Breathalysers

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Breathalyser FAQs

It doesn’t matter how big or small you are, or how much alcohol you usually drink – everyone’s liver and metabolism are different and the only way to find out if you are fit to drive or work is with an accurate and reliable digital breathalyzer.

Many people choose to use a breathalyser to check if they still have alcohol in their system the ‘morning after’.

This depends entirely on your personal or company requirements. Do you want or need a police grade breathalyser? Is accuracy important to you? Do the results need to be evidential?

We have a wide variety of different breathalzyers to suit different needs – see our Help Me Choose page for more information.

A breathalyser measures the alcohol in your lungs by generating and measuring a small amount of electricity when the alcohol from the breath sample comes in contact with the sensor.

When you drink alcohol, it is digested in the stomach and passes through the stomach wall into the blood stream. Broadly speaking, neat alcohol (such as a straight whisky, for example) taken on an empty stomach is likely to enter the bloodstream more quickly than, say, a milk-based cocktail drink after a big meal. This does not mean you will become more intoxicated from the straight whisky – it’s just that the effect is likely to be felt more quickly.

Once in the blood stream, the alcohol flows round the body and generates the usual effects on the body and brain. As the blood passes through the liver, it is gradually filtered out from the bloodstream, reducing at each “pass” until there is no longer any residual alcohol in the body.

Alcohol also passes through the alveoli in the lungs. As you breathe, and oxygen passes into the bloodstream, some of the alcohol in your blood ‘evaporates’ into the air in your lungs. It is this alcohol that a breathalyser is designed to measure. This is why it is necessary to measure deep lung air when using a breathalyzer. It’s also why it is important not to drink within 15 minutes of testing – otherwise alcohol that remains in your mouth will be blown directly into the detector, at far higher concentrations than is the case from alcohol that has passed through the stomach, into the bloodstream, and into the air you breathe out. Clearly the concentrations are often very low and the sensors have to be very sensitive to detect the levels involved – hence why it is so important not to smoke or drink before using them and why obtaining an accurate and consistent sample of air is so important.

In short, police breathalyzers are considerably more accurate.

Police breathalysers have an accuracy of less than ±2%. Some personal breathalysers can be anywhere up to ±40%.

We can and do supply police-grade breathalyzers such as the Draeger 6820 to customers who require a high degree of accuracy and reliability for personal use, or simply want the best.

In recent years there has been a large number of personal breathalyzers introduced to the market. These devices generally make use of cheaper semi-conductor based sensors which estimate the concentration of the sample based upon one or two pre-calibrated points; typically 0.03% and 0.10% BAC. At these values they tend to be quite accurate, but away from their datum points the drift can be quite dramatic – anything up to 30-35% variance on cheaper models is not unusual. Semi-conductor breathalysers are dramatically cheaper; whereas a typical police breathalyzer costs upwards of £900, many semi-conductor devices sell for less than £50.

To get the most from your personal breathalyser, use it regularly to monitor the change in your level of intoxication, rather than looking at a single specific reading.

Always wait at least 15 minutes after drinking or smoking (or you risk damaging the sensor) and then test yourself, trying to blow steadily and consistently. Take 3 tests, each approximately 2 minutes apart and compare the readings. If one is substantially different to the other two, try once more. When you have three readings that are within a reasonable difference of each other, take an average and wait 30 minutes – then test again. Don’t be surprised if the reading is not exactly the same every time. Carry on testing every 30 minutes until you get a zero reading. You may well find that the reading initially INCREASES, between the first few tests and the next – this is because it takes time for the alcohol to be absorbed into the blood stream from your stomach. You will also probably find that the level does not drop by the same amount every half hour – and this is one of the main reasons for buying a breathalyser, to see how YOUR body reacts and how long it takes to absorb the alcohol. You can repeat the test the ‘morning after’ to ensure that the alcohol has left your system and you do not find yourself still over the limit.

You can use our guide to units of measurement to get some idea of how your readings compare, but if you intend to drive – do NOT drink! The only safe limit is zero.

