Breath Test and Blood Alcohol Science in Massachusetts: The Alcotest 9510, the Regulations, and the Blood Rules

Every Massachusetts OUI case that includes a number, a 0.09, a 0.11, a 0.15, rests on chemistry, physiology, and a regulated machine. The number reaches the jury only if the machine worked, the operator followed the regulations, and the sample measured what the Commonwealth says it measured, and each of those premises can be tested. This page explains the science behind breath test and blood alcohol evidence in Massachusetts: how the Alcotest 9510 measures alcohol, what the test sequence regulations require, how alcohol moves through the body, why the timing of a test matters, and how blood results reach a courtroom. The companion page on Massachusetts breathalyzer defense covers the litigation built on this science, and the firm’s OUI and DUI defense page covers the offense itself.

The Legal Framework for BAC Evidence in Massachusetts

Massachusetts prosecutes operating under the influence on two theories under G.L. c. 90, § 24 (1) (a) (1): a per se theory, that the defendant operated with a blood alcohol percentage of 0.08 or greater, and an impaired ability theory, that the defendant operated while under the influence of intoxicating liquor. Blood alcohol content can be measured by a breath test or a blood test, G.L. c. 90, § 24 (1) (e), and in practice the breath test is the more common of the two. For a breath test to be valid, G.L. c. 90, § 24K requires that it be performed by a certified operator using a certified infrared breath-testing device, and the statute directs the Secretary of Public Safety to promulgate regulations on the methods, techniques, and criteria for the tests, to run a statewide training and certification program for operators, and to provide for periodic certification of the devices. Those regulations are found at 501 CMR 2.00, and they are examined section by section below, because a test that does not comply with them is a test the defense can attack.

How the Alcotest 9510 Measures Breath Alcohol

The device used in Massachusetts is the Draeger Alcotest 9510. It is a dual-sensor instrument: it measures the same breath sample two different ways, by infrared absorption and by an electrochemical fuel cell, and it compares the results. The Supreme Judicial Court described the technology in detail in Commonwealth v. Camblin, 471 Mass. 639 (2015), a case about the Alcotest’s predecessor, and the principles carry forward to the 9510.

Infrared Absorption

The infrared measurement rests on a principle of physical chemistry: molecules absorb electromagnetic radiation, and only radiation of certain wavelengths will be absorbed by a molecule of a given compound. The device shines infrared light through the breath sample chamber. Ethanol molecules in the sample absorb part of that light, so less light reaches the detector than the source emitted, and the device computes the alcohol concentration from the difference. When a valid test occurs in Massachusetts, the infrared reading, not the fuel cell reading, is the measurement used to report the result. Camblin, 471 Mass. 639.

The Electrochemical Fuel Cell

The second sensor is an electrochemical fuel cell. Electrodes in the cell oxidize the alcohol in the breath sample, and the oxidation creates an electric current. The current is proportional to the alcohol content of the sample, and the cell’s sensors measure it. The fuel cell serves as a check on the infrared measurement rather than as the reported result.

The Tight Agreement Requirement

For the device to produce a result, the infrared and fuel cell readings must be in tight agreement with one another. If the two readings do not agree, the test aborts. The manufacturer’s position, described in the Camblin record, is that the two technologies together make the instrument specific to ethanol even though neither sensor alone is: an interfering substance that affects the two sensors differently produces disagreement, and disagreement ends the test. Whether the design accomplishes that in every case was contested by the defense experts in Camblin, and that contest is discussed below.

The Regulated Test Sequence Under 501 CMR 2.00

The Secretary’s regulations translate the statute into a step-by-step procedure, and every step generates a record the defense can demand.

The 15-Minute Observation Period

Under 501 CMR 2.13, the breath test operator must observe the arrestee for no less than 15 minutes immediately before the test. The purpose is to ensure that nothing enters the mouth, because residual alcohol in the mouth, rather than alcohol in deep lung air, inflates a reading. If anything is introduced into the mouth during the period, the 15 minutes must restart. If the device itself reports the presence of mouth alcohol, the test sequence ends and the observation period begins again. An observation period conducted from the front seat of a cruiser while the officer drives, or cut short at the station, is a recurring and productive subject of cross-examination.

The Two Breath Samples and the Control Standard

Under 501 CMR 2.14, a valid breath test sequence consists of one adequate breath sample analysis, one control standard analysis, and a second adequate breath sample analysis. The two breath samples must agree within plus or minus 0.02 blood alcohol content units; if they do not, a new sequence must begin. The control standard is a sample of known alcohol concentration run between the two breath samples to confirm that the device is measuring accurately at the time of the test. The sequence must be administered by a certified operator on a certified device. Each element leaves a paper trail: the printed test record, the control standard lot, and the device’s calibration and certification history.

