7-minute read
Whether you’re a seasoned drinker or not, we often hear the term BAC when discussing the effects of alcohol on the body or on activities such as walking, driving, cycling or sobering up. But what does it mean, how do we measure it, and what else should we know about our ABCs BACs?
What does BAC mean?
BAC, which stands for Blood Alcohol Concentration, refers to the amount of alcohol in a person’s bloodstream.
The C in BAC is often mistaken to stand for the word content rather than concentration, which is incorrect since the same amount (content) of alcohol could present differing BAC levels in two individuals. This occurs for several reasons, but let’s use the example of a male and a female with comparable body weights to explain this.
Example: A male and a female, weighing the same amount, drink one standard drink of the same alcohol over the same amount of time and at the same rate. 1
Despite this similarity, the female, compared to her male counterpart, will present a higher BAC reading than the male. This occurs mainly due to three significant differences between males and females:
- Enzyme levels: Gastric alcohol dehydrogenase – the enzyme that triggers the metabolisation of alcohol in the stomach and helps break down roughly 15% of alcohol consumed – is found in higher concentrations in men than in women.
Males have approximately 50% more of this enzyme in their body, meaning that by the time alcohol has reached the small intestine for further absorption, there is less of it left to be absorbed in the stomach of men when compared to women.
This difference in enzyme levels will increase a woman’s BAC by approximately 7% higher than the man’s in this example.
- Percentages of body fat and muscle differ between men and women: Men are generally larger than women and have a greater ratio of muscle to fat. On the other hand, women naturally have a higher percentage of body fat than men. Blood flows through muscles in higher amounts than it does in fat, meaning that alcohol becomes more diluted in a man’s body due to the greater blood volume. In other words, the consumption of the same standard drink will present more concentrated in a woman’s bloodstream than a man’s.
- Percentages of water volume in the body: This goes the same for water volume in the body, with a woman’s body being composed of approximately 45-50% water compared to a man’s 55-65% water. In this case, the lower amount of fluid results in higher concentrations of alcohol in the bloodstream of women.
This is just one example of the ways that the same amount of alcohol can present a different reading in two individuals, which is why, rather than measuring how many drinks a person has had, a BAC determines how intoxicated an individual is and the effects alcohol may have on them 2.
How does BAC increase?
An individual’s Blood Alcohol Concentration will increase if one drinks faster than the body’s liver can process the alcohol. As a standard guideline, it takes your liver one hour to process one standard alcoholic drink. Alcohol processing after that differs, with this rate continuing for males and females processing subsequent drinks every two hours.
How is BAC measured?
There are a variety of methods used to measure BAC, such as:
- Blood Tests: These tests measure alcohol content directly from blood and are often considered more accurate and reliable than other test methods. While testing meters that provide rapid results are available, they are not widely used. As a result, most BAC blood test samples are analysed in a lab, with results taking hours or days to obtain.
- Breathalysers: Breathalysers are the most common and widely used test method. They involve blowing into a machine that detects the alcohol concentration of exhaled air blown into the device. When this method is used, your breath alcohol concentration is measured.
- Saliva Tests: Saliva tests involve a testing strip that changes colour when exposed to saliva with alcohol. These tests provide a less accurate approximation of BAC levels when compared to blood and breath testing.
- Urine Tests: Used in scenarios where breath tests and blood tests aren’t possible, BAC urine tests are the most uncommon method used.
Note: When using personal devices such as breathalysers to measure your BAC, it is always important to take into account the calibration of the device, its accuracy and margin of errors. If you have alcohol in your system, it is best to travel home by means other than driving.
