What is a DUI-DWI Breathalyzer and how does it work?

Although regularly referred to as a DUI, in North Carolina, driving under the influence is defined as a DWI-driving while intoxicated. A breathalyzer is a device used to estimate blood alcohol content (BAC) from a sample of an individuals breath in order to establish evidence for a charge of DWI-driving while intoxicated. Although a generic name today, the original “Breathalyzer” was a brand name of a series of models designed to produce evidence for DWI’s that were manufactured by Smith and Wesson. Today, the most common brand names are the Intoxilyzer, Intoximeter, AlcoScan, Alcotest, AlcoSensor, Alcolizer, and Datamaster. The NHTSA (National Highway Traffic Safety and Administration) governs the Conforming Products List of breathylzers that are approved for evidentiary and preliminary screening use for DUI-DWI testing.

Analyzers do not measure actual blood alcohol concentration, which requires a blood sample. They only estimate BAC by indirectly measuring the alcohol from an individuals breath. A Charlotte DWI Lawyer should know that within testing, there are two common types of technology that are generally used: a Desktop tester that utilizes infrared spectrophometer technology, and electrochemical fuel cell technology. Hand held field sobriety devices are generally based on electrochemical fuel cell, and are used in field sobriety testing known as PBT (preliminary breath test), PAS (preliminary alcohol screening), or POA (point of arrest) testing.

Once an individual has blown into a device, a district attorney or commonwealth attorney may use this as evidence toward a defendant’s guilt for blowing a BAC of.08% or higher. Even though blowing a BAC of.08% or higher isn’t necessary to be convicted of a DWI, the breathalyzer reading will then be offered into evidence. Certain devices are admissible in court, while others are not. The SD-2 and the Alcosensor III are know as PBT’s (Preliminary Breath Tests) and are generally not admissilbe in court for the prosecution of a DWI, even though they are used to establish probable cause for an arrest. The Intoxilyzer 5000 is an example of a Evidentiary Breath Testing Device (EBT) used in Mecklenburg-North Carolina and surrounding counties, and is admissible in court as evidence toward a person’s intoxication for a DWI in Charlotte-Mecklenburg County.

Eventhough a breathalyzer’s reading may be admissible into court, a Charlotte DUI lawyer may be able to defend these readings by finding a common source of error. Competent Charlotte DWI lawyers know that breathalyzers can be very sensitive to certain variables such as outside temperature and a subjects temperature. If you choose the right Charlotte DWI Attorney, it should also be common knowledge that breathing patterns can also significantly affect test results. A common source of error that may occur happens when NC Law Enforcement or breathalyzer administrators fail to recalibrate in accordance to strict guidelines that governs officer training, instrument maintenance, and instrument calibration. Due to this, certain DWI-DUI agencies around the world such as the police in Victoria Australia factor in a 20% tolerance on readings.

Calibration differs in the type of device that is used for Mecklenburg County DWI’s. Most handheld devices use silicon oxides sensors to determine BAC. This requires proper software to calibrate the accuracy of the sensors, which deteriorate over time. However, as technology has advanced, many new models have self calibrating devices or sensors that are easily replaced to avoid calibration to take place in a North Carolina DWI lab.

A major problem with some older machines are that they identify ethenol known as ethyl alcohol that is found in liquor or alcoholic beverages as well as other substances that have a similar molecular structure. Some of these models pass a person being tested for a DUI-DWI through a solution of potassium dichromate that oxidizes the ethenol into a substance known as acetic acid that changes the color during the process. This color change is used to determine a persons BAC reading. A problem that can occur is due to potassium dichromate being a strong oxidizer that can cause numerous alcohol groups to oxidize by producing false positives for a result which is then applied as DWI evidence in North Carolina.

Competent Charlotte DWI Lawyers also know that other problems may arise from interfering compounds. The NHTSA (National Highway and Traffic Safety Association) has found that individuals that diet and are diabetic can have acetone levels that are hundreds and even a thousand times higher than found in an average person. Acetone is an example of a substance that has been found to be falsely identified as ethenol by some breathalyzers when testing for a DWI-DUI; however, most new machines now use filters that separate substances such as acetone.

