Breath Alcohol Testing: What the 0.04 Threshold Really Means

The Two-Step Testing Process

DOT breath alcohol testing always involves two steps: a screening test and, if the screening result is 0.02 or higher, a confirmation test. The screening can use an approved device, but the confirmation must be conducted on an Evidential Breath Testing (EBT) device — a specific type of instrument approved by the National Highway Traffic Safety Administration (NHTSA) and listed on the Conforming Products List.

The confirmation test is conducted at least 15 minutes after the screening to reduce the chance of residual mouth alcohol affecting the result. The confirmation result — not the screening result — is the official result of record. An Alcohol Testing Form (ATF) documents both steps.

The 0.04 Violation Threshold

A confirmed BAC of 0.04 or higher is a DOT alcohol violation. The consequences are immediate and mandatory: the employee must be removed from safety-sensitive duty before the workday ends. They cannot return to a safety-sensitive function until they have completed a Substance Abuse Professional (SAP) evaluation, any required treatment or education, and a return-to-duty alcohol test with a result below 0.02.

The violation is also entered into the DOT drug and alcohol testing record, which follows the employee to future safety-sensitive employers. This is not a matter of employer discretion — the removal and SAP referral are required by regulation regardless of the employer's internal policy preferences.

The Cautionary Range: 0.02 to 0.039

A confirmed result between 0.02 and 0.039 is not a DOT violation — but it still has consequences. Under 49 CFR Part 40, an employee with a result in this range must be removed from safety-sensitive duty for a minimum of 24 hours. There is no SAP referral required, and the employee can return to duty after the waiting period without a return-to-duty test.

However, employer policy may impose stricter consequences for results in this range. Some companies treat anything above 0.02 the same as a violation. Whatever the policy says, it must be applied consistently — and it must not be less strict than what the federal regulation requires.

A Result Below 0.02

Any confirmed result below 0.02 is a negative for DOT purposes. The employee has no restriction and may continue working in their safety-sensitive role. However, the test result and the testing occasion are still documented on the ATF and maintained in the employer's records.

Why Documentation Is Critical

Every breath alcohol test must be documented — the device used, the device's calibration status, both test results, the time of each test, and the employee's identification. The Breath Alcohol Technician (BAT) who administers the test completes and signs the ATF. The employee also signs to certify that the test was conducted.

A result without proper documentation is legally vulnerable. If an employment action is challenged, the ATF and supporting records are the primary evidence that the test was conducted correctly. This is why the collection process matters as much as the result itself.

Non-DOT Alcohol Testing

Non-DOT alcohol testing programs can use similar EBT devices and follow similar procedures, but the threshold for action is set by employer policy rather than federal regulation. Many employers adopt the 0.04 standard for consistency, but a policy of 0.02, 0.05, or any other threshold is legally permissible as long as it is applied consistently and does not violate applicable state employment laws.