Natural Gas Odor-Intensity Testing: Field Controls, Human Factors and Audit-Ready Records

Natural-gas odor-intensity testing evaluates the diluted gas-and-air mixture at which a qualified tester detects or recognizes the odor. It does not directly measure the chemical concentration of individual odorant compounds.

That distinction matters. A defensible field test depends on more than obtaining a reading: the sampling location, active gas sources, weather, tester readiness, instrument condition, sample path and documentation can all affect how the result should be interpreted.

Burgess Pipeline Services supports operators with vendor-neutral testing preparation, field execution and documentation. The operator remains responsible for approving its procedures and determining applicable requirements; BPS does not provide legal advice.

What an Odor-Intensity Result Can and Cannot Show

An odor-intensity test can document human response to a controlled gas-in-air dilution at a particular location and time. Depending on the operator’s procedure and instrument, results may include a threshold-detection level, a readily detectable level or another defined intensity observation.

The result should not be represented as:

• A chemical odorant-concentration measurement

• Proof that every part of a distribution system has the same odor intensity

• Identification of a leak location

• A substitute for combustible-gas or toxic-gas detection

• A stand-alone determination of regulatory compliance

Instrumental concentration analysis and human odor-intensity testing answer different questions. They can support one another, but one should not be relabeled as the other.

Start With the Current Approved Procedure

Federal odorization requirements include periodic sampling with an instrument capable of determining the percentage of gas in air at which the odor becomes readily detectable. Operators must translate applicable requirements into current, approved operating procedures. See 49 CFR §192.625.

ASTM D6273 provides standardized methods related to natural-gas odor intensity. Field personnel should use the current licensed edition, the applicable operator procedure and the current instrument manual. This article does not reproduce or replace those documents.

Before mobilization, confirm:

• Which result or results the procedure requires

• Required locations and testing intervals

• Tester qualifications and readiness restrictions

• Acceptable instrument and sample-path configurations

• Calibration or functional-check requirements

• Documentation, exception and escalation requirements

Select a Representative Sampling Location

A convenient sample point is not automatically representative. The test plan should account for the system’s current configuration, including active supply sources, gates, regulators, loops, pressure zones and unusual flow conditions.

Document why the location represents the gas being evaluated. Consider whether:

• The intended source or injection point is active

• Gas has had sufficient opportunity to mix

• Alternate gates or sources can affect the location

• Flow can reverse or stagnate

• Low-demand branches or system extremities need separate evaluation

• Temporary operations have changed the normal flow path

One passing result at one point should not be generalized to an entire looped, multi-source or master-meter system without a documented basis. See the BPS guide to field odorant verification for additional sampling-location considerations.

Control Environmental and Site Conditions

Field conditions can interfere with both the instrument and the tester. Follow the operator procedure and instrument manufacturer’s limits.

Before starting, record:

• Wind and whether the test position is sheltered

• Rain, snow, temperature and other relevant conditions

• Nearby odorant, fuel, exhaust, chemical or process odors

• Ventilation and potential recirculation

• Sample pressure and any pressure-regulation arrangement

• Whether instrument intake and exhaust paths are unobstructed

Manufacturer instructions for commonly used odor-intensity instruments caution against testing in unsuitable wind or precipitation and note that environmental extremes can affect operation. If conditions invalidate a test, record the reason and repeat it under acceptable conditions rather than omitting the unsuccessful attempt.

Address Tester Readiness and Olfactory Fatigue

Human response is part of the measurement, so tester condition must be controlled rather than assumed.

Use the current operator procedure to address:

• Qualification and training

• Smoking, vaping, eating, drinking, chewing gum or strongly flavored products

• Illness, allergies, congestion or temporary loss of smell

• Exposure to odorant or other strong odors before the test

• Rest or recovery between repeated observations

• Independence from coaching or knowledge of an expected result

Do not prompt the tester toward a target reading. Where practical, document tester readiness before revealing previous results or expected values.

