Blood alcohol content

Blood alcohol content or blood alcohol concentration (abbreviated BAC) is the concentration of alcohol in a person's blood. BAC is most commonly used as a metric of intoxication for legal or medical purposes. It is usually expressed in terms of volume of alcohol per volume of blood in the body. That is a unit-less ratio commonly expressed as parts per million (PPM) or as a fractional percentage. That is a decimal with 2-3 significant digits followed by a percentage sign, which means 1/100 of the previous number (E.g. 0.820%). Since measurement must be accurate and inexpensive, several measurement techniques are used as proxies to approximate the true parts per million measure. Some of the most common are listed here: (1) Volume of alcohol per volume of exhaled breath (eg. 0.08 mL/L), (2) Mass per volume of blood in the body (Eg: 0.08 g/L), and (3) Mass of alcohol per mass of the body (Eg: 0.08 g/Kg).

The number of drinks consumed is a poor measure of BAC, largely because of variations in weight, sex, and body fat.

Effects at different levels

Unless a person has developed a high tolerance for alcohol, a BAC rating of 0.20% represents very serious intoxication, and 0.35%–0.40% represents potentially fatal alcohol poisoning.^[1] 0.40% is the accepted LD₅₀, the dose that is lethal for 50% of adult humans.^[2]

Units of measurement

There are several different units in use around the world for defining blood alcohol concentration. Each is defined as either a mass of alcohol per volume of blood or a mass of alcohol per mass of blood (never a volume per volume). 1 milliliter of blood is approximately equivalent to 1 gram of blood, 1.06 grams to be exact. Because of this, units by volume are similar but not identical to units by mass.

Legal limits

For purposes of law enforcement, BAC is used to define intoxication and provides a rough measure of impairment. Although degree of impairment may vary among individuals with the same BAC, BAC can be measured objectively and is therefore legally useful and difficult to contest in court. Most countries disallow operation of motor vehicles and heavy machinery above prescribed levels of BAC. Operation of boats and aircraft are also regulated.

Limits by country (BAC: Blood Alcohol Content)

The alcohol level at which a person is considered to be legally impaired varies by country. The list below gives limits by country. These are typically BAC (blood alcohol content) limits for the operation of a vehicle.

Zero tolerance, (It is illegal to have any alcohol in your blood while driving in these countries.)

Since there is always some amount of alcohol even in non-drinkers' bodies, they have to have some legal guidelines for determining what behavior is illegal. Often that guideline is something like impairment in driving to any degree that can be shown to be probably caused by recent alcohol consumption).

• Romania
• Saudi Arabia
• Slovakia
• United Arab Emirates
• Brazil
• Bangladesh
• Czech Republic
• Hungary
• Canada - new drivers undergoing graduated licensing in Ontario, Northwest Territories, Manitoba, Alberta, British Columbia and Nova Scotia

0.02%

• China
• Estonia
• Poland
• Norway
• Sweden
• Puerto Rico (for drivers 18-20 years old)^[7]

0.03%

• India (note: In the State of Kerala, a policy of zero tolerance has developed.)^[8]
• Japan^[9]
• Russia
• Uruguay^[10] (0.00% for truck/taxi/bus drivers)^[11]

0.04%

• Lithuania (0.02% for drivers in their first two years after gaining a driving license)
• Canada: Saskatchewan - provincial offense

0.05%

• Argentina (0.02% for motorbikes, 0.00% for truck/taxi/bus drivers)
• Australia (0.02% for Australian Capital Territory learner, probationary & convicted DUI drivers, 0.02% for truck/bus/taxi, 0.00% for learner drivers, provisional/probationary drivers (regardless of age) and DUI drivers in all other states)
• Austria
• Belgium
• Bulgaria
• Canada: British Columbia, Ontario, Manitoba, Newfoundland, Nova Scotia, Quebec - provincial offence
• Costa Rica^[12]
• Croatia
• Denmark
• Finland
• France (0.025% for bus drivers)^[13]
• Germany (0.00% for learner drivers, all drivers 18-21 and newly licensed drivers of any age for first two years of licence)
• Greece
• Hong Kong
• Iceland
• Italy
• Israel
• Latvia (0.02% for drivers in their first two years after gaining a driving license)
• Luxembourg
• Macedonia (0.00% for drivers in their first two years after gaining a driving license)
• Netherlands (0.02% for drivers in their first five years after gaining a driving license)
• Peru
• Portugal
• Serbia
• Slovenia (0.00% for drivers in their first two years after gaining a drivers licence, drivers under 21 and common drivers, such as buses, trucks...)
• South Africa
• Spain (0.03% for drivers in their first two years after gaining a driving license and common carriers, such as buses, trucks...)
• Switzerland
• Thailand
• Turkey

