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How to Calculate Blood Alcohol Content

How to Calculate Blood Alcohol Content

Blood Alcohol Concentration (B.A.C) is a measure to calculate the amount of alcohol in your blood. The B.A.C limit in the US is 0.08% (This is calculated in percentage terms hence, it will indicate the alcohol percent in your blood.), which implies that if your B.A.C is 0.08% or above then it is illegal.
Foram Mehta
Last Updated: Apr 22, 2018
The minimum age limit to consume alcohol is 21, in the US and DUI - Driving under the influence of alcohol is considered as a zero tolerance crime. The reason why, there is a limit to alcohol consumption is because, it has a direct effect on the brain. Alcohol as consumed, rushes into your bloodstream and directly reaches the brain. This could lead to a Fetal Alcohol Syndrome or even accidents due to drunk driving.
The effect of alcohol at different levels of B.A.C is different. Blood alcohol content of 0.08% makes a person lose his balance, leads to impairment of memory and loss of self-control. If the B.A.C level reaches 0.25 in a person, he reaches a very critical stage where, his mental, physical and sensory functions are severely impaired. It is very dangerous to cross the blood alcohol level of 0.25 as it may lead to coma or even death.
Different Methods for Calculating B.A.C
1. Breath Alcohol Testing
This test is performed with the help of a device called Breathalyzer. It is a device which is used to determine the B.A.C using a breath sample. These are handheld devices which consumers can use on a regular basis. However the results are not 100% accurate, as it does not calculate the B.A.C directly but, based on the alcohol content found in the breath of the user.
How it works
When anyone exhales into a Breathalyzer, if ethanol is present, it gets oxidized to acetic acid at the anode.
The following is the chemical reaction:
CH3CH2OH(g) + H2O(l) → CH3CO2H(l) + 4H+(aq) + 4e-
Now, the atmospheric oxygen is reduced at the cathode.
O2(g) + 4H+(aq) + 4e- → 2H2O(l)
The reaction is of, oxidation of ethanol to acetic acid and water, which is as follows:
CH3CH2OH(l) + O2(g) → CH3COOH(l) + H2O(l)
Finally, the electric current passed is measured by a microprocessor and the alcosensor gives an approximation of the BAC.
Accuracy: Not reliable if the test is done hours after the consumption of alcohol.
2. Saliva Alcohol Testing
In this method of B.A.C testing, an oral fluid sample is collected and tested.
How it works
A Blood Alcohol Saliva test, basically involves using a test kit. The kit contains a cotton tipped absorbent strip. This strip is then to be moistened by running it through the mouth. Once this is done, a colored line moves up depending on the quantity of alcohol consumed. However this is not the best technique for detection as in a few cases, the effect stays only for a few hours and also adulteration products are easily available.
Accuracy: 98% if tested at the right time.
3. Sweat Patches Alcohol Testing
In this method of testing, sweat patch samples of the suspect are collected using 'Sweat Test Kits' and are then tested. This is a very simple and a less expensive practice for detecting B.A.C.
How it works
Sweat patches are salt-impregnated absorbent pads. Here a person needs to wear the patch consistently for up to 2 weeks. The amount of ethanol collected on the patch indicates the amount of alcohol consumed.
Accuracy: 100%
4. Blood Alcohol Testing
In this method of blood alcohol testing, a blood sample is taken to measure the concentration of alcohol content in the blood.
How it works
To measure the blood alcohol content, Gas Chromatography is used to test the blood sample. This is the most common method used by forensic scientists. Its drawback is that, it is a time-consuming method of testing. Blood alcohol testing is one of the most expensive ones but the best way to test the blood alcohol content. This is generally used if the saliva or the breathing tests indicate that your blood alcohol is above 0.08%.
Accuracy: 100%
5. Urine Blood Alcohol Testing
In this method, a urine sample of the alcoholic is collected, and tests are conducted to check the amount of alcohol present. This is very similar to a blood test. However, this test is not very reliable as the alcohol consumed by a person, would pass out in the form of urine in just two hours. However, this is the most common test used by the highway agency's traffic officers.
Accuracy: Not reliable
6. Hair Alcohol Testing
This is the latest technique of testing B.A.C. This test is used in cases, where one wants to detect usage of alcohol or drugs over a period of time.
How it works
In this practice the hair sample is cut close from the scalp and is then tested. Approximately 100-120 hair strands are required for this test. The hair follicle normally covers a span of 30-90 days, hence this can be used to test the presence of alcohol and drugs, accurately. The hair follicle is not affected by foreign particles like bleach or dye, unless shaved. In this test, a series of assessments called FAEE, fatty acid ethyl esters and EtG, or ethyl glucuronide EtG alcohol tests are done to measure the amount of FAEE and EtG markers. These markers are only found in a person's hair, if he/she has consumed alcohol. The more alcohol a person has consumed, the more markers will be present. This test can help in clearly differentiating between non-drinkers, social drinkers and heavy drinkers. This method is relatively more expensive and time-consuming than other tests.
Accuracy: 100%
B.A.C tests are used by employers and cops, and even parents and colleges to monitor discipline so as to avoid health hazards and also by doctors for clinical purposes. These tests are also self used to monitor one's own B.A.C level. It is best to monitor your own B.A.C level when you are out of your state, to ensure that you are not breaking any law as the B.A.C limits vary from state to state between 0.05 to 0.08.
The punishment for driving under the influence of alcohol/drugs could be as severe as suspension of your license or arrest along with a huge fine. So the next time you plan to get drunk keep a B.A.C tester in your pocket!