Leferenc®

rvitJb Publications

NBS Special

Publication

480-41

NAT'L INST. OF STAND & TECH

Breath Alcohol Sampling

Simulator (BASS) for

Qualification Testing of

Breath Alcohol

Measurement Devices

Law Enforcement

Equipment

Technology

U.S. DEPARTMENT OF

COMMERCE

National Bureau of

Standards

-QC

IQO

.U57

NO. 480-41

1981
r
NBS Special Breath Alcohol Sampling

Publication

480-41

KATIOJtAL BUREAU

or wtAtWAMua

UBBART

JUL 9 1981

/lot (h

Simulator (BASS) for .^^ / Qualification Testing of v^^^

Breath Alcohol

Measurement Devices

by

A. Flores

Transportation Systems Center

Cambridge, MA 02142

and

L. K. Eliason and Y. C. Wu

Center for Consumer Product Technology

National Bureau of Standards

Washington, DC 20234

prepared for the

National Highway Traffic Safety Administration

U.S. Department of Transportation

Washington, DC 20590

Issued July 1 981 U.S. DEPARTMENT OF COMMERCE

Malcoinn Baldrige, Secretary

NATIONAL BUREAU OF STANDARDS

Ernest Ambler, Director
Library of Congress Catalog Card Number: 81-600075

National Bureau of Standards

Special Publication 480-41

Nat. Bur. Stand. (U.S.), Spec. Publ. 480-41, 31 pages CODEN: XNBSAV

U.S. GOVERNMENT PRINTING OFFICE WASHINGTON, DC: 1981

For sale by the Superintendent of Documents

U.S. Government Printing Office, Washington, DC 20402

Price $2.50

(Add 25 percent for other than U.S. mailing.)
FOREWORD

The National Highway Traffic Safety Administration (NHTSA) is engaged in a continuing effort to fulfill the objectives of the Highway Safety Act of 1968. To this end, NHTSA has implemented the development of Qualified Products Lists (QPL) for breath alcohol analysis instruments, and is pursuing the development of a QPL for speed measuring devices. In this effort, it is receiving technical support from the National Bureau of Standards' Law Enforcement Standards Laboratory

(LESL), whose overall program involves the application of science and technology to the problems of

crime prevention, law enforcement equipment, and criminal justice.

LESL is assisting the NHTSA Alcohol Countermeasures Program by the development of per- formance standards for the variety of instruments used to measure the blood alcohol content from

breath samples of suspected drunken drivers, and through related research. Among the tasks being performed by LESL for NHTSA are the preparation and publication of

technical reports on the results of its researches. This document is one such report.

Technical comments and suggestions are invited from all interested parties. They may be

addressed to the authors, or the Law Enforcement Standards Laboratory, National Bureau of Standards, Washington, DC 20234.

Lawrence K. Eliason, Chief

Law Enforcement Standards Laboratory

iii

CONTENTS

Foreword

Executive Summary ^-

1. Introduction j 2. Parameters to be Modeled by a Sample Simulator 2

3. BASS Design Objectives ^ Temperature ^ Volume and Time ^ Flow Rate and Pressure Alcohol Concentration ^

4. TSC Breath Alcohol Sampling Simulator ^

Design Approach

Assembly and Operation (j Determination of Sampling Parameters 12 Concentration-Time Profile \2

Pressure, Volume, and Rate of Delivery I7

5. Conclusions and Recommendations 24

Appendix A—References 25

V

EXECUTIVE SUMMARY

The U.S. Department of Transportation (DOT) Alcohol Countermeasures Program was

established by authority of the Highway Safety Act of 1968 in an effort to remove the drunken

driver from our Nation's roadways. State and local governments participating in this program

utilize evidential breath testers as a convenient means of measuring the blood alcohol content (BAG), of individuals suspected of drunken driving, for later use as evidence in the prosecution of those individuals whose BAG exceeds statutory limits. The National Highway Traffic Safety

Administration (NHTSA) encourages State and local government participation in the countermeasures program, permitting Federal funds from the program to be used to purchase

breath alcohol instrumentation, provided that the equipment is selected from the NHTSA

Qualified Products List. The analysis of the ethanol concentration of a suspect, displayed in units of BAG, is accomplished using a sample collected from a single breath that the accused delivers to the instrument. The physiological characteristics of humans vary widely from one individual to another. Since the BAG of a suspect is measured from a single breath, the differences in the

respiratory system of the individuals that comprise the driving population are of critical importance to the design of breath alcohol instruments, for an accurate analysis requires a sample

that is essentially "deep lung" or alveolar air. This report describes a Breath Alcohol Sample Simulator (BASS) that was developed by the DOT Transportation Systems Genter in cooperation with the National Bureau of Standards' Law

