Breathalysers play a critical role in law enforcement and public safety, but how reliable are they when it comes to measuring blood alcohol content (BAC)? The accuracy of these devices depends on various factors, including the technology involved, maintenance routines, and external conditions. Here’s a detailed look at the reliability of breathalysers and the factors that can influence their precision.

How Do Breathalysers Work?

Breathalysers estimate BAC by analysing the alcohol content in a person’s breath. While they don’t directly measure blood alcohol levels, they provide an approximate reading based on the concentration of ethanol in the exhaled air. Breathalysers rely on three main technologies:

1. Semiconductor Oxide Sensors
   These affordable devices work by using a tin-oxide material that reacts with ethanol, altering the electrical conductivity of the sensor. While they are suitable for personal or low-volume professional use, they are less accurate than other models and prone to interference from substances like ketones in diabetic or fasting individuals.
2. Fuel Cell Sensors
   Commonly used by law enforcement for roadside tests, fuel cell breathalysers oxidise the ethanol in a breath sample to generate an electrical current. The higher the alcohol content, the stronger the current. These devices offer higher accuracy and are less likely to give false positives from non-alcoholic compounds. Their reliability makes them a top choice for professional-grade testing.
3. Infrared Spectrometry
   Used in large, stationary machines, such as those in police stations, this technology measures how ethanol molecules absorb infrared light. It’s highly effective at isolating ethanol from other substances in a breath sample, ensuring extremely precise readings.

Factors Affecting Breathalyser Accuracy

Although breathalysers can be reliable, several factors can impact their accuracy. Understanding these variables is essential for interpreting the results correctly.

1. Calibration and Maintenance

Regular calibration and routine maintenance are vital to ensuring a breathalyser’s reliability. A breathalyser relies on sensitive sensors, such as fuel cell or infrared spectroscopy sensors, to measure Blood Alcohol Content (BAC). Over time, these sensors can degrade or drift from their baseline accuracy, producing skewed readings. For example, a device that hasn’t been calibrated might consistently under-report or over-report BAC levels. To prevent such errors, manufacturers typically recommend calibration at regular intervals, often after a specified number of uses or within six months. Adhering to the maintenance protocols outlined by the device’s manufacturer, such as sensor checks and battery replacements, also ensures the equipment remains in optimal working condition. Ignoring these guidelines could severely compromise the accuracy and reliability of results, possibly leading to miscarriages of justice or unsafe situations on the road.

2. External Substances

Breathalysers are designed to detect ethanol, the type of alcohol found in drinks, but other substances can interfere with the readings. For instance, using mouthwash or breath-freshening sprays containing alcohol before a test can result in inflated BAC levels. Even small traces of residual alcohol left in the mouth after taking a sip of wine or beer, if not given enough time to dissipate, may affect results. Furthermore, individuals following ketogenic diets or those with diabetes may produce higher levels of acetone in their breath. Some breathalysers, particularly older models or those based on semiconductor technology, can mistakenly register acetone as ethanol. This could cause false positives, indicating intoxication when the individual has had no alcohol at all. Modern fuel cell breathalysers, however, are less prone to such errors, providing a more reliable reading in such situations.

3. Waiting Periods Before Testing

To mitigate the effect of residual mouth alcohol, law enforcement and regulatory standards often advocate for a 15-20 minute observation period before conducting a breathalyser test. This waiting period allows any traces of alcohol in the mouth to evaporate, ensuring the breath sample reflects the individual’s true BAC. Skipping this step can lead to artificially elevated readings, potentially incriminating individuals unfairly. For example, if someone rinses their mouth with an alcohol-based product shortly before being tested, their result could be significantly higher than their actual BAC. Ensuring that the waiting period is respected is a fundamental best practice in administering breathalyser tests.

4. Environmental Conditions

Environmental factors, such as temperature, barometric pressure, and humidity, can affect the performance of breathalysers. Extreme heat may cause internal components to overheat, compromising their functionality, while freezing conditions may reduce the sensitivity of the sensors or even damage the device. High humidity levels could introduce extra moisture into the sample, potentially diluting the concentration of ethanol in the breath and leading to underestimation of BAC. Modern breathalysers are designed to function within specified environmental ranges, making proper storage and handling critical. Devices used in professional settings are usually better equipped to cope with these factors; for instance, they may include internal mechanisms to regulate temperature. Hand-held personal devices, however, may lack these safeguards, rendering their usability unreliable in extreme conditions.

5. Breath Sample Quality

The quality of the breath sample plays a pivotal role in determining the accuracy of a breathalyser test. For a reliable reading, the device must capture “deep lung air,” the air expelled from the alveoli in the lungs, where alcohol content closely correlates with blood alcohol levels. If the individual provides a shallow breath or blows too weakly, the device may record lower-than-actual BAC levels because it is analysing air from the upper airway rather than deep lung air. Police-grade devices like the Intoxilyzer 8000 have advanced features to detect incomplete samples, alerting the officer when the test isn’t valid. Personal or cheaper breathalyser models may not have this capability, making them more prone to errors if the sample isn’t provided correctly. Training on how to use the device properly, combined with better technology, can drastically improve the chances of obtaining accurate results.

Additional Considerations

Beyond these factors, technological advancements have played a major role in improving breathalyser accuracy and mitigating common pitfalls. For instance, dual-sensor breathalysers combine two types of sensor technologies to cross-verify results, reducing the likelihood of discrepancies. Additionally, the growing use of AI and machine learning in modern devices allows for real-time error detection, further enhancing reliability.

It’s also worth noting that while breathalysers are a reliable tool for estimating BAC, they don’t directly measure the alcohol concentration in the bloodstream. External validation, such as blood or urine tests, remains the gold standard in confirming intoxication levels. However, when used correctly and maintained properly, breathalysers are a valuable tool for enhancing road safety and deterring drink-driving behaviours.

Best Practices for Ensuring Accurate Breathalyser Results

To maintain breathalyser reliability, certain best practices should be followed:

• Routine Calibration and Servicing
  Regular calibration is essential to ensure sensors function correctly. This involves testing the device with a gas of known alcohol concentration and adjusting it if required.
• Proper Use by Trained Operators
  Law enforcement officers and other users must be trained to operate breathalysers correctly. This includes recognising signs of potential inaccuracies, ensuring proper sample collection, and observing waiting periods.
• Choosing the Right Technology
  For law enforcement and professional testing, fuel cell and infrared spectrometry devices provide higher reliability compared to semiconductor models. Assessing the specific needs before investing in a device can improve overall accuracy.
• Following Environmental Guidelines
  Manufacturers often specify the ideal conditions under which their devices should be used. Adhering to these guidelines minimises environmental effects on the results.

Reliability in Practice

While breathalysers are indispensable for roadside screening and public safety, no device is flawless. Regular maintenance, correct operation, and awareness of potential limitations are key to ensuring breathalyser reliability. For accurate BAC measurements, confirmatory tests like blood analyses may sometimes be necessary, especially in contested legal cases.

By understanding the factors affecting breathalyser accuracy, law enforcement agencies, workplaces, and individuals can better interpret results and reduce the likelihood of errors. When used responsibly, breathalysers remain one of the most effective tools for promoting road safety and preventing drink-driving incidents.