If you are under investigation for a DUI the arresting officer will offer you the opportunity to blow into a breath testing device. In South Carolina a machine called the Datamaster DMT is the breathalyzer machine. It basically takes your breath sample and uses infrared light to determine a calculated blood alcohol concentration based against a control or an internal standard that is measured at a .08, which is the legal limit in SC. It is important to remember that this blood alcohol reading is just one piece of evidence weighed against other evidence including bad or good driving, field sobriety tests, slurred speech, etc. A jury will weigh all of these factors to determine impairment. I had a client blow a .17 (more than twice the limit). All of the evidence pointed to him not being impaired except the breathalyzer reading. And the jury agreed he was not impaired. The breathalyzer is a machine and all machines have flaws. Part of my job is to investigate the machine and see if there are any issues with the machine and its history. A car is a machine. How often does your car get you from point A to point B but is not running correctly and is not reliable to get you from point A to point B. In many states the officer will offer you a PBT or portable breath test right there on the side of the road. For many reasons the logic behind having someone blow on the side of the road is fundamentally flawed junk science. Luckily, in SC we do not have those PBT roadside breath tests. We only have the Datamaster DMT.
Once arrested the officer will take you to the police station for your chance to blow. The officer has some procedures and protocol he or she must adhere to. He or she will read you a document instructing you of your options. Then there is a 20 minute waiting period. The purpose of this waiting period is to allow for any mouth alcohol to absorb into your blood. After the waiting period is over the machine will signal that it is ready to take your sample. You get a small window of time to blow a constant breath of what seems to be around 12 seconds. That is not an easy thing to do. If you cannot blow a constant breath then you will get marked as a refusal. If you do blow then the officer will print out the results and usually will tell you what you blew. If it is a .15 or higher then he will suspend your driving privileges in SC for one month. Your lawyer will help you with this suspension and will request a hearing and get you a temporary license usually within a week or so. You only get to blow one time. Does that seem fair? It seems the most fair way to get a more accurate idea of blood alcohol would be to take your blood. That is how they do it in Texas. In many states they allow at least two breathalyzer tests and they average the results. Statistically, that seems more fair. I tell clients and juries often that allowing someone one chance to blow is like having your suspected pregnant wife take one pregnancy test. You don't believe one test do you? No! You take another one and then go see the Board Certified doctor for a blood test before you start sending out baby announcements.
Long story short-- when you are given the opportunity in SC to blow into the breathalyzer you are NOT given that opportunity on the side of the road. You are given that opportunity within 2 hours of your DUI arrest at the police station and only given one chance to blow.