How Redlines Work

Redlines do not directly measure Blood Alcohol Concentration (BAC).  They interpret the volume of alcohol in a breath sample (Breath Alcohol Content, BrAC) in terms of BAC through using the internationally accepted correlation factor or ‘partition ratio’ between BrAC and BAC.  Note that in Australia and New Zealand, the legal limits are a measurement of BAC.

Each Redline test tube contains yellow crystals which turn green pro rata to the volume of alcohol present in the breath sample collected by the breath bag, and indicate that volume against a measurement of the legal drink-driving limit. 


Remember that BAC can continue rising for up to 2 hours after consuming your last drink.  There is no ‘rule of thumb’ regarding how much it will rise over any given period of time.  However, common sense should tell you that if you have consumed a lot of alcohol over a short period of time, it will rise more for longer than when compared to the same person consuming the same amount over a longer period.  Similarly, if you have consumed only a small amount of alcohol, it is highly unlikely that your BAC will keep rising for an extended period. 

Note also that it can take 10 hours or more for blood alcohol levels to return to zero after a high blood alcohol level has been reached.  Accordingly, Redlines should be used even well after the time of excessive consumption of alcohol.