Verify the Instrument and Sample Path

Create a traceable record connecting each result to the instrument and configuration used. Record:

• Instrument make, model and serial number

• Current calibration or verification status

• Required pre-test checks

• Configuration or relevant software version

• Regulator and sample-pressure information

• Tubing type and condition

• Purge or zero checks required by the procedure

• Any deviations, alarms or abnormal behavior

Sample tubing, fittings and regulators should be clean, appropriate for the service and free from residual odors that could influence the observation. Instruments must be operated within their approved limitations and applicable site controls. For the separate question of chemical measurement bias, review odorant sampling integrity and concentration testing.

Record Each Result Without Rewriting the Evidence

If the procedure distinguishes threshold detection from readily detectable odor, record them separately. Do not convert either result into a chemical concentration unless a separate validated measurement supports that value.

Retain:

• The original observations

• Repeated or invalid tests

• Deviations and their disposition

• Follow-up measurements

• The person performing and reviewing the work

A result that differs from expectations is information to investigate, not a number to normalize without a documented technical basis.

Restore and Check the Sample Connection

After testing, restore or isolate the connection according to the operator’s approved procedure. Document the final condition and any required leak check.

This is a small but consequential step. A California field inspection specifically identified the need to verify the connection after testing and to ensure personnel understood the complete testing process. The broader lesson is that the test record should show that the sampling connection was left in its intended condition.

Audit-Ready Odor-Intensity Test Record

A useful field record should capture enough context for another qualified person to understand what was tested and evaluate whether the result is usable.

Record element	What to capture
Location	Facility, sample-point ID and reason it is representative
System state	Active source, gate, regulator, loop or temporary configuration
Operating conditions	Flow direction or status, pressure and relevant demand conditions
Field conditions	Date, time, weather, wind and interfering odors
Tester	Identity, qualification and readiness confirmation
Instrument	Make, model, serial number and configuration
Verification	Calibration status and pre-test checks
Sample path	Regulator, tubing and connection information
Results	Threshold, readily detectable level or other required observations
Exceptions	Invalid tests, deviations, retests and corrective actions
Restoration	Final connection condition and required leak check
Review	Supervisor acceptance and follow-up responsibility

Testing frequency is operator- and jurisdiction-specific. The record should reference the procedure that established the applicable interval rather than presenting one frequency as universal.

When Human and Instrumental Results Disagree

A human odor-intensity result and a chemical-concentration result can disagree without either number necessarily being fabricated. They evaluate different properties and may be influenced by different factors. See Odorant Concentration vs. Odor Intensity.

Review:

1. Whether both samples represented the same gas and operating condition

2. Sampling location and flow path

3. Weather and interfering odors

4. Tester readiness and possible olfactory fatigue

5. Instrument checks, tubing, regulator and sample pressure

6. Timing between measurements

7. Changes in source gas, blend or system configuration

Repeat testing under the approved procedure when appropriate and retain both the original and follow-up evidence. Do not change injection settings solely to make two unlike measurements numerically agree.

Field Testing and Documentation Support

Burgess Pipeline Services can help operators plan representative testing locations, prepare field documentation and coordinate odorization verification with commissioning, maintenance and temporary-operation work.

For project support, call (323) 609-5009 or review our pipeline operations and maintenance services.

BPS provides operational support and documentation. The operator and applicable authority determine procedural and regulatory acceptance.

Frequently Asked Questions

Is odor intensity the same as odorant concentration?

No. Odor intensity describes human perception of an odorized gas-and-air mixture. Chemical concentration testing measures specified compounds using an appropriate analytical method.

Can wind affect an odor-intensity test?

Yes. Wind can disturb the controlled mixture or expose the tester to unrelated odors. Follow the approved procedure and instrument instructions, and document the conditions.

Does one passing test prove that the entire system is adequately odorized?

Not necessarily. The result represents the sampled gas under the documented configuration and conditions. Looped, multi-source and low-flow systems may require additional representative locations.

What should an odor-intensity test record contain?

At minimum, document the location, system configuration, conditions, tester, instrument, checks, sample path, original result, deviations, restoration and review.

Can BPS determine whether an operator is legally compliant?

BPS can support testing and documentation, but does not provide legal advice or make the operator’s regulatory determination.