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Effective and visible dust and odor control can significantly influence the perception of operations and dramatically improve the workplace environment.
By Michael Kelley

Workplace safety and risk management professionals will tell you that government air quality rules on dust emissions for workplaces other than mines are somewhat vague. Regulations for indoor processing of municipal solid waste (MSW), construction and demolition waste (C&D), and household/C&D recycling management are even less clear. The U.S. Occupational Safety and Health Administration (OSHA) and the Environmental Protection Agency (EPA) set general particulate levels, which are intended to cover all workplaces. So, when inspectors enter indoor waste processing and recycling facilities with low air quality and no dust control procedures in place, particle levels start getting measured. This is especially true if the inspection is sparked by dust and odor complaints.

With a greater understanding of waste management, municipalities and state governments are building localized processing centers for community and commercial drop-offs, rather than directing the public and garbage pickup contractors to offload at a landfill site. These smaller facilities are closer to residential areas and require a detailed dust and odor management plan. Environmental engineers who construct these comprehensive plans are increasingly including atomized mist technology to both address airborne particulates and effectively distribute odor suppressing chemicals.

Causes of Dust in Indoor Waste and Recycling Facilities
Whether it is a garbage truck with MSW, C&D drop off, or a private citizen emptying their pickup truck, off-loading can emit excessive dust. Other dust causing activities in waste terminals include disruption from front loaders as they separate material on the tipping floor, backdraft from dropping material through subfloors, or emissions from loading waste to other transport vehicles.

Indoor recycling dust can affect workers throughout their shifts. Separating small materials often requires vibration screening, which can emit plumes of particles. However, that is an automated process. At some point, workers are required to stand at a conveyor and hand separate materials. Although personal protective equipment (PPE) helps protect them, worker morale and workplace conditions are significantly improved when dust is controlled with atomized mist technology.

Indoor Dust Regulations
Although the air can look clean, regulated dust emissions are invisible to the naked eye, and the smaller they are, the more dangerous they are. Regulations are in place to protect not just workers but also the general public. Fitting workers with the proper PPE can be effective but does not properly extend to contractors and private citizens who also use the facility.

Complaints about dust and odor can prompt an OSHA or EPA inspection (or both). Investigators measure dust size by microns (µm) and volume in micrograms (µg) using personal detection devices worn by workers throughout a shift. Lightweight particulate matter (PM) as large as 200 µm—roughly the size of a small grain of sand—can remain airborne on normal ambient air currents. Particulates are no longer visible to the naked eye under 100 µm. At the size of <PM10 (the indoor air quality [IAQ] regulated size threshold for most airborne particles), the tiny particles avoid the body’s natural defenses and penetrate deep into the lungs.1 The human health effects of excessive PM exposure are well-established and are used to set the National Ambient Air Quality Standards (NAAQS).2

How Do Mist Cannons Work?
An automated indoor misting cannon has a high-powered fan at the back of a cone-shaped barrel. Mounted on the front (exit side) of the barrel is a ring manifold with multiple nozzles that fracture pressurized water into microdroplets roughly the same size as the airborne dust. The fan creates a powerful air stream that is concentrated in the barrel, directing the air at a high velocity out the front. The forced air carries millions of microdroplets and distributes them in a dust suppressive plume wherever the cannon is pointed.

The standard unit for indoor applications is equipped with 30 brass nozzles, which can also be specified in stainless steel or nylon. The premium-efficiency, three-phase direct drive fan motor delivers 9,200 CFM of air flow (260.5 CMM), while the optional single-phase motor provides 8,000 CFM (226.5 CMM).

With a coverage area of more than 6,100 square feet (566 square meters), the standard cannon configuration produces a throw of more than 100 feet (30 meters) but uses just 4.9 to 9.8 GPM (18.5 to 37.1 LPM) of water. Although most terminals are designed to control wastewater runoff, unlike hoses and sprinklers which use more than 75 GPM to operate, the atomized mist spreads to minimize pooling and runoff.

Indoor misting cannons can be set in specific locations throughout the operation and managed by remote control. The units are automated, so after being turned on, workers can leave to perform other tasks. This reduces labor costs from holding hoses and worker exposure to hazardous IAQ at the point of emission.

How is Atomized Mist Effective?
To be effective, droplet sizes need to be roughly the same size as the airborne particulates. Hoses and sprinklers are not appropriate for indoor applications, since they create droplets between 200µm and 1000µm. These would saturate the area, creating pooling, which introduces slip and fall hazards—another common OSHA violation.

Droplet sizes greater than 200µm do not offer airborne dust suppression due to the slipstream effect. Atomized mist, on the other hand, produces droplets in the range of 15µm to 200µm, small enough to collide with airborne particulates and pull them to the ground. There is little to no pooling and with proper indoor ventilation, the droplets follow the dust and absorb the particulates before they spread.

Controlling Odor
To control odor, the misting cannon can be fitted with a dosing pump for chemical additives. The pump can deliver a range of volumes from a minimum of 0.003 GPH (.009 LPH) to a maximum of 2.5 GPH (9.5 LPH).
Deodorizers have been found to be an effective control for the majority of industrial odor emissions, treating the smell on a molecular level. These chemicals work by replacing the odor-causing element in the structure of the odor molecule with an inert element. This makes the mist delivery system effective because the miniscule droplets have a great chance of interacting with the molecules in the air, especially if they are attached to a particulate.

When Workplace Safety is Public Safety
Regardless of whether the facility is open to the public or not, dust and odor emissions affect the community in a variety of ways. Workers exposed to low air quality can be prone to sickness, including respiratory issues and bacterial infections. Although research into the adverse health effects of living and working around waste management sites is in early stages, large scope studies conducted by the National Institutes of Health in recent years have revealed that local communities and workers can experience sickness, lower birth rates, and higher mortality.3 Researchers have recommended further studies to better understand the initial findings and inform regulatory policy moving forward. Moreover, the findings have not yet been tied to particulate emissions, but the correlation between air quality and public health is not a far leap.

Negative public perceptions of a local facility can have a serious impact on operations. Beyond complaints to government agencies like OSHA and the local EPA, there may be political implications affecting permitting and funding. Effective and visible dust and odor control can significantly influence the perception of operations and dramatically improve the workplace environment. The return on investment of a dust and odor management plan that includes atomized dust technology is relatively short once reduced labor for dust control, greater morale and fewer sick days are calculated. | WA

Michael Kelley is President, of BossTek, a global leader in dust and odor control solutions for the storage and handling of bulk materials, as well as controlling air quality during port unloading, recycling and scrap processing, mining, earth moving, and demolition activities. The company’s DustBoss product line uses atomized mist technology propelled by powerful fans to capture fugitive particles over a wide area. For more information, call (309) 693-8600 or visit .

Resources

Notes
U.S. Occupational Safety and Health Administration; Indoor Air Quality. U.S. Department of Labor, Indoor Air Quality in Commercial and Institutional Buildings. OSHA Publication 3430, (2011) https://www.osha.gov/sites/default/files/publications/3430indoor-air-quality-sm.pdf
U.S. Environmental Protection Agency; NAAQS Table. National Ambient Air Quality Standards (40 CFR part 50) https://www.epa.gov/criteria-air-pollutants/naaqs-table
Vinti, Giovanni; Bauza, Valerie, et al; Municipal Solid Waste Management and Adverse Health Outcomes: A Systematic Review. National Institutes of Health, Int J Environ Res Public Health. 2021 Apr; 18(8): 4331. Published online 2021 Apr 19. doi: 10.3390/ijerph18084331