- The presence of combustible dust in the air creates an unnecessary risk that can devastate an operation.
- Good indoor air cleaning also prevents buildup of nuisance dust on process equipment, electrical control panels and circuit boards, inspection equipment, and paperwork.
Plant explosions are unpredictable and usually deadly. The presence of combustible dust in the air creates an unnecessary risk that can devastate an operation. In fact, dust of any kind can have a huge impact on an industrial plant, with consequences that are as expensive as they are preventable.
Being suspended in an aerosol can make innocuous materials amazingly hazardous. Something that is mildly flammable can, by virtue of the intimate relationship between dust suspended in the air and the oxygen that is present, become an explosive mixture. Similarly, when breathed as an aerosol, the chemical attributes of some substances can become suddenly very aggressive. Lead or other toxic metals can enter the circulatory system very efficiently. Materials that ordinarily stay put suddenly move about on the mildest breeze and create hazards for equipment and people in areas that may be quite distant from the source of the contamination.
“Dust impacts people, who are forced to breathe unhealthy air,” says Charles Dix, engineer and co-owner, Carolina Hydro Technologies (www.carolina-hydro.com) in Providence, North Carolina. “Also, dust collects in motors, and a lot of electrical cabinets are not airtight. It can have an effect on product quality and the general housekeeping quality of a plant.”
Airborne contaminants occur in gaseous form or as aerosols, explains Ivan D. Ivanov, MD, PhD , team leader, occupational health, Department of Public Health and Environment, World Health Organization (WHO, www.who.int) in Geneva, Switzerland. “In scientific terminology, an aerosol is defined as a system of particles suspended in a gaseous medium, usually air, in the context of occupational hygiene,” he says. “Aerosols may exist in the form of airborne dusts, sprays, mists, smokes and fumes. In the occupational setting, all these forms may be important because they relate to a wide range of occupational diseases. Airborne dusts are of particular concern because they are well known to be associated with classical widespread occupational lung diseases, as well as with systemic intoxications such as lead poisoning, especially at higher levels of exposure.” Interest also is on the increase in other dust-related diseases, such as cancer, asthma, allergic alveolitis, and irritation, as well as a whole range of non-respiratory illnesses, which may occur at much lower exposure levels.
Certain industrial processes produce dust, which give rise to these health risks or concerns. “Hexavalent chromium is one that’s been in the media a lot for the metals industry,” explains Kirt Boston, global manager of Torit product technology at Donaldson Filtration Solutions (www.donaldson.com). “They’re concerned about employee exposure to the carcinogenic property of hexavalent chromium. Silica is another one that gets a lot of attention in foundries or in abrasive blasting and mining applications. Concerns on toxic properties of dusts and mists run the whole gamut. If you move into the pharmaceutical industries, potent compounds have their own sets of concerns and risks.”
Poor indoor air quality not only makes employees more prone to illness, causes lost production time, and leads to poor morale and lower productivity, it also can impact facility maintenance, adds says Travis Haynam, director of business development & technical sales at United Air Specialists (www.uasinc.com). “Dust migration and buildup throughout the factory adversely affects product quality and can create unsafe conditions such as slippery surfaces or even fire and explosion hazards,” he says. “For production equipment, dust increases wear and tear on bearings or moving parts and results in increased maintenance intervals, as well as reduced service life. All of these consequences lead to increased operating costs for the plant.”
Dust impacts the indoor air quality in many places. “One area you may not expect is the office working areas, where the dust and contamination infiltrate the ventilation systems and then show up inside parts of the building that aren’t exposed to the plant floor,” says Andrew Stewart, senior manager, sustainability, Grainger (www.grainger.com). “While the plant floor is a crucial place to ensure proper safety measures are taken to protect employees and ensure optimal air quality, it is also important to keep in mind those areas that you don’t immediately associate with being exposed to dust. Telltale signs of the infiltration are dark tiles or areas near the air flow vents. The cause is likely dust getting into the HVAC system, either through the fresh air intakes or the duct work seams are vulnerable to the dust entering them.”
Even with only a few pascals of negative or positive pressure difference between inside and outside, or between two different areas, air movement will occur, often through unexpected places, explains Michael Stuart, senior product marketing manager and T/IRT Level III thermographer certified per ASNT standards, Fluke Thermography (www.fluke.com). “This uncontrolled flow of air not only can have an impact on energy consumption, vis-a-vis loss of conditioned air, and thus increased heating or cooling costs, but it can flow through areas that are unclean, or not meant for normal airflow,” he says. “For example, air that moves through interstitial cavities inside of a wall to get from one side to another can get filtered through the insulating material — fiberglass bat, cellulose, and other materials. It inevitably will pick up dust, construction dirt, insulation fibers, and sometimes even materials deposited by vermin and insects over time. All of this could get pulled into areas where people work and contribute to air quality issues that could affect health or some processes.”
