Testing for Intoxication

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Transcript Testing for Intoxication

Testing for Intoxication
 Why
is it not practical to measure
an individual’s BAC by measuring
a sample of blood?
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
Breath Testing
Field Sobriety Tests
Breath Testing for Alcohol
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Remember: The alcohol in breath
samples is proportional to the alcohol
concentration in blood
Breathalyzer-developed in 1954; alcohol is
reacted with several reagents; the
reactions are measured by a
spectrophotometer.
Breathalyzer replaced by fuel cell and
infrared detectors in the 1970’s
Breath Testing for Alcohol

The key to accurate
measurements in
breath testing is to
obtain alveolar
breaths
Field Sobriety Testing
A portable breath tester can be used to
establish probable cause.
 Psychophysical tests
-Horizontal-gaze nystagmus
Divided-attention tasks
-walk and turn
-one-leg stand
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The Analysis of Blood for Alcohol
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Gas Chromatography is often used by
forensic labs to measure BAC
Medical professionals often use
spectrophotometric methods
Collection and Preservation of
Blood
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Blood samples must be stored in an
airtight container
Anticoagulants (EDTA, potassium oxalate)
must be added to prevent the blood from
clotting
Preservatives (sodium fluoride) must be
added to inhibit the growth of
microorganisms.
Blood Alcohol Laws
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In 1992, the US DOT recommended that
states adopt 0.08 BAC as the legal
measure of drunk driving.
The standard is 0.04 BAC for commercial
truck and bus drivers
Constitutional Issues
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Implied consent law – a person must
consent to a test for alcohol intoxication or
be subject to loss of license for a
designated period of time
Courts have ruled that the 5th amendment
only applies to testimonial evidence
Courts have also ruled that alcohol tests
do not violate 4th amendment rights.
The Role of the Toxicologist
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Beyond alcohol, toxicologists analyze a
wide variety of drugs and poisons
Some possible clues include:
-the victim’s symptoms
-postmortem pathological examination
-examination of personal items
-nearby presence of drug containers,
household chemicals, etc.
Challenges Facing the
Toxicologist
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Drugs and poisons may be present in tiny
amounts/concentrations
Few substances leave the body in the
same form that they entered; they are
metabolized (Example: heroin)
When a drug or poison is detected, its
toxicity must be determined
Collection of Toxicological Evidence
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For a deceased person, all body fluids and
tissues may be examined
For a living person, blood and urine
samples are analyzed
Drugs: detectable in blood for 24 hours;
detectable in urine for 72 hours
Hair samples may also be taken
Techniques Used in Toxicology
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Screening tests tentatively identify a
drug/poison or narrow down the
possibilities (TLC, GC, immunoassays)
Confirmation tests definitively confirms the
identity of a poison or drug (GC/Mass
spectrometry)
Detecting Non-drug Poisons
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Heavy metals – Lead, arsenic, mercury,
thallium
Cyanide
Carbon monoxide
Significance of Toxicological
Testing
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There are legal guidelines correlating Blood
alcohol concentrations and physical impairment
No such guidelines exist regarding all other
drugs.
Toxicologists must judge the manner in which a
drug affects an individual’s performance or
physical state.
For a deceased individual, toxicologists work
with medical examiners to determine the cause
of death
Significance of Toxicological
Testing
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Factors which affect drug-induced
behavior:
-age
-physical condition
-tolerance of the drug user
-interaction between multiple drugs (i.e.
alcohol & barbiturates/narcotics