Presentation on theme: "Testing for Intoxication. 2 Rate of Absorption Depends on: Amount of alcohol consumed The alcohol content of the beverage Time taken to consume it Quantity."— Presentation transcript:
2 Rate of Absorption Depends on: Amount of alcohol consumed The alcohol content of the 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
6 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
7 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 K 2 Cr 2 O 7 in sulfuric acid and water: 2K 2 Cr 2 O 7 +3C 2 H 5 OH + 8H 2 SO 4 2Cr 2 (SO 4 ) 3 + 2K 2 SO 4 + 3CH 3 COOH + 11H 2 O 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.
8 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.