Respirable Crystalline Silica: Low-Cost Controls and Respirator Fit Tests
Natalie Fox, CIH, CSP, a senior manager at Ramboll, discussed effectively reducing employee exposures to respirable crystalline silica at AIHce EXP 2018 in Philadelphia, Pa.
Fox was challenged to control exposures at two glass manufacturing facilities using the most cost-efficient, yet reliable, methods possible. The company that owned the facilities was seeking compliance with OSHA’s silica regulations but also wanted to limit the number of employees required to wear personal protective equipment and reduce the number of similar exposure groups (SEGs) included in scheduled sampling.
To determine where controls were necessary, Fox surveyed the entire facility with direct-reading instruments to create a respirable dust map, determined employee SEGs using job tasks and the map, and collected personal samples from the majority of the SEGs. She then implemented a variety of engineering and administrative controls, as well as improved respiratory protection.
“A lot of employee exposures can be controlled using work practice changes, housekeeping, and lower-cost engineering controls,” explained Fox. “Something like a batch with sand in it [is] really rough on the duct work and it's hard on the conveying systems. So there were a lot of fugitive emissions coming from there. So just going around repairing the ducts, making sure everything's tight so you're not getting any dust out of there, really made a big difference.”
But challenges remain. “Some exposures just can't be controlled through administrative or cost-effective engineering controls. You're going to have to spend the money,” Fox said. “Controlling specific non-routine tasks is really hard, especially maintenance activities. They do so many different things every day it's really hard to figure out what their exposures will be and how we're going to control those.”
She cautioned against quick fixes and urged IHs to never begin designing controls until they’ve conducted a thorough industrial hygiene study. “Determining appropriate controls is not quick. You don't want to rush engineering controls. You want to make sure that they're done right, because there's no one size fits all, even for similar facilities,” she explained.
Highlighting the 100-year history of respirators, Ziqing Zhuang, the human factors and ergonomics team leader in the Research Branch of the NIOSH National Personal Protective Technology Laboratory, talked about the role of respirators in the presence of respirable crystalline silica.
“We talk about engineering controls first, but it's very expensive and in some cases it’s not feasible,” Zhuang said. “So we end up using the last line of defense: respirators or respiratory protection.”
He outlined his respirator fit capability test for full-facepiece air-purifying respirators. The test is designed to ensure that a single-size respirator or family of respirators in multiple sizes or multiple model numbers is capable of achieving an initial fit on a specified percentage of the NIOSH bivariate test panel representing a range of face sizes. “The objective of our study was to evaluate the test methods and assess the capability of the existing respirator models to fit a 25-subject panel and then also come up with what may be a potential criterion to be used to determine whether a respirator or group of respirators would pass the test,” Zhuang said.
His team concluded that RFC, or respirator fit capability, calculated as panel passing rate is significantly different among the required fit factors and family of respirators tested. Researchers further concluded that test methods developed for half-mask respirators may also be appropriate for the respirator fit capability test of full-facepiece air-purifying respirators.