Breath Testing & Intox EC/IR II
The Intox EC/IR II is the evidential breath-test instrument North Carolina uses after a DWI arrest. Made by Intoximeters, Inc. of St. Louis, it measures alcohol with an electrochemical fuel cell while an infrared system watches the breath for mouth alcohol and confirms a deep-lung sample. Its number is only admissible if the officer held a valid permit and followed the state’s rules to the letter, and those rules are where many breath cases are won or lost.
What is the Intox EC/IR II?
The Intox EC/IR II is a desktop breath analyzer approved by the North Carolina Department of Health and Human Services (DHHS) for evidential testing in implied-consent cases. It is the machine you blow into at the jail, the police station or a mobile testing unit after arrest. It is not the handheld device an officer may use at the roadside, which is a separate “alcohol screening test” covered in our guide to the portable breath test in NC.
The rule that governs how the instrument is operated, 10A NCAC 41B .0322, took effect on November 1, 2007. As of November 2026 it approves two versions: the original Intox EC/IR II and an “Enhanced” model with serial number 10,000 or higher, added in 2020. DHHS’s Forensic Tests for Alcohol Branch posts Intoxilyzer 5000 maintenance histories only for 2005 through 2008 and EC/IR II histories from 2008 forward, which reflects the statewide switch from the older Intoxilyzer 5000. Our companion article compares the breath test instruments used in other states.
How the Intox EC/IR II works: a fuel cell plus infrared
The short answer: infrared decides when to take the sample and whether it is clean, and the fuel cell decides how much alcohol is in it. The “EC” stands for electrochemical (the fuel cell) and “IR” for infrared.
The fuel cell is a porous disk coated with platinum black and soaked in an acidic electrolyte. When a fixed volume of breath is drawn across it, ethanol is oxidized on the surface and produces an electrical current proportional to the amount of alcohol. The microprocessor converts that current into an alcohol concentration in grams per 210 liters of breath. The manufacturer states a measuring range of .000 to .440 g/210L and says the sensor does not respond to acetone.
As you blow, breath flows through a heated infrared chamber. Filters watch two ethanol channels and one carbon-dioxide channel. The IR system monitors the exhalation continuously and tells the instrument when deep-lung (alveolar) breath has arrived so the fuel cell sample can be drawn from the end of the breath. Tracking CO2 also lets the instrument tell human breath apart from a gas standard or room air.
Alcohol trapped in the mouth (from a recent drink, a burp or regurgitation) reads artificially high at the start of a blow and then falls. The IR system looks for that pattern and for a mismatch between the ethanol and CO2 profiles; if it sees one, it aborts the test. The fuel cell also checks its own reaction profile: methanol and isopropyl alcohol react differently, and detection aborts the test with an interferent message. Technical descriptions: Virginia Department of Forensic Science; Intoximeters specification sheet.
Breath is measured, not blood. The instrument assumes alcohol in deep-lung air reflects alcohol in the blood, and North Carolina’s per se offense is written in the same terms: 0.08 or more grams per 210 liters of breath or per 100 milliliters of blood under G.S. 20-138.1(a)(2). Because the law defines the offense in breath units, arguments about individual blood-to-breath ratios generally do not defeat a valid breath result, though they can matter when the defense challenges a test on other grounds. Our line-by-line guide to G.S. 20-138.1 explains all three ways the State can prove DWI.
The rules: G.S. 20-139.1 and 10A NCAC 41B
A breath result is admissible in North Carolina only if the test was performed under DHHS rules by a person holding a current DHHS permit for that type of instrument. That is the core of G.S. 20-139.1(b), and the courts must take judicial notice of the DHHS rules and the list of permitted analysts.
Breath-testing methods must require “at least duplicate sequential breath samples.” The results are admissible if the samples do not differ by more than 0.02, and only the lower of the two readings may be used to prove a particular alcohol concentration. Refusing to give the second or a later sample is treated as a refusal under G.S. 20-16.2(c), and the first (or lowest) result is admissible.
