Blood alcohol concentration decreases by 0.1-0.15‰ per hour.

Only time can lower your blood alcohol concentration; exercise, sauna or coffee does not make any difference.

The '6-hour rule' applies to all drivers, not only commercial drivers, and states that if you have been involved in a traffic incident that might be cause for a police investigation, you must not consume alcohol (or other intoxicants) in the first 6 hours following the incident. The reason being that the police in some cases might wish to collect blood samples from those involved if there is any suspicion of the incident having been caused by either party being affected by alcohol or other intoxicants.

There used to be a provision in the Road Traffic Act stating that your licence would be suspended for at least 2 years should you refuse to provide a blood sample. This provision does not exist any longer, and so today you are in reality unable to refuse; the Road Traffic Act now states a blood sample may be taken by force.