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SAN DIEGO DUI Focus What is the PAS Device?

by | Dec 21, 2013 | DUI Cases |


When I first speak to my clients about their San Diego DUI arrest they bring up the breath test in the field. It is mistaken for the chemical tests that are taken back at the station (unless there is a checkpoint or similar). There is a significant difference between the Preliminary Alcohol Screening (hereinafter PAS) device to the chemical tests.So what is the PAS Device in a San Diego DUI?A PAS is a device used in preliminary
breath tests to determine the blood-alcohol level of an individual.
When an officer pulls over someone they suspect have been drinking, the officer may
ask the suspected person if the officer can administer a preliminary breath test. The test is usually requested in the field sobriety phase of a San Diego DUI arrest.The PAS device is a hand-held device used in the field by officers to obtain
blood-alcohol levels of someone.  However, it usually can only be an indicator that alcohol is present.There are several different PAS systems,  but there are generally two main types in a San Diego DUI.  These are the Fuel cell devices and/or Taguchi gas sensor devices.a. Fuel Cell DevicesFuel cell devices measure the ethanol in a person’s breath.Some problems with
this test are that the device also reacts to acetaldehyde, methanol, isopropanol, and n-
propanol, and thus the test may be tainted by these substances.  Additionally,
the test reacts to temperature, and is subject to build-up which can cause a false reading.

Thus, fuel cell devices may pose evidentiary problems. The Alco-Sensor model IV is


one of the more commonly used PAS devises used in California, and has a black-dot and
green-dot version.b. Taguchi Gas Sensor

The gas sensor has small elements that attract alcohol in the breath, and give a reading
as a result. There are two types of gas sensor devices: passive and active. Both pose issues with temperature, as the sensitivity will change based on the
temperature. The passive device reads the air to determine whether alcohol is present
in the air of the car, but it will detect sources of alcohol in the car not related to the driver
(open containers or may be on the breath of another passenger).  However, it also
poses the same problem as the fuel cell devices in that in reads other substances in the air
as ethanol, and thus the results may be tainted as a result.


This is an important distinction in a San Diego DUI case.  It must be found out by a San Diego DUI attorney.   I have seen the officer does not know which one he is using.

a.  The Green一Dot PAS

The Alco-Sensor IV has both a black-dot version and a green-dot version.  The
green-dot and black-dot version both measure the BAC the breath of an individual
after they have blown into the machine. The green-dot version does not have
as many features as the black-dot version.

b.  The Black-Dot PAS

The black-dot version has memory retention, and has printing features that the green-

dot system does not have.  Both systems work fairly the same way, other than the
memory retention, printing features, and the black-dot system also has a battery back-up.  The black dot PAS will allow the defense attorney to question whether the office used the printing system to ensure he noted the right reading in the field during their San Diego DUI investigation.

So How does a PAS work?

The fuel cell devices and the gas sensor devices work in different ways. The fuel cell

devices work by burning up the ethanol in a fuel cell, thus giving a reading of the BAC.  As stated above, problems can arise when the device burns something other
than ethanol, but factors into the reading of the BAC.
Officers may take
precautions to make sure the problems do not arise, and it should be determined that the
officers followed the precautions.

The gas sensor devices work in a little different way, as they contain small elements
that attract alcohol in the breath. Many of the same problems also arise with
the gas sensor devices as does with the fuel cell devices in that temperaturé affects the
readings, as does the device reading acetaldehyde, methanol, isopropanol, and n-propa
propanol. Thus, again it should be determined whether the officers followed
precautions to help make sure problems do not arise in a San Diego DUI arrest.

I can tell you that unless this area is reviewed, the jury will just take the >PAS reading as the gospel.  There is a reading that there is a chemical sample back at the station.  Those tests are far more reliable.  It is important because these machines are determining whether someone drives home that night or will be spending time in jail.

Hire a Proactive, affordable, and quality defense when you are facing San Diego DUI charges. Whether you have been charged of a San Diego DUI, Poway DUI, La Mesa DUI, Santee DUI, Mission Valley DUI, Clairemont DUI, Point Loma DUI, La Jolla DUI, Carmel Valley DUI, Mira Mesa DUI, Pacific Beach DUI, Del Mar DUI, Carmel Valley DUI, Encinitas DUI, Oceanside DUI, Ocean Beach DUI, Escondido DUI, Vista DUI, San Marcos DUI, Carlsbad DUI, El Cajon DUI it is vital you need to hire an attorney who knows how to defend your rights and can determine if the government can prove their case. Contact the Law Office of Mark Deniz now for a free case evaluation.


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