Everyday we hear and read about drivers involved in accidents who are later charged with drunken driving, and later will hear about the accident on the news. The news will discuss the suspect’s blood alcohol level and the legal limit for blood alcohol. A driver might be found to have a level of 0.15, for example, and the legal limit is 0.08.
But what do those figures mean?
And how do police officers determine if a suspected drunken driver is actually legally drunk? You may have heard about a tool called a Breathalyzer – a device used in breath alcohol analysis – but may not know exactly how a person’s breath reveals how much he or she has had to drink.
It is important for our public safety that people who are drunk should not be on the road. Of the many thousands of traffic deaths each year in the United States, about 35 to 40 percent are related to alcohol. Drivers who are able to successfully pass police sobriety tests – those who can touch their noses or walk a straight line without falling over – still might be breaking the law by exceeding the legal limit for blood alcohol and be a hazard on the road. Police departments now use modern technology to determine impairment in suspected drunk drivers and to prevent fatalities.
Police departments and many individual officers are now equipped with breath alcohol testers (Breathalyzers are one type) to determine drunk driving suspects’ blood alcohol concentration (BAC). That’s because alcohol intoxication is legally defined by the BAC level.
Taking a blood sample out on the road and taking it back to the lab for analysis was not practical or efficient for arresting those who were suspected of driving while impaired (DWI) or driving under the influence (DUI). Urine tests for alcohol was just as impractical as blood sampling. Officials needed a less invasive way to measure BAC levels.
In the 1940s, the first breath alcohol testing devices were developed for police use. In 1954, Dr. Robert Borkenstein of the Indiana State Police invented the Breathalyzer, which is an efficient type of alcohol testing device used by many law enforcement departments today.
Alcohol that a person drinks will always appear in his breath. This is because alcohol is absorbed from that person’s mouth, throat, stomach and intestines into the bloodstream. Alcohol is not digested like food is, nor chemically changed in the bloodstream upon absorption.
When a person’s blood passes through his or her lungs, some of the ingested alcohol travels across the membranes of the lung’s air sacs and moves into the air. This process is one of alcohol’s main properties of evaporating from a volatile solution. So, the alcohol concentration from lung air is directly related to the alcohol concentration from the blood.
When the alcohol in the lung air is exhaled, it can usually be detected by any modern breath testing device. So, this allows any police officer to handle suspected drunk driver tests in a faster and simpler way. Instead of having to draw a suspected drunk’s blood to test his alcohol level, the officer is able to perform a quick test on that driver’s breath on the spot. He can instantly determine if there is a reason to arrest the driver.
The relationship between the alcohol concentration in the breath and the concentration in the blood lets us easily find out the BAC by measuring alcohol concentration level on the breath. The ratio of alcohol in the breath to that in the blood is 2,100:1. So, we can quickly calculate that 2,100 milliliters (ml) of lung air has the same amount of alcohol as 1 ml of blood.
For a long period of time, the US has kept the legal standard for drunkenness around 0.10, but now in all states have adopted the 0.08 federal BAC standard because the federal government put pressure on the states to lower the legal limit. The American Medical Association says that a person can become impaired when the blood alcohol level hits 0.05.
When a person’s BAC measures 0.08, it means that he or she has 0.08 grams of alcohol per 100 ml of blood.
Resources
Breathalyzers.net – distributes several different hand-held models, including the highly regarded AlcoMate Digital hand-held unit for consumers, and the Lifeloc FC for professional use.
Also see:
Alcohol breath tester
Types of alcohol tests
Alcohol testing using saliva
Blood alcohol testing
Breath alcohol test
