In this interview, News Medical speaks with Ram Parameshwar, associate manager of product management, calibration solutions at Mesa Labs, and Laurence R. Durio, principal at Durio Consulting Services, about the importance of flow calibration in industrial hygiene and occupational safety and health (OEHS) applications. They discuss the evolution of calibration techniques, the role of primary standards, common pitfalls that can invalidate samples, and practical strategies to ensure defensible exposure data.
Can you describe your role at Mesa Labs and the industrial hygiene profession?
Ram Parameshwar: I oversee product strategy and market development for our equipment portfolio and lead commercial, product management and marketing efforts. My background is in measurement and diagnostics, spanning industrial power generation, medical devices, and life sciences applications.
Lawrence R. Durio: Throughout my career, I have worked in OSHA enforcement, chemical manufacturing, consulting, and environmental health. Currently, I primarily work as an occupational health and environmental expert witness and teach certification courses for EPA, HUD, and DEQ. As an industrial hygienist in the field, my focus has always been on filing and getting the job done.
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What is flow calibration and why is it so important to industrial hygiene and OEHS professionals?
Laurence R. Durio: Calibration is the comparison of an instrument to a known standard, with emphasis on the “known.” In industrial hygiene environments we usually talk about airflow, but the same principles apply to other physical factors.
A calibrator, a device with known accuracy, is used to measure the flow rate. It usually goes beyond measuring flow. Also, adjust it to the desired value. We do this because we need to know how much air was drawn through the sample medium. Without knowing that, it is not possible to calculate air concentrations to compare with exposure limits.
Some equipment is designed to operate at specific flow rates. A good example is a cyclone separator used for silica sampling. Bioaerosol samplers and collision-based methods also require very specific flow rates. Calibration ensures the accuracy and validity of the results.
Why does an industrial hygienist need to know exactly how much air was drawn from the sampling medium?
Lawrence R. Durio: It all comes back to calculating concentration. Whether sampling gases, vapors, dust, fibers, or biological contaminants, you need to know both the amount of contaminant collected and the amount of air sampled.
If the amount of air passed through the sampling medium is not known, the exposure concentration cannot be accurately calculated. Without accurate calibration, the entire sampling effort is compromised.
Falsely high results can lead to unnecessary administration and expense. Falsely low results are even worse, as they can endanger employee health and environmental protection. I want to avoid both.
How did flow calibration methods evolve from soap bubble meters to modern primary standards?
Lawrence R. Dulio: When I started, I used a bubble meter. They worked pretty well for their time. A soap bubble is moved through a buret of known volume and timed with a stopwatch. Although this system was simple and cost effective, it had limited accuracy. Bubbles can pop, timing can change, and some commercially available burettes aren’t particularly accurate.
Tachometers later became common. These are simple visual flow indicators, but their accuracy is determined by fluid properties and cleanliness. Even small deposits inside the tube can affect the readings.
Bell provers and other volumetric devices followed, offering improved performance but often lacking in portability. Ultimately, a piston prover, which measures piston movement within a known volume over a measurement period, became the preferred solution. Although simple in concept, achieving the accuracy required by modern calibration standards required significant engineering effort.
What is the difference between primary and secondary standards?
Laurence R. Durio: Primary standards are based on directly measurable physical quantities such as volume, time, pressure, and temperature. These measurements comply with national and international standards.
Piston provers are the main standard because they measure the volume displaced by a piston and the time required for its movement. Calculations are direct and traceable.
Secondary standards are based on analogy or indirect measurements. They may use thermal properties, pressure changes, or vane motion, and often rely on algorithms to estimate flow. They can be useful, but they involve assumptions. Each additional assumption increases the chance of error. That is, when defensibility is important, the primary standard is generally preferred.
Why are temperature and pressure corrections so important when sampling gases and vapors?
Laurence R. Durio: Corrections for temperature and pressure are important because occupational exposure limits for gases and vapors are typically expressed using standard quantities rather than actual physical quantities.
Gases expand and contract due to changes in temperature and pressure. A temperature change of approximately 15 °C can result in a volume change of approximately 5%. Changes in elevation can have a similar effect.
Gas and vapor sampling standardizes temperature and pressure, as the body responds to the mass of inhaled pollutants, not just the concentration. If you are unable to apply the required fixes, your sample may become invalid.
