BREATH ALCOHOL ANALYSER

INTRODUCTION

Many humans are addicted to the psychoactive effects of alcohol thus, it is the most common, legal drug of choice. However, the influence of alcohol or the over-consumption of alcoholic drinks by humans is often the cause of crimes and violence, including fatal traffic accidents. Traffic deaths rank highest among all causes of death & alcohol related traffic fatalities rank highest within this category. Safety Agencies are challenged to locate intoxicated drivers and to remove them from the public roadways.

The analysis of alcohol in breath was considered a very desired and objective test specimen for determination of a vehicle operator’s breath-alcohol concentration and impairment level for evidential purposes. In the early 1950s, first Breathalyzer set the basis for the scientific acceptance of analyzing alcohol in breath. Law-Enforcement personnel implemented and administered these noninvasive and efficient tests as part of their drunk-driving enforcement.

THE TECHNOLOGY OF BREATH-ALCOHOL TESTING

The technology of breath-alcohol testing has changed fundamentally over the years. This was partially driven by general technology advancements and in part due to defense challenges. The following techniques describing the most recognized technologies used for preliminary (“screening”) and evidentiary breath-alcohol analysis as well as its advantages and disadvantages:

1. Wet-chemical Oxidation technology: 

The analytical principle was based on chemical oxidation by alcohol within a mixture of dichromate and sulfuric acid in vials. It paved the way for scientific acceptance of evidential breath alcohol testing by the international forensic community and the courts.

Advantages:

• Compact table-top package.
• Relatively quick analysis.
• Accurate and specific to alcohol.

Disadvantage:

• Minimum required breath volume < 60mL.
• The handling of the vials is critical as they contain sulfuric acid.
• The Breathalyzer’s biggest short-coming however, was the fact that the system was operator dependent.
• Growing legal attacks in the eighties were vulnerable to manipulation by the operator thus; the equipment was rapidly replaced by newer and less operator dependent instruments.

 2. Solid-state sensor technology:

Commonly called “Taguchi” cells, a metal oxide semiconductor based sensor manufactured by Figaro located in Japan. The Taguchi cell operates by adsorption of gas molecules on the surface of a semi-conductor. This transfers electrons due to the differing energy levels of the gas molecules on the semi-conductor’s surface. These types of instruments are sold mainly to the consumer markets as opposed to law enforcement. None of these sensor-type instruments are approved by the National Highway Safety Administration as evidential breath testers.

Advantages:

• The sensors are small in size and rather inexpensive to manufacture. Lowest priced breath testers.
• These instruments are sold in convenience stores and mail-order-catalogues.

Disadvantages:

•  The sensor is very unstable, drifty and non-specific to alcohol.
•  It reads all hydrocarbons (organic vapors) and will habitually produce false positive alcohol readings caused by smoker’s and car exhaust CO as well as many other environmental vapors and gases.
• This senor is partial pressure sensitive and therefore changes sensitivity with change in altitude and elevation.
• This sensor is sensitive to changes in ambient temperature, humidity and breath flow patterns.
• For these and other reasons, solid-state sensor instruments can’t be employed in evidential and legal applications.

3. Electro-chemical cell technology (“EC”):

Most commonly called “fuel-cell”. Fuel-cell technology for alcohol analysis was first introduced in the early 1970s by an Austrian researcher. The EC sensor requires a sampling system consisting of a piston or bellow pump assembly, applying a very precise amount (~ 1 ccm) of breath to the sensor. The volume consistency is highly important because the current produced by the sensor is proportional to the total number of alcohol molecules converted in the sensor.

 The sensor is composed of an immobilized electrolyte, flanked by an active and a passive electrode. The electrolyte and the electrode material are selected such that the alcohol to be measured is electrochemically oxidized and converted at the active electrode. The change in the electronic conductivity causes a rise in current flowing from the active to the passive electrode. The total electrochemical reaction is evaluated by time integration of the sensor’s current. This sensor’s life expectancy is approximately 4-5 years.

Advantages:

• The sensor is highly specific to alcohol.
• The measurement cannot be biased or influenced by endogenous substances such as acetone (diabetics and starving people), CO or Toluene.
• The sensor is highly sensitive, down to 0.1 ppm.
• Accuracy meets specifications for evidential instruments (NHTSA) and remains stable ≥ 6 months before having to calibrate it again.
• Its expected life term is approximately 5 years.

