An Introduction to Alcohol Screening Devices
The application of fuel cell technology
Counterpoint Volume 6: Issue 2 - Article 3 (April 2022)
An article for participants in the myCAMprogram
Jan Semenoff, BA, EMA
Forensic Criminalist
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Article information:2500 words (approximately 9-12 minutes)
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There have been significant advances in roadside alcohol screening technology over the last 40 years. New fuel cell devices offer an affordable and convenient way for officers at roadside to quickly determine a motorist's BrAC (Breath Alcohol Concentration). This article will introduce the general operation of roadside testers to provide an overview of what they are, how they should be used, and what limitations they have.
Fuel cell based breath alcohol analyzers
As we discussed in the article on fuel cells, these breath alcohol analyzers are known by many names:
- Roadside Breath Testers (RBTs)
- Portable Breath Testers (PBTs)
- Approved Screening Devices (ASDs)
- Passive Alcohol Screeners (PAS devices)
Regardless of what we call them, they are handheld devices that are used by the police, and daily by health & safety supervisors in workplaces where alcohol use must be strictly controlled.
Figure 1 - The Intoxilyzer SD-5
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Most screening devices are small, and fairly easy to operate. They function on battery power, and are calibrated according to the policy of the local governing policies. They don’t receive calibration checks during breath sampling, and as a result, the tests are conducted fairly quickly.
Most modern handheld screening devices operate using electrochemical fuel cells that contain a pair of platinum electrodes. From a chemical point of view, the ethanol introduced into the fuel cell is converted to acetic acid, producing a fixed number of free electrons per molecule of ethanol in the process.
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When a breath sample is introduced into the fuel cell, a small electrical current is generated. The current generated is directly proportional to the amount of ethanol in the sample. The greater the concentration of ethanol, the greater the amount of current generated.
From the fuel cell sensor, the current is fed to an electronic amplification system, and from there to a digital display.
Operating principles
The units are ready for use almost immediately following power-up. The start up sequence for most modern police roadside testers are within just a few seconds of pressing the power-on button. A sterile disposable mouthpiece is placed on the unit, appropriate directions given to the test subject, and a sample obtained. The reading is then displayed within a few seconds. A decision can then be made whether or not to release the motorist, suspend the license, or proceed with a criminal demand for an evidentiary sample.
Figure 2 - The flow indicator "FLO" on the Intoxilyzer SD-5.
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The unit must receive a sample with sufficient pressure to activate a pre-set pressure transducer. This pressure switch, or breath pressure flow sensor, is in place to ensure that the subject is blowing hard enough to ensure a sample of deep lung alveolar air is obtained. Once the pressure switch has been activated, a timing circuit is engaged that ensures the subject has blown long enough to obtain that sample of deep lung air.
Some units emit an audible tone when the test subject is blowing hard enough to activate the pressure transducer. Others show a light, or a digital display indicating "FLO", as shown here on the Intoxilyzer SD-5. If the test subject's breath flow drops below the minimum threshold, even momentarily, the tone and display will stop, and the unit will reset itself to accept another sample attempt.
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So, in general, two conditions must exist:
- The subject must be blowing forcefully enough to activate the pressure switch, and
- Sustain that amount of expiration for the full duration of the sample cycle.
Some very small statured people have difficulty in providing a sustained expiration for the full 5 seconds but have reached taper and are therefore providing deep lung air. However, even though they are actually expelling deep-lung air, they PBT does NOT recognize this situation because the defined parameters of the device itself have not been met. These individuals may be improperly charged with refusing a breath test. As an example, some individuals who suffer from Chronic Obstructive Pulmonary Disorder, COPD, or Asthma, are unable to blow long enough and hard enough to provide the required sample volume. See the article on COPD.
It should be noted that the officer could override this test requirement. If, in the opinion of the operator, the subject has provided a full expiration, and is presently delivering deep-lung air, the operator may capture the air sample prior to the timing sequence being completed. However, this "manual capture" feature is NOT available on all roadside testers, so you just have to know which device is being used in your jurisdiction, and the features it has... or doesn't have.
