Breath and Blood Tests
Breath testing devices used by law enforcement can be inaccurate because of the assumptions that all people metabolize alcohol at the same rate, ate the same amount of food, have the same metabolisms; and drank the same amount of alcohol. 

A portable breath test device (“PBT”), is not a breath test like an intoxilyzer 5000.  It is very small and used by police officers at the scene of the arrest.  The PBT is not approved by Texas Department of Public Safety for use in criminal prosecutions or in administrative license revocation proceedings.  Also, Texas will not allow the results of a PBT to be admissible in court.

Blood testing, produces a much more accurate result. But the results are often typically higher than those obtained by a non-contaminated breath test.

The validity of breath testing rests on assumptions that can be attacked by an experienced DWI attorney in a wide variety of cases:

Common Challenges To Breath Tests:
1. The Machine Was Not Properly Operated
2. The Machine Was Not Properly Maintained
3. The Machine Was Not Properly Calibrated
4. The Machine Was Affected By Radio Frequency Interference (Police Radio etc.)
5. The Machine Has An "Acceptable" Range Of +/- .02%
6. Your Body Temperature Was Greater Than 98.6
7. You Were Tested Within 2 Hours From Your Last Drink
8. You Have Medical Or Dental Problems That Make You An Improper Candidate For Breath Testing
9. The Officer Did Not Have You Under Continuous Observation For 15 Minutes Prior To Giving You The Breath Test
10. Your Symptoms And Drinking Pattern Are Inconsistent With The Test Result
11. Manufacturer does not warrant that the Intoxilyzer is fit for any particular purpose
12. Intoxilyzer is capable of breath preservation, however, DPS purposely fails to require the breath specimens to be saved, therefore, no independent testing can be done
13. Residual alcohol in the mouth increased the results

Field Sobriety Tests
Standardized field sobriety tests (“SFST”) are what the police use to try to determine if a person is intoxicated.  The only three SFSTs are as follows:

1. Horizontal gaze nystagmus (HGN) test;
2. One-leg stand test; and
3. walk and turn test.

These three tests were developed by researchers funded by the National Highway and Traffic Safety Administration (NHTSA).  It is this research that the police and prosecutors use to try and prove that a person is intoxicated. 

SFST’s are standardized because:
1. Tests are administered in the prescribed, standardized manner;
2. Standardized clues are used to assess the suspect's performance;
3. Standardized criteria are employed to interpret that performance

If any one of the standardized filed sobriety test elements are changed, the validity is compromised.  See NHTSA DWI Detection and Standardized Field Sobriety Testing Manuel.  

The fact that the tests are standardized makes it essential that your attorney is also trained and certified to administer the Standardized Field Sobriety Tests like a police officer. Dave McLane knows the NHTSA DWI Manual.  Therefore, he knows when an officer has failed to administer a SFST properly and can try to either get evidence thrown out of court or show how the tests were not administered properly so the results of the tests were compromised and therefore invalid.

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