An experienced Charlotte DUI Attorney knows that Homeostatice Variables are another factor that may cause a false reading due to breath machines assuming that individuals have a 2100 to 1 partition ratio when alcohol is converted in the breath to estimate alcohol in someones blood. By assuming that every individual has a 2100 to 1 partition ratio, a beathaylzer does not take into account that partition ratios can vary from 1300 to 1 all the way to 3100 to 1. If this is found it be true for an indiviual being tested for a DWI in Charlotte North Carolina by a police officer, an individual with a BAC of.07% and a partition ratio of 1500 to one may actually blow a reading of.10% which is above the legal limit of.08% by.02%. With this in mind, most individuals do have a 2100 to 1 partion ratio that was found in William Henry’s Law in 1803. Yet, certain studies have shown that up to 1.8% of the population may have a partition rate below 2100.

Probably the most common cause of producing a false reading is mouth alcohol. Machines that test for DUI and DWI’s assume that when someone is blowing, alcohol is coming from alveolar air, which comes deep from a persons lungs. However, alcohol may register in a device from the mouth, throat, or stomach. This is why certified DUI-DWI breathalyzer operators usually observe an individual for 15 minutes or more before administering a test in order to charge someone with driving under the influence.

Mouth alcohol can cause problems because it is not absorbed through the bodies stomach and intestine, which passes through the blood to the lungs. Due to this, a very small amount of alcohol in someone’s mouth, throat, or stomach may cause a much higher than normal reading.

Recent drinking, belching, burping and acid reflex are the main source of mouth alcohol. This is found when alcohol in the form of a liquid or gas rises up to the tissue in the esophagus or oral cavity. Dentures and individuals with Periodental disease can also trap alcohol in the mouth causing a false reading in a breathalyzer leading to a Driving While Intoxicated in Charlotte, North Carolina.

As discussed above, testing an individual too early for a DUI or DWI, while their body is absorbing alcohol may cause an inaccurate reading due to alcohol absorption lasting from 45 minutes to 2 hours. In the absorbtive phase, alcohol is not proportionaly distributed throughout the body, causing certain parts of the body to have a higher BAC than others.

Once an individual has blown, as noted above, this reading will be introduced into evidence during a trial for driving under the influence. To assist the district attorney in Charlotte DUI prosecution, evidence of Retrograde Extrapolation may be introduced. A Charlotte DWI Lawyer is normally required to explain this process, which attempts to provide the BAC back in time while an individual was driving by applying mathematical formulas known as the Widmark factor. Although this factor is highly criticized, it is just another reason why hiring a competent DUI-DWI Lawyer in Mecklenburg County North Carlina is necessary to your defense.

What North Carolina law calls the test

In North Carolina a breath test is a “chemical analysis”, which G.S. 20-4.01 defines as “a test or tests of the breath, blood, or other bodily fluid or substance of a person to determine the person’s alcohol concentration or presence of an impairing substance, performed in accordance with G.S. 20-139.1”. Breath, blood and urine are all chemical analyzes. A driver asked to give one of them has no statutory right to substitute another; what the driver does have is the separate right, dealt with below, to obtain an additional analysis.

The same section answers the objection that a breath instrument does not measure blood. Alcohol concentration is defined in two alternative units — “grams of alcohol per 100 milliliters of blood” or “grams of alcohol per 210 liters of breath” — so a breath figure is not treated in law as an estimate of a blood figure. It is a measurement expressed in its own statutory unit.

What the rules then decide is not whether the number may be mentioned in court but how much work it can do there. Under G.S. 20-139.1(b) the results of a chemical analysis “shall be deemed sufficient evidence to prove a person’s alcohol concentration” where the analysis was “performed in accordance with the rules of the Department of Health and Human Services” and the analyst held the permit the subsection requires. That is a rule about proof, and it is not the same as a rule about admissibility.