If no ethanol is present in the subject’s expiration, the unit is available for an immediate re-test, as the fuel cell is already at zero voltage. Unless the BrAC obtained is very high, the unit should be ready to clear itself of residual ethanol on the fuel sensor and analyze a second sample within a minute or two, depending upon the previous BrAC level.
The breath sampling system
The instruments are often controlled by an onboard microprocessor, and are easy to operate. The analytical functions, including the breath sampling procedure, are completely automated in most devices, and do not require operator input. More importantly, neither the operator nor donor can influence the readings and analysis of the sample.
When the subject provides a sample through the disposable mouthpiece, the flow rate is monitored using the breath pressure flow sensor. The pressure output of the donor is compared to their exhalation time by a microcontroller which measures five seconds of exhalation.
Once the donor has blown hard enough to activate the breath pressure flow sensor, and long enough for the five second timing circuit, the microcontroller activates a solenoid in the sampling system. This solenoid draws in a fixed volume of sample air (the only other other variable) from the mouthpiece and passes it directly into the fuel cell. The volume of air is typically about 1 millilitre. This is smaller than a cube of sugar.
It should be noted that the minimum sampling conditions are factory-defined, and can only be written into the instrument’s memory by someone who has access to the necessary software.
Figure 3 - The Intoxilyzer SD-2 requires a manual capture of the breath sample.
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Figure 4 - The operator keeps their finger on the READ button until the maximum BrAC reading has registered.
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On some older handheld units, like the Intoxilyzer S-D2, the microcontroller does not activate a solenoid automatically, but indicates by a light that the operator may capture the sample manually. A button is pushed, and a known-volume sample captured and analyzed.
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Officers are typically taught to allow the device capture the sample of air or when indicated to capture by the light. Once the subject begins to taper off their exhalation, it is assumed that deep lung air is being obtained. The sample is captured and subsequently analyzed for the presence of ethanol.
Obtaining a breath sample
Figure 5 - The Intoxilyzer Model 400
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To illustrate how a breath sample is obtained, we will use the Intoxilyzer Model 400 as an example. Most units will operate in a similar fashion. Pressing and releasing the ON-OFF switch turns on the roadside screener. At this point, indicator lights begin to scroll, followed in turn by the individual bar segments on the digital display. Then a beeper activates. These start-up tests are done to indicate to the operator that all digital display, indicator lights, and audible notification components are working correctly. Once the breath test sequence has begun, the ON-OFF switch is inhibited, and cannot be turned off.
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At the end of the scrolling display check, the “Wait” light is activated, and the sampling system draws in an air sample. This constitutes an ambient air check. The current time and date may displayed, and the instrument software does an internal check of the fuel cell sensor to purge any residual ethanol from previous samples. As well, if the fuel cell is too cold, the instrument will automatically heat the sensor to the workable temperature range.
The “Wait” light continues to show until the fuel cell is completely purged of residual ethanol, and the minimum operating temperature has been reached. During this readying phase, it is not possible to obtain a breath sample from the subject as the breath sampling system is inhibited.
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Figure 6 - The WAIT light indicates the Intoxilyzer 400 is warming up, purging any residual alcohol, and getting ready to accept a breath sample.
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The operator should be observing the instrument throughout this readying phase to ensure:
- The instrument is functioning correctly
- The indicator digital segments are all working, and
- That no low battery indicators or error messages are displayed.
Figure 7 - When the READY light comes on, the unit is capable of accepting a breath sample.
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When the appropriate conditions are met, the “Ready” light comes on, also indicated by an audible tone. The unit may or may not display the instrument’s test number, depending upon the setup of the instrument.
As soon as the “Ready” light comes on, the instrument is ready to accept a breath sample from the donor. The operator should use a fresh and sealed mouthpiece and attach it to the instrument in such a way that the operator’s fingers don’t touch the mouthpiece end.
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The operator should then carefully remove the wrapper from the blowing end, and offer the blowing end to the subject with the appropriate explanations. Often, the wrapper is retained by the operator as a sanitary means of getting the mouthpiece off the instrument and discarded without contacting the mouthpiece itself.
Different instruments use different size mouthpieces, which are not typically interchangeable. In general, they are designed to offer minimal resistance to breath flow, while generating the small positive pressure necessary at the breath sampling port for a sample capture.