Certification of the Device and the Operator

Section 24K assigns the certification work to the Office of Alcohol Testing, the state laboratory known as OAT. OAT certifies devices periodically, maintains their calibration records, and trains and certifies operators. The reliability of OAT’s own work is not a technicality. Its annual certification practices were the subject of the most consequential OUI litigation in Massachusetts history, described below.

How Alcohol Moves Through the Body

Alcohol does not appear in the blood the moment it is swallowed. As the Supreme Judicial Court has explained in describing the underlying science, consumed alcohol passes from the stomach and intestines into the blood, and a person’s blood alcohol level changes over time through absorption and elimination. Commonwealth v. Colturi, 448 Mass. 809 (2007). A drink finished minutes before driving is still being absorbed during the drive and for some time after it ends. The consequence is that a person’s blood alcohol level is a curve, not a constant, and a test measures one point on that curve, at the station, not the point that matters legally, which is the moment of operation.

Rising Blood Alcohol and the Time-of-Operation Problem

The gap between the time of driving and the time of testing is the rising blood alcohol problem. Because absorption continues after the last drink, a driver’s blood alcohol level can be higher at the station than it was behind the wheel, a possibility the case law has long acknowledged. Estimating the level at the time of operation from a later test is called retrograde extrapolation, a calculation that works backward from the test result using rates of absorption and elimination. Colturi, 448 Mass. 809 n.2.

In Colturi, the Supreme Judicial Court held that the Commonwealth need not present expert retrograde extrapolation testimony as a condition of admitting a breath test result, so long as the test was conducted within a reasonable time after the defendant’s operation, and that delay between driving and testing goes to the weight of the evidence rather than its admissibility. See also Commonwealth v. Marley, 396 Mass. 433, 438 to 439 (1985). For the defense, that ruling limits the argument without ending it. The later the test, the weaker the inference that the station number matches the driving number, and a jury that understands the absorption curve understands why a 0.09 at midnight does not prove a 0.08 at 11:15.

Mouth Alcohol and Interfering Substances

The breath test assumes that the sample comes from deep lung air, where alcohol concentration tracks blood concentration. Alcohol in the mouth itself, from a recent drink, a regurgitation, or anything else that puts alcohol into the oral cavity, defeats that assumption, which is why the regulations impose the 15-minute observation period and why the device aborts a sequence when it reports mouth alcohol. 501 CMR 2.13.

Interfering substances are a separate question. In the Camblin litigation, the defense experts asserted that compounds with a carbon-oxygen bond absorb infrared radiation in the same 8 to 10 micron region the device examines, naming acetone, acetic acid, acetaldehyde, ethyl acetate, and methanol among them, and that neither the infrared sensor nor the fuel cell is specific to ethanol standing alone. The manufacturer’s response was the dual-sensor design: the two technologies respond differently to interferents, the readings must tightly agree, and disagreement aborts the test. The Supreme Judicial Court found the record on ethanol specificity thin enough to require a reliability hearing, Camblin, 471 Mass. 639, and after that hearing the court sustained the finding that the device was reliable, Commonwealth v. Camblin, 478 Mass. 469 (2017). The lasting point for the defense is procedural as much as scientific: Camblin establishes that statutory and regulatory compliance does not immunize a breath test device from a scientific reliability challenge under the Daubert–Lanigan standard.

OAT, Ananias, and Hallinan: When the Numbers Could Not Be Trusted

The science of the machine assumes honest, documented calibration, and for most of a decade Massachusetts did not have it. In the consolidated Ananias litigation, a District Court judge found that the Office of Alcohol Testing had no written protocols for annual calibration and certification of the Alcotest 9510 until September 15, 2014, and held results from devices calibrated and certified between June 1, 2011 and September 14, 2014 presumptively unreliable. The litigation then uncovered that OAT had withheld hundreds of failed calibration worksheets from the defense, misconduct that led to a negotiated resolution, notice to roughly 27,000 affected defendants, and a judicially supervised exclusion of Alcotest 9510 results that did not end until April 18, 2019.

In Commonwealth v. Hallinan, 491 Mass. 730 (2023), the Supreme Judicial Court converted that history into a rule: a defendant whose case included an Alcotest 9510 result from a test taken between June 1, 2011 and April 18, 2019 is entitled to a conclusive presumption of egregious government misconduct in a motion to withdraw a guilty plea or for a new trial. The defendant must still show that the misconduct influenced the decision to plead, but the first element is established as a matter of law. The firm’s post on the exclusion era from Ananias to Hallinan tells the full story, and the breathalyzer defense page explains how Hallinan motions are litigated today.