The roadside screening device and the evidentiary instrument are different in law

North Carolina treats the handheld device used at the roadside and the instrument used at the jail as two different things. The roadside device is governed by G.S. 20-16.3, which permits an officer to require an alcohol screening test in the circumstances that section specifies — reasonable grounds to believe the driver has consumed alcohol together with a moving traffic violation or a crash, or an articulable and reasonable suspicion of an implied consent offense where the driver has been lawfully stopped or otherwise lawfully encountered — and which provides that requiring the test does not in itself constitute an arrest.

The limit on that device is express. Under G.S. 20-16.3(d) what may be used is “the fact that a driver showed a positive or negative result on an alcohol screening test, but not the actual alcohol concentration result”, together with a refusal to submit to it, and it may be used in deciding whether reasonable grounds exist. The number itself is not evidence of the offense, and no screening test is a valid one under the section unless the device used is one approved by the Department of Health and Human Services.

What must be read to the driver before the evidentiary test

Before an evidentiary chemical analysis is administered in North Carolina, G.S. 20-16.2(a) requires the driver to be notified orally and in writing of a fixed set of matters. The first is that “you have been charged with an implied-consent offense”, that any test may be refused but that a refusal means the license “will be revoked for one year and could be revoked for a longer period of time under certain circumstances”, and that “an officer can compel you to be tested under other laws”. The notice continues: “the test results, or the fact of your refusal, will be admissible in evidence at trial”; the driving privilege “will be revoked immediately for at least 30 days” on a refusal or on a result at or above the figure that applies to that driver; and, after release, the person “may seek your own test in addition to this test”.

The notice also carries a right with a clock attached. The driver “may call an attorney for advice and select a witness to view the testing procedures remaining after the witness arrives, but the testing may not be delayed for these purposes longer than 30 minutes from the time you are notified of these rights”, and the same advisement adds that the test must be taken at the end of the 30 minutes even if no attorney has been reached and no witness has arrived. Whether that half hour was given, and when it began, is a question of fact that the district court can be asked to decide.

Two samples are required, and only the lower one is used

A single breath reading does not prove an alcohol concentration in North Carolina. G.S. 20-139.1(b3) requires “the testing of at least duplicate sequential breath samples”, and provides that the results of the analysis of all breath samples “are admissible if the test results from any two consecutively collected breath samples do not differ from each other by an alcohol concentration greater than 0.02”.

Where two samples agree within that tolerance, the statute then discards the higher figure: “only the lower of the two test results of the consecutively administered tests can be used to prove a particular alcohol concentration”. The requirement operates as a check on the instrument rather than as a concession to the driver, and declining to complete the sequence is not a way round it. The same subsection makes a refusal to give the sequential breath samples necessary for a valid chemical analysis a refusal under G.S. 20-16.2(c), and provides that a refusal to give the second or subsequent sample leaves the sample already given admissible.

Permits, Department rules and preventive maintenance

Whether a breath reading is deemed sufficient evidence of a person’s alcohol concentration turns on the two conditions in G.S. 20-139.1(b). The analysis must have been performed in accordance with the rules of the Department of Health and Human Services, and “the person performing the analysis had, at the time of the analysis, a current permit issued by the Department” authorizing that person to perform a breath analysis on the type of instrument used. Where either condition fails, what the State loses is the statutory shortcut to proving the number, not automatically the right to offer the evidence.

Outright inadmissibility is dealt with in a different place, and the statute hands it to the defense. Under G.S. 20-139.1(b2), where the defendant objects and demonstrates that “preventive maintenance procedures required by the regulations of the Department of Health and Human Services had not been performed within the time limits prescribed”, the results of the breath analysis are not admissible in evidence. The interval and the records that prove it are set by the Department’s rules, which is why the maintenance log for the particular instrument is routinely requested.

