Alcohol Breath Analyzer Accuracy

About half of all alcohol-related traffic accident fatalities involve drivers with a Blood Alcohol Concentration (BAC) of about .16 or higher. A significant proportion of such high-BAC drivers are hard core drunk drivers; they repeatedly abuse alcohol and drive while intoxicated. Hard core drunk drivers are a major threat to the safety of themselves and others. Breath analyzers are a major tool in convicting such dangerous offenders.

Breath analyzers (Breathalyzer, Intoxilyzer, Alcosensor, Alcoscan and BAC Datamaster are common brand names) don't actually test blood alcohol concentration (BAC), which requires the analysis of a blood sample. Instead, they estimate BAC indirectly. Different types of machine use different techniqes and larger machines generally yield better estimates than do hand-held models. Therefore, some states don't permit data or "readings" from hand-held machines to be presented as evidence in court. South Dakota does not even permit evidence from any type or size breath tester but relies entirely on blood tests to ensure accuracy and protect the innocent.

A major problem with some machines is that they not only identify the ethyl alcohol (or ethanol) found in alcohol beverages, but also other substances similar in molecular structure. Those machines identify any compound containing the methyl group structure. Over one hundred compounds can be found in the human breath at any one time and 70 to 80 percent of them contain methyl group structure and will be incorrectly detected as ethyl alcohol. Important is the fact that the more different ethyl group substances the machine detects, the higher will be the false BAC estimate.

The National Highway Traffic Safety Administration (NHTSA) has found that dieters and diabetics can have acetone levels hundreds and even thousand of times higher than that in others. Acetone is one of the many substances that can be falsely identified as ethyl alcohol by some breath machines.

One investigator has reported that alcohol-free subjects can generate BAC readings of about .05 after eating various types of bread products.

Substances in the environment can also lead to false BAC readings. For example, an alcohol-free subject was asked to apply a pint of contact cement to a piece of plywood and then to apply a gallon of oil-base paint to a wall. The total activity lasted about an hour. Twenty minutes later the subject was tested on an Intoxilyzer, which registered a BAC of .12 percent. This level is 50% higher than a BAC of .08, which constitutes legal intoxication in many states.

Ignition Interlocks

An ignition interlock is a device installed in a vehicle to prevent its use if a driver has been drinking alcohol. It includes a breath testing device into which the driver must blow before starting the engine.

The blood-alcohol concentration (BAC) limit for starting the car is very low, under .025, which is less than 1/3 the legal limit of .08. Therefore drivers are advised by authorities not to eat or smoke before trying to start their vehicles. Otherwise, the device may prevent them from driving.

Repeat DUI offenders to get ignition interlock: blood-alcohol level must be below .025 to start car., 10-1-03.

Similarly, a painter with a protective mask spray painted a room for 20 minutes. Although a blood test showed no alcohol, an Intoxilyzer falsely reported his BAC as .075.

Any number of other products found in the environment can cause erroneous BAC results. These include compounds found in lacquers, paint removers, celluloid, gasoline, and cleaning fluids.

Other common things that can cause false BAC levels are alcohol, blood or vomit in the subject's mouth, electrical interference from cell phones and police radios, tobacco smoke, dirt, and moisture.

Breath testers can be very sensitive to temperature and will give false reasings if not adjusted or recalibrated to account for ambient or surrounding air temperatures. The temperature of the subject is also very important. Each one degree of body temperature above normal will cause a substantial elevation (about 8%) in apparent BAC.

Many breath testing machines asume a 2,100-to-1 ratio in converting alcohol in the breath to estimates of alcohol in the blood. However, this ratio varies from 1,900 to 2,400 among people and also within a person over time. This variation will lead to false BAC readings.

Physical activity and hyperventilation can lower apparent BAC levels. One study found that the BAC readings of subjects decreased 11 to 14% after running up one flight of stairs and 22-25% after doing so twice. Another study found a 15% decrease in BAC readings after vigorous exercise or hyperventilaion.

Some breath analysis machinnes assume a hematocrit (cell volume of blood) of 47%. However, hematocrit values range from 42 to 52% in men and from 37 to 47% in women. A person with a lower hematocrit will have a falsely high BAC reading.

Failure of law enforcement officers to use the devices properly or of administrators to have the machines properly maintained and re-calibrated as required are additional sources of error.

Research indicates that breath tests vary at least 15% from actual blood alcohol concentration. At least 23% (that's about one out of every four) of all individuals tested will have a BAC reading higher than their actual BAC.

