubber, these devices can effectively mitigate the risk factors for explosion, as follows:
- The use of water reduces the heat source and dust cloud.
- Wet scrubbers eliminate the dust dispersion essential for combustion by aggregating dust particles within water droplets.
What type of dust collector is best: wet or dry?
There is no simple answer to this question, and it depends on some important considerations:
- Where will the dust collector be installed?
- Which air quality standards are you required to meet?
- What size of dust particles is involved?
- Are you required to recover and reuse any collected dust particles or discard them?
- Is the dust combustible, flammable, and/or explosive?
- Will the dust require special treatment and handling based on its being poisonous, toxic, corrosive, and/or carcinogenic?
- How much dust do you need to collect, handle and potentially dispose of?
When choosing a dry system, baghouse collectors are recommended for the largest dust loads, cartridge dust collectors may be better for dry and free-flowing dust, and reverse air collectors may be best if you need to save on energy costs or have limited access to a supply of quality compressed air.
When considering a wet scrubber system, keep in mind that some dusts can become water-reactive or can become sticky when they come in contact with water. Some dusts may float in water; others may sink or dissolve in water. Some scrubbers are only suitable for gas-phase contaminants and are not suited for dust removal. Following are three types of recommended wet scrubbers for dust collection:
Impinjet® Wet Scrubbers
Impinjet® wet scrubbers efficiently collect particulates and clean, cool, and absorb vapors and gases. They have low water recirculation requirements and minimum pressure drop, are resistant to fouling, and are available with capacities as high as 200,000+ CFM.
A Venturi scrubber collects fine particulates and mists using the differential between high-velocity gases and free-flowing water to create fine droplets that can entrap contaminants and hold them in suspension. They can remove very small particles and can be coupled with Impinjet scrubbers for maximum efficiency.
Eductor Wet Scrubbers
Eductor scrubbers can remove both soluble gases and particulates by inducing a gas flow using high-pressure liquid focused into a Venturi throat. There is no need for a separate exhaust fan or blower to transport the contaminant-laden airstream to the filtration device.
It is important to note that choosing between dry dust collection and a wet scrubbing option may not be a binary choice. In certain situations, the best solution may be to combine the two systems.
Again, this article is by no means a comprehensive resource and is only intended as a convenient educational overview. Contact Sly for your specific industrial dust safety questions. We are always here to help you customize the best dust safety solution for your facility.