Blood Tests: Consent, Warrants, and Hospital Records

Blood alcohol evidence follows different rules, and three recent Supreme Judicial Court decisions define them. Under G.L. c. 90, § 24 (1) (e), when blood is drawn by or at the direction of police, the results are admissible in an OUI prosecution only with the defendant’s consent, and a search warrant is not a substitute for that consent. Commonwealth v. Bohigian, 486 Mass. 209 (2020). The same consent requirement applies when the blood was drawn by a third party, such as hospital staff treating the driver, but chemically analyzed at the direction of police: in Commonwealth v. Moreau, 490 Mass. 387 (2022), the State crime laboratory’s analysis of hospital-drawn blood without consent was suppressed. The consent requirement does not extend to arithmetic. In Commonwealth v. Gannett, SJC-13659 (May 23, 2025), the court held that when a hospital has already tested a driver’s blood in the course of treatment, a State analyst’s mathematical conversion of the serum or plasma result in the medical records into a blood alcohol percentage is not an analysis requiring consent, and the converted figure is admissible.

The science matters here too. Hospitals commonly test serum or plasma rather than whole blood and report the result in milligrams per deciliter, and serum values run higher than whole blood values, which is why a conversion is performed before the number is expressed as a blood alcohol percentage. A defense review of a blood case therefore starts with what was tested, serum or whole blood, who tested it, at whose direction, with what consent, and how the conversion was done, because after Bohigian, Moreau, and Gannett each of those answers controls whether the number is admissible at all.

Refusals: Inadmissible at Trial, Consequential at the Registry

A driver’s refusal to take a breath test cannot be used against the driver at trial. Under art. 12 of the Massachusetts Declaration of Rights, refusal evidence is inadmissible, Commonwealth v. McGrail, 419 Mass. 774 (1995), so the jury never hears that a test was declined. The refusal has administrative consequences instead: license suspensions that run from 180 days to lifetime depending on prior offenses, set out on the firm’s license suspension guide. The decision a driver faces at the station is examined on the firm’s page on whether to take the breathalyzer.

What the Science Means for the Defense

A breath or blood number is the end of a chain: statute, regulation, machine, chemistry, and human procedure. The defense examines every link. The first is the paperwork, the device’s calibration and certification records from OAT, the operator’s certification, and the printed test sequence with its control standard result and two-sample agreement. The second is the procedure, above all the 15-minute observation period, reconstructed minute by minute from booking video and cruiser logs. The third is the timing, because Colturi makes delay a weight argument and the absorption curve gives the jury a reason to doubt that the station number was the driving number. The fourth is the science itself, where Camblin preserves the right to challenge the machine’s reliability directly. These are the same tools the firm applies in sobriety checkpoint cases, where the breath test is often the only number the Commonwealth has, and they are answered in plain terms in the firm’s breath test and BAC FAQs.

The consequences of the number do not end with the criminal case. A conviction or a continuance without a finding built on a breath or blood test can bring school discipline for college and university students, licensing board questions for nurses, physicians, and other licensed professionals, and immigration consequences for non-citizens. Each of those processes follows its own rules, and each belongs in the defense plan from the first day.

Who Attorney Serpa Represents

Attorney Serpa represents drivers across Greater Boston whose cases turn on a number: first offenders confronting a 0.08 or 0.09 reading, licensed professionals and commercial drivers for whom any alcohol finding is a career risk, drivers whose blood was drawn in a hospital after a collision, and defendants with old convictions built on Ananias-era breath tests. He handles the criminal case and advises on the Registry process. Call 617.936.0201 for a confidential consultation.

Massachusetts Courts Where Attorney Serpa Tries These Cases

Breath and blood test cases are tried where the OUI is charged. Attorney Serpa tries these cases in the Boston Municipal Court and in the district courts of eastern Massachusetts, including Quincy, Dedham, Cambridge, Woburn, Lynn, and Framingham. He has tried cases in these buildings for thirty years.

Related Serpa Law Office resources

The breathalyzer defense page applies this science in litigation, and the firm’s post on why a breathalyzer result does not establish guilt makes the trial argument. The field sobriety test defense page covers the roadside tests, the page on sobriety checkpoints and DUI roadblocks covers arrests that begin without driving evidence, the Massachusetts OUI FAQs address the charge broadly, and the profile of Attorney Joe Serpa describes the trial practice behind these pages.