Insufficient Breath on an Alcohol Test: What DOT Procedure Requires

What counts as an insufficient breath sample under 49 CFR Part 40?

A driver has provided an insufficient sample when they attempt to blow into the evidential breath testing (EBT) device but can't generate the minimum volume of breath the instrument requires to produce a valid reading — typically 1.5 liters, sustained for the duration the device specifies. This is different from refusing to blow at all or walking away from the collection. The employee is actively trying, and the device simply isn't registering enough air. Part 40 calls this scenario out specifically because it has its own procedure, separate from both a normal test and a refusal, precisely because good-faith physical limitation is common enough that DOT built a path for it rather than treating every failed attempt as misconduct.

What does the BAT do when a first attempt comes back insufficient?

The breath alcohol technician (BAT) doesn't stop after one try. Part 40 requires a second attempt, and the BAT explains the physical technique again — a deep breath, a firm seal around the mouthpiece, and a steady, sustained exhale rather than a short puff. Most insufficient-sample cases at this stage resolve on the second or third try once the employee understands what a "sustained exhale" actually means, since the instruction sounds simple but the motion isn't always intuitive under stress. If a valid sample still hasn't been produced after a reasonable number of attempts using proper technique, the BAT moves to the next stage rather than continuing indefinitely.

What happens if the employee still can't produce a sample?

The BAT documents the attempts and refers the employee for a medical evaluation by a physician the employer designates, who determines whether a medical condition explains the inability to produce sufficient breath volume. This is not the BAT's call to make — a BAT observes and documents the physical attempts but has no authority to diagnose a medical cause. The referral has a clock attached: the evaluation needs to happen promptly, and until it's resolved, the situation is treated as an incomplete test rather than a violation or a cleared result.

Outcome of medical evaluation	How it's treated
Physician confirms a medical condition prevents adequate breath volume	Not a refusal; documented and the alcohol testing episode is closed out per the physician's determination
No medical explanation found	Treated as a refusal to test, with the same consequences as a positive result
Employee doesn't complete the medical evaluation	Also treated as a refusal

How is this different from a refusal to test?

A refusal is a conduct problem — the employee declines, leaves, or otherwise doesn't cooperate with the process. An insufficient sample starts as a physiological event: the employee is cooperating and attempting the test but can't hit the volume threshold. The two can converge, though. If the medical evaluation doesn't turn up a qualifying condition, or the employee skips the evaluation, Part 40 reclassifies the event as a refusal after the fact, with the same removal-from-duty and Clearinghouse consequences as any other refusal. The distinction matters enormously for the employee in the moment but collapses if the medical explanation doesn't hold up.

Are there medical conditions that commonly explain insufficient breath volume?

Respiratory conditions such as COPD, severe asthma, or other conditions that reduce lung capacity are the typical explanations a physician documents. The evaluating physician makes this determination through an actual exam, not a self-report from the employee, which is why the referral step exists as a formal medical evaluation rather than an honor-system exception.

How should the BAT document an insufficient-sample event?

Every attempt, with the volume and time reading the device produced for each one, the coaching given between attempts, and the exact point at which the BAT moved to the medical referral. This record is what an evaluating physician and, later, the employer rely on to reconstruct whether procedure was followed correctly. A vague note like "couldn't blow enough" without attempt-by-attempt detail leaves the case file thin if the outcome is later disputed.

How Foster trains BATs to handle insufficient-breath situations

Foster's BAT certification course spends dedicated time on the insufficient-sample procedure specifically because it's easy to get wrong under pressure — a rushed BAT can either give up too early, before exhausting the coaching and retry steps Part 40 actually requires, or treat a genuine physical struggle as a refusal without going through the medical evaluation referral. We drill the difference between coaching a technique problem and recognizing when it's time to stop attempts and refer out, along with the specific documentation each attempt needs on the Alcohol Testing Form. Employers running programs through Foster get BATs who've practiced this exact sequence in training, not just read about it, which matters because insufficient-breath cases come up often enough to need a practiced response but rarely enough that undertrained technicians can freeze on the details. Programs that pair BAT training with regular on-site testing support and properly calibrated instruments reduce the odds of an ambiguous reading in the first place.

FAQ

Does an insufficient breath sample automatically mean drug use or intoxication?

No. Insufficient volume is a physical measurement problem, unrelated to whether alcohol is present. A driver with a completely clean system can still fail to produce enough breath volume due to a respiratory condition.

How many attempts does Part 40 require before moving to a medical referral?

The regulation doesn't set a fixed attempt count; it requires the BAT to make a genuine effort to coach a valid sample using proper technique before concluding the attempts aren't succeeding. The BAT's documentation of each attempt is what shows this step was actually followed.

Who pays for the medical evaluation after an insufficient breath sample?

The employer is responsible for arranging and covering the cost of the evaluation, since it's a required step in completing the DOT-mandated testing process, not an optional exam the employee requests.

Can the same driver be evaluated by their own physician instead of an employer-designated one?

The initial evaluation is performed by a physician the employer designates. The employee's own physician's records may be considered as part of that evaluation, but the determination itself comes from the employer-designated evaluator under Part 40's process, not a self-selected doctor.

Does an insufficient-sample event show up in the DOT Clearinghouse?

Only if it's ultimately determined to be a refusal — either because no medical explanation was found or the employee didn't complete the evaluation. If the physician confirms a genuine medical condition, it isn't reported as a refusal or violation.