Tiny Particles: Big Booms
The benefits of portable industrial vacuums for combustible dust mitigation.
In a galaxy not so far away (okay, our galaxy), an all-pervading and powerful dark force lurks: dust. It is omnipresent and its potentially disastrous effects are inescapable, even in space.
According to new research from the Laboratory of Atmospheric and Space Physics (LASP) at the University of Colorado Boulder, microscopic hypervelocity dust (from two to 20 microns in size) creates tiny plasma explosions when impacting with NASA’s Parker Solar Probe which can damage the probe and disrupt operations.
While it may be fascinating for scientists to study the effects of plasma explosions in space caused by hypervelocity dust, combustible dust in the plant environment is not as enchanting. Though the mechanism for dust explosions is different in space than it is here on earth, the size of dust particles that can damage the $1.5 billion solar probe, are the same size particles that can cause catastrophic loss of life and property in the manufacturing realm when concentrations exceed safe levels.
Half of all fugitive dusts in manufacturing and processing environments are smaller than 10 microns and invisible to the naked eye which is perhaps why some facilities have misconceptions about the risk at their facility. The culprit behind many secondary dust explosions is the accumulation of dust above eye level such as overhead beams, joists, duct work and the tops of equipment. In addition, catastrophic dust incidents that garner the greatest attention tend to focus on the most egregious offenders with inches deep combustible dust accumulations which may lead some to incorrectly assume that only the most derelict companies experience dust explosions.
According to data from Dust Safety Science there are, on average, three dust explosions and 40 dust fires per month and facilities with combustible dusts should adopt a mindset of “when, not if,” conditions are amplified for a combustible dust incident.
Although the majority of recorded incidents occurred in agricultural, food and wood products industries,2 nearly all industries produce some type of combustible dust during the manufacturing process.
Each combustible dust, or combination of dusts, has unique thresholds for when accumulation levels become hazardous. A general rule of thumb from OSHA and NFPA suggests that a buildup of combustible dust in excess of 1/32 of an inch, more than five percent of a facility’s floor area (including overhead areas such as beams, joists, duct work, walls and the tops of equipment), creates a hazardous condition, with some dusts having even lower thresholds.
In space there is no equipment to mitigate dust to protect expensive space crafts, however, here on earth, in the plant environment, there are several mitigation strategies and equipment options that reduce combustible dust hazards.
Preventing the escape of dust from processing and manufacturing activities, through the use of vacuum conveyors which prevent fugitive dust from escaping into the environment during material transfer is the first line of defense in reducing combustible dust hazards. However, even the most protected facilities that utilize multiple types of equipment to prevent combustible dust from entering the environment or building designs that reduce the ability for dust to accumulate, must still develop housekeeping schedules to mitigate combustible dust hazards.
One of the fastest and most economical ways to mitigate combustible dust accumulations is with the use of heavy-duty portable industrial vacuums, designed specifically to stand up to the rigors of industrial use.
Unlike hardware-store, shop-type vacuums that pose sparking hazards, industry-specific portable vacuums that are for commercial applications and not 24/7 production have the suction power to grab onto a bowling ball and the ability to handle very fine combustible powders. The difference between heavy-duty industrial vacuums and their asthmatic cousins is equivalent to sending a commercial aircraft to the sun in place of the rover.
One of the biggest advantages of portable industrial vacuums is their flexibility for operating anywhere in the plant without the need for large stationary vacuum cleaners that are pricey and require explosion venting and permits.
From intrinsically safe, air-powered vacuums to explosion-proof electric powered units and vacuum cleaning units that operate much like stationary central vacuums that accommodate multiple operators at once, portable vacuum cleaners for combustible dust are configurable to meet facility-specific requirements.
Working with an expert in vacuum technology with tribal knowledge, passed down through time, across a range of industries and tens of thousands of materials, safeguards life, property and profits, through proper selection of vacuum cleaning equipment. Portable air-powered vacuum cleaners come in a range of configurations and are versatile enough to be used to clean coal dust in electric power production, with fine bakery flour and starches, pharmaceutical ingredients, metal powders for 3D printing and a host of applications where combustible dust exists. There are even air-powered submerged recovery vacuum cleaners for explosive powders, such as smokeless powder used in ammunition production.