Read the statute on ncleg.gov ↗The DHHS rules live in Subchapter 41B of Title 10A of the North Carolina Administrative Code. The breath-test rules that matter most:
| Rule | What it requires | Why it matters |
|---|---|---|
| 41B .0101 (definitions) | A 15-minute observation period immediately before each sample: no alcohol or other fluids, no eating, smoking, vomiting or regurgitation. Dental devices and oral jewelry need not be removed. | The observation period exists to keep mouth alcohol out of the result. |
| 41B .0101 (accuracy) | The instrument checks itself against a 0.08 standard (a wet simulator or an ethanol gas canister); a reading of 0.08 or 0.07 is accepted. | A failed accuracy check should stop the test. |
| 41B .0322 | The operating steps: verify time and date, confirm the observation period, start the sequence, enter data, verify accuracy, collect two samples, print the record. If the samples differ by more than 0.02, collect a third or fourth sample when prompted. | Skipped or out-of-order steps are a basis for suppression. |
| 41B .0323 | Preventive maintenance at least every four months; gas canisters replaced before expiration, or simulator solution changed every four months or after 125 tests. | Late maintenance can make results inadmissible on objection. |
| 41B .0301–.0308 | Chemical analyst permits: initial permits, limits, renewal and revocation. | No current permit for that instrument type means no admissible result. |
Step by step: what happens in the breath-test room
A North Carolina breath test follows a fixed order: rights, a waiting period, observation, the instrument’s self-checks, and then two breath samples. Here is the sequence the statutes and rules describe.
- Implied-consent rights, orally and in writing
Before testing, the chemical analyst must advise you of your rights under G.S. 20-16.2(a), including the consequences of refusal and your right to call a lawyer and pick a witness.
- Up to 30 minutes for a lawyer or witness
Testing may not be delayed for these purposes longer than 30 minutes from the time you are notified of your rights. A witness who arrives in time must be allowed to observe.
- The 15-minute observation period
The analyst must confirm that you did not drink, eat, smoke, vomit or regurgitate in the 15 minutes before each sample. The rule allows the analyst to observe while operating the instrument.
- Self-checks and an accuracy check
The instrument runs diagnostics, purges with room air (an “air blank”), and analyzes a known 0.08 standard. An accepted result is 0.08 or 0.07.
- Two breath samples
When the screen says PLEASE BLOW, you give a long, steady breath. The instrument then asks for a second sample. If the two results are more than 0.02 apart, it prompts for more.
- The printed test record
The instrument prints the record, and the lower of the two agreeing results becomes the reported alcohol concentration.
Each step leaves a paper or electronic trail: the rights form, the time of notification, the observation start time, the test record, and the officer’s affidavit. Our checklist on North Carolina DWI breath testing records lists what to request, and the breath test timeline case study shows how the timestamps fit together. A separate article covers what counts as a willful refusal.
How to read an Intox EC/IR II test record
The test record (often called the “ticket”) is a printed summary of who ran the test, on which instrument, and what each step showed. Reading it line by line is the fastest way to spot a problem.
The labels below come from Intox EC/IR II records published by the DHHS Forensic Tests for Alcohol Branch. Exact wording and layout can vary with the instrument’s software version, so compare your own record line by line.