 Disadvantages:

• EC based instruments cannot observe the breath alcohol concentration throughout the subject’s exhalation . This doesn’t allow detection of alveolar breath (“deep lung air”), mouth alcohol, belching, burping, Gastro Esophageal Reflux Disease (GERD) and residual alcohol trapped under dentures or alcohol from bleeding gums.
• The EC sensor is cross sensitive to other alcohols such as methanol and isopropanol.The EC sensor’s output is temperature dependent and suffers short term fatigue if the sensor is exposed to a series of successive alcohol containing tests.
• EC based instruments are not accepted for evidential use in many countries, states and jurisdictions.

4. Infrared Spectroscopy (“IR”):

IR technology (IR Spectra-photometry) based breath-alcohol testers were first introduced in the mid-1970s. IR instruments have become the standard worldwide for legal, evidential breath analysis.

The analytical concept is based on the Beer-Lambert Law of physics, the “Law of absorption”. It addresses the linear relationship between absorbance and concentration of an absorber of  electromagnetic radiation. Alcohol vapor introduced into an absorption chamber will absorb some of that IR radiation transmitted through the chamber. The amount of IR absorption is in direct proportion to the quantity of alcohol present (breath-alcohol). However, only IR-radiation of a specific wavelength will absorb alcohol. The two predominantly utilized wavelengths are centered at 3.39 and 9.5 μm. The latest generation instrumentation monitors IR absorption at 9.5 μm because the measurements are far less prone to interference from any hydrocarbons and acetone which absorb IR energy at 3.4 μm.

The most significant benefits of “real-time” IR absorption analysis (continuous measurement) requires understanding the dynamics of alcohol in the human breath. Some of these dynamics relate to gas exchange in the mucus membranes, residual alcohol in the upper respiratory tracks, belching, burping, Gastro Esophageal Reflux Disease (GERD), exhaled air volume, breath flow rates and the subject’s breathing pattern.

Only IR technology is capable of addressing these dynamic, physiological factors to determine a legitimate, rightful and legally as well as forensically justifiable breath alcohol measurement.

Advantages:

• IR based equipment observes the breath-alcohol concentration throughout the subject’s exhalation. This allows the plot of the entire IR-absorption curve and the instrument’s intelligence to assure that.
• The breath sample was of alveolar nature.
• No residual or mouth alcohol was present.
• The recorded absorption curve can be presented in court if the case is challenged.
• The IR system does not have a limited life expectancy, will not fatigue with successive, high alcohol concentration test series and remains extremely stable for years.
• These instruments are equipped with many other important peripherals and functionalities (please observe “Other required performance features for evidential breath testers” below).
• IR instruments are today’s standard worldwide for legal, evidential breath-alcohol analysis and consequently face fewer legal challenges than all other breath testing devices and technologies. 

Disadvantages: 

• IR instruments are larger in size thus, not suitable for portable, handheld operation.
• These instruments are more expensive than handheld (screening) equipment employing solid-state or EC sensors.

Various human specimens can be considered for measuring a person’s alcohol concentration level. All body fluids as well as expired breath are legitimate specimens for alcohol concentration measurements. However, the two most popular methodologies for medico legal alcohol testing are blood analysis and breath analysis.

Roadside tests or so called screening tests are conducted with handheld, mainly EC based instruments. These instruments are portable, battery operated and provide quick test results.The main objective of these tests are for confirmation of probable cause for submission to an evidential test procedure.

CARBON MONOXIDE ANALYZER (CO ANALYZER)

INTRODUCTION

As we know that the cost of fuels are increasing day by day ,the high cost of fuels makes an economic necessity to increase the efficiency of the fuel , harness it to fullest and to minimize excess air levels and thermal air stack losses . Efforts toward combustion efficiency optimization, however, must be aimed at reducing total energy loss. This requires achieving minimum unburned combustible, as well as thermal stack losses. More precise control of air/fuel ratio, optimized for minimum total energy loss, can yield significant gains in efficiency and result in substantial savings in reduced fuel consumption.