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Figure 8 - The officer should place the mouthpiece on the device without touching the lipped end.
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Figure 9 - The "lipped" end (left), and the "restricted" end (right).
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The positive-pressure effect in many breath testers is achieved by making the exhaust side of the mouthpiece a slightly narrower diameter than the lipped blowing side. It is essential that the donors are offered the correct side when delivering a sample.
If the donor blows through the exhaust end, no positive pressure will be developed, and the pressure transducer and timer circuitry will not be activated. The donor may appear to be blowing sufficiently but the instrument will indicate that the subject is not providing a suitable sample.
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It is also essential that a new mouthpiece be used for each breath test. Condensation from the exhaled breath can form on the inside of the mouthpiece and cross-contaminate subsequently obtained samples. Health concerns also make it imperative that only a new sealed mouthpiece is used for each donor.
Qualified roadside screeners are generally instructed to ask the donor subjects when they last ingested anything by mouth, whether alcohol, food, or tobacco products. Remember that some medications contain ethanol. Foods, even “non-alcoholic” foods or beverages may contain trace amounts of ethanol that would render the testing process invalid.
If the subject has consumed anything, most manufacturers of breath alcohol testing instruments recommend a minimum delay in testing of about fifteen minutes before taking a breath sample. However, I rarely see this in practice. Often the tests are done within minutes of the vehicle stop.
Even though it is generally considered that a 10-12 minute wait will disperse traces of fresh mouth ethanol, other variables exist. Traces of alcohol may be present on the subject’s dentures or dental work. Breath sprays, applied at the moment of the vehicle stop, may also contain ethanol. Some gums have soft “squirting” centers. Some cough drops also contain soft cough-medicine type centers. Some cough medicines contain ethanol.
Keep in mind that fuel cell devices can not employ any sort of residual alcohol detection system. They cannot determine if mouth alcohol contamination from burping or recent consumption is present. In practical applications, the 15-20 minute waiting period is often done only if the subject has indicated, or the officer has reason to suspect, recent consumption of any substance.
Most units can obtain readings in the 0 - 0.400 grams/100mL range (From no ethanol to levels approaching fatal alcohol toxicity. Some can read up to 0.650 grams - Well beyond the level of alcohol toxicity).
Some units are able to provide the breath test reading as a numerical result (i.e. - 0.081 g/dL). Others use PASS, WARN, and FAIL lights to indicate a general range of the breath reading:
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In some jurisdictions the BrAC readings generated by these devices are considered evidentiary results that may result in criminal prosecution. The units must be able to print out the results, and have a timing circuitry that locks out testing during a deprivation and observation period.
Many units have an onboard memory to store the results of the last 150 tests or so, which can be downloaded to provide date, times, and breath data for statistical analysis. The actual operating software of the instrument is written into non-erasable Read Only Memory, and cannot be modified.
Limitations of fuel cell technology
Typically, the training program for police officers in the use of roadside screening devices is between 2 - 8 hours in duration. Although the instruments are generally fairly easy to use, they are by no means fool proof (because fools are rather ingenious.) Because of the lesser degree of training of roadside testers and the need to continually calibrate the instruments themselves, most jurisdiction only allow them to be used as preliminary ethanol screening devices.
Also, fuel cells are will drift over time as their electrolytic solution is depleted and must therefore be routinely recalibrated.
Typically, the training program for police officers in the use of roadside screening devices is between 2 - 8 hours in duration. Although the instruments are generally fairly easy to use, they are by no means fool proof (because fools are rather ingenious.) Because of the lesser degree of training of roadside testers and the need to continually calibrate the instruments themselves, most jurisdiction only allow them to be used as preliminary ethanol screening devices.
Also, fuel cells are will drift over time as their electrolytic solution is depleted and must therefore be routinely recalibrated.
Practice Tip: |
From a practical standpoint, the modern fuel cell based breath alcohol testers are fairly reliable. However, when they fail, they do so without warning, and often over a short time period. When fuel cells are at the end of their serviceable life, they have tendency to provide wildly inaccurate readings, both far below and far above the "true" BrAC level. As such, those maintenance and calibration records, along with the daily logs, are important clues that establish the reliability, or lack of reliability, of the readings obtained.
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