When a breath alcohol test result is not what was expected, or there are volatile substances such as cleaners, disinfectants, or solvents at the test location, practitioners go back to checking what the sensor actually detects. A fuel cell sensor is a sensor type that turns the electrical signal produced by an electrochemical reaction with alcohol in the breath sample into a reading. However, the name of the sensor type alone does not tell you that it does not react to any other substance at all.
Selectivity refers to how well a sensor responds to the target substance, alcohol, while distinguishing the effects of other substances. Selectivity can be interpreted only by looking together at the substances included in detection or interference tests, their concentrations, and the conditions under which the sample was exposed, rather than at a short phrase in a product description. It is more accurate to read a list of tested substances not as a claim that the sensor perfectly distinguishes everything in every environment, but as data showing the range that has been checked.
A "fuel cell" label does not replace a test list
An electrochemical or fuel cell label is information about the measurement principle. It tells you the method is designed to measure alcohol, but it does not automatically explain whether the sensor reacts to a specific cleaner ingredient or a specific solvent vapor. Selectivity becomes concrete only when there is data that actually compares the target substance with candidate interfering substances.
DATECH's official product information for the AF-40BT lists a premium electrochemical sensor. However, if the published product information does not give a test list, concentrations, and test results for individual interfering substances, you cannot conclude from the sensor type on that page alone that a particular substance has no effect. Sensor type information and substance-by-substance test information need to be managed separately as different kinds of evidence.
In the list, link the conditions before the substance names
When you look at a list of tested substances, first separate the target substance from the candidate interferents. The target substance is the alcohol you want to measure. Candidate interferents are substances that may be present in the site air or in the sample alongside it, and that are examined to see whether they change the reading. Do not treat two things as the same substance just because their product names or smells are similar. Where possible, check against the ingredient information in the safety data sheet.
Next, check the test concentration and unit. Even for the same ingredient, results at different concentrations are hard to compare directly. How the sample was mixed with air, whether it was a single substance or a mixture of several, how long the sensor was exposed, and the temperature and relative humidity also determine the range to which the result applies.
| What to check | What to read in the data | The range you can judge |
|---|---|---|
| Target substance and candidate interferents | Substance name, ingredient information, test concentration and unit | What the test was trying to detect and what it was trying to distinguish it from |
| Sample and environmental conditions | Air mixing method, exposure time, temperature, relative humidity | The range of conditions to which the test result can be applied |
| Test result and applicable model | Change in reading, judgment criteria, device model tested | Which device and conditions the result applies to |
Only when all the items in the table are present can you compare site conditions with test conditions. For example, if there is only a substance name and no concentration, the question of possible exposure at lower or higher concentrations on site remains open. Conversely, even if the test result says there was no change, you must not read that as the same result for mixed samples or for different temperature conditions.
Use "no effect" only within the confirmed boundaries
A test result showing no significant change in reading for a particular candidate substance is useful for a selectivity review. However, that statement has meaning only within the tested substance, concentration, exposure method, environmental conditions, and judgment criteria. If you stretch it to mean the same result is guaranteed at other concentrations or in air with other combinations, you go beyond what the data says.
So in the review record, it is better to write "We confirmed the result for this substance under specific test conditions in the published data" than "This substance has no effect." The same applies to substances not on the list. The fact that a substance is not on a published list is neither evidence that it has an effect nor evidence that it does not. Leave it as an unconfirmed item and clearly note why further review is needed.
Turn product names at the site into candidate test substances
As a hypothetical example, consider a workplace that uses a spray cleaner in an area close to the alcohol test location. At the observation stage, do not stop at simply noting that there is a cleaner smell. Write down where and when the cleaner is used, the distance to the test location, the ventilation status, and the ingredients listed in the safety data sheet for the product used. This reduces the error of treating one product name as a single test substance without regard to its actual ingredients.
At the interpretation stage, look for whether the listed ingredients appear on the candidate interferent list in the manufacturer's or test data. If they do, check whether the test concentration and temperature and humidity conditions are comparable to the exposure situation on site. If they do not, the possible action is not to spray the cleaner directly into the breathalyzer to see the reaction, but to ask the manufacturer or a testing body what can be reviewed, based on the ingredient information and usage situation. Arbitrary injection cannot be a way to verify selectivity because of safety concerns and the risk of damaging the device.
In this example, the completion standard is not getting a blanket guarantee for every chemical. It is complete when, for each high-priority ingredient at the test location, you have recorded the published test conditions, the parts comparable with the site, and the parts not yet confirmed, kept separate from one another. With that record in place, when a reading is questioned, you can check it again against the confirmed range instead of guessing.
Read accuracy specifications and selectivity data separately
An accuracy figure does not mean the same thing as selectivity either. The ±0.005 %BAC accuracy in the official AF-40BT information is a specification stated under the reference conditions of 0.100 %BAC and 25 ℃. This figure is information about the range within which readings may be displayed under that reference. It is not a test result explaining whether a particular cleaner or solvent affects the reading.
Display range, accuracy, operating temperature, and sensor type are all information needed to interpret results, but none of them replaces another. When you review selectivity, look at the substance-by-substance test list and conditions. When you review accuracy, look at the reference concentration and temperature. When you review suitability for the site, compare the actual exposure environment separately. With this separation, a list of tested substances becomes not marketing copy but working data that divides the range the sensor has been checked for from the range that needs further review.