0.08%

• Canada^[14] - criminal offense
• Malaysia
• Malta
• Mexico
• New Zealand (0.03% for drivers under 20)
• Puerto Rico (for drivers 21 years and older)^[15]
• Ireland^[16]
• Singapore^[17]
• United Kingdom^[18] (0.02% for operators of fixed-wing aircraft)
• United States Drivers under 21 (the most common US legal drinking age), however, are held to stricter standards under zero tolerance laws. Adopted in varying forms in all states, these laws hold the driver to much lower BAC levels for criminal and/or license suspension purposes, commonly 0.01% to 0.05%. Many states have statutory regulations regarding driving while "under the influence" of an intoxicant and a different law for driving beyond the legal blood alcohol concentration. A large number of laws apply from Federal regulatory bodies, states, counties, and cities. For further information on U.S. laws restrictions on alcohol sales, see Alcohol laws of the United States by state. Federal Aviation Administration: 0.01% for operators of common carriers, such as buses, for pilots 0.019% to fly, .039 without loss of medical (no fly until .019 or below), .04 permanent revocation of license for pilots, no alcohol within 8 hours per Federal Aviation Regulations^[19]
• BAC measures and proxies (such as breath PPM and blood BAC measured as mass/volume) are commonly coded into the law to provide prima-facie cases (much like speed limits). A driver measured to be over the allowed BAC level has automatic penalties. But even below those levels, drivers can have civil liability and other criminal guilt. For example, in some state statutes (e.g, AZ), any driving impairment to any degree caused by alcohol consumption can be a civil or criminal offense in addition to other offenses at higher BAC levels.

Limits by country (BrAC: Breath Alcohol Content)

In certain countries, alcohol limits are determined by the Breath Alcohol Content (BrAC), not to be confused with BAC.

• In Greece, the BrAC limit is 25 microgrammes of alcohol per 100 millilitres of breath. The limit in blood is 0.50 g/l.
  • BrAC 25–40 = €200 fine
  • BrAC 40–60 = €700 fine, plus suspension of driving license for 90 days(introduced in 2007, ^[20])
  • BrAC >60 = 2 months imprisonment, plus suspension of driving license for 180 days, plus €1,200 fine
• In Hong Kong, the BrAC limit is 22 microgrammes per 100 millitres of breath (as well as other defined limits)
• In The Netherlands and Finland, the BrAC limit is 220 microgrammes of alcohol per litre of breath (μg/l, colloquially known as "Ugl").
• In Singapore, the BrAC limit is 35 microgrammes of alcohol per 100 millilitres of breath.^[17]
• In Spain the BrAC limit is 25 microgrammes of alcohol per 100 millilitres of breath and 15 for drivers in their first two years after gaining a driving licence and common carriers.
• In the United Kingdom the BrAC limit is 35 microgrammes of alcohol per 100 millilitres of breath (as well as the above defined BAC).

Other limitation schemes

• For South Korea, the penalties for different BAC levels include
  • 0.01–0.049 = No Penalty
  • 0.05–0.09 = 100 days license suspension
  • >0.10 = Cancellation of car license.
  • >0.36 = Arrest
  • Getting caught driving while drunk three times in five years; or twice in three years results in arrest.^{[citation needed]}

Also, operation of motor boats or other vehicles may have limits different from motor vehicles. For example, while cars driving requires <0.05‰ BAC, steering a motorboat requires a less stringent <.10‰ BAC.

Test assumptions

Blood alcohol tests assume the individual being tested is average in various ways. For example, on average the ratio of BAC to breath alcohol content (the partition ratio) is 2100 to 1. In other words, there are 2100 parts of alcohol in the blood for every part in the breath. However, the actual ratio in any given individual can vary from 1300:1 to 3100:1, or even more widely. This ratio varies not only from person to person, but within one person from moment to moment. Thus a person with a true blood alcohol level of .08 but a partition ratio of 1700:1 at the time of testing would have a .10 reading on a Breathalyzer calibrated for the average 2100:1 ratio.

A similar assumption is made in urinalysis. When urine is analyzed for alcohol, the assumption is that there are 1.3 parts of alcohol in the urine for every 1 part in the blood, even though the actual ratio can vary greatly.

Breath alcohol testing further assumes that the test is post-absorptive—that is, that the absorption of alcohol in the subject's body is complete. If the subject is still actively absorbing alcohol, their body has not reached a state of equilibrium where the concentration of alcohol is uniform throughout the body. Most forensic alcohol experts reject test results during this period as the amounts of alcohol in the breath will not accurately reflect a true concentration in the blood.

