When applied to alcohol breath testing it means that who ever operates the breath test machine is doing so in accordance with the Texas Breath Alcohol Testing Regulations. These regulations can be found in Title 37 of the Texas Administrative Code, Part 1, Chapter 19, Subchapter A.
Rule 19.4 governs the proper method for administering a breath test to a person arrested on suspicion of driving while intoxicated. Rule 19.4(c) deals specifically with the what the breath test operator has to do in order for a breath test to be valid.
The Texas Breath Alcohol Testing Program Operator Manual states that the operating temperature of the reference sample device ("simulator") is 34 degrees C plus or minus .2 degrees C. The manual states that the "operator may verify the correct temperature by observing the thermometer on the front of the device."
The simulator has a heating element to warm the alcohol solution to the proper temperature, a thermostat to maintain that temperature and a stirring paddle to ensure an even temperature inside the jar.
The simulator is used "to verify the accuracy and calibration of the [intoxilyzer]." The breath test machine analyzes the alcohol concentration inside the simulator as a part of every breath test.
In Scillitani v. Texas, No. 14-08-00430-CR, (Tex.App.--Houston [14th Dist.] 2011), the Houston Court of Appeals was asked to determine whether or not the breath test operator was required to verify the temperature of the solution inside the simulator.
The court rejected Mr. Scillitani's argument on the grounds that nowhere in the breath test regulations does it state that the breath test operator must verify the temperature of the solution inside the simulator.
According to Rule 19.4(c)(4), in order for a breath test to be valid, the result of the machine's analysis of the solution inside the simulator must be within .01 g/210 L "or such limits as set by the scientific director." That rule did not change when the breath test regulations were updated effective March 2006.
There's a problem with the court's conclusion, however. The simulator is supposed to be a tool used to calibrate the breath test machine. The breath test machine sucks in a certain amount of vapor from the headspace gas inside the simulator. That vapor is then analyzed to determine its alcohol concentration and to compare it with the predicted value. But if the solution is outside the designated tolerance, can we trust that the machine is calibrated properly?
If you take a jar of water and alcohol and seal it, Henry's Law* says that the alcohol concentration in the headspace above the solution should be the same as the alcohol concentration of the solution. Heat up the solution and the molecules will become more active and the alcohol concentration will rise. Reduce the temperature and the opposite will occur.
Even if the vapor from the simulator is within .01 g/210 L of the predicted value, if the temperature is outside the required tolerance, questions must be raised about whether the breath test machine is calibrated correctly. Is the actual value different from the predicted value because the machine isn't working? Is it because the simulator solution wasn't mixed properly in the first place? Is it because the sample chamber is contaminated in some way? These are all legitimate questions that can't be answered without knowing the actual temperature of the simulator solution.
Now let's think about this logically for a second. Why would the manual produced by the Department of Public Safety and used to train both breath test operators and technical supervisors state that the temperature of the simulator solution must be within a certain tolerance of 34 degrees C if it wasn't necessary to verify that temperature? Why not just rely on the machine's analysis of the vapor from the simulator? Why put a thermometer on the simulator?
If the question is whether or not a breath test was conducted properly, then shouldn't we be looking at the Texas Breath Alcohol Testing Program Operator Manual, the book used to train breath test operators, to make that determination?
* Henry's Law is remarkably similar to the Hermetic concept of "As above, so below." You can also find it in the so-called Emerald Tablet, the foundation of the alchemists' belief system. The breath test machine conducts its own form of alchemy by turning a measurement of length into a volumetric measurement.