Wednesday, June 23, 2010

Where does that California DUI breath test number come from? (Government's attempt to convert breath to blood v. Henry's Law)

Where does that California DUI breath test number come from? (Answer: The Government's attempt to convert breath to blood.)

California DUI lawyers point out that breath test estimators do not directly measure blood alcohol content or concentration, which requires the analysis of a blood sample. Instead, they attempt to estimate Blood Alcohol Concentration (BAC) indirectly by measuring the amount of alcohol in one's breath.

"Henry's Law" is one of the gas laws, formulated by William Henry in 1803.

The mass of a gas which will dissolve into a solution is directly proportional to the partial pressure of that gas above the solution.

Henry's Law is the principle that, at equilibrium, the amount of gas dissolved in a given volume of liquid is directly proportional to the partial pressure of that gas in the gas phase.

A California DUI breath test estimator tests a person's end expired air which is gaseous.

IF all of the possible variables remain constant, the government - which authorizes use of California DUI breath test machines - maintains one can determine a person's partition ratio that relates to the amount of ethanol in the gas (breath) to the liquid (blood).

Henry's Law, according to Wikipedia, states that:

At a constant temperature, the amount of a given gas dissolved in a given type and volume of liquid is directly proportional to the partial pressure of that gas in equilibrium with that liquid.

An equivalent way of stating the law is that the solubility of a gas in a liquid at a particular temperature is proportional to the pressure of that gas above the liquid. Henry's law has since been shown to apply for a wide range of dilute solutions, not merely those of gases.

This assumes a closed system. But the lung is not a closed system.

Alcohol or ethanol is a volatile compound.

If one alters the California DUI breath test estimator's temperature, flow, or pressure, Henry’s Law is violated. That means the partition ratio, which is the predictable relationship between the liquid phase and the gaseous phase, cannot therefore be known.

As the California courts recently suggest, the partition ratio (Henry's law constant), under controlled laboratory conditions, has been measured by different
scientists. For ethanol in water, they measured and reported different values, ranging from 1200 to 1, up to 2300 to 1.

What happens when one blows into a breath test estimator?

No person ever exhales at a constant flow or pressure.

No person maintains the same temperature as she or he exhales.

There are also elevated breath temperatures in patients with certain medical conditions (e.g. asthma). There could easily be enough of an increase in a person's breath temperature to substantially affect hand-held Preliminary Alcohol Screening (PAS) breath readings based on their 34 degree presumption setup, something a little extra that you could point to rather than just the usual existing variance among the general population. No breath test estimator has a breath temperature function.

In sum, there is no predictable and usable partition ratio for California DUI breath test estimators. So, one really cannot relate the amount of alcohol in gas (breath) to liquid (blood).

California DUI breath test results are highly variable and often unreliable.

California DUI attorney prosecutors must deal with the reality that there are a number of inaccuracies with breath testing.