A breathalyser result is one of the key pieces of evidence in drink driving cases. But does a breathalyser always give a correct reading? Every measuring instrument has a tolerance for error, and every test must be carried out in accordance with a specific procedure – and failures in either respect can form an effective basis for challenging the result.
Permitted Measurement Errors – What the Regulations Say
Polish metrological regulations set out precisely what the permitted uncertainty of measurement is for evidential breathalysers. For results up to 0.4 mg/l in exhaled breath, the permitted error is ±0.02 mg/l. For results above 0.4 mg/l, it is ±5% of the measured value.
What does this mean in practice? If the breathalyser showed 0.25 mg/l – the threshold between a misdemeanour and a criminal offence is 0.25 mg/l in exhaled breath – the actual concentration could be anywhere between 0.23 and 0.27 mg/l. Where a result is close to a legal threshold, this tolerance can determine how the conduct is classified.
In per mille terms: for results up to 0.8 per mille, the error is approximately ±0.04 per mille; for results above 0.8 per mille, it is ±5% of the measured value.
The Most Common Grounds for Challenging a Result
Invalid Calibration of the Device
An evidential breathalyser is a measuring instrument subject to mandatory metrological supervision. It must hold a valid calibration certificate. An expired calibration – even by a few days – can result in the test result being treated as inadmissible as evidence. The calibration date for a specific device can be established by submitting a request for access to public information.
Failure to Observe the Fifteen-Minute Observation Period
Before the test begins, the officer is required to observe the driver for at least fifteen minutes. During this time the driver must not smoke, eat, drink or chew gum. The purpose is to eliminate the effect of residual alcohol in the mouth, which could inflate the reading. Skipping this requirement constitutes a procedural breach and can undermine the reliability of the measurement.
Incorrect Administration of Two Measurements
The procedure requires two measurements to be taken no less than fifteen minutes apart. The results must not differ from each other by more than the permitted measurement error. If the difference is greater, or if one of the measurements was not taken, the test result can be effectively challenged.
Respiratory Conditions
Certain medical conditions – chronic obstructive pulmonary disease, asthma, emphysema, respiratory tract inflammation – can affect the result of a breath test. These conditions can cause an abnormal distribution of alcohol in the exhaled air or affect its concentration in the sample. In such cases, a medical or toxicology expert’s opinion may show that the result does not reflect the actual blood alcohol concentration.
Exposure to Alcohol Vapours
A breath test can be distorted by alcohol vapours present in the mouth or in the air the driver was breathing. This affects people working in the chemical or cosmetics industry, those using alcohol-containing inhaled medications, and those who used alcohol-containing liquids immediately before the check – such as mouthwash or certain sprays.
How to Act When Challenging a Result
Request a blood test. The law guarantees the driver the right to request verification of the breathalyser result by a blood test. A blood test is a more precise method and provides more data for a toxicology expert’s analysis. The request should be made immediately – ideally at the roadside.
Read the test record carefully. The record should contain the times of both measurements, the device’s serial number, the calibration date and the results of both measurements. Any discrepancy between the record and the procedural requirements is a potential basis for challenging the evidence.
Keep records of your medical condition. If you have a respiratory condition or take medication that may have affected the result, medical documentation can be important evidence. Let your lawyer know about this as early as possible.
Act quickly. The sooner a lawyer reviews the case, the more opportunity there is to identify procedural failings – before the pre-trial stage closes.
When a Measurement Error Is Decisive
A result close to a legal threshold, combined with a demonstrated procedural irregularity or the device’s margin of error, may lead a court to apply the in dubio pro reo principle – resolving doubts in the defendant’s favour. In practice, this can mean the conduct being classified as a misdemeanour rather than a criminal offence, which fundamentally changes the penalty, the length of the driving disqualification and the consequences for the defendant’s criminal record.
A breathalyser result is important evidence – but it is neither the only evidence nor infallible. Every measurement has its tolerance; every procedure has its requirements. The right to a defence includes the right to challenge evidence – including breathalyser readings.
Contact Us
If you have doubts about the correctness of a breathalyser test or the procedure applied during a check, it is worth discussing the matter with a lawyer as soon as possible.
It pays to be properly prepared: both in knowing what you can claim and in having a clear strategy.
We handle cases for drivers in Poznań and across the Wielkopolska region, with in-person and online consultations available for clients elsewhere in Poland.
Adwokat Marta Krzyżanowicz and Adwokat Michalina Koligot Law Firm “Adwokat dla Kierowców w Poznaniu”
ul. Adama Mickiewicza 18/3, 60-834 Poznań
tel. +48 795 001 536 · +48 531 335 713
kontakt@adwokatdlakierowcy.pl · www.adwokatdlakierowcy.pl
This text is for general information purposes only and does not constitute legal advice. Every case requires individual analysis.
