Understanding the difference between accuracy and precision is crucial for interpreting colorimetric gas detector tube readings. This article clarifies these terms and their relevance to Sensidyne detector tubes.
Accuracy vs. Precision – Both are important!
- Accuracy: Refers to the agreement between a detector tube reading and the actual concentration of the target gas.
- Precision: Indicates how closely repeated measurements with the same detector tube cluster around the average value.
These terms are distinct. A detector tube can be precise (consistent readings) yet inaccurate (systematically deviating from the true value).
Industry Standards for Detector Tube Accuracy
- The generally accepted accuracy for detector tubes is ±25% of the reading.
- This is based on historical certification programs by NIOSH and AIHA.
- Current certification by the Safety Equipment Institute (SEI) upholds this standard.
Standard Deviation and Detector Tube Precision
Sensidyne/Kitagawa detector tube handbooks include standard deviation values. These values represent the precision of the tubes, not their accuracy.
A low standard deviation indicates consistent readings, but it doesn’t guarantee accuracy. For instance, expired detector tubes might produce similar readings (high precision) that significantly deviate from the actual gas concentration (low accuracy).
Optimizing Detector Tube Accuracy
Several factors influence detector tube accuracy:
- Temperature and Humidity: Aim for conditions close to 20°C and 50% relative humidity for optimal accuracy.
- Tube Age: Fresh tubes offer better accuracy than those nearing expiration. Refrigeration extends shelf life and improves accuracy (ensure tubes reach room temperature before use).
- Pump Type: Hand pumps with rubber bulbs or “thumb pumps” generally have wider accuracy variations compared to high-precision hand pumps.
- Compatibility: Mixing detector tube brands with pumps can significantly compromise accuracy due to flow rate differences. Consult the supplier for compatibility information.
- Leak Checks: Regularly check pumps for leaks to maintain optimal accuracy.
- Stain Length: Longer stain lengths generally improve accuracy. Choose a tube that provides a stain length in the upper half of its range when multiple ranges are available.
By understanding the distinction between accuracy and precision and following these best practices, you can ensure reliable measurements with Sensidyne detector tubes.
For more information, please contact:
Aaron W. Apostolico, CIH, CSP, CIEC
Corporate Industrial Hygienist
Product Applications and Research Manager – Health & Safety Products
Sensidyne, LP
T: +1 727-530-3602 x684