Metabolism and excretion

This article needs additional citations for verification. Please help improve this article by adding reliable references. Unsourced material may be challenged and removed. (May 2007)

Alcohol is removed from the bloodstream by a combination of metabolism, excretion, and evaporation. The relative proportion disposed of in each way varies from person to person, but typically about 92 to 98% is metabolised, 10% is excreted in urine^[21], and 1 to 5% evaporates through the breath. A very small proportion (less than 0.5%)^{[citation needed]}is also excreted in the sweat, tears, etc. Excretion into urine typically begins after about 40 minutes, whereas metabolisation commences as soon as the alcohol is absorbed, and even before alcohol levels have risen in the brain.

Alcohol is metabolised mainly by the group of six enzymes collectively called alcohol dehydrogenase. These convert the ethanol into acetaldehyde (an intermediate that is actually more toxic than ethanol). The enzyme acetaldehyde dehydrogenase then converts the acetaldehyde into non-toxic Acetic acid.

Many physiologically active materials are removed from the bloodstream (whether by metabolism or excretion) at a rate proportional to the current concentration, so that they exhibit exponential decay with a characteristic halflife (see pharmacokinetics). This is not true for alcohol, however. Typical doses of alcohol actually saturate the enzymes' capacity, so that alcohol is removed from the bloodstream at an approximately constant rate. This rate varies considerably between individuals; experienced male drinkers with a high body mass may process up to 30 grams^{[citation needed]}(38 mL) per hour, but a more typical figure is 10 grams (12.7 mL) per hour. Persons below the age of 25^{[citation needed]}, women, persons of certain ethnicities, and persons with liver disease may process alcohol more slowly. Many East Asians (e.g. about half of Japanese) have impaired acetaldehyde dehydrogenase; this causes acetaldehyde levels to peak higher, producing more severe hangovers and other effects such as flushing and tachycardia. Conversely, members of certain ethnicities that traditionally did not brew alcoholic beverages have lower levels of alcohol dehydrogenases and thus "sober up" very slowly, but reach lower aldehyde concentrations and have milder hangovers. Rate of detoxification of alcohol can also be slowed by certain drugs which interfere with the action of alcohol dehydrogenases, notably aspirin, furfural (which may be found in fusel oil), fumes of certain solvents, many heavy metals, and some pyrazole compounds. Also suspected of having this effect are cimetidine (Tagamet), ranitidine (Zantac), and acetaminophen (Tylenol) (paracetamol).

Currently, the only known substance that can increase the rate of metabolism of alcohol is fructose. The effect can vary significantly from person to person, but a 100g dose of fructose has been shown to increase alcohol metabolism by an average of 80%.^[22]

Alcohol ingestion can be slowed by ingesting alcohol on a full stomach. Spreading the total absorption of alcohol over a greater period of time decreases the maximum alcohol level, decreasing the hangover effect. Thus, drinking on a full stomach or drinking while ingesting drugs which slow the release of acetaldehyde, will reduce the maximum blood levels of this substance, and decrease the hangover. Alcohol in non-carbonated beverages is absorbed more slowly than alcohol in carbonated drinks.^[23]

Retrograde extrapolation

Retrograde extrapolation is the mathematical process by which someone's blood alcohol concentration at the time of driving is estimated by projecting backwards from a later chemical test. This involves estimating the absorption and elimination of alcohol in the interim between driving and testing. The rate of elimination in the average person is commonly estimated at .015 to .020 percent per hour, although again this can vary from person to person and in a given person from one moment to another. Metabolism can be affected by numerous factors, including such things as body temperature, the type of alcoholic beverage consumed, and the amount and type of food consumed.

In an increasing number of states, laws have been enacted to facilitate this speculative task: the BAC at the time of driving is legally presumed to be the same as when later tested. There are usually time limits put on this presumption, commonly two or three hours, and the defendant is permitted to offer evidence to rebut this presumption.

Forward extrapolation can also be attempted. If the amount of alcohol consumed is known, along with such variables as the weight and sex of the subject and period and rate of consumption, the blood alcohol level can be estimated by extrapolating forward. Although subject to the same infirmities as retrograde extrapolation—guessing based upon averages and unknown variables—this can be relevant in estimating BAC when driving and/or corroborating or contradicting the results of a later chemical test.

