Real-Time Detection Systems: Measuring Exposures
Experts discussed the use and potential limitations of real-time detection systems in measuring exposures at AIHce EXP 2018.
Emanuele Cauda, a senior service fellow at NIOSH’s Pittsburgh Mining Research Division, highlighted real-time respirable dust monitors as a tool that can be utilized in several IH/OH environments. He explained that they are extremely useful for relative measurement and before-and-after comparisons, as well as characterizing exposure.
“Real-time respirable dust monitors are used in any type of environment where there is respirable dust, whether construction, oil and gas, mining, or general industry,” Cauda said. “The big question has been in these cases when we used this information from real-time dust monitors, how confident are we of the accuracy of the data? We all know that humidity, particle size, and particle refractive index of the dust can affect the accuracy of real-time respirable dust monitors.”
Cauda went on to explain that calibration is key. “Any professional would need to do a calibration of a real-time dust monitor for each environment,” he said. “You can overestimate or underestimate greatly the concentration level using a real-time dust monitor. It's okay if you're aware that you have that limitation when using these gadgets.”
Cauda is also the deputy director for the NIOSH Center for Direct Reading and Sensor Technologies. The NCDRST is a virtual center founded in 2014 and is currently focused on the NIOSH initiative known as “right sensors used right.”
“The idea for the Center is really to guide and create documents and information and material that can help industrial hygienists in the field to do the right thing in the right way,” Cuada said. “This is information that users should be aware of and should have to make the right decision about which monitor to pick and to use in the field.”
Variability and Comprehensive Exposure Assessment
Philip Smith, PhD, CIH, FAIHA, of the OSHA Salt Lake Technical Center, Industrial Hygiene Chemistry Division, discussed the strengths and weaknesses of real-time detection to facilitate comprehensive exposure assessment and measurement of intra-sampling period variability.
“Exposures are not static. We know that they are typically not static during even a single sampling period,” said Smith. “If we look at an exposure, we may just sample for a single day and hope that represents the true exposure, and in most instances it really does not. We spend a lot of time worrying about the variability inherent to a sampling and analysis procedure—maybe the variability from the lab analysis, variations in pump speed, etc. In reality, the major variability is actually true variability and not just error. It's actually that the exposures differ from day to day, and for a period even within a day, from one brief moment to another.”
High-quality data regarding intra-day exposure concentration variability depend on the selection of sensors with adequate sensitivity and selectivity for a target airborne contaminant, and the verification that such sensors are to be used within their linear dynamic range. The use of non-dispersive infrared sensors for measuring second-to-second exposure concentrations of carbon dioxide was provided as an example where these data quality requirements may be met.
Smith concluded that intra-day exposure variability is of high importance for fast-acting stressors, that comprehensive exposure assessment should consider both day-to-day and intra-day exposure variability, and that real-time detection is the only way to assess intra-day exposure variability.
In stressing the importance of correctly-used real-time detection tools, Smith offered this quote, attributed to G. Brennan Gisclard: “It must be remembered that when we hold an air sampling device in our hands, we may also hold the life of a fellow human being. They both deserve the best we have to offer.”