testing for intoxication

Testing for Intoxication

2

Rate of Absorption

Depends on:

Amount of alcohol consumed

The alcohol content ofthe beverage

Time taken to consume it

Quantity and type of food present in the stomach

Physiology of the consumer

3

BAC: Blood Alcohol Content

Expressed as percent weight per

volume of blood

Legal limit in all states is 0.08

percent

Parameters influencing BAC:

• Body weight

• Alcohol content

• Number of beverages consumed

• Time since consumption

BAC Calculation

Male

BAC =

Female

BAC =

Burn-off rate of 0.015 percent per hour, but can vary:

0.071 (oz) (% alcohol)

body weight

0.085 (oz) (% alcohol)

body weight

://health.discovery.com/tools/calculators/alcohol/alcohol.html

Blood Alcohol Calculator

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Field Tests

Preliminary tests—used to determine the degree of suspect’s physical impairment and whether or not another test is justified

Psychophysical tests—three basic tests:• Horizontal gaze nystagmus (HGN): follow a pen or small

flashlight, tracking left to right with one’s eyes. In general, wavering at 45 degrees indicates 0.10 BAC.

• Nine-step walk and turn (WAT): comprehend and execute two or more simple instructions at one time

• One-leg stand (OLS): maintain balance; comprehend and execute two or more simple instructions at one time

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The Breathalyzer

More practical in the field

Collects and measures alcohol content of alveolar breath

Breath sample mixes with 3 ml of 0.025 percent K2Cr2O7 in sulfuric acid

and water:2K2Cr2O7 +3C2H5OH + 8H2SO4 2Cr2(SO4)3 + 2K2SO4 + 3CH3COOH + 11H2O

Potassium dichromate is yellow; as concentration decreases, its light absorption diminishes, so the breathalyzer indirectly measures alcohol concentration by measuring light absorption of potassium dichromate before and after the reaction with alcohol.

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Generalizations

During absorption, the concentration of alcohol in arterial blood is higher than in venous blood.

Breath tests reflect alcohol concentration in the pulmonary artery.

The breathalyzer also can react with acetone (as found in diabetics), acetaldehyde, methanol, isopropyl alcohol, and paraldehyde, but these are toxic and their presence means the person is in serious medical condition.

Breathalyzers now use an infrared light-absorption device with a digital readout. Prints out a card for a permanent record.

Breath Testers• Breath testers that

operate on the principle of infrared light absorption are becoming increasingly popular within the law enforcement community.

Breath Testers• Many types of breath testers are designed to

analyze a set volume of breath.

• The captured breath is exposed to infrared light.

Breath Testers

• It’s the degree of the interaction of the light with alcohol in the captured breath sample that allows the instrument to measure a blood alcohol concentration in breath.

• Some breath testing devices also use fuel cells.

Field Testing• Law enforcement officers typically use field

sobriety tests to estimate a motorist’s degree of physical impairment by alcohol and whether or not an evidential test for alcohol is justified.

• The horizontal gaze nystagmus test, walk and turn, and the one-leg stand are all considered reliable and effective psychophysical tests.

Field Testing• A portable, handheld, roadside breath tester may

be used to determine a preliminary breath-alcohol content.

Gas Chromatography Testing• Gas chromatography offers the toxicologist the

most widely used approach for determining alcohol levels in blood.

Drunk Driver Kills Cyclist

Idiots.