Indoor air quality (IAQ) impacts a plant’s profitability, productivity, and safety, but what does a plant manager use to gauge it? OSHA has exposure levels and specific air sampling procedures to measure regulated dust hazards, but, because IAQ can be impacted by a number of factors, several different types of testing may be needed to determine if a plant has a problem. Factors that can negatively impact indoor air quality include temperature, humidity, poor ventilation, mold from water damage, or exposure to chemicals.
Measuring temperature, humidity, and air flow is a good start, but inspecting and testing of the ventilation, heating, and air conditioning systems should be performed, too. Like all environments, there is no one definitive test for air quality, explains Lawrence Schoen of Schoen Engineering. “You need to know what the potential sources are and therefore what you are looking for and measure these substances at times and places appropriate to the process, depending on the sources,” he says. “Industrial hygienists use personal monitors which can supplement area measurements.”
To properly measure indoor air quality, a certified industrial hygienist should be consulted so your operation can be reviewed to determine the most appropriate way to measure the air quality at your plant, agrees Travis Haynam, director of business development & technical sales at United Air Specialists (www.uasinc.com). “This might include sampling of worker breathing zones for an extended period of time to obtain an accurate representation of actual worker exposure,” he says. “Opacity, or the degree to which light is not allowed to travel through, is a quantifiable measure of particulate matter in the air which can also be utilized to evaluate a plant’s indoor air quality.”
Simple and easy inspection techniques start with a visual assessment, says Andrew Stewart, senior manager, sustainability, Grainger (www.grainger.com). “If dust is collecting on work areas and equipment, this is a fast and obvious signal that there is likely a larger air quality issue present,” he warns. “Fumes from work equipment such as forklifts operating within the plant, wear and tear from belts, tires, rollers, conveyers, and the products they are moving are catalysts for dust that impact indoor air quality and need to be addressed. Outdoor ventilation, such as like wedging doors open to cool or provide fresh air, often bring in road dust and particulates from neighboring businesses that will contribute to the collection of dust in a plant.”
More advanced ways to measure indoor air quality involve using specific equipment like rotary or thermal anemometers, air flow capture hoods, and air velocity monitors, suggests Stewart. “Keeping air filters clean and checked regularly is also critically important in order to remove contamination that the filters collect and prevent them from moving back into the building environment,” he says.
More and more, the rules and guidelines are requiring that the air be constantly monitored for filtered condition, so some systems include secondary or monitoring filters, says Kirt Boston, global manager of Torit product technology at Donaldson Filtration Solutions (www.donaldson.com). “They’ll put a HEPA filter downstream of the collector with the idea being that it polishes off the air stream,” he explains. “They do an extremely good job of filtering, but they don’t have a very long life if you throw a lot of material load at them, so you end up putting in a HEPA filter to ensure the quality of the air never drops, and the primary filter is there to perform the filtering the majority of the time extend the life of the HEPA filter indefinitely, baring an upset condition.”
A lot of standards require that secondary/monitoring filter, says Boston. “What you’re doing is taking a filtering device like a HEPA filter that has very high efficiencies — they’re 99.97 at .3 microns — so they do an absolutely phenomenal job of removing particulate, but they have a distinct disadvantage in that they are non-cleaned and they show pressurized relatively quickly if you start to throw dust at them, which is not great if you’re trying to filter all the air in your plant on a regular basis, but it does create a nice performance behavior when it comes to monitoring a dust collector,” he explains. “If that dust collector were to develop a mechanical leak, if a bag were to be torn or a cartridge were to have a hole in it or somebody put a filter in backward and a gasket’s been compromised, that dust that’s now passing through the collector, when it gets to the HEPA filter, is arrested. It doesn’t get back into the plant and the HEPA filter shows a rapid increase in pressure drop, so that it’s an easy performance parameter to monitor in terms of pressure drop, and it’s a quick indicator that something’s wrong upstream. When there isn’t anything going wrong upstream, then most primary filters, if they’re of any quality, are going to deliver very clean air to the HEPA filter and it’s going to spend the majority of its life allowing clean air to go through it. It won’t show any measurable increase in pressure drops. There’s an initial capital cost, but there isn’t an annual replacement expense and it’s not a monthly replacement expense, if you were trying to do it without having the primary filter.”
The pressure-drop data can be worked into a control logic system, so that, if the pressure drop on the HEPA suddenly spikes, an alarm goes off and the operations group is notified that there’s something wrong with the collector that’s creating the problem, offers Boston. “We’re seeing the same kind of things, even within the operational monitoring of the dust collector itself, so you’ll have controls that monitor pressure differential and they now are starting to have alarm functionalities,” he says.
“With companies being more sensitive to maintenance and operational expenses, they’re trying to monitor the performance of the systems much more actively to ensure that the systems are maintaining operational designed performance,” explains Boston. “Measuring air quality in the plant has always been a challenge. From an industrial hygiene standpoint and the worker exposure standpoint, there are lots of different ways that they can survey what the employees are being exposed to, from lapels to ambient measurements around the facility.”