There are many units of measurement available. The standard unit of measurement for breathalysers is microgrammes of alcohol per 100ml of breath, or µg/100ml.

The English and Welsh drink driving limit is 35µg/100ml.

Other units of measurement include:

  • mg/L
  • %BAC
  • milligrammes of alcohol per 100ml of blood or Promille
  • milligrammes of alcohol per 100ml of urine
µg/100ml mg/L %BAC Promille Urine
50 0.500 0.12 115 152
English/Welsh drink driving limit 35 0.350 0.08 80 107
Scottish drink drive limit 22 0.220 0.05 50 67
15 0.150 0.04 35 46
European commercial drink drive limit 9 0.090 0.02 20 28
Zero 0 0 0 0 0

England and Wales has the highest drink drive limit in Europe. The legal limit for alcohol levels in the body while in control of a vehicle in England and Wales is 35µg (microgrammes) of alcohol in 100ml of breath. This is also expressed as 80mg of alcohol per 100ml of blood or 0.08% BAC (Blood Alcohol Content).

Scotland reduced their drink drive limit to 22µg/100ml in December 2014 to bring them in line with most other European countries. This is also expressed as 50mg of alcohol per 100ml of blood or 0.05% BAC (Blood Alcohol Content).

Reading under this limit does not mean you are not impaired – the only safe limit is zero – and many people (including us) believe that the English and Welsh drink drive limit of 35 microgrammes is far too high to be in control of a vehicle.

For those involved in the transportation industry much stricter limits apply, but in principle aircrew, maritime and railway employees are all subject to a limit that is just one quarter of the above, 9µg/100ml.

See more information on European Drink Drive Limits.

In short, semi-conductor sensors can be triggered by substances other than alcohol. Fuel cells sensors are considerably more reliable and accurate but are more expensive. Fuel cell sensors are also much larger than a semi-conductor; the larger the sensor, the better it can produce the electrical current needed to detect levels of alcohol – giving more reliable and consistent results. The size of the AlcoDigital Platinum Lite fuel cell sensor is 30mm².

You will also find that fuel cell sensors are more durable – they can be used frequently while maintaining their strong levels of accuracy and with regular annual calibration, fuel cell sensors can last for years and years.

Initially, breathalysers were developed with a full cell sensor. In order to produce a more economic device for personal use, various semi-conductor based sensors have been developed; these use varying levels of software complexity to translate their readings into equivalent values such as BAC%, mg/l and microgrammes.

Semi-conductor based breathalyser sensors are more susceptible to drift (where the values produced gradually vary as the unit gets older or is used more), saturation/contamination (for example if the user has been smoking or drinking recently) and variations in temperature. However, for general personal use a semi-conductor sensor can produce some perfectly acceptable results, provided some margin of error is allowed by the user.

Semi-conductor based sensors also have a narrower range of sensitivity and are more complex to calibrate. For employers or enforcement agencies requiring a reliable and consistent reading over the full range of use, only professionally-approved devices with fuel cell sensors such as the AlcoDigital EON or Draeger 6820 are going to produce the required levels of accuracy and reliability.

Users should also bear in mind that the accuracy of a particular sensor quoted in the specifications has been measured under strict laboratory conditions immediately following calibration. Due to the variations described above, and particularly the limitations of sampling, it is unlikely that such specific accuracy is likely to be obtained on a repeatable basis by the user in a real world scenario. Sensor saturation with alcohol, or contamination with smoke during a test, can quickly destabilise the sensor software and lead to unreliable results. Anyone using a personal breathalyzer should leave a substantial margin of error and take into account general factors such as what and when they’ve been drinking. You cannot rely solely on a personal alcohol detector to determine your level of intoxication.

When alcohol comes in contact with the sensor, it generates a small amount of electricity. The electricity is measured and converted into the breathalyser reading.

