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Legislation Sections Database at defencecounsel.com for:
Criminal Code of Canada
Failure or refusal to comply with demand
254.(5) Everyone commits an offence who, without reasonable excuse, fails or refuses to comply with a demand made under this section.
This section creates two breath refusal offences: refusal or failure to blow into a roadside screening device (ASD) and refusal or failure to blow into an Intoxilyzer at the police detachment.
If you wish to raise a medical defence you will need the in-person attendance of your asthma or other specialist doctor at the trial. A letter from your doctor is not enough. Retaining a medical doctor to come to Court will be extremely expensive and may be resisted by your doctor(s). The Ontario Medical Association has issued a letter to doctors suggesting that anyone, even persons with one lung, can blow into one of these devices. Most doctors have not conducted scientific testing with screening devices or evidentiary breath equipment and so their evidence or the letter from the OMA should be seen in that context.
Better defences may relate to failure to blow where the instrument or device is not being operated properly (e.g. wrong mouthpiece used on the ASD) or where there is an instrument malfunction (e.g. Intoxilyzer flow sensor or accidental re-calibration).