 Flue gas concentration of carbon monoxide is a reliable and accurate indication of burner flame stoichiometry and the completeness of combustion. It is the most sensitive indicator of unburned combustibles losses. Used as a primary combustion efficiency parameter, in conjunction with oxygen analysis, carbon monoxide offers significant advantages in controlling combustion at optimum levels of excess air. Controlling air/fuel ratio to an optimum level of carbon monoxide assures minimum total energy loss, and maximum efficiency, independent of variations in burner load, fuel type and fuel quality. The measurement is relatively unaffected by air in-leakage, and burner maintenance requirements are immediately identified .

OPERATING PRINCIPLE

The CO analyser  utilizes infrared absorption spectroscopy to continuously measure CO concentration in combustion flue gases. The infrared source is mounted directly on the flue gas duct or stack on the side opposite from the receiver. Infrared energy is radiated by the source, through the flue gas, to the receiver. The receiver employs gas filter correlation and narrow band pass optical filtration with a solid state detector to determine the absorption of radiation by CO in the flue gas. These principles are illustrated in block diagram form in below given Figure . Infrared energy, radiated by the source, passes through the flue gas, where a portion of the energy is absorbed by any CO present. The remaining energy passes through the receiver window, focusing lens and, alternately, through two gas cells. One of the two cells is filled with CO,the other, nitrogen. These are inserted alternately in the optical path at a fixed frequency. Energy at the wavelengths of interest is, effectively, fully absorbed in the CO reference cell; however, energy is transmitted through the nitrogen cell without further absorption. After passing through the narrow bandpass filter, the remaining energy impinges upon the detector. Two energy levels are sensed alternately by the detector: source radiation reduced by the flue gas and reference cell CO and source radiation reduced by flue gas CO only. The resulting signals are rationed and compared with the rationed signals developed under zero CO calibration conditions. The comparative difference in ratios is used to compute flue gas CO concentration. The calibration source and span calibration cell are inserted into the optical path during automatic zero and span calibration of the instrument.

INFRARED SOURCE

The infrared source module emits broadband infrared radiation, including the waveband of interest, from 4.5 to 4.9 microns. The source consists of a stainless steel body with a conical surface for uniformity of surface temperature and maximum emissivity. The source is heated to a temperature of 1,112°F (600°C) and is controlled at this temperature to assure constant intensity. The source is fully insulated and enclosed in a carbon steel mounting sleeve designed for welding directly to the duct.

Since the IR source module is installed such that the source surface is flush with the inner wall of the duct, the source is not subject to coating or particulate buildup in most applications. Consequently, there is no purge air requirement to maintain source cleanliness. Due to the large diameter of the source surface, focusing is not required, and the source contains no focusing optics whatsoever. An added benefit of the large diameter source is insensitivity to duct vibration and elimination of the need for constant realignment otherwise required of focused systems. Maintaining the source temperature at 1,112°F (600°C) requires powering the heater at a nominal 50% duty cycle, extending the heater element life considerably. The operating life of the infrared source is approximately four

times that of conventional infrared sources

INFRARED RECEIVER MODEL

The infrared receiver module is designed to house the optics, detector and necessary electronics and hardware to determine absorption of infrared radiation emitted by the infrared source module. The infrared receiver module is designed to house the optics, detector and necessary electronics and hardware to determine absorption of infrared radiation emitted by the infrared source module.

In situ CO instrumentation employing thermoelectrically cooled, photoconductive detectors, the receiver employs a non-cooled pyro electric detector. Not only does this provide reliable, stable performance at high ambient temperature, it completely eliminates the maintenance associated with thermoelectric cooling systems.

FLUE GAS TEMPERATURE MEASUREMENT

The absorption of infrared radiation by carbon monoxide in combustion flue gases is a function of flue gas temperature. The temperature affects the density of the gas and, therefore, the number of molecules encountered by the radiation. In addition, temperature variations induce variations in the infrared absorption characteristics of carbon monoxide. To account for these variations, flue gas temperature must be measured continuously. Temperature data is input to the receiver module and communicated to the control module. The control module software is fully characterized to provide accurate temperature compensation over the full flue gas temperature range of 200°F to 600°F (93°C to 316°C).

References :

Rosemount Analytical-Product Data Sheet PDS 106510A