For those with a technical interest, when the user exhales into the breathalyzer, any ethanol present in their breath is oxidized to acetic acid at the anode: CH3CH2OH(g) + H2O(l) →CH3CO2H(l) + 4H+(aq) + 4e- At the cathode, atmospheric oxygen is reduced: O2(g) + 4H+(aq) + 4e- →2H2O(l). The overall reaction is the oxidation of ethanol to acetic acid and water: CH3CH2OH(l) + O2(g) →CH3COOH(l) + H2O(l). The electrical current produced by this reaction is measured, processed, and displayed as an approximation of overall blood alcohol content by the breathalyzer.

UK Certified Breathalyzers assume that the subject being tested has a 2300-to-1 partition ratio in converting alcohol measured in the breath to estimates of alcohol in the blood. This measure is in direct proportion to the amount of grams of alcohol to every 1 ml of blood. However, this assumed partition ratio varies from 1300:1 to 3100:1 or wider among individuals and within a given individual over time. Assuming a true blood-alcohol concentration of .07%, for example, a person with a partition ratio of 1500:1 would have a breath test reading of .10% over the legal limit. Most individuals do, in fact, have a 2300-to-1 partition ratio in accordance with William Henry’s law, which states that when the water solution of a volatile compound is brought into equilibrium with air, there is a fixed ratio between the concentration of the compound in air and its concentration in water but it is important to appreciate that this ratio is constant at a given temperature; very few “personal” breathalyzers incorporate a temperature check in their software/hardware solutions. Breath leaves the mouth at a temperature of 34 degrees Celsius. To ensure that variables such as fever and hypothermia could not be pointed out to influence the results in a way that was harmful to the accused, most instruments are calibrated at a ratio of 2300:1, underestimating by 9 percent. In order for a person running a fever to significantly overestimate, he would have to have a fever that would likely see the subject in the hospital rather than driving in the first place. Thus, a machine using a 2300-to-1 ratio could actually overestimate the BAC. As much as 14% of the population has a partition ratio above 2300, thus causing the machine to under-report the BAC.

The temperature of the subject is very important, due to homeostatic variables. Breathalysers can be very sensitive to temperature and will give false readings if not adjusted or recalibrated to account for ambient or surrounding air temperatures.

Breathing pattern can also significantly affect breath test results. One study found that the BAC readings of subjects decreased 11-14% after running up one flight of stairs and 22-25% after doing so twice. Another study found a 15% decrease in BAC readings after vigorous exercise or hyperventilation. Hyperventilation for 20 seconds has been shown to lower the reading by approximately 32%.

On the other hand, holding one’s breath for 30 seconds can increase the breath test result by about 28%.

The National Highway Traffic Safety Administration (NHTSA) also found that dieters and diabetics may have acetone levels hundreds or even thousand of times higher than those in others. Acetone is one of the many substances that can be falsely identified as ethyl alcohol by some breathalysers. However, fuel cell based systems are non-responsive to substances like acetone.

A study in Spain showed that metered-dose inhalers (MDIs) used in asthma treatment are also a cause of false positives in breath machines. In general, evidential breathalysers such as the Draeger 6820 are highly resistive to such issues as they are specifically designed for testing an “unwilling” subject. This why a personal, semi-conductor type breathalyser should never be used for testing anyone other than the owner, who is well aware of anything they may have taken that could affect the result.

Products such as mouthwash or breath spray can ‘fool’ some breathalysers by significantly raising test results. Listerine mouthwash, for example, contains 27% alcohol.

A breathalyser is calibrated with the assumption that the alcohol is coming from alcohol in the blood diffusing into the lung, rather than directly from the mouth, so it applies a partition ratio of 2100:1 in computing blood alcohol concentration – resulting in a false high test reading.

To counter this, police officers are not supposed to administer a breath test for 15 minutes after the subject eats, vomits, or puts anything in their mouth. In addition, most instruments require that the subject be tested twice, at least two minutes apart. Mouthwash or other mouth alcohol will have somewhat dissipated after two minutes and cause the second reading to disagree with the first, requiring a retest.

