Page 22 - OHS, January/February 2022

COMBUSTIBLE DUST
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.1
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.
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. There are several mitigation strategies and equipment options that reduce these 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 dust.
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.
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 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.
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,
18 Occupational Health & Safety | JANUARY/FEBRUARY 2022
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