If you get arrested for DUI in Colorado, you must take an evidentiary breath test or blood test to measure your BAC. Here are five key things to know about breath tests:

1. Colorado’s “express consent” law states that refusing to take an evidentiary breath or blood test triggers a one-year driver’s license revocation.
2. This license revocation holds even if you are not ultimately convicted of DUI.
3. Evidentiary breath tests are different than preliminary breath tests, an optional investigatory tool police offer DUI suspects during traffic stops.
4. Colorado’s “express consent” law pertains not only to DUI and DUI per se arrests but also to DWAI and UDD arrests.¹
5. There are many ways to contest DUI breath test results, including showing that the breathalyzer was faulty or that you had residual mouth alcohol.

The following chart compares evidentiary breath tests and blood tests in DUI cases.

	DUI Blood Tests	DUI Breath Tests
Accuracy	Generally more accurate	Less accurate, can be affected by acid reflux, GERD, mouth alcohol, and more
Invasiveness	Invasive, requires blood draw	Non-invasive, requires breathing into a device
Time to results	Longer, typically weeks	Immediate results
Administration	Requires medical professional	Can be administered by law enforcement
How it measures alcohol	Direct measurement of blood alcohol content (BAC)	Estimates BAC based on breath alcohol content
Detects drugs?	Yes	No
Retention of sample	Sample can be retained for future testing	No sample retention
Refusal consequences	Driver’s license suspension	Driver’s license suspension

To help you better understand the law, our Colorado DUI defense lawyers discuss the following:

• 1. What is the difference between a preliminary roadside breath test and DUI breath test?
• 2. Should I choose a breath test or a blood test?
• 3. What happens if I refuse the test?
• 4. What are the testing procedures?
• 5. What is the science behind DUI breath tests?
• 6. Can I fight the test results in court?

Also see our general article on Colorado DUI chemical tests: Breath, blood, refuse?

1. What is the difference between a preliminary roadside breath test and DUI breath test?

When you are pulled over for a traffic violation or suspected drunk driving, a law enforcement officer may ask you to take a roadside preliminary breath test (PBT). You may decline to take this preliminary breath test without legal consequence. Like all so-called field sobriety tests, the roadside breath test is just a tool to help the officer decide whether to arrest you.²

The only real advantage to agreeing to a preliminary DUI breath test is that if you blow a “negative” result (a BAC of less than 0.05% BAC, or .02% if you are under 21), the officer will most likely let you go.

2. Should I choose a breath test or a blood test?

Even the best Colorado DUI lawyers disagree about whether it is preferable to choose a breath test or a DUI blood test if you are given the choice. And you must be offered a choice unless:

• The officer has a reasonable basis to suspect you of DUI of drugs (DUID) (in which case a blood, saliva and/or urine test may be required),³
• You are under twenty-one and the alleged violation is solely a violation of Colorado’s “zero tolerance” underage drinking and driving law (UDD) (breath test required),⁴
• Extraordinary circumstances – such as bad weather or malfunctioning equipment — prevent completion of your chosen test within two hours of your driving,⁵ or
• You are unable to take a DUI breath test (due to a medical condition or because you are unconscious or dead).⁶

Once you have made your choice, you will ordinarily not be allowed to change it.⁷ Each choice has its advantages and disadvantages.

The primary advantage of a breath test is that it is easy and non-invasive. But unlike a blood sample, breath can’t be saved and independently retested. And while, in general, Colorado DUI breath tests are fairly reliable, they are less reliable than DUI blood tests. While this can make it easier to challenge in court, it also means a DUI breath test will give you more false “positives.”

In the end, it’s a personal choice.

3. What happens if I refuse the test?

Refusing to take a Colorado DUI chemical test will result, among other negative consequences, in an automatic one-year revocation of your Colorado driver’s license, whether or not you are convicted of DUI or DWAI. You will also be designated a Colorado “persistent drunk driver,” even if it is your first arrest.

You may challenge a suspension based on a chemical test refusal by requesting an “express consent” hearing at the Colorado DMV, but you must do so within 7 days of the suspension. You may also request reinstatement of your license after it has been suspended for at least two months.

Read more in our article, What is Colorado’s express consent law?

4. What are the testing procedures?

Colorado law enforcement agencies use the Intoxilyzer 9000 (I-9000) for evidential breath alcohol testing (EBAT). The I-9000 measures how many grams of alcohol are present per 210 liters of your breath. This number is then mathematically converted to the equivalent blood alcohol concentration (also known as blood alcohol content), or “BAC.”

Under Section 42-4-1301 of the Colorado Revised Statutes, EBAT testing must be done in strict accordance with 5 CCR 1005-2. These are the rules pertaining to testing for alcohol and other drugs as promulgated by the Colorado Board of Health.

Among the requirements of 5 CCR 1005-2 are that Colorado EBAT must be performed:

• on a “Certified EBAT Instrument”
• in a “Certified Laboratory,” and
• by a “Certified EBAT Operator.”

