Shulou(Shulou.com)11/24 Report--

We often hear or see traffic accidents caused by drivers' drunken driving. in the news reports of accidents, we often talk about the amount of alcohol in the driver's blood and the legal limit of alcohol in the blood. For example, a driver may be tested for blood alcohol levels of 0.15, while the legal limit is 0.08. But what do these numbers mean? How do the police determine whether drivers suspected of drunk driving are legally ingested? You may have heard of a breath alcohol tester, but you'd rather know how a person's exhaled gas indicates his alcohol intake.

For the sake of public safety, it is important to prohibit drivers from driving after drinking. In 1999, 42000 people died in traffic accidents in the United States, 38% of which were related to alcohol. Even drivers who can pass a sobriety test of touching their nose or walking in a straight line may still exceed the legal limit of blood alcohol content and become road killers. As a result, the police use some of the latest techniques to test the alcohol levels of suspected drunk drivers and take them off the road.

Many traffic police on duty use breath alcohol testing equipment (breath alcohol tester is one of them) to determine the blood alcohol concentration (BAC) of drunk driving suspects. In this article, we will study the scientific principles and technologies contained in these breath alcohol testing equipment.

1. The legal basis for testing drunk driving is the blood alcohol concentration (BAC) level. However, it is neither practical nor efficient for drivers suspected of drink driving (DWI) or drunk driving (DUI) to be detained in the laboratory after blood samples are collected at the scene. Urine alcohol testing proved to be as impractical as blood sampling. What we need is a way to measure indicators related to blood alcohol concentration without invading the driver's body.

In the 1940s, breath alcohol testing devices were first invented for use by the police. In 1954, Dr. Dr. Robert Borkenstein of the Indiana State Police Department invented the breath alcohol tester, which is still used by law enforcement agencies today.

Let's take a look at how these devices work.

two。 The principle of the test is that the alcohol a person drinks will be absorbed into the bloodstream by the mouth, throat, stomach and intestines, and then exhaled out of the body.

Alcohol is not digested after ingestion, nor does it undergo chemical changes in the blood. Because alcohol is volatile, when blood flows through the lungs, it evaporates from the blood, so some alcohol enters the gas in the alveoli through the alveolar membrane. The alcohol concentration in the alveolar gas is related to the alcohol concentration in the blood, and when the alcohol in the alveolar gas is exhaled, it can be detected by a breath alcohol test device. The traffic police do not have to take the driver's blood to test their alcohol levels, but by testing the driver's breath on the spot, they can immediately know whether the driver is drunk driving.

Because the concentration of alcohol in the breath is related to the concentration of alcohol in the blood, the traffic police can calculate the BAC by measuring the amount of alcohol in the breath. The ratio of alcohol in the breath to alcohol in the blood is 2100. This means that 2100 milliliters of alveolar air contains the same alcohol as 1 milliliter of blood.

According to the American Medical Association, when the blood alcohol concentration reaches 0.05, the body will be damaged. If a person's blood alcohol concentration is measured at 0.08, that means 0.08 grams (80 milligrams) of alcohol per 100 milliliters of blood. For many years, the standard of drunk driving implemented in our country is 80 mg of alcohol per 100 ml of blood, which will be replaced by 0.08 below.

Now, the traffic police have several different devices that can measure BAC.

3. There are three main types of breath analyzer breath alcohol analysis equipment, which are based on different principles:

Breath Alcohol Tester-using a chemical reaction with alcohol to produce color changes

Breath drunkenness meter-detection of alcohol by infrared (IR) spectroscopy

Detection of Chemical reaction of Alcohol in fuel Cell by Alcohol Sensor III or IV-

Regardless of the type, each device has an air outlet, a tube for the driver to blow, and a sample room to store air. The rest of the device varies depending on the type.

Breath alcohol tester the breath alcohol tester includes:

A system for collecting respiratory samples from suspects

Two glass bottles containing a chemical reaction mixture

A photovoltaic system connected to an instrument to test color changes associated with chemical reactions

In order to measure alcohol content, the driver has to blow into the instrument. The exhaled gas sample reacts with a mixture of sulfuric acid, potassium dichromate, silver nitrate and water in a small bottle. The measurement principle is based on the following chemical reactions:

In this reaction:

Sulfuric acid dissolves alcohol in the air into a liquid solution.

Ethanol reacts with potassium dichromate to form chromium sulfate, potassium sulfate, acetic acid, water.

