Short Answer

DOT alcohol testing uses a two-stage process: screening, and if needed, confirmation. A Screening Test Technician (STT) administers an initial screening test using an alcohol screening device (ASD). If that screening result is below 0.02, the test is negative and the process ends there. If the screening result is 0.02 or above, the employee must take a confirmation test on an evidentiary breath testing device, administered by a Breath Alcohol Technician (BAT), after a required waiting period. A confirmed alcohol concentration of 0.04 or greater is treated as a DOT alcohol rule violation.

The Two Stages Explained

Alcohol testing is intentionally built as a two-step process so that a single instrument reading does not, by itself, end someone's career. The STT's screening test is a first check. Only a result at or above 0.02 requires anyone to move to the second stage.

The confirmation test is performed by a BAT on an evidentiary breath tester. Part 40 builds in a waiting period, generally referred to as 15 minutes, before the confirmation test can be administered, along with other procedural safeguards such as an air blank check on the instrument. These safeguards exist because alcohol on the breath can, in rare circumstances, produce a falsely elevated first reading, and the waiting period allows that possibility to clear.

What "Alcohol Concentration" Means

Alcohol concentration, as defined under 49 CFR Part 40, is measured in grams of alcohol per 210 liters of breath. That is the number the ASD and the evidentiary breath tester both produce and report.

A confirmed alcohol concentration of 0.04 or greater is one of the outcomes that constitutes a DOT alcohol and drug rule violation, alongside a verified positive drug test or a refusal to test. A confirmed result below 0.02 is treated as a negative alcohol test. Results in between those two figures involve additional Part 40 provisions; the precise consequences for that intermediate range are technical and best confirmed directly against 49 CFR Part 40 or with a DOT-qualified professional rather than assumed from a general summary.

The Roles Involved

Two distinct roles carry out alcohol testing. The STT instructs and assists the employee and operates the ASD during the screening stage. The BAT instructs and assists the employee and operates the evidentiary breath tester during the confirmation stage. The same person can sometimes be qualified to serve in both roles, but the two functions are defined separately under 49 CFR Part 40.

Where This Fits Into Return to Duty

An employee returning to safety-sensitive duty after a DOT alcohol violation must, among other requirements, have an alcohol result below 0.02 on the Return to Duty test. That threshold is set out separately at 49 CFR § 40.305 and is distinct from the screening and confirmation process described above, which applies whenever an alcohol test is conducted for any DOT purpose.

Applicable Regulations

• 49 CFR § 40.3 defines alcohol concentration, BAT, and STT.
• 49 CFR § 40.285(b) identifies a confirmed alcohol concentration of 0.04 or greater as a DOT rule violation.
• 49 CFR § 40.267 lists procedural "fatal flaws," including a confirmation test conducted before the required waiting period ends, that cancel an alcohol test outright.
• 49 CFR § 40.305 sets the below-0.02 threshold required for a Return to Duty alcohol test.

Professional Observation

In my experience, employees are often surprised to learn that the screening test alone does not decide anything. Many assume a single breath test number is the final word. It isn't. The confirmation test, performed on a different instrument by a different technician after a waiting period, is what actually determines the outcome.

Common Misconceptions

Misconception

Any positive reading on the initial screening device counts as a DOT alcohol violation.

Reality

Only a confirmed result of 0.04 or greater, produced by the confirmation test, constitutes a violation under 49 CFR § 40.285(b). A screening result between 0.02 and the confirmation stage still requires the confirmation test to be performed.

Why the Confusion Occurs

People often use "positive" loosely to describe any non-zero reading, without distinguishing between an initial screening number and a confirmed result.

Frequently Asked Questions

Can the same person operate both the ASD and the evidentiary breath tester for the same test?

The STT and BAT roles are defined separately in the regulation, though the same individual can be trained and qualified for both functions depending on the collection site's setup.

Does a screening result below 0.02 ever get reported as anything but negative?

No. A screening result below 0.02 ends the process as a negative alcohol test.

Related Articles

• DOT Drug Testing Process
• What Is a Return to Duty Test?
• What Is the Insufficient Breath Procedure?

Primary Authorities/Sources

• 49 CFR § 40.3, Definitions
• 49 CFR § 40.285, When is a SAP evaluation required?
• 49 CFR § 40.267, Problems that always cancel an alcohol test
• 49 CFR § 40.305, Return to Duty test requirements

Need Help Understanding an Alcohol Test Result?

If a test result affects your DOT status, confirm the next steps with your employer's DER or a DOT-qualified Substance Abuse Professional.

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