| Line on the record | What it means | What to check |
|---|---|---|
| Serial Number / Test Record Number | Which instrument ran the test, and the sequential number of the test | Match the serial number to the DHHS preventive-maintenance history for that instrument |
| Test Date / Test Time | When the sequence ran | Compare with the time of driving, arrest, rights advisement and the observation start |
| System Check / DIAG | The instrument’s internal diagnostics | Anything other than a pass should end the test |
| AIR BLK | Air blank: room air purged through the system, expected to read .00 | A non-zero blank can signal contamination or a problem in the room |
| ACCY CHK, Lot Number, Exp Date | The accuracy check against the 0.08 standard, plus the gas canister or simulator lot and expiration | Accepted value is 0.08 or 0.07; the standard must not be expired |
| Subject tests | Each breath sample and the time it was taken | The two results must be within 0.02 |
| Reported AC | The alcohol concentration reported, in g/210L | It should be the lower of the agreeing results |
| Permit Number / Analyst’s Name / Officer’s Name / Agency / Citation Number | Who ran the test and for which charge | Confirm the analyst’s permit was current for the Intox EC/IR II on that date |
One practical point: the instrument reports results to two decimal places. In an unpublished 2013 decision, State v. Moore, the Court of Appeals rejected an argument that dropping the third digit hurt the defendant, reasoning that truncation works in the driver’s favor. That fits the North Carolina Supreme Court’s older view in State v. Shuping (below) that the accuracy-check tolerance protects the defendant rather than creating a margin of error.
Chemical analyst permits and preventive maintenance
Only an officer with a current DHHS permit for the Intox EC/IR II can give an admissible test, and the instrument must be on its four-month maintenance schedule. Both can be checked against public DHHS records.
The Forensic Tests for Alcohol Branch, which has trained North Carolina officers in breath testing since 1964, runs the initial operator course and an Intox EC/IR II recertification course through the NC Justice Academy portal. Its maintenance and permit history page posts monthly preventive-maintenance records for the EC/IR II by year and individual permit-history reports. Under the maintenance rule, a technician confirms the gas canister pressure (at least 51 psi) or the simulator temperature (34 °C ± 0.2), runs a full test sequence and diagnostics, and records a “Pass.” The signed record must be kept for at least three years.
The law limits how far maintenance can be used as a defense. Under G.S. 20-139.1(b2), a result is excluded only if the defendant objects and shows that required maintenance “had not been performed within the time limits prescribed.” In State v. Simmons, 205 N.C. App. 509 (2010), the court rejected a maintenance challenge where the simulator solution had been changed 23 days before the test. A real gap in the records is powerful; a vague claim that the machine “might” have been off is not.
What North Carolina courts have said about the Intox EC/IR II
The appellate cases mostly ask whether the analyst followed the rules: was the observation period honored, were the samples “sequential,” and does a valid result prove the per se offense. These decisions shape what arguments are realistic.
An Intox EC/IR II timed out when the driver could not give a second sample. After a reset, a second reading came 11 minutes after the first. The court held the two tests were still sequential, they did not need to appear on the same ticket, and no new observation period was required because the original observation was not broken. It reversed the suppression order.
Read the opinion ↗The officer saw chewing gum after the first EC/IR II sample, had it removed, and took the second sample without restarting the 15-minute observation period. The lead opinion said the results should have been excluded but found the error not prejudicial given the other evidence. With two judges concurring only in the result, the case does not settle the gum question, but it shows observation-period problems are taken seriously.
Read the opinion ↗On an Intoxilyzer 5000, two valid readings taken within 18 minutes, with insufficient samples in between, satisfied the consecutive-test requirement. The reasoning carries over to the EC/IR II: an insufficient blow produces no result to compare, so it does not break the sequence.
Read the opinion ↗Readings of .20 and .19, taken 11 minutes apart with two insufficient samples between them, counted as consecutive tests. The court reasoned that a contrary rule would let a person defeat testing by deliberately blowing poorly.
Read the opinion ↗The statutory language making a chemical analysis “sufficient evidence” of alcohol concentration is not an unconstitutional mandatory presumption. A properly admitted result is prima facie evidence that the jury may accept, but is not required to accept.
Read the opinion ↗The 0.01 tolerance allowed on the accuracy check is not a margin of error in the subject’s test. It is a safeguard that favors the defendant, and a valid reading at the legal limit is sufficient evidence of the per se element.
Read the opinion ↗For a deeper treatment of how these rules apply in court, the UNC School of Government’s “Rules for Breath Tests in DWI Cases” and its discussion of Forney are well worth reading.