BAC and Driving
When the police pull over a driver for a random alcohol breath test, breathalysers are often used. In Australia, the legal BAC limit a driver can have depends on their licence type and territory; however, in general:
- Learner and provisional licenced drivers must have a 0.00% BAC if driving
- Full-licenced and all other drivers must be under 0.05% BAC
If you are a truck or heavy vehicle driver, carry dangerous goods, or drive a public vehicle, your limit can be one of two BACs depending on the state or territory you drive in:
- 0.02% BAC if you drive a heavy vehicle with a GVM of over 13.9 tonnes
- 0.00% BAC if you drive a heavy vehicle with a GVM of over 4.5 tonnes
Part of the Five Fatal Factors, 30% of road fatalities can be attributed to drink-driving, with drivers of such collisions reported to have a legal limit of over 0.05% at the time of the crash 3
Effect of Alcohol on the body at different BACs
Alcohol tolerance and biological factors such as age, sex, weight and height will affect how quickly one’s BAC rises over time. Additionally, the rate of alcohol consumption and whether food is consumed during or before a night of heavy drinking will also affect the onset of such symptoms 4.
While not a strict guideline, individuals may exhibit the following physiological effects at their respective blood alcohol levels:
| Blood alcohol level | Physiological effect |
| 0.01–0.04% | Lightheaded – Relaxed, sociable, warm sensation, minor impairment in judgment. |
| 0.05% | Legally Impaired – It is now illegal to drive at this BAC level as you are considered legally impaired. |
| 0.05-0.07% | Buzzed – Euphoric, more friendly/talkative, lowered inhibition, minor impairment in judgement, reasoning and memory, and some motor skill impairment. |
| 0.08–0.12% | Very Impaired – Stimulant effects decline, mood swings begin, moderate to significant impairment of driving skills. |
| 0.12–0.15% | Drunk – Motor function and judgment severely affected, staggered, or slurred speech, depressive effects pronounced, severe impairment of driving skills. |
| 0.15–0.2% | Very Drunk – Appears drunk, a strong state of depression – can intensify negative emotions, nausea, disorientation, and dizziness. Blurred vision, judgment, motor function and driving skills are further impaired. |
| 0.2–0.3% | Dazed or Confused – Likely to vomit, show signs of incontinence and alcohol intoxication, assistance required to walk, can blackout or lose consciousness, inadequate breathing. |
| 0.3 and above | Fatal – May fall comatose and could result in death. |
Why does your BAC matter?
Small amounts of alcohol can affect an individual’s concentration, judgment and motor function. Despite making one feel happy, alcohol is a depressant. It will slow the body down until it becomes difficult to perform activities you may be able to complete sober, such as driving.
When your own safety and the safety of others are involved, it’s important to come prepared with a Plan B when it comes to drinking and arranging your travels. Public transport with a sober friend, a designated driver or a rideshare are all viable options for getting home after a night out.
For more information 5 on BAC limits depending on where you live, your licence and what you drive, check out the table below:
BAC Alcohol Limits baded on Licence & Vehicle Type 5
| Vehicle/Licence Type | ||
| State/Territory | Drivers of cars, light trucks and motorcycles |
Drivers of trucks, taxis, buses and private hire car |
| ACT | Zero BAC if you hold a:
Below 0.05 BAC if you:
|
Zero BAC if you drive
0.02 BAC if you drive:
|
| New South Wales | Zero Bac if you hold a:
Drivers not listed must have a BAC below 0.05 |
0.02 BAC if you drive:
|
| Northern Territory | Zero BAC if you hold a:
Or
Drivers not listed must have a BAC below 0.05 |
Zero BAC if you drive:
Or
Drivers not listed must have a BAC below 0.05 |
| Queensland | Zero BAC if you hold a:
Or
Drivers not listed must have a BAC below 0.05 |
Zero BAC if you drive:
Drivers not listed must have a BAC below 0.05 |
| South Australia | Zero BAC if you hold a:
Or
Drivers not listed must have a BAC below 0.05 |
Zero BAC if you drive:
|
| Tasmania | Zero BAC if you hold a:
Or
|
Zero BAC if you drive:
|
| Victoria | Zero BAC if you hold a:
Or
Drivers not listed must have a BAC below 0.05 |
Zero BAC if you drive:
|
| Western Australia | Zero BAC if you are a:
Drivers not listed must have a BAC below 0.05 |
Zero BAC if you drive:
Drivers not listed must have a BAC below 0.05 |
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