COMPARISON OF A BREATHALYZER MODEL 900B PROTOTYPE

COMPARISON OF A BREATHALYZER MODEL 900B PROTOTYPE WITH THE BREATHALYZER MODEL
900A
Yale H. Caplan, Bruce A. Goldberger, and Gilman E. Physioc Office of the Chief
Medical Examiner, Baltimore, Maryland, U.S.A.
Summary. National Draeger has recently developed a prototype Model 900B
Breathalyzer to serve as a semi-automated digital readout device for breath
ethanol testing.
Statistical evaluation of a single Model 900B prototype (#1) with the
established Model 900A resulted in variation (SD and range) in the 900B greater
than that of the 900A. Although such variation would be within acceptable
limits for a preliminary single unit comparison, it is likely to be too great
to meet various state requirements for precision and accuracy and/or to
maintain appropriate field tolerance over an extended period of time. A
Breathalyzer 900B prototype (#2) later submitted with additional modification
produced results closer to those experienced with the 900A.
INTRODUCTION
National Draeger, Inc. has developed a new breath test instrument, the
Breathalyzer 900B. The new instrument utilizes the Breathalyzer 900/900A
breath collection chamber and photometer assembly. However, the electronics of
the instrument have been redesigned. A microprocessor controlled stepper motor
has been added to enable automated balancing of the photometer. Digital
results are displayed and a printer has been added. In addition, the physical
construction of the Breathalyzer 900/900A was modified. The top panel is
attached with a hinge such that the photometer assembly, breath collection
chamber and pc board are readily accessible.
Two Breathalyzer 900B prototype instruments were submitted by National Draeger,
Inc. for evaluation. Prototype #1 was the original unit and Prototype #2 was a
modified unit. Breathalyzer 900B - Prototype #2 modifications included the
replacement of the normal light source with a halogen bulb, the use of a full
nut on the drive system and installation of faster responding photocells.
STUDY PROTOCOL
The following protocol (adapted from the U.S. Department of Transportation's
"Standard for Devices to Measure Breath Alcohol") was used to evaluated each
instrument:
1. Breathalyzer 900B - Prototype #1
A. Evaluation was performed during a three month period.
B. Testing was performed coincident with testing of a Breathalyzer 900A.
C. Simulator solutions were prepared daily from a stock simulator solution
traceable to NIST to provide vapor ethanol concentrations of 0.100, 0.200 and
0.300 g/210L.
D. The daily testing sequence included 3 tests at 0.100 and 0.200 g/210L
766
vapor ethanol concentrations and 4 tests at 0.300 g/210L vapor ethanol
concentration. A maximum of 10 samples was delivered from any simulator.
E. A total of 60 tests were performed at the 0.100 and 0.200 g/210L vapor
ethanol concentrations and 80 tests at the 0.300 g/210L vapor ethanol
concentration.
F. Mean, standard deviation, coefficient of variation and range were
determined at each concentration.
2. Breathalyzer 900B - Prototype #2
A. Evaluation was performed during a two week period.
B. Simulator solutions were prepared from a stock simulator
traceable to NIST to provide vapor ethanol
concentrations of 0.050, 0.100, 0.150, 0.200 and 0.300 g/210L.
solution
C. A total of 12 tests were performed at each concentration.
D.
Mean, standard deviation, coefficient of variation and range were
determined at each concentration.
RESULTS
Breathalyzer 900B - Prototype #1 :
Utilizing a range of vapor ethanol concentrations, statistical analyses
revealed greater variability of test results at each concentration when
compared to a Breathalyzer 900A. Results of the evaluation for the
Breathalyzer 900B - Prototype #1 and the Breathalyzer 900A are indicated on
Tables 1 and 2.
Purge blank readings obtained during the evaluation were variable and slightly
elevated with a mean of 0.010 g/210L, standard deviation of 0.0052 g/210L and
range of 0.003 to 0.026 g/210L.
Breathalyzer 900B - Prototype #2 :
Utilizing a range of vapor ethanol concentrations, statistical analyses
revealed good accuracy and precision at each concentration. Results of the
evaluation of the Breathalyzer 900B - Prototype #2 are indicated on Table 3.
Purge blank readings obtained during the evaluation were more consistent with a
mean of 0.007 g/210L, standard deviation of 0.0028 g/210L and range of 0.003 to
0.014 g/210L.
DISCUSSION
Two prototypes of the Breathalyzer 900B were evaluated at several vapor ethanol
concentrations. Accuracy and precision were assessed using a protocol adapted
from the U.S. Department of Transportation's "Standard for Devices to Measure
Breath Alcohol". The Breathalyzer 900B - Prototype #1 produced accurate
results, but lacked sufficient precision. In addition, slightly elevated and
767
variable purge blank values were observed. The Breathalyzer 900B - Prototype
#2 produced accurate and precise results with acceptable purge blank values.
Improvements to the Breathalyzer incorporated into the new Breathalyzer 900B
include :
a. semi-automated operation including fully automated balancing of the
photometer
b. test results are displayed digitally and can be printed
c. bulb alignment not necessary with new halogen bulb
d. hinged cover permits greater accessibility to the photometer assembly,
breath collection chamber and pc board
The Breathalyzer 900B still requires additional modifications including changes
to the drive system. The current indirect drive system should be replaced by a
direct drive system to improve precision. In addition, it would be
advantageous to include the printer within the housing of the unit, rather than
as an external unit.
CONCLUSIONS
Statistical analyses indicate that the Breathalyzer 900B - Prototype #2 met or
exceeded the performance requirements adapted from the U.S. Department of
Transportation Standard for quantitative breath-alcohol analyzers. In addition,
the unit yielded results similar to those observed with a Breathalyzer 900A.
Note that the studies described were limited to accuracy and precision. The
results indicate that the Breathalyzer 900B -Prototype #2 is suitable for
consideration as a breath-alcohol analyzer. However, more extensive studies
would be necessary, including the examination of several production units, in
order to ensure the validity of the instrument for use in a breath-alcohol
testing program.
Address for correspondence :
Office of the Chief Medical Examiner
111 Penn Street
Baltimore, Maryland 21201
U.S.A.
768