Interscan Keeps Stressing The Importance Of Good Calibration

There are millions of toxic gas detectors in service, ranging from personal alarm monitors to elaborate systems featuring many points of detection with data acquisition and feedback control features. This is hardly surprising since OSHA mandates Permissible Exposure Limits (PELs) for more than 600 air contaminants.

Unfortunately, one key point is often overlooked—or at best is glossed over. That key point is calibration. After all, modern direct-reading gas detectors are not absolute methods in themselves. Rather, they require calibration against a known standard. For most substances, these calibration standards are supplied in the form of gas blends in cylinders (with the target gas mixed with pure air or nitrogen); permeation devices; or specialized calibration gas generators.

Unlike gas blends in cylinders, one of the latter two methods can handle many of the more difficult compounds—such as formaldehyde, chlorine dioxide, and hydrazine. Yet, gas blends in cylinders are more widely employed, owing to their perceived ease of use.

An additional complication arises from the notion of "bump testing." This procedure involves testing the gas detector with a non-quantitative higher concentration mixture, for the purpose of assuring that its alarm function is working properly.

The problem with bump testing is that most OSHA PELs are based on an 8-hour time-weighted average of exposure, which goes well beyond an instantaneous "alarm" concentration level. As such, a true quantitative calibration is required, which, ironically would take nearly the same time as a bump test. In fact, it is difficult to escape the conclusion that bump testing serves to trivialize the importance of true calibration. More than that, the reality that seeking ppm level measurements of toxic gases requires care in analytics is lost.

Interscan encourages all users of gas detectors to ensure that their units are calibrated properly, and stands ready to help. The company especially recommends its SENSOR EXPRESS^® program.