An episode of the popular science show MythBusters tested a number of methods that supposedly allow a person to fool a breathalyzer test. The methods tested included the use of breath mints, onions, denture cream, mouthwash, pennies and batteries; all of these methods proved ineffective. The show noted that using items such as breath mints, onions, denture cream and mouthwash to cover the smell of alcohol may fool a person but since they don’t actually reduce a person’s BAC (Blood Alcohol Content), there is no effect on a breathalyzer test regardless of the quantity used.

Pennies supposedly produce a chemical reaction, while batteries supposedly create an electrical charge, yet neither of these methods affected the breathalyzer results.

The Mythbusters episode also pointed out another complication – it would be necessary to insert the item into one’s mouth (eat an onion, rinse with mouthwash, conceal a battery) to take the breath test and then remove the item – all of which would have to be accomplished discreetly enough to avoid alerting the police officer administering the test. It would likely be very difficult, especially for someone in an intoxicated state, to be able to accomplish such a feat! In addition, the show noted that breathalyser tests are often verified with blood tests, so even if a person somehow managed to fool a breath test, a blood test would certainly confirm a person’s guilt. However, it is not clear why a negative breath test would be verified by a subsequent blood test.

One of the most common causes of falsely high breathalyzer readings is the existence of mouth alcohol.

A breathalyser assumes is that the alcohol in the breath sample came from alveolar air (air exhaled from deep within the lungs). However, alcohol may have come from the mouth, throat or stomach for a number of reasons.

Passive testing devices are extremely susceptible to these issues. To help prevent mouth-alcohol contamination, certified breath-test operators are trained to observe a test subject carefully for at least 15-20 minutes before administering the test. Additionally, all professional breathalyzers require the subject to blow throw a tube or mouthpiece to produce a specific sample size from which the concentration is devolved.

The problem with mouth alcohol being picked up by the breathalyzer is that it was not alcohol absorbed by the stomach and passed through the blood to the lungs. In other words, the machine’s computer is mistakenly applying the partition ratio and multiplying the result. Consequently, a very tiny amount of alcohol from the mouth, throat or stomach can have a significant impact on the breath-alcohol reading.

Other than very recent drinking, the most common source of mouth alcohol is from belching or burping. This causes the liquids and/or gases from the stomach, including any alcohol, to rise up into the soft tissue of the oesophagus and oral cavity, where it will stay until it has dissipated. For this reason, police officers are supposed to keep a drink driving suspect under observation for at least 15 minutes prior to administering a breath test.

Mouth alcohol can also be created in other ways.

  • Dentures, for example, can trap alcohol.
  • Periodontal disease can create pockets in the gums which will contain the alcohol for longer periods.
  • Recent use of mouthwash or breath freshener containing fairly high levels of alcohol.

The only approved instrument currently available that is certified to detect mouth alcohol is the Draeger 7510, released in 2010.

The word ‘breathalyser’ was originally trade-marked by a US company better known for its guns; Smith & Wesson, but was later sold to European Company Dräeger and has become known as a general trademark for all such instruments. In the USA it was more common to spell the breathalyzer with a “z” and this has also become more common throughout the world.

The original breathalyzer was based upon a crystal-filled tube, with a bag to ensure a correct sample was taken and was introduced into the UK by Dräeger in 1967.  Several other manufacturers produced tubes without bags, however without the bag to determine a correct sample size the results were far too unreliable for law-enforcement use.

In 1979 Dräeger produced the first digital breathalyzer, allowing multiple tests to be carried out far more accurately.

Breathalyzers, like most things, come in all shapes and sizes. It is often difficult to know where to start when deciding what breathalyzer is right for you. For a start, what do all these different breathalyzer approvals mean – CE, FDA, Home Office, EN Approval?

Some may apply to your use of the breathalyzer more than others; some apply specifically to the breathalyzer accuracy and purpose  – please visit our Breathalyzer Product Approvals page for more information.

If you have any queries regarding the approvals relating to your device, please contact us.

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