Six beers, seven hours' sleep and a 08:00 commute
Thomas is 24, weighs 82 kg and is at a cabin with friends. Between 20:00 and 24:00 on Friday he drinks six 0.5-litre beers at 4.7 % alcohol. He goes to bed at 00:30 and sleeps seven hours. At 07:30 on Saturday he has two slices of bread, a large glass of water, a hot shower and two cups of coffee. At 08:00 he gets into the car to drive 15 km to work on a quiet county road. He feels completely fine. His friend tells him: «Six beers over four hours - your body burns about one beer an hour, so you'll be at zero by morning. And you've eaten and showered.» The car is his, insured and newly inspected; the only thing in question is Thomas.
1. Estimate his blood alcohol at 08:00 using a recognised method, and say whether he may legally drive.
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Use Widmark: grams of pure alcohol ÷ (body weight × r), where r ≈ 0.7 for a man.
- Alcohol: 6 × 0.5 L × 4.7 % = 141 mL pure ethanol ≈ 111 g.
- Peak concentration: 111 ÷ (82 × 0.7) ≈ 1.9 ‰ if it had all been absorbed at once.
- In reality absorption is spread over four hours, and he eliminates roughly 0.10–0.15 ‰ per hour during that time, so his level at about 00:30 was probably in the region of 1.3–1.6 ‰.
- From 00:30 to 08:00 is 7.5 hours, removing roughly 0.75–1.1 ‰.
That leaves something in the order of 0.4–0.8 ‰ at 08:00. Even the most favourable end of that range is twice the Norwegian limit, which is 0.2 ‰. He may not drive, and the spread in the estimate is itself the point: you cannot know your own figure, so you cannot gamble on it.
The friend's rule of thumb («one beer an hour») confuses one unit with one 0.5-litre 4.7 % beer, and ignores body weight. A single 0.5-litre beer of that strength raises a man of 82 kg by roughly 0.3 ‰ - more than the entire legal limit.
2. He decides to wait until 12:00. Where does that leave him, and does anything he does in the meantime change the result?
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Waiting helps, but 12:00 is not a safe answer either. From a plausible 1.3–1.6 ‰ at 00:30, a further 11.5 hours at 0.10–0.15 ‰/h removes 1.15–1.7 ‰. He would probably be at or near zero by midday - but the upper end of the estimate does not get there, so 12:00 is a guess, not a calculation. The only way to know is a breath test.
What does not change the result:
- Coffee. Caffeine makes a drunk person feel awake; it does not remove ethanol.
- A shower, cold air, food, water or vomiting. Elimination happens in the liver at a fixed rate of roughly 0.1–0.15 ‰/h, and nothing you eat, drink or do speeds it up.
- «Feeling fine». Tolerance and habit mean the impairment is there while the subjective feeling is not. He is also sleep-deprived, which compounds reaction time.
What does change the result: not getting in the car. The realistic options are a taxi, a colleague, public transport, or telling his employer he cannot come in. Fifteen kilometres of county road is not a low-risk exception - rural roads have the highest share of serious crashes in Norway.
3. Suppose he drives and is stopped. What are the realistic consequences at 0.8 ‰ compared with just over 0.2 ‰?
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The Norwegian limit is 0.2 ‰, among the strictest in Europe, and the consequences step up sharply.
- Just over 0.2 ‰: a fine, normally calculated as around 1.5 times gross monthly salary, plus loss of the driving licence for roughly a year and a demand to retake the theory and practical tests. No prison in the normal case.
- Around 0.8 ‰: the case goes beyond a fixed fine. The courts' guidelines treat levels above 0.5 ‰ as normally calling for a short unconditional prison sentence (of the order of two to three weeks) on top of the fine and licence loss. At 0.8 ‰ his licence would be gone for a long period, and if he drives for a living it ends that job too.
- Aggravating factors in his case: he is young and newly qualified, he was sleep-deprived, and he had knowingly drunk six beers within four hours of driving. Insurance consequences often follow - an alcohol-related crash can affect cover and future premiums.
The exact sentence is for the court, and the guidelines are revised from time to time. But the structure is fixed: at 0.2 ‰ his life becomes expensive; at 0.8 ‰ it changes course.