Where Intox EC/IR II results can be challenged
Most successful breath-test challenges are procedural: a rule was skipped, a record is missing, or a timeline does not add up. Attacking the science in the abstract rarely works because the legislature has made a valid result sufficient evidence.
- Observation period. Was there a continuous 15 minutes immediately before each sample? Did anything go into the mouth, or did you burp or vomit? Forney shows the issue is live.
- Rights and the 30-minute window. Were you advised orally and in writing? Was a witness who arrived in time turned away? Our article on State v. Knoll and access to witnesses explains why this matters.
- Permit status. Was the analyst’s Intox EC/IR II permit current on the test date?
- Maintenance. Was the instrument inside its four-month window, and was the gas standard unexpired?
- Sequential samples. Were the results within 0.02, and is the reported number the lower one?
- The stop and the arrest. A perfect breath test still falls if the stop or probable cause was unlawful. See State v. Parisi and our guide to reviewing DWI evidence.
Procedure matters too. In district court, a challenge to the breath result is usually raised by a pretrial motion to suppress, and in some cases the State may offer a chemical analyst’s affidavit instead of live testimony if it gives notice at least 15 business days ahead and the defense does not object in writing at least five business days before the proceeding (G.S. 20-139.1(e1)–(e2)). Missing that objection deadline can waive the right to cross-examine the analyst.
The machine does not decide your case. The rules around the machine do, and those rules leave a paper trail.Adkins & Purkey
The DMV side: what an Intox EC/IR II result triggers
A breath result of 0.08 or more (0.04 for a commercial vehicle, any alcohol for a driver under 21) triggers an immediate civil license revocation of at least 30 days, separate from the criminal case. A refusal, including refusing the second sample, carries a 12-month DMV revocation under G.S. 20-16.2(d).
A result of 0.15 or more also requires the officer and analyst to send a sworn affidavit to the Division of Motor Vehicles under G.S. 20-16.2(c1), and 0.15 is a key number for ignition interlock. For the details, see the 30-day civil revocation, limited driving privileges, ignition interlock and our complete guide to DMV consequences.
Those numbers explain why the State invests in breath testing, and why the defense has to take the instrument seriously. More context is in our North Carolina alcohol-impaired driving statistics.
Test your knowledge of the Intox EC/IR II
Five quick questions on the rules that decide whether an Intox EC/IR II reading can be used.
How long must the analyst observe you before a breath sample?
- 5 minutes
- 15 minutes
- 30 minutes
10A NCAC 41B .0101 defines a 15-minute observation period immediately before the sample. The 30-minute figure is the attorney-and-witness window under G.S. 20-16.2(a)(6).
Your two samples read 0.11 and 0.09. What happens?
- The average, 0.10, is reported
- The higher, 0.11, is reported
- They are within 0.02, so both are admissible and the lower, 0.09, is used
G.S. 20-139.1(b3) allows a difference of up to 0.02 and requires use of the lower result.
Which part of the EC/IR II actually measures the alcohol for the reported result?
- The fuel cell
- The infrared bench
- The printer
The electrochemical fuel cell quantifies the alcohol; infrared monitors the breath, detects mouth alcohol and decides when to draw the sample.
You give one good sample and then refuse the second. What is the legal effect?
- No result can be used
- It is a refusal, and the first result is admissible
- The officer must get a blood warrant
Under G.S. 20-139.1(b3), refusing a later sample is a refusal under G.S. 20-16.2(c), and the first (or lowest) result is admissible.
How often must an Intox EC/IR II receive preventive maintenance?
- Every 30 days
- Once a year
- At least every four months
10A NCAC 41B .0323 requires maintenance at least once every four months. The 30-day interval applies to roadside screening devices.
From Breathalyzer to Intox EC/IR II: North Carolina’s instrument history
North Carolina has used three generations of evidential breath instruments, and the case law tracks each one.
