In Canadian impaired driving law, timing is everything. The Criminal Code requires breath samples be taken “as soon as practicable”—typically interpreted as within two hours of driving. This seemingly simple requirement creates one of the most effective defences to DUI charges when police fail to comply.
The Legal Requirement
Section 320.28 of the Criminal Code specifies that breath samples must be taken:
- As soon as practicable
- Within two hours of driving (for presumption of accuracy)
When samples are taken within two hours and proper procedures are followed, the results are presumed to accurately reflect your blood alcohol concentration while driving.
When samples are taken after two hours, this presumption disappears. The Crown must prove your BAC exceeded 0.08 while you were actually driving—a significantly harder task.
What “As Soon As Practicable” Means
“As soon as practicable” doesn’t mean immediately—it means within a reasonable time given the circumstances. Courts accept some delay for:
- Transport time to the police station
- Waiting for a qualified breath technician
- Setting up the testing equipment
- The mandatory 15-minute observation period
However, delays must be justified. Unnecessary delays violate the “as soon as practicable” requirement.
“The two-hour window isn’t automatic. Police must continuously work toward completing breath testing without unnecessary delays. When we identify unjustified delays, the Crown often cannot prove the accused was over 0.08 while driving,” says experienced DUI lawyer in Toronto – Alexander Karapancev from Karapancev Law.
Common Delay Problems
Defence lawyers scrutinize timelines for unjustified delays:
Unnecessary paperwork: Officers completing unrelated administrative tasks before starting the testing process.
Socializing or breaks: Officers chatting, taking coffee breaks, or handling personal matters rather than immediately proceeding with testing.
Waiting for specific technicians: Waiting for a particular technician when others were available.
Equipment not ready: Testing equipment wasn’t set up or calibrated in advance, causing delays.
Transport decisions: Taking the accused to a distant testing location when closer ones were available.
Inadequate staffing: Police failing to have sufficient resources available for timely testing.
Custody delays: Excessive booking procedures before breath testing begins.
Consequences of Unjustified Delay
When delays are unjustified:
Loss of presumption of accuracy: The Crown can no longer rely on the presumption that breath test results reflect BAC while driving.
Evidence potentially excluded: In serious cases, courts may exclude breath results entirely under the Charter.
Weakened Crown case: Without presumption, the Crown must call expert toxicology evidence to establish BAC at time of driving—expensive and often unavailable.
Increased likelihood of acquittal: Many cases where delays exist result in acquittals or withdrawn charges.
Alcohol Elimination and Rising BAC
The two-hour timing requirement exists because alcohol concentration changes over time:
Elimination: Your body eliminates alcohol at approximately 10-20 milligrams per 100ml per hour (highly variable).
Absorption: Alcohol continues absorbing into your bloodstream for 30-90 minutes after consumption.
These factors mean your BAC at the time of testing may differ significantly from your BAC while driving.
Rising BAC scenario: You had your last drink shortly before driving. While driving, your BAC was under 0.08, but by the time testing occurred 90 minutes later, your BAC had risen above 0.08.
Elimination scenario: You were over 0.08 while driving, but your BAC dropped below 0.08 by the time testing occurred due to natural elimination.
The “Last Drink” Defence
Delay issues often support the “last drink” or “bolus drinking” defence:
You consumed alcohol shortly before driving. While driving, the alcohol hadn’t fully absorbed, and you were under 0.08. By the time testing occurred, absorption was complete, and you tested over 0.08.
This defence requires:
- Clear timeline of drinking
- Evidence of consumption immediately before driving
- Toxicologist expert testimony
- Significant time gap between driving and testing
When police delays push testing beyond two hours, establishing this defence becomes easier because the Crown cannot rely on presumption.
Burden of Proof Issues
When testing occurs after two hours or with unjustified delays:
Crown must prove: Your actual BAC while driving exceeded 0.08.
How they prove it: Expert toxicologist testimony using:
- Breath test results
- Estimated elimination rates
- “Back calculation” to determine BAC at time of driving
Problems with back calculation:
- Elimination rates vary significantly between individuals
- Absorption timing is highly variable
- Assumptions may be unreliable
- Creates reasonable doubt
Many Crowns withdraw charges rather than proceed with expensive, uncertain expert evidence.
Documentation and Evidence
Defence lawyers carefully review:
- Police occurrence reports (detailed timelines)
- Breath technician notes
- Approved instrument printouts (timestamps)
- Video evidence (timestamps showing delays)
- Radio transmissions (establishing when demands were made)
Even small discrepancies can reveal unjustified delays.
Strategic Considerations
Not every delay benefits the defence:
Delays favoring Crown: If you were barely over 0.08 while driving, delay allowing alcohol elimination might reduce your test results below 0.08—helping the Crown avoid charges.
Delays favoring defence: If you had rising BAC, delay pushes results higher, but testing beyond two hours removes presumption—helping the defence.
Understanding how delay impacts your specific case requires careful analysis.
The Bottom Line
The two-hour rule and “as soon as practicable” requirement create powerful defences in impaired driving cases. Police must work diligently to complete breath testing promptly, and any unjustified delays can undermine or destroy the Crown’s case.
If you’re facing DUI charges, your lawyer should immediately analyze the timeline from stop to testing. Even short, unjustified delays can be enough to raise reasonable doubt or result in exclusion of evidence.
Timing matters immensely in impaired driving cases. What seems like an open-and-shut case based on breath test results may actually have significant timing-based defences that experienced counsel can identify and pursue successfully.
Don’t assume breath test results are conclusive. The timing of those tests, and whether police followed proper procedures in obtaining them promptly, can be the difference between conviction and acquittal.
