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TC 17/SC 7 : Breath Alcohol Analysers
April 2006
C.2 MEASUREMENT ALCOHOL DURING EXHALATION / DETERMINATION OF THE
ALCOHOL PLATEAU
Curves of the alcohol concentration as a function of time obtained from a human exhalation
Theoretical curves:
By considering an average dead anatomical volume of 150 ml, a theoretical curve of the alcohol
concentration (expressed in %) according to time and volume of the breath can be calculated starting
from the following formula:
⎡ D * (100 − C (i −1) ) * (t i − t (i −1) ) ⎤
C i = C (i −1) + ⎢
⎥
Vm
⎣
⎦
(C 0 = 0) ; i = incremental indice
where C = alcohol concentration (expressed in %)
D = flow rate (L/s)
t = time of exhalation (s)
Vm = dead anatomical volume (L)
In theory, the alcohol concentration representative of alveolar air is obtained in the last third of the
time of expiry (concentration superior to 99 % of the maximum value)
Standard uncertainty on the alcohol concentration determined by a plateau and its variations must be
taken into account in the global calculation of the expending uncertainty of the test facilities in
accordance with the requirement of chapter A.3. (note : 1/3 EMT)
1st Committee Draft Recommendation on Breath Alcohol Analysers
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