Silver nitrate is a catalyst that speeds up the reaction without participating in a chemical reaction. In addition to transferring alcohol from the gas, sulfuric acid may also provide the necessary acidic conditions for the reaction.

In this reaction, the red-orange dichromate ion turns green when it reacts with alcohol; the degree of color change is directly related to the amount of alcohol discharged from the air. To determine the alcohol content in the air, the reacted mixture is compared with an unreacted mixture in the photovoltaic system to generate an electric current that moves the needle in the instrument from the stationary position. The operator then rotates the knob to bring the needle back to its original position, and the more the knob rotates, the higher the alcohol content, thus reading the alcohol content.

The chemical composition of alcohol

The alcohol in alcoholic beverages is ethanol. The molecular structure of ethanol is as follows:

Where C is carbon, H is hydrogen, O is oxygen, and each connector is a chemical bond between atoms.

The hydroxyl group on the molecule (Omurh) is the functional group of alcohols. There are four bonds in this molecule:

Carbon-carbon (Cmurc)

Carbon-hydrogen (Cmurh)

Carbon-oxygen (Cmuro)

Hydrogen-oxygen (Omurh)

Chemical bonds between atoms are common pairs of electrons. Chemical bonds are very much like springs: they can bend and stretch. These properties are of great significance for the determination of ethanol in samples by infrared spectroscopy.

4. Breath intoxication tester

A schematic diagram of a breathalyzer. A quartz lamp (infrared light source), B blow inlet, C exhalation outlet, D sample chamber, E lens, F filter impeller, G photocell, H microprocessor this device uses infrared spectroscopy to identify molecules according to the infrared light absorbed by molecules.

The molecules vibrate constantly, and these vibrations change when the molecules absorb infrared light. Changes in vibration include bending and stretching of various bonds. Each bond in the molecule absorbs different wavelengths of infrared light. Therefore, in order to identify ethanol in the sample, you must observe the wavelengths of the chemical bonds in ethanol (Cmuro, Omurh, Cmurh, Cmurc) and measure the absorption of infrared light. The wavelength of absorption can identify ethanol, and the amount of infrared absorption tells you the amount of alcohol.

In the breathalyzer:

The lamp produces a broadband (multi-wavelength) infrared beam.

The broadband infrared beam passing through the sample room is focused by the lens on the rotating filter wheel.

The filter wheel contains a narrow-band filter for the wavelength of the chemical bond in ethanol. The light passing through each filter is detected by the photocell and here it is converted into an electrical pulse.

The electrical pulse is transmitted to the microprocessor, which interprets the pulse and calculates the BAC based on the absorption of infrared light.

5. Alcohol sensor III or IV modern fuel cell technology (which may power our cars and even our homes in the future) has been used in respiratory alcohol detectors. Fuel cells are used in devices such as alcohol sensors III and IV.

The fuel cell has two platinum electrodes sandwiched with porous acid electrolytes. When the gas exhaled by the suspect flows through one side of the fuel cell, platinum oxidizes all alcohol in the gas, producing acetic acid, protons and electrons. Electrons flow through the wire from the platinum electrode. The wire is connected to the galvanometer and the platinum electrode at the other end. Protons pass through the lower part of the fuel cell and combine with oxygen and electrons on the other side to form water. The more alcohol is oxidized, the greater the current. The microprocessor measures the current and calculates BAC.

Operators of breath alcohol testing devices must be trained in the use and calibration of the equipment, especially if the test results will be used as evidence of drunk driving tests. Law enforcement officers can carry portable breath testing devices that have the same principle as full-size devices. However, the judge's decision may be based on the accuracy of the breath test, so prosecutors prefer to get results from full-size equipment.

Oxidation of alcohol

If hydrogen is dropped from the carbon to the right of ethanol in the presence of oxygen, you will get acetic acid, which is the main component of vinegar. The molecular structure of acetic acid is as follows:

Where C is carbon, H is hydrogen, O is oxygen, the connector is a single bond between atoms, and the symbol "=" is a double bond between atoms. When ethanol is oxidized to acetic acid, it also produces two protons and two electrons.

Author: Craig Freudenrich

Translation: depth

Revision: floor-sweeping monk

Original link: How Breathalyzers Work

This article comes from the official account of Wechat: Institute of Physics, Chinese Academy of Sciences (ID:cas-iop), author: Freudenrich

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