The observation period exists because of mouth alcohol

The minutes before a breath sample is collected in North Carolina are regulated. The Department’s rules in Title 10A, Subchapter 41B of the Administrative Code define an observation period as one during which a chemical analyst observes the person to be tested to determine that the person has not “ingested alcohol or other fluids, regurgitated, vomited, eaten, or smoked in the 15 minutes immediately prior to the collection of a breath specimen”. The same rule permits the analyst to observe while carrying out the operational procedures on the instrument.

The rule exists for the reason its wording implies: alcohol lingering in the mouth or brought up from the stomach is not the deep lung air the instrument is designed to sample. Whether the observation actually took place, who conducted it and what occurred during it are questions of evidence, and they are litigated in district court.

Refusing the instrument has consequences of its own

A wilful refusal in North Carolina is not a neutral choice. Where the Division receives a properly executed affidavit that the person wilfully refused, G.S. 20-16.2(d) directs revocation of the license for 12 months, “effective on the thirtieth calendar day after the mailing of the revocation order” unless the person requests a hearing in writing before that date. That revocation is administrative and does not depend on the outcome of the criminal charge.

The refusal is also evidence. The notice required by G.S. 20-16.2(a) tells the driver in terms that “the test results, or the fact of your refusal, will be admissible in evidence at trial”. A refusal case is therefore not a case without evidence of impairment; it is a case in which the evidence is the driving, the officer’s observations and the refusal itself. The pretrial civil revocation under G.S. 20-16.5 runs alongside it, because a wilful refusal is one of the findings that supports that revocation.

Blood, warrants and the right to an additional test

Where breath is refused or unavailable, North Carolina turns to blood, and one duty to seek a warrant is written into the statute for a defined category of case. G.S. 20-139.1(b5) provides that where a person charged with a violation of G.S. 20-141.4 refuses to give a blood sample, “a law enforcement officer with probable cause to believe that the offense involved impaired driving or was an alcohol-related offense made subject to the procedures of G.S. 20-16.2 shall seek a warrant to obtain a blood sample”. That duty belongs to that category of case; it is not a general rule that a warrant must be sought after every refusal on every impaired driving arrest.

A separate provision is permissive rather than mandatory. Where a person refuses a test under the section, G.S. 20-139.1(d1) allows any law enforcement officer with probable cause to compel a blood or urine sample without a court order if the officer “reasonably believes that the delay necessary to obtain a court order, under the circumstances, would result in the dissipation of the percentage of alcohol in the person’s blood or urine”. Whether the circumstances of a particular stop met that description is decided on the evidence in the individual case.

The driver has a countervailing right in the same section, and the assistance owed in support of it is narrower than the right itself. G.S. 20-139.1 provides that “nothing in this section shall be construed to prohibit a person from obtaining or attempting to obtain an additional chemical analysis”. Where the person “is not released from custody after the initial appearance”, the agency having custody “shall make reasonable efforts in a timely manner to assist the person in obtaining access to a telephone to arrange for any additional test”. That is a duty to give access to a telephone, not a duty to arrange, transport or pay for the test. An additional analysis speaks to the same period only if it is obtained close in time, because alcohol concentration changes hour by hour.

The reading is evidence, not the case

A breath result carries statutory weight in North Carolina. G.S. 20-139.1(a) makes “a person’s alcohol concentration or the presence of any other impairing substance in the person’s body as shown by a chemical analysis” admissible in evidence in an implied consent case, and where the conditions of subsection (b) are met the results are deemed sufficient evidence to prove the concentration. That is a rule of sufficiency, not a rule of conclusiveness. It relieves the State of having to prove the number by some other means; it does not stop the defense from attacking how the number was produced.

It works in both directions. A driver who submits to a blood analysis may under G.S. 20-138.1(a1) “use the result in rebuttal as evidence that the person did not have, at a relevant time after driving, an alcohol concentration of 0.08 or more”. And a low reading does not end the prosecution: the appreciable impairment route in G.S. 20-138.1(a)(1) is available whatever the instrument said.

Common questions

Written for North Carolina law and reviewed by David P. Sheehan, attorney, Charlotte. General information, not legal advice — see the disclaimer.

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