Mouthwash and breathalyzers

Some things go great together, like wine and olives, beer and softball, marihuana and Cheezies – but other combinations can have disastrous results. Take, for example, mouthwash and breathalyzers.

It’s great to have fresh breath, and many people in BC take dental hygiene very seriously. A problem arises, however, if you use mouthwash shortly before blowing into a breathalyzer. Mouthwash and breathalyzers don’t mix. And here’s why:

In BC the police use roadside breathalyzers to issue IRP DUI driving prohibitions. These devices are also referred to as “Approved Screening Devices” or “ASD” because they were approved to screen drivers for the purpose of deciding whether they should be forced to provide a breath sample into an accurate evidence machine. The devices used for issuing IRPs, i.e. the Alco-Sensor IV Screener and the Alco-Sensor FST, do not distinguish the source of the alcohol.

Regardless of how much you’ve had to drink, air from the lungs contains only a small concentration of alcohol. The ASDs capture a miniscule amount of air as it passes through the internal tubing of the device. They are sensitive devices. When functioning properly, they will take this small amount of air containing a small amount of alcohol and make calculations about the breath-alcohol content. The internal processor and software then calculates an approximate blood-alcohol content and provides a reading on the display.

The problem is that the device has no way to determine the source of the alcohol fumes. A tiny bit of residual alcohol in your mouth will read as an extremely high blood-alcohol concentration. The ASD has no way to distinguish whether it is testing alcohol from your mouth, alcohol from your lungs or a combination of the two.

Mouthwash and breathalyzers

Most mouthwash contains alcohol, sometimes at fairly high concentrations. Of the nine advertised brands of Listerine, seven contain a significant concentration of alcohol. Unlike beverages, which most people swallow fairly quickly, mouthwash is swished around to each corner and pocket of the mouth. The intention is for the mouthwash to get in between all the teeth, in and around the gums and deep into the space between your gums and your cheeks.

If you use mouthwash shortly before blowing into an ASD breathalyzer, you can expect an artificially elevated reading. You can get a false Fail or Warn very easily if you blow into the breathalyzer shortly after using mouthwash.

The Mouthwash Defence

Lots of people use mouthwash to disguise the smell of alcohol on their breath. This is a poor strategy. It might seem like a good idea at the time, but using mouthwash in the hopes of getting through a roadblock after drinking too much is simply a big mistake. However, if you used mouthwash and the police issued you a driving prohibition, you may have a defence to your IRP.

The police are not trained to ask when a person last used mouthwash. They should ask drivers when they finished their last drink, but even this is so rarely properly put to a driver. So the basis of a mouthwash defence relies on the evidence advanced at the review hearing for those who dispute their IRP driving prohibitions.

Studies have shown that alcohol in the mouth can contaminate a breath sample up to 40 minutes after last consumption or introduction of alcohol into the mouth. The police instructions are to wait 15 minutes from the time of the last drink, which is too short of a period of time as far as we’re concerned. However, mouthwash rarely comes to the mind of even the most experienced police officer.

Mouthwash is usually a big problem when you blow into a breathalyzer. Nevertheless, it can provide a valid defence to the allegation that you blew Fail on an ASD because mouthwash and breathalyzers are a bad combination.