With combustible dust present in a facility, the use of an intrinsically safe vacuum that adheres to Class II Division 2 design may be necessary even in non-Class II Division 2 areas. Early in OSHA’s Combustible Dust National Emphasis program, the agency issued numerous citations for using standard vacuum cleaners where Class II Division 2 equipment is required.
Air-powered vacs operate on the Venturi principle and by design create their own vacuum without motors, heated surface or moving parts, making them intrinsically safe. Intrinsic safety is covered under OSHA Regulations (Standards - 29 CFR), hazardous (classified) locations 1910.307 and 1926.407.
Intrinsically safe designs are unable to release thermal or electrical energy including electrical sparks and arcs, flames, hot surfaces, static, electromagnetic radiation, and chemical reactions, which can cause ignition of flammable materials like combustible dusts.
Venturi designs uses regular shop air, passed through the venturi, to develop a powerful vacuum stream which draws air and material through the vacuum lines.
Variable orifice Venturi units allow for adjustable suction power between 8 inches of mercury (Hg) to a maximum of 16 inHg, providing versatility of use throughout a facility without the need for separate vacuum cleaning systems.
When purchasing air-powered units, it is essential to pay attention to the amount of CFM required to produce suction power. An air-powered vacuum with lower CFM requirements, sometimes half of seemingly comparable systems, may have a higher purchase price; however, many times the difference between initial cost is recouped within few months through compressed air savings.
Since Venturi powered vacuum cleaners have no moving parts, and are therefore virtually maintenance free, except for occasional replacement of filters and exhaust mufflers, it is not unusual to see them in service for 20 to 30 years, making them the most economical and reliable systems for dust mitigation.
Buyers of air-powered vacuum cleaners should seek out manufacturers that offer lifetime guarantees for their Venturi units, ensuring they are getting the most bang for their buck.
Vacuum cleaning equipment with ATEX certification marks and documentation, issued by a recognized third party that attests equipment complies with a set of directives and standards set by the EU for controlling explosive atmospheres, demonstrates that equipment is designed to operate safely in hazardous environments with combustible dusts.
Neither OSHA nor NFPA have standards for non-electric equipment used in hazardous-rated environments. Nationally Recognized Testing Laboratories (NRTL), recognized by OSHA, can issue certifications of air-operated vacuum cleaners for hazardous environments commensurate with NFPA guidelines for equipment in hazardous locations.
When the use of portable air-powered vacuum cleaners is not feasible, electric-powered explosion proof vacuums suitable for use in for Class II, Group F & G combustible dust environments must meet OSHA, UL or CSA, and NFPA guidelines for NRTL approved components, such as certified explosion proof motors and all product contact parts made with anti-sparking stainless steel.
Electric powered vacuum cleaners are available in single phase and three phase options with vacuum equalizer kits that allow the use of off the shelf static conductive collection bags that eliminate dust clouds associated with dumping debris.
Continuous bagging industrial vacuum models are also available for combustible dusts. These units not only eliminate dust clouds associated with dumping of drums or rigid collection container, but also avoid a potential cause of back injury by eliminating the need to lift large bags of dust and debris from containers.
When simultaneously vacuuming by multiple users is needed, or for larger spread-out facilities where a central vacuum system would be cost prohibitive, portable breakaway central vacuum systems that have the ability to operate within smaller fixed networks, or as portable vacuum systems, are available.
These larger portable units utilize positive-displacement rotary-lobe vacuum pumps that provide 50 percent more vacuum power with consistent airflow for quick recovery of materials from large piles and over long distances. There is always a cheaper version of something that you can buy, but cheaper does not always equate to long term cost savings.
Energy costs, ease of use and time-saving technologies, such as tool-less assembly and quick, dust free filter cleaning technologies are all factors that provide facilities more bang for their buck when purchasing heavy duty combustible dust vacuum cleaners for hazard mitigation.
The easier a piece of equipment is to use, such as portable vacuum cleaners, the more likely operators are to regularly use them as directed by safety protocols.
Working with a seasoned vacuum technology expert with deep knowledge of materials characteristics and NFPA guidelines as it relates to combustible dust promises a system that enables facilities to comply with combustible dust standards specific to plant needs.
This article originally appeared in the February 1, 2022 issue of Occupational Health & Safety.