Other legal requirements of Colorado DUI breath testing include:

• Two valid samples that differ by no more than 0.02 grams per 100 milliliters of blood alcohol (the lower reading will be used);
• The test must occur within two-hours of driving;
• A 20-minute “deprivation period” during which the test subject must not eat, belch, regurgitate or insert any foreign material into the mouth;
• The breath samples must contain “deep” end-expiratory air from the lungs;
• The operator must use a clean mouthpiece for each breath sample provided by the subject;
• The operator must observe the subject continuously through the completion of the second breath sample;
• The operator must sign a properly completed EBAT report indicating the test was performed in compliance with these and other procedures; and
• All printouts generated from the certified EBAT instrument for the subject must be retained for a minimum of 5-years.

5. What is the science behind DUI breath tests?

Ethanol–the alcohol in alcoholic drinks –is largely absorbed in your stomach and small intestine. From there, most of it passes directly into your bloodstream. A small amount of alcohol, however, is excreted into the breath via the lungs.⁸

Lung tissue is made of air pockets called “alveoli,” which are surrounded by tiny blood-rich membranes. A fraction of the alcohol circulating in the blood crosses the membranes and evaporates into the alveoli. During exhalation, air is forced out of the alveoli and ultimately emerges from the lungs into the person’s breath.

When we exhale, air emerges in the following order:

1. from the mouth/nasal area, then
2. from the throat and upper airway, and finally
3. from the lungs.

“Deep lung” air–also known as “end expiratory” air– is the last to leave your mouth. So as you exhale, breath alcohol levels start out low and rise until they reach a peak or plateau as deep lung air is exhaled. This is why you must blow hard when taking a breath test.

Older people and those with certain medical conditions may have trouble generating the volume of air required. Those people will be required to take a DUI blood test.

However, unlike Colorado DUI blood tests–which directly measure the amount of alcohol in your blood–EBAT machines such as the Intoxilyzer 9000 measure the grams of alcohol present per 210 liters of your breath. They then mathematically converts this number into the equivalent BAC.

Since the conversion approximates BAC, Colorado DUI breath tests contain an inherent margin of error, even when performed correctly and under ideal conditions.

6. Can I fight the test results in court?

There are many legal defenses to a Colorado drunk driving charge.

DUI breath testing errors fall into two basic categories:

• Errors by law enforcement personnel, and
• Failure to comply with Colorado EBAT procedures.

Police error

Colorado and federal law require law enforcement personnel to observe certain procedures before a DUI breath test can be used against you (or even legally administered). Challenges to DUI breath tests based on police error can include:

• No probable cause to pull you over
• No reasonable suspicion that you were driving drunk
• Failure to advise you that you may refuse a preliminary breath test
• Failure to advise you of the consequences of a chemical test refusal
• Failing to offer you the choice of a DUI breath test or DUI blood test
• Not conducting the test within two hours of your driving.

EBAT operator error

Colorado regulations require strict adherence with proper EBAT testing procedures to avoid false positives. Possible errors the EBAT operator and/or lab can make include:

• improper calibration of the breath testing device,
• improper training of personnel,
• failure to observe you for a continuous 20-minute period before administering the test,
• environmental contamination of the breath sample, and
• sloppy record-keeping,

Other factors that can result in false positives include:

• certain medical conditions (such as GERD or hypoglycemia),
• “rising blood alcohol” levels (when the alcohol in your system is not fully absorbed at the time of your breath test, for example when you’ve just had “one for the road”),
• environmental factors such as radio frequency interference,
• residual mouth alcohol, and
• personal differences in alcohol partition ratios.

These last two merit further discussion.

Residual mouth alcohol

After you drink anything containing alcohol, some of the alcohol remains in the mucosal linings of the mouth. This is known as “residual mouth alcohol.” However, since Colorado EBAT tests are calibrated to measure end-expiratory air, residual mouth alcohol can create falsely high BAC readings from a DUI breath test.

Sources of residual mouth can include:

• recently consumed alcohol, even if it’s not enough to make you legally drunk (“one for the road”),
• cough syrup, or
• mouthwashes or breath sprays that contain alcohol.

Residual mouth alcohol usually dissipates after 15-20 minutes, however. This is why Colorado breath testing regulations require that the EBAT operator observe you continuously during a 20-minute deprivation period before starting a DUI breath test.

Partition ratios: our lungs absorb blood alcohol at different rates

As discussed above, Colorado DUI breath tests must mathematically convert the amount of alcohol in the lungs to an equivalent BAC. But not everyone’s lungs absorb alcohol from the blood at the same rate. As a result, DUI breath tests only approximate BAC levels.

Colorado, like many other jurisdictions, uses a conversion factor — known as a “partition ratio” — of 2,100 to 1. This ratio operates on the assumption that the amount of alcohol in 2,100 milliliters of your breath is the same as the amount of alcohol in 1 milliliter of your blood.

In reality, however, partition ratios can vary widely—not just in the general population, but within an individual, depending on the day, the person’s body temperature, the ambient room temperature and other factors. This is particularly important when your BAC is at or close to the Colorado legal limit for DUI or DWAI.

Colorado Legal Defense Group
4047 Tejon Street
Denver, CO 80211
(303) 222-0330

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