At the same time, some particulate analysis methods are based on actual volumetric flow rates and should not be standardized. It is important to follow the requirements of the particular method used.
What regulatory and professional guidance should industrial hygienists be aware of when calibrating equipment?
Laurence R. Durio: Professional practice and regulatory requirements are generally aligned. The standard expectation is that pre- and post-sampling calibrations stay within ±5%.
Both OSHA and NIOSH recommend highly accurate calibration practices, and many methods recommend or require the use of primary standards. OSHA’s substance-specific standards often mandate primary standards to provide defensible measurements.
Some environmental methods are even more stringent and may require accuracy levels close to 1%. The important point is that calibration is not something we make up along the way. There is established professional and regulatory guidance that we must all follow.
Can you give me an example of how improper calibration methods can affect sampling results?
Laurence R. Durio: One example is regulatory sampling done using equipment that cannot be properly calibrated for the environment in which it will be used.
This equipment was used in a very hot and corrosive process environment and eventually failed, producing falsely high readings. Based on these measurements, one facility received reports of contaminant concentrations that were not actually present.
The situation escalated through multiple levels of review and ultimately became part of a major legal dispute. What opened the door to contesting the findings was the fact that the equipment was not properly calibrated and unsuitable for the conditions of use.
Calibration is not the only factor that affects data quality, but it is the first step. If the calibration is invalid, everything after that is questionable.
Which performance characteristics are most important when evaluating a flow calibrator?
Ram Parameshwar: Accuracy over the entire flow range is important, especially at the low flow rates used for gas and steam sampling. Reliability is equally important.
Industrial hygienists often have multiple sampling pumps on site, but typically only one calibrator. If the calibrator fails, the entire sampling operation can be compromised.
The ability to compensate for temperature and pressure is also important, especially when working in different geographic locations and environments where those factors can have a significant impact on flow measurements.
What final advice can you give to industrial hygiene professionals who want to secure defensible exposure data?
Lawrence R. Durio: When in doubt, check your method and follow it. Use the right equipment for your application, keep your calibrators within operating limits, and document everything.
Calibration is the basis of defensible exposure data. If there is no legitimacy in the first step, the rest are meaningless.
Ram Parameshwar: I would like to add that professionals should work with qualified OEMs and authorized service providers. Proper maintenance, calibration traceability, and certification all contribute to data reliability and ultimately support better decision-making for worker health and safety.
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About Ram Parameshwar
Ram Parameshwar is an associate manager of product management for calibration solutions at Mesa Labs. He oversees product strategy and market development for the company’s instrumentation portfolio. Ram has a background in industrial instrumentation, calibration, and diagnostic technology and leads commercial, product management, and marketing efforts that support product adoption, business growth, and improved customer outcomes.
His work focuses on helping organizations achieve measurement integrity and traceability across regulated industrial, environmental, and life sciences applications.
About Lawrence R. Durio
CIH’s Lawrence R. Durio is president of Durio Consulting Services and a certified industrial hygienist with more than 50 years of experience in occupational and environmental health. His career includes OSHA enforcement, chemical manufacturing, industrial hygiene consulting, large-scale remediation projects, and exposure assessment program development.
He has supported clients across the United States with complex industrial hygiene challenges, hazardous materials management, regulatory compliance, and expert witness services. In addition to his consulting work, Lawrence teaches EPA, HUD, and DEQ certified courses and is widely known for his hands-on expertise in sampling integrity, exposure monitoring, and real-world industrial hygiene applications.
About Mesa Labs, Inc.
Mesa Labs leverages technical expertise and innovation to improve the quality of life for patients, workers, and consumers around the world. Our products and services directly impact critical environments that advance medical advances, keep industries moving, and ensure the safety of the products we use every day.
who are we
Our business encompasses a group of niche brands, including Agena Bioscience, Gyros Protein Technologies and Mesa Labs, serving highly regulated markets. We seek opportunities at the cutting edge of biomedical science and quality assurance in research and clinical settings.
how we work
With over 700 employees around the world, we are passionate about connecting our skills to a greater purpose. Every day, we work with a unique customer-centric vision to protect vulnerable populations by empowering every employee to make a real difference.
what we make possible
Our multinational businesses have a long history of outperforming the market and compounding financial returns while positively impacting global health and safety. Mesa’s high-growth strategy prioritizes application leadership and customer-first solutions.
