Tools of the IH trade
November 1, 2007
What does the word instrumentation mean to the industrial hygiene (IH) or safety professional? I suspect it means more than, say, the words gas detection. Perhaps it infers more complexity and capability in the detection of toxic gases and vapors?
Yet one dictionary defines instrumentation as “instruments for a particular purpose,” and an instrument is defined as “a measuring device for determining the present value of a quantity under observation.” Compare that with the definition of detect: “to determine the presence of.”
None of these definitions meshes with conventional wisdom. Gas detection does more than “determine the presence of,” and instrumentation infers far more than “determining the present value of.” In fact, if we look at the range of instrumentation available to today’s industry professional, conventional nomenclature short-changes the products.
Take, for example, the single- or multi-gas detector. It determines the presence of a target compound, measures the concentration and compares that with preset alarms, while often discriminating the target gas from others present. By the way, that same dictionary defines the word measure as “the extent or quantity of something, ascertained especially by comparison with a standard.” Now that’s a dictionary definition that fits the bill!
Todayâ€™s toolboxGas detection comes in many interesting “flavors.” There are specific gas detectors and there are broad spectrum detectors â€” each with its own niche. Often they are packaged together. For example, a broad spectrum photoionization detector (PID), together with a broad spectrum LEL sensor, together with specific sensors for O2, CO, H2S and other toxics for confined space entry or first response. Even PIDs and flame ionization detectors (FIDs) are packaged together.
Despite their value, these categories of detectors do not have identification capability; they rely on human input. A PID detects most all VOCs if they are present, but to measure the concentration of a particular VOC or VOCs requires the operator to select the right response factor from the unit’s menu. The same is true for LEL. The biggest advantage of broad spectrum screening devices is that they detect a broad spectrum of VOCs, eliminating the need for a toolbox full of individual analyzers. The biggest disadvantage of broad spectrum screening devices is that they detect a broad spectrum of VOCs, requiring the operator to determine the nature of the response before converting the unit’s output to concentrations of a specific target.
In order to identify what is present, and then to determine the concentration of one or more targets, we turn to one or more types of analyzers.
Gas chromatography and mass spectrometry are examples of instrumentation that is frequently used to separate mixtures into their component parts. When combined (gc/ms), they allow the identification and measurement of the constituents of complex mixtures such as toxic chemicals in plant air. IR acoustic and Raman spectroscopy provide identification and quantification capability for gases, liquids and solids.
Once we know within reasonable limits what is present, we can then monitor long-term. Experience has shown that we don’t necessarily need to analyze for each component continuously. Instead, we can monitor the total, and provided we select the operating parameters of our monitor right, we can safely assume that if the total is less than the alarm threshold for the target, the atmosphere is in compliance. One example is a continuous PID that monitors TVOC (total volatile organic compounds).
The need for instrumentationWhat drove the development of these various types of instrumentation? Need!
In the 1930s, an altruistic bird lover offered a cash reward for the first practical sensor to replace the canary then in use as a CO detector in coal mines in Northern England. Gas chromatography was introduced into the analytical lab in the 1950s. One of the early detector options was PID, credited to the esteemed Dr. James Lovelock. Dr. Lovelock was also responsible for one of the most significant developments in environmental analysis, the Electron Capture detector, without which it would not have been possible to track the spread of DDT in the environment.
PID migrated from the lab to the field in the 1970s when health issues related to the carcinogenic nature of vinyl chloride demanded detection capability not provided by the existing FID technology, which was unable to discriminate between vinyl chloride and a background that contained significant concentrations of methane. The 10.2 eV lamp used in those early hand-held PIDs detected vinyl chloride in OSHA’s steadily decreasing target range without interference from the methane in the background.
Later, as the Super Fund program ramped up, the need to detect, identify and measure unknowns had gas chromatography follow PID into the field and provide analytical capability that previously was available only in the lab. These same products were later automated to provide continuous multi-component analysis of complex workplace atmospheres. Other heretofore lab techniques, such as infrared, also moved into the real-time world of area monitoring. Even the mighty gc/ms, the heavyweight champion of analytical technologies, was slimmed down and repackaged so that it could provide data in the field.
Recently, developments in the area of instrumentation have been focused more on issues raised by Homeland Security concerns, resulting in such technologies as Ion Mobility Spectroscopy, Surface Acoustic Wave and Laser Raman becoming more prominent.
Progress continuesMeanwhile, development continues with the goal of improving the performance of the workhorse technologies in use every day. One example, the ubiquitous PID, when equipped with Fence Electrode Technology, can now handle humidity at levels that seriously degraded performance in the past. Single-gas monitors have become almost throwaway devices at such low cost as to defy imagination a few years back.
Where do we go from here? Will some micro or nano technology emerge that will make everything else obsolete? While it is questionable that will happen, it is clear that instrumentation will continue to play a key role in the day-to-day activities of the industrial hygiene/safety professional. The need to detect, identify, analyze, measure and monitor requires instrumentation â€” however we define it!