Air Sampling and Air Flow Adjustment, Time to Change the Dialogue to Modern Terms

The issues: the terms many learned academically or through industry training such as, calibration, primary/secondary standards are no longer appropriate based on modern standards. We do not calibrate sampling pumps we are setting and verifying flow rates.

Within the science of metrology and flow measurement, the concepts that many of us grew up with, primary (bubble burette) and secondary standard (as with rotameters [rotometers])…those terms are now effectively antiquated even though they are very commonly used. We are not calibrating air sampling pumps. In International Standards Organization/International Electrotechnical Commission (ISO/IEC) standard 17025, calibration means a service from a qualified, accredited firm to provide those services. Think of those certified firms calibrating balances in a laboratory as a simple example. We are determining and adjusting flow rates, not calibrating.

We are determining and adjusting flow rates, not calibrating

With sampling pumps, we are measuring flow into a sampler. There are no primary and secondary calibrators, only traceable (through annual calibration) [BIOS Defender, TSI calibrator etc.] or non-traceable (as with rotameters) "working standards."

The ASTM standard D5337 – 23, Standard Practice for Setting and Verifying the Flow Rate of Personal Sampling Pumps, is an international standard practice that defines these issues and terminology. A link to the standard practice is below. It must be purchased if not a member with download ability.

ASTM D5337: Standard Practice for Setting and Verifying the Flow Rate of Personal Sampling Pumps

Notice in the title: “…for Setting and Verifying the Flow Rate…” this has been changed over the years from “calibration.” This standard practice focuses on personal sampling pumps but the concepts are the same for the high volume [“hi-vol”] pumps used in asbestos work.

Traceability means "the property of a measurement result whereby the result can be related to a reference through a documented unbroken chain of calibrations, each contributing to the measurement uncertainty."

Reference: Joint Committee for Guides in Metrology (2012) International vocabulary of metrology — Basic and general concepts and associated terms (VIM) (International Bureau of Weights and Measures (BIPM), Sèvres, France), 3rd Ed. BIPM, IEC, IFCC, ILAC, ISO, IUPAC, IUPAP and OIML, JCGM 200:2012 (2017 version with minor corrections and informative annotations) Available at https://jcgm.bipm.org/vim/en/.

Examples of traceable working standards, there are others in the marketplace:

The examples above are traceable to meet ISO/IEC requirements. The most important aspect is that these devices are required to be sent back to the manufacturer for service to maintain traceability. If one were to go past the date required for service, they should not be used until the manufacturer re-certifies the device.

While we can use the traceable standards in the field, not all are robust enough for rough handling or being dropped to the floor. Significant damage can occur. Should this happen, it necessitates servicing before continued use.

Examples of the most commonly used non-traceable working standards:

With the devices we need to verify flow measurements with a traceable standard. That is, to know what the actual air flow may be for the given divisions on the rotameters. These cannot be used as is from the manufacturer. For the high flow rotameter on the left, I do not recommend using the lower divisions for personal sampling pumps. Use the rotameter seen on the right.

These devices are perfectly acceptable should the be verified with a traceable standard periodically. There are no federal rules on this in the U.S., but not less than annually is a common procedure. In the pic above, the hi-flow rotometer has a metal ball as the flow indicator. This likely has more impact on the interior surface than the glass bead in the low flow rotometer. If used with regularity, the hi-flow rotometer may need to be revalidated more often, perhaps at every 6 months.

Of great importance, your firm must have a standard operating procedure (SOP) for this work...from determining the flow positions on a rotameter to determining and verifying flow rates on sampling pumps with traceable or non-traceable working standards. Without this and service records for your chosen traceable standard, it will not go well should your data be challenged. It is very common in depositions for defendant's experts to ask these questions, and in detail.

Here's an issue that we need to visit...the open face method of using a rotameter. Unfortunately this is not appropriate to the science of flow measurements despite that many of us were taught to "calibrate like you sample." This method was also described in an EPA guidance document we call the Silver Book (EPA 600/4-85-049, November, 1985). Unfortunately as much as I and others taught this method for years, its not the most accurate nor is it technically correct.

So, the old terminology of primary and secondary standards will likely persist for years, but these terms are not in the lexicon of international standards such as ASTM D-5337. We are not calibrating air sampling pumps or rotameters. So, we need to change old habits and think about terms like “setting and verifying the flow rate” and “traceable or non-traceable working standards.”

Hope this helps...I know it's a big change, but it's time to come in line with modern analytical terms and technology expectations.

All the best!

Copyright, Thomas G. Laubenthal, July 2025. Use for information exchange is OK. No other uses without permission from the author.