Blood alcohol content calculation

BAC can be roughly estimated using a mathematical approach. Mathematical BAC estimations can be useful for calculating a BAC level that is not currently testable, or a level that may be present in the future. While there are several ways to calculate a BAC, one of the most effective ways is to simply measure the total amount of alcohol consumed divided by the total amount of water in the body—effectively giving the percent alcohol per volume water in the blood.

Gender plays an important role in the total amount of water that a person has. In general, men have a higher percent of water (58%) than women (49%). This fact alone strongly contributes to the generalization that men require more alcohol than women to achieve the same BAC level. Additionally, men are, on average, heavier than women. The more water a person has, the more alcohol is required to achieve the same alcohol:blood ratio, or BAC level. Further, studies have shown that women's alcohol metabolism varies from that of men due to such biochemical factors as different levels of alcohol dehydrogenase (the enzyme which breaks down alcohol) and the effects of oral contraceptives.^[24]

It is not strictly accurate to say that the water content of a person alone is responsible for the dissolution of alcohol within the body, because alcohol does dissolve in fatty tissue as well. When it does, a certain amount of alcohol is temporarily taken out of the blood and briefly stored in the fat. For this reason, most calculations of alcohol to body mass simply use the weight of the individual, and not specifically his water content.

Recent cases of high blood alcohol levels

In November 2007, a driver was found passed out in her car in Oregon. A blood test showed her blood alcohol level was 0.550. She was charged with several offenses, including two counts of driving under the influence of an intoxicant, reckless endangerment of a person, criminal mischief and driving with a suspended license. Her bail was later set at $50,000 since she had several previous convictions for similar offenses.^[25][26][27]

In December 2007, a driver was arrested in Klamath County, Oregon after she was found unconscious in her car which was stuck in a snow bank with its engine running. Police were forced to break a car window to remove her. After realizing she was in alcohol induced-coma, they rushed her to the hospital where a blood test showed her blood alcohol level was 0.720. She reportedly was released from the hospital the next day.^[25][28] She was subsequently charged with drunk driving.^[29]

In July 2008, a driver was arrested after he ran into a highway message board on Interstate 95 in Providence, Rhode Island. A breath test showed his blood alcohol level was at 0.491 and he was raced to the hospital where he was sedated and placed in a detoxification unit. He was subsequently charged with driving while intoxicated and resisting arrest.^[30][31] He was later sentenced to one year probation, a $500 fine, 40 hours of community service and a one-year loss of his driver's license. The police later stated that his blood alcohol level was the highest they had ever seen for someone who hadn't died of alcohol poisoning.^[32] It was later estimated that the driver had consumed 10-14 drinks over the course of 1–2 hours.^[25], based on the standard levels of elimination which as documented previously can vary by up to 300%.

In December 2009, a South Dakota woman was found behind the wheel of a stolen car with a measured blood alcohol content of .708, almost nine times the state's limit of .08, thus becoming the highest recorded level of alcohol toxicity for the state. After she was hospitalized, she was released on bond and subsequently found the next day in another stolen automobile while under the influence.^[33]

Highest recorded blood alcohol level/content

In December 2004, a man was admitted to the hospital in Plovdiv, Bulgaria after being struck by a car. After detecting a strong alcohol odor, doctors at a hospital conducted a breath test which displayed the man's blood alcohol content at 0.914% Concerned that their equipment was malfunctioning, doctors also performed five separate lab tests, all of which confirmed the man's incredible BAC.^[34] The man was treated for serious injuries sustained in the crash but survived.^[35] There have been cases reported in which individuals have supposedly survived BACs of over 1% but only limited information is available.^[36]

In March 2009, a 45-year-old man was admitted to the hospital in Skierniewice, Poland after being struck by a car. The blood test shows blood alcohol content at 1.23%. The man survived. He did not remember either the accident or people he drank with.^[37]

Notes

References

• Carnegie Library of Pittsburgh. Science and Technology Department. The Handy Science Answer Book. Pittsburgh: The Carnegie Library, 1997. ISBN 9780787610135.
• Perham, N. R., Moore, S. C., Shepherd, J. P. & Cusens, B. (2007). "Identifying drunkenness in the night time economy". Addiction, 102(3), 377–380.
• Taylor, L., and S. Oberman. Drunk Driving Defense, 6th edition. New York: Aspen Law and Business, 2006. ISBN 978-0735554290.

External links

• Wisconsin DOT BAC calculator
• International Blood Alcohol Limits
• Blood Alcohol levels with practical exercises
• b4udrink.org developed by The Century Council in conjunction with University of Illinois, Urbana-Champaign
• Comprehensive International BAC (Blood Alcohol Content) Limits Prescribed legal driving limits for over 250 jurisdictions.