Breathalyzer®
Breathalyzer®
Accidents or crimes can occur when one or more of those involved are intoxicated. Impaired driving is the obvious example. In the United States, at least 25,000 people die in alcohol related traffic accidents each year, representing about 500 people each week. In fact, alcohol-related traffic accidents are the leading cause of death among Americans aged 16–24.
The determination of alcohol level can be an important part of an ongoing investigation. Returning to the example of a traffic accident, one of the early facets of an investigation can be the determination of the alcohol level of a driver. Often a police officer needs to ascertain whether a person is legally impaired. Several tests of coordination (i.e., walking a straight line, touching the tip of the nose with a finger) can be helpful indicators. But, determination of blood alcohol levels via a Breathalyzer® test is a critical part of the assessment of sobriety.
An initial Breathalyzer® measurement is often conducted at the scene of the accident, since normal metabolic processes in the body will reduce the alcohol level within hours.
Measurements of alcohol level are most conveniently taken by monitoring expired air. The Breathalyzer® is one of three different devices that can be used. It is the most popular device for portable, at-the-scene use. The instrument uses a color reaction to detect alcohol; the degree of color change is related to the alcohol level in the breath.
The result is typically expressed as the blood-alcohol concentration (BAC), which represents the grams of alcohol per 100 milliters of blood. The legal BAC limit can vary between jurisdictions; 0.08% is a typical limit. So, for example, if a suspect’s breathalyzer reading was 0.15%, they would be legally impaired. If they were driving a vehicle, they would be charged with driving while impaired (DWI) or driving under the influence (DUI).
The development of the devices that could monitor alcohol in the breath dates back to the 1940s. In
1954, Dr. Robert F. Borkenstein of the Indiana State Police invented the modern-day Breathalyzer®.
The Breathalyzer® relies on the fact that, when consumed, alcohol is not altered in the bloodstream and on the volatility of the compound (the tendency of the compound to evaporate from solution). The latter is important when alcohol-laden blood passes through the tiny channels in the air sacs of the lungs. There, alcohol’s volatility encourages its passage across the channel membranes into the lung, where it can be exhaled.
A Breathalyzer® detects this expired alcohol. When someone blows into a Breathalyzer®, the device detects both the volume of air expired and, as described below, the amount of alcohol present. The ratio of the amount of alcohol in the breath to the blood alcohol level is 2,100:1. By determining the amount of alcohol in the volume of expired air, a calculation of blood alcohol concentration can be made. This calculation is done as described below.
When air is blown into a Breathalyzer®, it bubbles through a mixture of potassium dichromate, sulfuric acid, silver nitrate, and water. The sulfuric acid acts to remove the alcohol from the air into the aqueous solution. In the solution, the silver nitrate acts as a catalyst (a compound that speeds up the rate of reaction without directly participating in the reaction) in the reaction that follows.
In this reaction, the alcohol (ethanol) reacts with the reddish-orange potassium dichromate to produce the greenish-colored chromium sulfate, potassium sulfate, and acetic acid. The degree of the color change corresponds to the amount of alcohol that is present.
To determine the degree of the color change, and so calculate the alcohol level, it is necessary to compare the test solution to an unreacted solution. The latter control solution is contained in another compartment in the Breathalyzer®. The control solution is in a photocell; an electric current that is produced causes a needle in the device to move from its resting place. The operator then turns a knob to move the needle back to its resting place and then records the alcohol level from the position of an indicator on the knob relative to a scale.
Other versions of Breathalyzers® can perform the calculations automatically and display the alcohol level as a digital read-out. With improvements in technology, the Breathalyzer® has become smaller. Some models are so small that they can be attached to a key chain. Forensically-approved version are larger, but are still portable enough to be taken to the scene of an investigation.
Two other alcohol detection devices can be used. They do not detect ethanol in the color-dependent fashion of a Breathalyzer®. An Intoxilyzer® detects alcohol using infrared spectroscopy, while an Alco-Sensor® detects alcohol based on its use as fuel in another type of chemical reaction.
See also Forensic science; Serology.
