Odorant Concentration vs. Odor Intensity: What's the Difference?
Updated: Sep 10
If you have researched how to verify odorization in a natural gas system, you have probably encountered two different measurements. Odor-intensity testing uses controlled dilution and a person's sensory response to determine when odor becomes readily detectable. Concentration testing uses an instrument response to estimate or measure selected odorant compounds under a defined method. These approaches answer different questions, so the project plan should identify which evidence is required.
Odor Intensity Testing: Measuring Detectability
Odor-intensity instruments mix a gas sample with air at known ratios while a qualified tester determines when the odor becomes readily detectable. The instrument controls or documents dilution; the human response remains part of the observation. Where 49 CFR 192.625(f) applies, the rule calls for periodic sampling with an instrument capable of determining the percentage of gas in air at which odor becomes readily detectable. The operator must determine the applicable procedure, locations, frequency, acceptance basis and records. A device or isolated observation should not be described as automatically demonstrating compliance.
Concentration Measurement: Reading the Number Directly
An electrochemical odorant analyzer works differently. Instead of asking whether gas is detectable at a diluted ratio, it reads the actual odorant concentration in the gas stream, in parts per million, for a specific odorant like TBM or THT. There's no threshold judgment involved. The instrument reports a number, and that number can be logged, trended over time, and compared directly against a target concentration.
Where This Distinction Actually Matters
Troubleshooting odor fade: a concentration result can show how the measured value at one location and time compares with an operator-defined target. Interpret it with the method range, calibration, sample conditions, blend response and downstream operating state.
Verifying pickling progress: tracking concentration across multiple cycles shows a trend line, not just a pass or fail at the end.
Documenting for a specific odorant blend: a concentration reading is tied to the specific chemical you're measuring, which matters when a system uses a particular TBM or THT blend rather than a generic mixture.
Comparing results across sites or over time: numerical results can support trending when the method, instrument status, calibration basis, gas matrix, sample location and operating conditions are sufficiently consistent and documented.
How a Portable Concentration Analyzer Works
Our portable odorant analyzer uses an electrochemical sensor selected for field measurement of TBM or THT concentration during pickling, commissioning, and routine verification. Results depend on the selected sensor range, calibration, sampling procedure, potential cross-sensitivities, and the odorant blend being measured.
Choosing the Right Tool for the Job
Neither approach is universally better; they answer different questions. Where 49 CFR 192.625(f) applies, the selected method must address the rule's detectability requirement and the operator's procedures. A concentration analyzer can support odor-fade troubleshooting, conditioning trends or blend-specific investigation, but a concentration result does not by itself establish compliance with a human-detectability requirement. For regulatory background, see our breakdown of
49 CFR 192.625, and for general odorization terminology, our Comprehensive Odorization Glossary.
Project Support
Need a field plan that separates instrument concentration readings from odor-intensity checks? Review BPS odorization operations support for sampling locations, records, and project-specific verification.
