Chemical Evidence

Chemical Evidence involves the results gathered from the collection and testing of blood, breath, and urine samples to determine a suspect’s blood-alcohol concentration (BAC). In 2000, urine tests in California were discontinued except when neither breath nor blood tests are available.

Chemical Evidence is often the cornerstone for a DUl / DWl / Drunk Driving prosecution. A sample of the driver’s breath, blood, or urine taken shortly after the act of driving supplements the arresting officer’s observation. When an arresting officer in California requests that a DUI / DWI / Drunk Driving suspect submit to and complete a chemical test, the suspect has the option to comply or refuse. This “option” is called “implied consent” or “informed consent”. Implied consent laws exist because the courts have upheld the belief that if a person opted to drive on the state’s roadways, and thereby obtained the benefit of this public expenditure of money, then the person also has implicitly agreed to submit to giving a breath, blood, or urine sample to the police so that analysis for alcohol (and drugs) can be performed. If the suspect refuses to submit to and complete a chemical test, 3 consequences could result:

His/her license may be suspended/revoke for:

  • 1 year, if there are no prior DUI / DWl/ Drunk Driving convictions within 10 years.
  • 2 years, if there is a separate prior DUI / DWI / Drunk Driving conviction within 10 years.
  • 3 years, if there are 2 or more separate prior DUI/ DWI/ Drunk Driving convictions with 10 years.

His/her sentence may be increased because of sentence enhancements statutes

At trial, the jury may assume that the defendant refused to submit and complete a chemical test because the defendant knew the results would reflect that he/she was intoxicated.

If a suspect chooses to submit and complete a chemical test, the identity and integrity of the sample shall be maintained from the time of collection through analysis, reporting, and adjudication. Procedures for collection of these samples must comply with the following the rules and regulations established in the California Code of Regulations under Title 17, Division 1, Chapter 2, Subchapter 1, Group 8. Among other guidelines, Title 17 dictates that samples of blood or urine shall be tested only by a laboratory approved and licensed by the California Department of Health Service (CA DHS) and in accordance with regulations established by the DHS.

To learn more about the 3 different types of chemical tests that help build a case’s Chemical Evidence, please click below:

Breath Tests

A breath test is a practical yet indirect way for the police to estimate a suspect’s Blood-Alcohol Concentration (BAC). The amount of alcohol in a properly collected breath sample is governed by the amount of alcohol in the blood of the suspect’s lungs so it is vital that all residual mouth alcohol is eliminated before a test is conducted.

Currently, California uses desktop models to collect a suspect’s breath sample, with the most commonly used being the Intoxilyzer 5000. It utilizes the infrared spectrophotometric method of analysis, which is based on the fact that different molecules absorb light energy at different frequencies. In the case of alcohol, absorption of light takes place in the band range from 3.380 to 3.398 microns. The Intoxilyzer 5000 shoots a beam of infrared light through a captured breath sample and measures how much of it is absorbed in the above mentioned band range; the more light energy absorbed, the higher the BAC.

Police officers typically attend a breath testing school and are taught only what the designers of the instrument feel is necessary for the officers to know. In fact, many states have constructed elaborate certification systems that are a highly sought-after training by police officers. NOTE: Police officers have no constitutional duty to preserve breath samples, and there is no requirement for a second test sample as there is with blood or urine tests.


  • results are obtainable in minutes as opposed to hours for laboratory reports
  • results are obtainable in easy-to-read digital display and printed readout
  • shortens amount of custody time
  • low operator skill requirements
  • low cost
  • little invasiveness of the human body.
  • breath samples are difficult to preserve
  • must rely upon cooperation of the suspect
  • require a waiting period of 15-20 minutes before administering to eliminate residue mouth alcohol
  • interference from foreign sources, i.e. radio frequency interference (RFI)
  • interference by other objects/odors/contaminants in mouth.

California Code of Regulations
The CCR is available at the offices of County Clerks or County Law Libraries and lOO,state depository libraries.

CMI, Inc. Home Page
CMI, Inc. is the manufacturer of the Intoxilyzer line of breath alcohol testers.