The PBT is the preliminary breath test. It’s also referred to as a portable breath test. It is a small machine that the officer can carry in his or her vehicle that allows them to get a general reading of a suspect’s blood alcohol content. The suspect blows into it, and it registers a number. It’s frequently used in DUI, DWI, and APC arrests.
What’s the Difference Between the PBT and the Breath Test at the Station?
The big difference between the PBT and the breathalyzer at the station is that the results from the station breathalyzer are what will be used to revoke somebody’s license, and the result of that test can be used in court to prove intoxication. The machine used in Oklahoma is the Intoxilyzer 8000.
The PBT is not considered scientifically accurate enough to use for the purpose of license revocation. There are numerous models of PBT, and there is no standardization. In contrast, the model of the breathalyzer machine used in Oklahoma is the same all over the state. There is a standardized procedure for administering a breath test on the Intoxilyzer, but there is no standard method of administering a PBT.
Is the PBT Voluntary or Mandatory in Oklahoma?
Sometimes, the officer will administer the preliminary breath test prior to administering the field sobriety tests. This is incorrect. The reason is that if the officer sees the reading on the PBT, then it will cloud their evaluation of the person’s performance on the field sobriety tests. The officer will then analyze the performance of the SFSTs based on a belief that the suspect is impaired at a certain level.
Officers are sometimes tricky when getting people to blow into a PBT. They will not ask somebody if they would like to blow into the PBT. They will get the machine set up, put the mouthpiece in it, stick it in somebody’s face, and say, “Here, blow into this.” That makes it seem like the PBT is not optional, but it is. You do not have to blow into a PBT in Oklahoma.
What Happens if I Refuse to Blow Into the PBT?
If somebody refuses the PBT, then the officer will have to use other observations to determine whether probable cause exists to arrest an individual for impaired driving. The officer will have to take into account things such as their observation of the suspect’s driving, SFST performance, an odor of alcohol emanating from the individual, what the individual said, whether the individual was unsteady on their feet, and other indicators of intoxication. The result from the PBT is just one of many potential indicators of intoxication. There is no criminal or driver’s license penalty for refusing to blow into a PBT.
What Affects the Results of a PBT?
There are numerous things that can result in a false PBT result. Residual mouth alcohol and breath contaminants can cause a preliminary breath test result to be higher than actual blood alcohol content. It takes approximately 15 minutes for residual alcohol to be eliminated from the mouth. Therefore, the officer is supposed to ensure that the subject has not consumed any alcohol for 15 minutes prior to using the PBT. An officer rarely does this. Other substances can skew the results high on a PBT. These include chloroform, acetone, and cigarette smoke.
Two factors can cause a PBT result to be lower than the actual blood alcohol content. These are breath sample cooling and breath sample composition. If the captured breath sample is allowed to cool before it’s analyzed, some of the alcohol vapor in the breath may turn to liquid and precipitate out of the sample. If that happens, then a subsequent analysis of the sample will yield a low BAC. Breath composition is the mixture of the tidal breath and alveolar breath. Tidal breath is breath from the upper part of the lungs and the mouth. Alveolar breath is deep lung breath. Breath testing should be conducted on a sample of alveolar breath. This is obtained by having the suspect blow into the PBT instrument until all air is expelled from the lungs.
A factor that can cause either a low or high preliminary breath test result is radio frequency interference. It can also prevent a breath test device from producing any result. Most officers have a radio that’s very close to their body, which can be very close to the PBT when the officer is asking a suspect to blow into it.
There are accuracy limitations on PBTs. They are not calibrated to the same standards as the breath test machine at the station.
Is a Preliminary Breath Test Admissible in Oklahoma Courts?
The administration of a PBT or its result is not currently admissible in Oklahoma courts. This is because the preliminary breath test is not considered reliable enough to use in the criminal prosecution against somebody. Its use is not standardized, and it’s not calibrated to the degree that the Intoxilyzer is.
Source: NHTSA’s 2018 DWI Detection and Standardized Field Sobriety Testing student manual