CSI And Toxicology
CSI And Toxicology
Richard Saferstein (Former Chief Forensic Scientist) gives expert video advice on: What is forensic toxicology?; What is the legal blood alcohol limit for driving in the US?; How long is alcohol detectable in a person's body? and more...
What is forensic toxicology?
Forensic toxicology is the study or the ability to study the human body for the presence of drugs and poisons. So the forensic toxicologist will normally undertake an analysis of blood, urine and perhaps if we're dealing with the deceased, body organs in order to determine what foreign drugs or what foreign poisons are present in the body.
What is the legal blood alcohol limit for driving in the US?
In all states in the United States the legal limit is .08 percent. We call that the per se level. By per se, we mean that the level is the only thing that the state has to prove in terms of getting a conviction for drinking and driving. Just that level and no other, I think, is necessary for conviction in a drinking and driving case.
How long is alcohol detectable in a person's body?
That depends on how much alcohol you drink. For example, the for sale label in all states in the United States is .08%. A normal human being naturally eliminates alcohol at the rate of .015% per hour. If you reach a level of .08, you're going to figure that it's going to take just a bit more than five hours to eliminate the level of .08% blood alcohol that's present in your body. How long it ultimately takes to eliminate all the alcohol will depend on how much you have to drink.
How does a forensic toxicologist analyze a person's breath to determine alcohol levels?
Normally, in the United States and throughout the world, many people who are thought to be under the influence of alcohol while driving are tested at some point in the investigation with a breath-testing device. Now this test can come about at the time the automobile is stopped because many jurisdictions allow for portable breath-testing devices to be brought to the roadside. And an individual will blow into these devices and a number will be registered, and if that number is in excess, for example, of the per se level, which in the United States is 0.08 percent, that individual will then be brought back to the police station for further investigation. Now, at the police station, either a blood sample can be taken from the suspect for testing in the toxicological laboratory for alcohol content, or that suspect can be subject to a more comprehensive and sophisticated breath test. The breath test is a test that allows one to correlate the breath alcohol that is being measured with the blood alcohol level, and there is a correlation that is well-accepted in the legal community, and the result of a breath test will then be equivalent to the result of a blood test.
What methods does a law enforcement officer use to test blood-alcohol level?
When a driver is stopped as being suspected of driving under the influence of alcohol, the officer will first look at the general demeanor of the driver. And then will probably administer what we call standardized field sobriety tests that is have the driver get out of the car walk a straight line heel to toe, or conduct what we call the one leg stand keeping one leg raised while counting to 30. If the officer still thinks there's a good chance that, that individual is impaired the officer normal will carry a portable breath test device and will administer a quick breath test to that individual. If that individual registers a reading greater than .08 percent in all states in the U.S. that driver will then be arrested taken back to the police station where more extensive testing will be conducted.
What methods does a forensic toxicologist use to test blood-alcohol level?
There are two ways of testing an individual for blood-alcohol content. There is a test by breath and there is a test by blood. If the latter is the test of choice, the blood sample will be collected from the individual and sent to the forensic laboratory where it is analyzed by gas chromatography for the presence of alcohol . The gas chromatograph is an instrument that separates the alcohol from other constitutes that may be present in the blood and makes for the identification of alcohol and at the same time quantifies what tells us the amount of alcohol that was present in the blood. So, it is the gas chromatograph that is the key instrument for testing blood for its alcohol content in the toxicology laboratory.
How does a forensic toxicologist test hair for drugs?
When an individual takes a drug into his or her body, a portion of that drug becomes attached to the root structure of human hair. As time goes on, as the hair grows - and hair grows at the rate of about a half an inch a month - that drug remains embedded in the hair. At some point, a hair will be removed from the body if indeed we are interested in testing that hair for the presence of the drug. The hair will be extracted for drugs and tested by various analytical techniques that are available in the toxicology laboratory. The important thing to remember is that we can, we being the forensic toxicologist, detect the presence of drugs in the hair long after the intake of that drug. For example, if you have a hair length of five inches in length, that means that we can detect the hair up to ten months after intake.
What are common poisons a forensic toxicologist looks for in CSI?
Carbon monoxide, cyanide, and thallium are probably the more common non-drug poisons. I should add that these kind of toxic materials outside of carbon monoxide are not very common in today's day and age. Typically, forensic toxicologists will encounter drugs, particularly drugs of abuse when they're dealing with individuals who are suspected of overdosing.