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Tip 5:          Blood Alcohol Level

Whenever I hear about drinking and driving violations I hear things like “twice the legal limit” and “way over the limit.” What does that mean?

Anthony C.,   U Mass, Frosh

What’s the difference between BAC and BAL?

Sue M.,   University of Florida, Sophomore

They say that the legal BAL limit for driving is .08.  What does that mean?   How many drinks will it take for me to reach a .08 BAL?

Zina B.,   New York University, Sophomore

Blood Alcohol Level (BAL) refers to the ratio of blood to alcohol in the bloodstream.  BAL, also known as Blood Alcohol Concentration (BAC) or Blood Alcohol Content (BAC) is represented as a percentage. 


Zina, here’s an analogy that may help you understand what those numbers represent. Picture a shelf with 10,000 compartments. Each compartment is filled with a drop of blood. If I replace one drop of blood with one drop of alcohol, the shelf now has a BAL of .01%.  If I replace 8 drops of blood with 8 drops of alcohol, then the shelf has a BAL of .08%.


State laws set a BAL of .08% as the level at which you are considered legally intoxicated.  Therefore Anthony, “twice the legal limit” would be a BAL of .16%.  It is important to realize however, some studies indicate a BAL as low as .03% affects your ability to drive and increases the likelihood of an alcohol related car crash. The probability of a crash begins to increase significantly at a BAL of .05% and climbs rapidly above .08%. 


If you have an average metabolic rate you will metabolize – breakdown – approximately one drink per hour.  So, if you drink more than one drink per hour the alcohol backs up in your bloodstream resulting in an increase in BAL.  The rate at which the BAL increases depends upon how much alcohol you consume, how quickly you consume it as well as your metabolic rate.  That is, the faster you drink, the faster your BAL increases. And, most important, the higher the BAL, the greater the level of impairment – or how messed up you may be.  To answer your second question Zina, you’ll have to refer to the chart in the back of this book to determine how many drinks during what period of time will bring you to a BAL of .08%. (See Appendix:  Body Weight Index)



Know yourself.  Know how many drinks and what types of drinks consumed over what period of time will result in a lower-risk BAL of .05% as well as a higher-risk BAL of .08% or more. 

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