Page 10 - OHS, May 2021

COMBUSTIBLE DUST
for all combustible dusts. Companies really need someone who has intimate knowledge of how chemicals react in certain environments and has experience in NFPA standards to help them choose the right combustible dust vacuum cleaner.
In some applications, small portable air or electric powered drum-style units will suffice, while others require large electric and diesel-powered units for multiple users and filtration systems capable of capturing particles that are invisible to the naked eye. Somewhere in between are portable breakaway systems that combine the portability of drum style units and benefits of central vacuum cleaning units without the cost.
While there are intrinsically safe electric industrial vacuum cleaners available, the most economical solution for cleaning combustible fugitive dust are air-operated vacuums. Beyond the fact that air operated vacuum cleaners use no electricity and have no moving parts to create spark hazards, well-built air operated vacuum cleaners are grounded in five ways beginning with the air line that supplies compressed air to the units. Because most plants have compressed air lines made from iron that conduct electricity, air operated vacuums use static conductive high pressure compressed air lines. In addition to the static conductive air lines, static conductive hoses, filters and casters which are employed to further reduce risk. Finally, a grounding lug and strap that travels from the vacuum head down to the 55-gallon drum, eliminates the potential for arcing.
Air operated vacuums for combustible dust are safer in terms of grounding, they also work more efficiently in the industrial environment than commercial or industry specific vacuum cleaners, such as agricultural vacuums which are great for farm use but not necessarily suited to rugged industrial applications where environmental safety, ergonomics and productivity matter. Vacuum cleaners designed specifically to withstand rigorous 24/7 operation can deliver consistent performance that adds to a company’s bottom line in heavy use industrial facilities.
These units are easy to maneuver and support one operator up to 50 feet away from the vacuum and also provides excellent suction for overhead cleaning in hard-to-reach areas with the use of wand extensions, reducing the time and mess involved in more manual cleaning methods that disperse
If portable intrinsically safe vacuum cleaners are the “muscle cars” of the combustible dust world, then central vacuum cleaning systems are top-of-the-line luxury vehicles. Stationary central vacuum systems are ideal for environments requiring continuous 24/7 operation and the simultaneous use of up to 20 pickup points. These systems employ powerful stationary industrial vacuum cleaners that have strategically placed piping throughout a facility connecting hoses to a common line.
When designing a central vacuum cleaning system, factors that must be considered are characteristics of the material cleaned, such as: abrasiveness, corrosiveness, flammability or explosion hazard. More factors include: volume collected, bulk density, particle size, filtration goals, maximum temperature, total number of pick-up points, the number of simultaneous operators, hose size, longest vertical and horizontal tubing runs from vac, available floor space and collection container considerations.
Some manufacturers use regenerative blowers as a vacuum source in central vacuum systems which have the airflow but not the simultaneous vacuum. Regenerative blowers look appealing
because they show a lot of airflflow for a given horsepower, but they do not generate enough vacuum to move material over distances in tubing when vacuum pressure goes up, i.e., when the job gets harder, performance is lost.
Traditionally, central vacuum systems require a bag house with either a chemical suppression system or an explosion venting system to meet NFPA and OSHA standards which often lead to outdoor installation, bringing other challenges such as air permits as well as construction permits.
There are also smaller central vacuum systems that can service up to three operators at once with piping runs up to 200 feet while conforming to NFPA standards for indoor installation because the “dirty volume” is less than eight cubic feet, allowing installed units without the need for an explosion vent or chemical suppression system. These smaller indoor installations can avoid air permitting requirements with many local municipalities while returning HEPA-filtered air into the plant environment.
In larger less centralized facilities where sizing a central vacuum system would be cost prohibitive due to power necessary to suck dusts from one end of the facility to the other, breakaway central vacuum systems are a cost-effective solution.
Breakaway vacuum systems operate much like central vacuums with fixed tubing networks, but units are portable, much like the portable air-operated vacuums, and utilize several smaller tubing networks. For instance, if a user is working in a 100-by-200-square-foot area and there are two more areas in another building, individual tubing networks are created and the vacuum cleaning unit is able to break away from one tubing network and rolled to the next network and so on and so forth.
Breakaway vacuum systems avoid costs and delays that may occur with central vacuum cleaner applications, providing the convenience of a multi-inlet central vac, with the energy efficiency and flexibility of a portable vacuum.
The smaller central vacuums and the portable air operated vacuums allow for indoor operation because breakaway vacuum systems have a filter separator and collector less than eight cubic feet. It does not need an explosion vent to use it in Class II, Division 1 & 2 areas, per NFPA standards and OSHA regulations.
With the largest models of breakaway systems able to move five tons of powder in an hour from 30 feet away, these units are capable of generating high vacuum and excellent airflow, so they have the ability to pull massive amounts of material over distances. Central vacuum cleaning systems with strategic tubing networks and portable vacuum cleaners allow manufacturers the ability to clean up spills and perform regular cleaning to mitigate buildup of combustible dusts in hard-to-see areas, maximizing ROI.
Doan Pendleton is the President of VAC-U-MAX located in Belleville, New Jersey. Pendleton’s professional experience includes over 30 years of experience in the design, engineering, manufacturing and marketing of dry bulk material transfer systems and industrial vacuum cleaning systems, with application expertise in the food, pharmaceutical, plastics and non-woven industries.
REFERENCES
1. https://www.osha.gov/OshDoc/Directive_pdf/CPL_03-00-008.pdf
10 Occupational Health & Safety | MAY 2021
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