More accurate breathalyser

Press, Volume CXIII, Issue 33189, 31 March 1973, Page 12

More accurate breathalyser

I By

Dr E. C. ROBERSON)

After years of research into the problem of correlating the concentration of ethyl alcohol on the breath with that in the blood an important factor in the relationship between intoxication and proneness to accidents on the road —two British scientists h.t\e evolved an instrument that will show at a glance exactly how much alcohol there is in the blood.

It is so cheap to manufacture that drivers may consider buying one themselves so that they can decide whether they ought to get behind the wheel. Statistical experiments relating the probability of road accident to the level of alcohol in a driver’s blood show that the probability begins to rise sharply at a blood alcohol level of about 75 milligrams of alcohol per 100 millilitres of blood. In the surveys carried out in a number of countries to establish this correlation blood alcohol levels have been measured in samples of breath taken from large numbers of drivers, including a significant number who had had accidents. The alcohol levels were determined with breathalyser apparatus correlated with blood alcohol levels measured by precise laboratory' analytical techniques. With the correlation established and accepted in many countries, these experiments have led to legislation prescribing fixed penalties for drivers convicted of having more than a given level of blood alcohol. The levels vary considerably from country to country; the level is zero in Eastern European countries, including the Soviet Union, 50 milligrams in Scandinavia, 80 milligrams in the United Kingdom, including Northern Ireland. Simple test To help police screen suspects, and to help the public itself, a simple test is used in which the blood alcohol level is related to the concentration of alcohol in the breath. This level is in turn dependent on the breath alcohol level being in equilibrium with the blood level in the lung. The concentration of blood alcohol changes with time, rising quickly as the alcohol is imbibed and falling slowly as it is burned up in the body and not replaced. The equilibrium level in breath will change in parallel with blood alcohol; it will also be affected by the depth and rapidity of breathing. The success of screening methods depends on the certainty with which the tester can say that the suspect has more than the statutory amount of alcohol in the blood. No indication The test now used by the police in Britain and in most other countries gives a

reliable indication of alcohol levels in the neighbourhood of the statutory limit but it gives no indication of the amount by which the statutory limit is exceeded. Experience in Northern Ireland indicates that 90 per cent of suspects have more than 150 milligrams of alcohol and a great deal of time and money has to be wasted to prove the real level. In the present test the suspect is asked to blow through a tube containing the indicator chemical and fill a plastic bag with breath within a specified time. The chemical indicator is yellow potassium chromate suspended in silica gel; the chromate oxidises the alcohol and turns green in the process. The alcohol level is measured by the length of the crystal column which turns green — the length which turns green showing against the statutory limit which is indicated by a mark on the tube. Confusion caused Not only is the demarcation between green and yellow less than sharp, but the length of colour change beyond the line gives no real indication of the blood alcohol content above the statutory limit —a cause of confusion in many cases. The waste of time — and money — involved in such cases can be eliminated if the police and public, and their legal advisers, all accept the readings given by a reliable and accurate blood alcohol meter used in the field, providing of course that a precise analytical test can be offered to resolve doubtful cases. The breathalyser now developed by Dr B. M. Wright and Dr T. P. Jones relies on the catalytic oxidation of alcohol in a specially designed fuel cell which collects the alcohol from the breath and uses it to generate a voltage. The alcohol is only oxidised to acetic acid which means that the cell is specific for alcohol. • Shown on meter The generated voltage is amplified in a small, solid state circuit and displayed on a meter calibrated in milligrams of alcohol per 100 millilitres of blood. The meter scale is linear, so that the confusion which is sometimes caused by today’s tests is overcome. To take a test a suspect simply blows through a large-bore tube in the instrument, which is about the size of a cigarette packet. The breath sample is then drawn off from the tube through a capillary by a small battery powered pump which sucks 2cc of breath through the fuel cell. The alcohol in the sample is absorbed on to a platinumblack coated disc — a fuel cell electrode — on which it is immediately oxidised, simultaneously producing the voltage and indicating the alcohol content on the meter Cheap to make Tests can be repeated every few seconds while the suspect continues to blow a lungful of breath through the meter. It is therefore very easy to follow the changes in alcohol concentration that occur due to the exchange mechanisms at work in the lung and the respiratory tract. It is also easy to determine quickly and accurately the maximum concentration of alcohol in the breath and hence in the bloodstream. The speed of operation, the accuracy and the linearity of the scale all mean that the new instrument can be used by the police of any country, no matter what the local statutory limit for blood alcohol may be. It is also cheap to manufacture in quantity so that it could be bought by drivers themselves so that they can decide with confidence whether to drive or not. A step towards establishing the instrument will be the tests shortly to be carried out in the United States and in South Wales. —From ’Spectrum”