- 1964The state’s breath-alcohol program (today the DHHS Forensic Tests for Alcohol Branch) begins training North Carolina officers in breath testing.
- 1984Breathalyzer-era testing under the then Department of Human Resources regulations: State v. Shuping addresses the instrument’s 0.01 simulator tolerance.
- Through 2008The Intoxilyzer 5000 era. State v. Shockley (2009) involves a 2006 Intoxilyzer 5000 test, and DHHS posts 5000 maintenance histories for 2005–2008.
- 2006S.L. 2006-253 requires “at least duplicate sequential breath samples” and makes valid results “sufficient evidence” of alcohol concentration.
- Nov. 1, 200710A NCAC 41B .0322, the Intox EC/IR II operating rule, takes effect.
- Apr. 1, 2020DHHS amends the rules to approve the Intox EC/IR II “Enhanced” (serial number 10,000 and higher).
- 2024State v. Forney addresses gum and the observation period on an EC/IR II.
What to do if you took an Intox EC/IR II test
Get your paperwork together, write down your own timeline while it is fresh, and have the test record reviewed against the rules before any court date. The details fade quickly; the documents do not.
- Keep the copy of your test record and your rights form
- Write down when you were stopped, arrested, read your rights and tested
- Note anything you ate, drank, chewed or smoked, and any burping or vomiting before the test
- Note whether you asked for a lawyer or witness, and whether anyone arrived
- Find your revocation paperwork and its dates (see the DMV section above)
- Gather any medical conditions or medications that affect breathing
- Bring everything to your consultation (see preparing for your DWI consultation)
If this is your first step, start with first steps after a Lake Norman DWI arrest and our full North Carolina DWI guide. The sentencing levels article explains how alcohol concentration can affect punishment.
From our book
Charged with DWI in North Carolina?
The book’s science chapters walk through breath testing in plain English, from the observation period to the printed record, written by a former DWI arresting officer and his law partner.
Intox EC/IR II: frequently asked questions
What breath machine does North Carolina use for DWI?
North Carolina uses the Intoximeters Intox EC/IR II, including an “Enhanced” model with serial number 10,000 or higher, approved under 10A NCAC 41B .0322. The rule took effect November 1, 2007.
Is the Intox EC/IR II the same as a roadside breathalyzer?
No. The EC/IR II is the evidential instrument used after arrest, and its numeric result can be used in court. Roadside devices are alcohol screening tests under G.S. 20-16.3, and only their positive or negative result, not the number, may be used.
Why do I have to blow twice?
G.S. 20-139.1(b3) requires at least two sequential breath samples. They must agree within 0.02, and only the lower result may be used to prove your alcohol concentration.
Can burping or vomiting affect an Intox EC/IR II test?
Yes. The rules require a 15-minute observation period with no regurgitation or vomiting before each sample, because mouth alcohol can raise the reading. The instrument also tries to detect mouth alcohol with its infrared system.
How do I check whether the instrument was maintained?
Use the serial number on your test record and compare it with the preventive-maintenance histories that the DHHS Forensic Tests for Alcohol Branch posts online. Maintenance is required at least every four months.
Can a breath test be thrown out?
Yes, if the State cannot show the test followed the DHHS rules and was given by a permitted analyst, or if the stop or arrest was unlawful. Each case turns on its own records.
Adkins & Purkey, PLLC
Talk to a North Carolina DWI lawyer
If you blew into an Intox EC/IR II, we can review your test record, the officer’s paperwork and the DHHS maintenance and permit records with you. Offices in Huntersville (Lake Norman) and Locust (Stanly County), serving Charlotte, Mecklenburg, Iredell, Cabarrus, Stanly and courts across North Carolina.
General North Carolina legal information as of November 2026, not legal advice for any specific case. Reading this article does not create an attorney-client relationship. Attorney advertising.
.jpg){kind=link}
.jpg){kind=link}