BAC and BrAC are two methods used to measure the amount of alcohol in an individual’s system, each with its own advantages and limitations. Understanding the differences between Blood Alcohol Concentration (BAC) and Breath Alcohol Concentration (BrAC) is essential for both legal and practical purposes.
Let’s see the difference between the two and how they’re measured.
What is BAC?
Blood Alcohol Concentration (BAC) is a measurement that determines the amount of alcohol present in a person’s bloodstream. It is expressed as the mass of alcohol per volume or mass of blood, typically in grams of alcohol per 100 millilitres of blood.
BAC is typically used in pre-employment, during employment and for cause-based random tests. BAC can be measured through blood tests.
What is BrAC?
Breath Alcohol Concentration (BrAC) is a measurement that indicates the amount of alcohol present in a person’s breath. It is expressed as the weight of alcohol per volume of breath, typically measured in grams of alcohol per 210 litres of breath (g/210L).
BrAC is commonly measured using breathalysers. This method is widely used in roadside testing, workplace screenings, and other scenarios where quick and reliable results are needed.
BAC vs BrAC
BAC measures alcohol concentration in the blood, while BrAC measures alcohol level in breath. Let’s see how both of these are measured.
How Is BAC Measured?
When alcohol is consumed, it is absorbed into the bloodstream and can be measured as Blood Alcohol Concentration. This Blood Alcohol Concentration (BAC) can be measured through several methods, like blood tests, urine tests, and hair tests. The most direct and accurate method is a blood test, where a sample of blood is drawn and analysed to determine the amount of alcohol present in the bloodstream.
Typically, BAC is measured in grams of alcohol per 100 millilitres of blood expressed as a percentage. For example, a BAC of 0.05% means that there are 0.05 grams of alcohol in every 100 millilitres of blood.
How Is BrAC Measured?
When alcohol in the bloodstream comes in contact with the alveoli of the lungs, it can be exhaled out of the body in the form of breath. This Breath Alcohol Concentration (BrAC) is measured using breathalysers, which are devices designed to estimate the amount of alcohol in a person’s breath. When a person exhales or talks into a personal or workplace breathalyser, the device analyses the breath sample and calculates the alcohol content.
This is typically expressed in grams of alcohol per 210litre of breath (g/210L). This measurement can then be used to estimate BAC through a standardised conversion ratio.
Converting BrAC to BAC
It is possible to convert Breath Alcohol Concentration (BrAC) to Blood Alcohol Concentration (BAC) by using a standard conversion ratio, reflecting the relationship between the concentration of alcohol in a person’s breath and blood. The commonly accepted ratio is 1:2100, meaning that 1 millilitre of blood contains the same amount of alcohol as 2100 millilitres of breath.
For example, if a breathalyser measures a BrAC of 0.25 g/210L, it can be estimated as a BAC of approximately 0.012%%. This is just an estimate, as factors like individual metabolism and physiology can influence the precise BAC. Still, this conversion is widely used in legal and clinical contexts and the 2100:1 ratio remains a reliable standard for converting BrAC to BAC.
What Can Impact BAC Results?
Some factors can impact Blood Alcohol Concentration (BAC) results, these are:
- Body Weight and Composition: Alcohol is distributed throughout the body’s water content. So people with higher body weight typically have lower BAC levels after consuming the same amount of alcohol as a person of lower body weight.
- Gender: Men and women process alcohol differently due to variations in body composition and enzyme levels. Generally, women may have higher BAC levels than men after consuming the same amount of alcohol.
- Metabolism: People with a faster metabolism may see lower BAC levels because their bodies metabolise alcohol more quickly.
- Food Intake: Food with high-protein content can slow the absorption of alcohol, leading to lower BAC levels.
What Can Impact BrAC Results?
These factors can influence Breath Alcohol Concentration (BrAC) results:
- Breathing Pattern: Hyperventilating or holding one’s breath can cause fluctuations in BrAC readings, potentially leading to either lower or higher measurements.