Where the dust settles
A classic example there is when you look at large weld applications or robotics where the dust from the process can actually impact wear and tear on the equipment and the machinery, explains Boston. “Product quality is another one that gets driven often where dust from one process starts interfering or influencing operations in other areas of facilities,” he says. “Another example is optics on lasers, where, if you’re not performing good control of the contaminant you’re producing in the process, then all of a sudden your optics are getting fogged or filthy and you’re having to do more regular maintenance on the equipment to keep it operational. We also often see customers who will look at a need to go toward mitigation of dust to improve paint quality or finish quality in another area of the facility.”
Workplace comfort impacts a lot of locations, where operators are simply performing more efficiently if they’re in a more comfortable environment, says Boston. “None of that even addresses issues where it’s purely driven by the fact that the dust has some hazardous property that you have to mitigate in order to avoid problems with worker safety and health,” he says.
“Excessive dust is a potential health hazard to employees in the plant,” explains Tomm Frungillo, vice president of focus markets & Latin America sales at Camfil Farr Air Pollution Control (www.camfilfarr.com). “There are countless documented cases of workers who are healthier and more productive when the indoor air is clean of dust and fumes, with reductions experienced in a wide range of symptoms from headaches and nasal congestion to more serious and chronic upper respiratory problems.”
To protect workers against these hazards, OSHA has established permissible exposure limits (PELs) for hundreds of dusts ranging from nonspecific or nuisance dusts to highly toxic substances, says Frungillo. “These limits are based on 8-hour time-weighted average (TWA) exposure,” he explains. “The limits are extremely strict for toxic substances such as lead and silica. Though a high-efficiency HVAC filtration system can produce excellent indoor air quality in many types of environments, it is not designed to capture the high levels of dust generated in most manufacturing workplaces (Figure 1). If the process dust is hazardous, dust collectors will need to be equipped with very high-efficiency filtration media to meet OSHA and other emission requirements. Meeting these requirements should be first and foremost in any dust collection game plan. Failure to comply may result in fines, production shutdowns or costly litigation.”
Figure 1: Good indoor air cleaning prevents buildup of nuisance dust on process equipment, as well as more breathable air for workers.
Good indoor air cleaning also prevents buildup of nuisance dust on process equipment, electrical control panels and circuit boards, inspection equipment, and paperwork, a common occurrence that can interfere with everyday plant operations, adds Frungillo.
Enduro Composites (www.endurocomposites.com), a manufacturer of engineered fiberglass reinforced plastic (FRP) products and systems for industrial applications, located in Houston, Texas, needed an NFPA-compliant, high-performance dust collection system. United Air Specialists partnered with its local representative, Air Cleaning Solutions (www.aircleaningsolutionstexas.com), to provide an SFC Series downward-flow system to remove FRP emissions from a compression molding process. Due to the potentially explosive nature of the dust, the SFC Series unit is equipped with explosion relief vents to ensure facility and worker safety while removing pollutants from the environment, which allows the facility to meet NFPA 68 standards. In the unlikely event of an explosion, the explosion vent equipped cartridge collector can safely relieve the generated pressure and direct the explosion in a controlled manner in order to prevent damage or injury in adjacent areas.
United Air Specialists also partnered with local representative, Wabash Environmental Products (www.wabashenv.com) in West Layafette, Indiana, to provide a dust collection solution on a new bar-straightening line application at a metal processing facility. Initially, the plant had installed a used shaker-type media dust collector, but it was ineffective at collecting the emissions. As a result, dust was covering the walls, floor and machinery in the new production bay causing maintenance and safety issues. Additional challenges presented by this application included the need for a special hood system design to collect the dust but not interfere with the machinery operator or the flow of the material and locating the collector as close to the bar straightener as possible to minimize the amount of overhead ductwork due to an overhead crane running the full length of the bay. The SFC Series cartridge dust collection system was selected due to its ability to capture the finer steel-scale particulate that was emitted from the straightening process, thus preventing it from migrating throughout the facility. This helped the company achieve a significant reduction in maintenance costs since it was previously washing floors and equipment every two days to deal with the nuisance dust. To further improve the efficiency of the system, the SFC was integrated with the process so the dust collector would start and stop when the line was powered on and off, which led to additional operational savings. And, the flexibility to configure the SFC met the need for a custom designed system.