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By Mike Bacidore, chief editor
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.
“OSHA has established permissible exposure limits (PELs) for hundreds of dusts.”
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.usainc.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.”