- Residual Alcohol in the Mouth: Recently consumed alcohol or alcohol-containing products (such as mouthwash or breath sprays) can leave residual alcohol in the mouth, leading to temporarily elevated BrAC readings.
- Time Since Last Drink: Shortly after drinking, BrAC levels may be higher as alcohol is still being absorbed into the bloodstream. As the body metabolises alcohol, BrAC levels will decrease.
- Body Temperature: Higher body temperatures can increase the volatility of alcohol in the lungs, leading to higher BrAC readings. Conversely, lower body temperatures may result in lower readings.
- Health Conditions: Certain medical conditions, such as gastroesophageal reflux disease (GERD), can cause alcohol to travel back up the oesophagus, potentially affecting the accuracy of BrAC measurements.
Pros and Cons of BAC
Pros of BAC
- Accuracy: BAC offers a direct and precise measurement of alcohol in the bloodstream, making it highly reliable.
- Legal Standard: Widely recognised in legal settings, particularly for determining intoxication levels.
- Comprehensive: Provides detailed insight into current intoxication and can be measured through multiple methods
Cons of BAC
- Invasive: Requires blood samples, which are uncomfortable and need medical personnel.
- Delayed Results: Processing takes time, leading to slower availability of results.
- Costly: More expensive due to the need for specialised equipment and professional handling.
Pros and Cons of BrAC
Pros of BrAC
- Non-Invasive: BrAC is measured using breathalysers, making it quick and easy without the need for blood samples.
- Immediate Results: Provides instant feedback, ideal for on-the-spot testing like roadside checks.
- Cost-Effective: Less expensive compared to BAC testing, with no need for medical personnel or lab processing.
Cons of BrAC
- Less Accurate: BrAC is an estimate and may be less precise than BAC, with potential variability based on factors like breathing patterns.
- Environmental Sensitivity: Results can be influenced by external factors like temperature and humidity.
- Residual Alcohol: Recent alcohol consumption or use of alcohol-containing products can temporarily elevate BrAC readings, leading to false positives.
BAC vs BrAC: Which One Should You Choose?
The choice between BAC and BrAC depends on the specific requirements of your situation.
Choose BAC if precise blood alcohol measurements are necessary. BAC is the standard for determining intoxication levels and is recognised in court cases, which makes it the preferred method when definitive results are needed.
Choose BrAC for quick, non-invasive alcohol testing, particularly in settings like roadside checks, workplace screenings, or personal use. BrAC is convenient, cost-effective, and provides immediate results, which makes it ideal for situations where rapid assessment is required.
Legal Limit of BAC and BrAC In Australia
In Australia, the legal limit for Blood Alcohol Concentration (BAC) while driving is generally 0.05%. This means that drivers must have less than 0.05 grams of alcohol per 100 millilitres of blood. This limit applies to most fully licensed drivers.
For Breath Alcohol Concentration (BrAC), the equivalent legal limit is 0.25 mg/L, reflecting the standard conversion ratio of 2100:1 between BrAC and BAC.
However, stricter limits apply to certain categories of drivers:
Learner and Provisional Drivers (P-platers): Must maintain a BAC of 0.00%, meaning no alcohol is permitted in their system.
Drivers of Heavy Vehicles, Commercial Vehicles, and Public Transport: Also typically required to have a BAC of 0.00%.
FAQs about BAC and BrAC
Is BrAC and BAC the same?
BAC and BrAC are both units of measurements to measure the amount of alcohol present in one’s body. But both are different in the sense that BAC measures blood content in the blood, while BrAC measures blood content in the breath.
What is the ratio of the BrAC to the BAC?
To convert BrAC to BAC, the typical ratio is 2100:1 which means that 1 millilitre of blood contains the same amount of alcohol as 2100 millilitres of breath.
How is BrAC measured?
BrAC is measured using breathalysers. The candidate is asked to exhale or talk into the breathalyser, where the alcohol concentration in the breath is measured.