One writer has observed that

Breath testing, as currently used, is a very inaccurate method for measuring BAC. Even if the breath testing instrument is working perfectly, physiological variables prevent early reasonable accuracy....Breath testing for alcohol using a single test instrument, should not be used for scientific, medical or legal purposes where accuracy is important. 1


There are good ways to virtually eleminate being unfairly conviced of impaired or intoxicated driving. One is to choose not to drink, another is to pace the rate of drinking and follow other tips for maintaining a low BAC, and another is to select a designated driver.

  1. Don't Drink - If you choose not to drink, you'll find that it's not a big deal to decline a drink. Here are some possibilities:
    • No thanks.
    • No thanks; I feel good enough already.
    • Sorry, my analyst won't let me.
    • I can't because I get high on grape juice.
    • Not now -- I'm testing my willpower.
    • No thanks -- I want a clear head to appreciate you fully.
    • Not right now -- the party's wild enough as it is.
    • Sorry, I never drink on Friday (or whatever day it is).
    • Sorry, I promised my parents (spouse, date, etc.) that I wouldn't.
    • No thanks -- I prefer to watch.
    • No thanks -- Suzie (or whoever) can't stand me when I drink.
    • Sorry -- I'm taking medication.
    • No thanks, but I'd love to have a Pepsi.
    • Sorry, but I'm the designated driver.
    • You can also "lose" alcohol drinks or order such drinks as water, orange juice, seltzer with a twist of lemon, or any of a number of other beverages that lool like alcohol beverages. Most people don't really pay much attention to how much others are drinking and you might find that you actually enjoy yourself as much or more without becoming intoxicatecd. There's no hangover and it's certainly much safer.
  2. Maintain Low BAC - If you choose to drink but wish to keep your BAC low, here are some tips:
    • Don't be fooled. The contents of the typical bottle or can of beer, glass of wine, or liquor drink (mixed drink or straight liquor) each contain virtually identical amounts of pure alcohol. When it comes to alcohol, a drink is a drink is a drink and are all the same to a breathalyzer.
    • Know your limit. If you are not sure, experiment at home with your spouse or some other responsible adult. Explain what you are attempting to learn. Most people find that they can consume one drink per hour without any ill effects. Also, experiment with the Drink Wheel, which can be very informative.
    • Eat food while you drink. Food, especially high protein food such as meat, cheese and peanuts, will help slow the absorption of alcohol into your body.
    • Sip your drink.
    • Avoid "chugging" contests or other drinking games.
    • Skip a drink now and then. Having a non-alcohol drink betwen alcoholic ones will help keep your blood alcohol concentration down, as does spacing your alcohol drinks
    • Beware of unfamiliar drinks. Some drinks, such as zombies and other fruit drinks, can be deceiving as the alcohol content is not easily detectable. Therefore, it is difficult to space them properly.
  3. Use or Be a Designated Driver
    • Consider either using or being a designated driver. A designated driver is simply a person who agrees to abstain from alcohol and be responsible for driving others home. The others are free to drink or not as they choose. Many establishments provide free non-alcohol beverages to designated drivers.
    • Designated drivers have probably saved 50,000 lives and spared many more thousands of people from suffering injury from druink driving. 2 Over nine out of 10 Americans who attend social evernts where alcohol is served woould like to see designated drivers used. 3 And the proportion of people either using or being a designated driver has increased dramatically over time. Over 73,000,000 Americans either serve as a designated driver or are driven home by one. 4

A designated driver helps friends and family:

There are a number of advantages to the designated driver concept.

The non-drinker has a legitimate and respected role at a social function where alcohol is served. There is no stigma to abstaining because the designated driver is considered an important member of the group. Being a designated driver can also help legitimate a personal choice not to drink.

The designated driver approach prevents driving under any level of impairment because that person consumes no alcohol. It doesn't require a driver or passenger to determine if a person is too impaired to drive.

The server or host can offer a positive alternative to drunk driving by encouraging a groups to designate a driver.

The designated driver concept is easy to understand, simple to implement, costs nothing, and is effective. 6

Tips for designated drivers:

Breathalyzers may be inaccurate and often lead to unjust fines, imprisonment, loss of employment, and other serious problems but you needn't worry if you choose not to drink, to maintain a low BAC, or to use a designated driver.

References and Readings

filed under: Drinking and Driving

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