Mitigating Combustible Dust is Not a Housekeeping Activity—Rather Hazard Abatement

Mitigating Combustible Dust is Not a Housekeeping Activity—Rather Hazard Abatement

When equipment works efficiently and simplifies a task, the task is more likely to be performed by workers regularly and correctly.  

Dust control is not a single point action item. Even with the use of vacuum conveyors that keep dusts contained during material transfer from one process machine to the next, coupled with dust collection systems designed to capture airborne dusts, it is relatively impossible to eliminate all dust and inevitably fugitive dust will settle on both vertical and horizontal surfaces. The safest method of abating accumulations of combustible dust is with industrial combustible dust vacuum cleaners.

Fugitive dust, tiny particles that float through the air, is part of the manufacturing process. Half of all fugitive dusts are smaller than 10 microns and invisible to the naked eye. Some dusts can hang in the air for days before settling on rafters, ledges and equipment.

Dust in industrial processing and manufacturing environments is not simply dirt, it most often contains hazardous particles that pose serious threats to workers’ health such as dangerous respirable dusts like silica or combustible dusts responsible for dust fires and dust explosions. The misconception that mitigating combustible dust accumulations is a standard housekeeping activity and not a hazard abatement activity is a clear barrier to prevention of combustible dust explosions, and it was one of the prominent discoveries addressed in the U.S. Chemical Safety and Hazard Inspection Board’s (CSB) “Dust Hazards Learning Review” report.

Born from the CSB’s ongoing investigation of the 2017 Didion Mill combustible dust explosion that killed four workers and injured the remaining 15 employees present that evening (resulting in $1.8 million in OSHA fines), the report noted that cost of abatement, complacency and a general lack of awareness of combustible dust risk (even by supervisors and safety managers), were factors that could contribute to a perfect storm, of sorts, leading to catastrophic dust explosions.

The National Fire Protection Agency (NFPA) has several standards that address combustible dust; however, the lack of an OSHA combustible dust standard relegates most combustible dust hazard citations under the general duty clause. Although the CSB report noted that housekeeping is the “foremost” control utilized across most industries for combustible dust risk reduction, it also acknowledged that “housekeeping is often sacrificed for ‘more important’ maintenance items directly impacting problems.” OSHA defers to Chapter 7 of NFPA 654 (2020), Standard for the Prevention of Fires and Dust Explosions from the Manufacturing, Processing, and Handling of Combustible Particulate Solids. Chapter 7 deals specifically with Dust Hazard Analysis and section 7.2.3, Layer Depth Criteria Method suggests immediate cleaning occurs when dust accumulations reach 1/32 inch-thickness, approximately the thickness of a paper clip, over a surface area of at least five percent of the floor area of the facility or any given room. Other “Mass Methods” are also approved by NFPA 654 (2020) in Chapter 7 to determine the dust hazard in a facility. Though the NFPA standard includes a more detailed approach in calculating surface dust hazards, OSHA’s directive, CPL 03-00-008, that provides instructions for inspectors administering OSHA’s Combustible Dust National Emphasis Program (NEP) notes:

“Rough calculations show that the available surface area of bar joists is approximately five percent of the floor area and the equivalent surface area for steel beams can be as high as 10 percent.”

This information is vital for plant managers, supervisors, safety managers and employees to understand. It demonstrates the need for just about any facility with exposed overhead areas and combustible dust to prioritize this serious hazard with regularly scheduled abatement cleaning.

In addition to the misconception that combustible dust abatement is more a matter of “tidying up,” the CSB report revealed the false impression that dust collectors and vacuum cleaners are one in the same. While the three primary technologies to control dusts (vacuum conveyors, dust collectors and vacuum cleaners) all use vacuum (negative pressure) to operate, they are distinctly different devices, that perform separate and unique functions.

Vacuum conveyors use high-pressure suction to transfer a large volume of materials from one process machine to the next. Because they are fully enclosed, dust does not escape from transfer points, thus reducing the amount of fugitive dust in the plant and also reducing cleaning frequency.

Dust collectors are air-pollution control devices that use low-pressure suction to pull airborne dust from nearby processes.