Brian Hoyle
Breathalyzer®
Breathalyzer®
Accidents or crimes can occur when one or more of those involved are intoxicated. Impaired driving is the obvious example. In the United States, at least 25,000 people die in alcohol related traffic accidents each year, representing about 500 people each week. In fact, alcohol-related traffic accidents are the leading cause of death among Americans aged 16–24.
Alcohol can also fuel domestic disturbances and other altercations between people that result in injury and death.
Traffic accidents and violent incidents can lead to a forensic investigation. Thus, alcohol is closely tied to forensic science .
The determination of alcohol level can be an important part of an ongoing investigation. Returning to the example of a traffic accident, one of the early facets of an investigation can be the determination of the alcohol level of a driver. Often a police officer needs to ascertain whether a person is legally impaired. Several tests of coordination (i.e., walking a straight line, touching the tip of the nose with a finger) can be helpful indicators. But, determination of blood alcohol levels via a Breathalyzer® test is a critical part of the assessment of sobriety.
An initial Breathalyzer® measurement is often conducted at the scene of the accident, since normal metabolic processes in the body will reduce the alcohol level within hours.
Measurements of alcohol level are most conveniently taken by monitoring expired air. The Breathalyzer® is one of three different devices that can be used. It is the most popular device for portable, at-the-scene use. The instrument uses a color reaction to detect alcohol; the degree of color change is related to the alcohol level in the breath.
The result is typically expressed as the blood-alcohol concentration (BAC), which represents the grams of alcohol per 100 milliters of blood. The legal BAC limit can vary between jurisdictions; 0.08% is a typical limit. So, for example, if a suspect's breath-alyzer reading was 0.15%, they would be legally impaired. If they were driving a vehicle, they would be charged with driving while impaired (DWI) or driving under the influence (DUI).
The development of the devices that could monitor alcohol in the breath dates back to the 1940s. In 1954, Dr. Robert F. Borkenstein of the Indiana State Police invented the modern-day Breathalyzer®.
The Breathalyzer® relies on the fact that, when consumed, alcohol is not altered in the bloodstream and on the volatility of the compound (the tendency of the compound to evaporate from solution). The latter is important when alcohol-laden blood passes through the tiny channels in the air sacs of the lungs. There, alcohol's volatility encourages its passage across the channel membranes into the lung, where it can be exhaled.
A Breathalyzer® detects this expired alcohol. When someone blows into a Breathalyzer®, the device detects both the volume of air expired and, as described below, the amount of alcohol present. The ratio of the amount of alcohol in the breath to the blood alcohol level is 2,100:1. By determining the amount of alcohol in the volume of expired air, a calculation of blood alcohol concentration can be made. This calculation is done as described below.
When air is blown into a Breathalyzer®, it bubbles through a mixture of potassium dichromate, sulfuric acid, silver nitrate, and water. The sulfuric acid acts to remove the alcohol from the air into the aqueous solution. In the solution, the silver nitrate acts as a catalyst (a compound that speeds up the rate of reaction without directly participating in the reaction) in the reaction that follows.
In this reaction, the alcohol (ethanol) reacts with the reddish-orange potassium dichromate to produce the greenish-colored chromium sulfate, potassium sulfate, and acetic acid. The degree of the color change corresponds to the amount of alcohol that is present.
To determine the degree of the color change, and so calculate the alcohol level, it is necessary to compare the test solution to an unreacted solution. The latter control solution is contained in another compartment in the Breathalyzer®. The control solution is in a photocell; an electric current that is produced causes a needle in the device to move from its resting place. The operator then turns a knob to move the needle back to its resting place and then records the alcohol level from the position of an indicator on the knob relative to a scale.
Other versions of Breathalyzers® can perform the calculations automatically and display the alcohol level as a digital read-out. With improvements in technology, the Breathalyzer® has become smaller. Some models are so small that they can be attached to a key chain. Forensically-approved versions are larger, but are still portable enough to be taken to the scene of an investigation.
Two other alcohol detection devices can be used. They do not detect ethanol in the color-dependent fashion of a Breathalyzer®. An Intoxilyzer® detects alcohol using infrared spectroscopy , while an AlcoSensor® detects alcohol based on its use as fuel in another type of chemical reaction.
see also Crime scene investigation; Evidence; Indicator, acid-base.