Industrial vacuum cleaners are precision cleaning machines that use high-pressure suction to pick up accumulated dirt and debris from fine dust to irregular-shaped clumps of material. Industrial vacuum cleaners often add to the bottom line through reduced labor, minimizing production downtime for cleaning, enhancing quality control, reclaiming valuable raw materials, mitigating ergonomic and respiratory illness and injury and of course, by removing the potential for dust fires and explosions.

There is no one size fits all industry-specific vacuum cleaning solution because no two applications are alike. Working with a responsible manufacturer with intimate knowledge of OSHA and NFPA standards as well as decades of experience working with combustible dust and tens of thousands of materials contributes to overall plant safety goals, compliance and aids hazard analysis. There are many factors that expert industrial vacuum cleaning manufacturers consider when choosing a vacuum cleaning system to fit a customer’s goals including material characteristics, quick evacuation of materials, volume collected, bulk density, particle size, total number of pick-up points, the number of simultaneous operators, floor space, etc. It is important to note that vacuum cleaners can be vulnerable to ignition, so it is essential to purchase a combustible dust vacuum cleaner that is properly grounded to eliminate the possibility of explosion.

For example, drum-top compressed-air-operated vacuums have bumper to bumper bonding and grounding for combustible dust vacuums include static conductive high-pressure compressed air lines, static conductive hoses, filters, casters and a grounding lug and strap that travels from the vacuum head down to the 55-gallon drum dolly that eliminates the potential for uncontrolled static discharge. When necessary, additional anti-sparking product contact options can be incorporated into systems.

Outside of traditional stationary central industrial vacuum cleaners, there are three types of portable industrial vacuum cleaners for combustible dust that provide facilities with an economical, minimal footprint and flexible solution to mitigating fugitive dusts in the plant: ATEX certified compressed-air operated vacuums, explosion proof electric powered combustible dust vacuum cleaners and submerged recovery industrial vacuums for reactive powders.

Compressed-air-operated vacuum cleaners are the most economical and energy efficient industrial vacuums due to their lower upfront cost and lower yearly maintenance costs that quickly surpass any expense of compressed air production.

These vacuums operate on the Venturi principle and by design create their own vacuum without motors or moving parts. The absence of moving parts or motors also means that units generate no heat (perfect for combustible dust), making them intrinsically safe, meeting NFPA 70 requirements. They last longer because there are no parts to fail or service. These air-powered units have unique pulse jet filter cleaning systems that, with the push of a button, backwashes accumulated dust from the filter, eliminating the need to manually clean the unit, virtually eliminating filter blinding, making them easier and cleaner to use without needing to stop to clean the filters.

Compressed-air-powered industrial vacuums for use in combustible settings have been around since 1954 when the first alternative-energy vacuum was designed specifically to combat explosive textile dust. Variable orifice Venturi units allow operation with the lowest air consumption possible yet enables users to double the vacuum level by increasing the amount of compressed air when additional suction is necessary for difficult cleaning tasks such as vacuuming high-density materials, viscous liquids or at longer vacuum distances. Facilities should consider purchasing compressed-air-powered units from manufacturers that offer a lifetime guarantee on their Venturi components. For certain reactive powders submerged recovery (SR) vacuum cleaners, that also operate with compressed-air-operated and are ATEX certified, utilize a specialized vacuum technique to immerse and disperse the powders within a vacuum cleaner.

Submerged recovery vacuum cleaners draw combustible dust through a “bath” of liquids in high-hazard applications, such as vacuuming solid rocket propellant and NFPA 484 metal powders. This technique is suitable for water-reactive metal dusts through the careful selection of a non-water inerting liquid. For Class 2, Group F & G areas where compressed air is not available or when facilities require continuous duty vacuums or multiple users, portable explosion proof electric-powered vacuum cleaners are safe for use with combustible dust and meet UL/C-UL and NFPA guidelines with a variety of power and vacuum source options.

When it comes to mitigating fugitive combustible dusts, manufacturers and processors should choose vacuum cleaning systems from manufacturers who deal solely with vacuum technology and provide good design documentation to help facilities comply with NFPA record-keeping standards—and one that offers static control guarantees. Vacuum cleaning manufacturers that deal only with vacuum technology know the tools and have the experience to make combustible dust abatement a cost savings activity. When equipment works efficiently and simplifies a task, the task is more likely to be performed by workers regularly and correctly.

This article originally appeared in the September 2021 issue of Occupational Health & Safety.

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    October 2021

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