Enforcement Standards Laboratory to provide an objective, reproducible mechanical substitute for human subjects in the evaluation of the performance of the breath sample collecting systems of breath alcohol instruments. Prior to undertaking the design of BASS, the results of earlier studies involving drinking human subjects were reviewed to analyze the relationship of the ethanol

concentration in a single breath (exhalation) as a function of time. These data were expanded upon

during the current laboratory research with non-drinking human subjects in a series of experiments using individuals with a range of vital capacities and respiratory capability. The

concentration of GO2 as a function of exhalation time for single breath samples was monitored for each subject when blowing into three tubes of different flow resistance, which approximated the range of resistance offered by commercially available evidential breath testers. These data,

combined with statistical data on the range of vital capacities of the U.S. driver population, serve

to establish the parameters that must be controlled in order to insure that the BASS can reproduce

the extremes of single breath exhalations. Each of the essential parameters that must be controlled to produce a substitute for human

breath is discussed, and the capability of the BASS to achieve that degree of control is described,

together with the detailed design and operating characteristics of BASS. Data are presented that establish the need for a three-segment ethanol vapor concentration profile, in which the time and

volume are controlled to produce a continuous sample that will allow the sample collection system

of breath alcohol analysis systems to be evaluated. Three specific BASS delivery cycles are recommended that include the range of vital capacities and flow rates, encountered in the driving

population, which must be accommodated by an evidential breath tester to insure that the analysis of BAG is accomplished using a sample that is essentially deep lung air.

It is recommended that the BASS be incorporated into the NHTSA standards for breath

alcohol testing instruments as the basis for all future qualification testing to eliminate the need of human subjects to evaluate the breath collecting capability of such instruments.

vii

BREATH ALCOHOL SAMPLING SIMULATOR (BASS)

FOR QUALIFICATION TESTING OF BREATH

ALCOHOL MEASUREMENT DEVICES

A. Flores

Transporlalion Systems Center, Cambridge, MA 02142

L. K. Eliason, Y. C. Wu*

National Bureau of Standards, ff'ashington, DC 20234

The blood alcohol content of an individual suspected of driving while intoxicated is often measured

through the analysis of a breath sample using an evidential breath tester (EBT). Two factors determine the

ability of an EBT to provide an accurate analysis of alcohol concentration: a) the capability of obtaining an

appropriate breath sample, and b) the inherent accuracy of the analytical instrument. This report characterizes the relevant breath parameters and describes a breath alcohol sample simulator (BASS) that was developed as a means of reproducing accurate equivalents of human breath. The report discusses measurements made on human subjects to establish values for parameters the BASS must accommodate, and to demonstrate the validity of the BASS as a replacement for human drinking subjects with different levels of alcohol content and a range

of physiological characteristics.

Key words: Blood alcohol analysis; blood alcohol content; breath alcohol content; breath sampling; evidential breath testers; human respiratory characteristics; intoxication.

1. INTRODUCTION

The Highway Safety Act of 1968 has resulted in the establishment of a nationwide Alcohol Countermeasures Program of the National Highway Traffic Safety Administration (NHTSA). The

goal of the program is to remove drunken drivers from the roads. In pursuing this goal the NHTSA provides funds to assist the State and local governments in the procurement of breath

alcohol test equipment.

All states have accepted blood alcohol concentration (BAG) as part of the legal basis for prosecution of individuals arrested for driving while intoxicated. Blood alcohol concentration (BAG) is universally accepted as evidence in the prosecution of individuals charged with driving while intoxicated. The Uniform Vehicle Code [1] recognizes breath alcohol measurement as a means for determining BAG. Trained police officers can perform

breath analyses more easily than blood analyses. Moreover, some investigators claim that breath

analysis is a better test of impairment of driving ability because of the variability of ethanol content of the blood sample, which is dependent upon the part of the body from which the sample

is obtained [2]. A number of commercially available breath alcohol testing devices give sufficiently accurate

results to justify their use as evidence in the prosecution of allegedly drunk drivers. These devices,

known as evidential breath testers (EBT's), utilize various instrumental techniques and principles of measurement [3].

* Center for Consumer Product Technology, National Engineering Laboratory.

' Numbers in brackets refer to references in appendix A.

1
In 1972, NHTSA initiated a program with the Law Enforcement Standards Laboratory

(LESL) of the National Bureau of Standards (NBS) to develop standards for EBT's and to establish a Qualified Products List (QPL). (State and local governments may use Federal funds from alcohol countermeasure programs for the procurement of equipment on the QPL only.) The standard for evidential breath testers was published by NHTSA in the Federal Register in 1973 [4], and the standard for calibration equipment in 1975 [5] . Two factors determine the ability of an EBT to provide an accurate analysis of alcohol

concentration: a) the capability of obtaining an appropriate breath sample, and b) the inherent accuracy of the analytical instrument. The precision and accuracy of the EBT are readily

determined by replicate measurements using vapors of known alcohol concentration. However, in order to determine if a given instrument collects an appropriate human breath sample, it is necessary to correlate the breath-estimated BAG reading of the instrument with either actual blood

alcohol concentration, or with breath that is known to have the same concentration of alcohol as

air in the alveoli of the lungs. The standard issued in 1973 required determination of the breath sampling characteristics of EBT's through direct correlation of blood analysis with instrument

readings of breath alcohol concentration. The breath and blood samples were taken on as nearly a simultaneous basis as possible. Later, an improved test method to evaluate the breath sampling characteristics of EBT's and

other breath alcohol instruments was developed to serve as the basis for QPL acceptance. The

alcohol concentration is first determined for a single breath of one subject, then compared to the instrument reading obtained after the same subject repeatedly inhales and exhales (rebreathes) the same air into a collapsed plastic bag. The measured alcohol concentration of the single breath sample is typically about 10 to 20 percent lower than that of the rebreathed levels. Rebreathed

breath samples very closely approach the alcohol concentration of that portion of the breath that is in equilibrium with the pulmonary blood [2,6] (see also sec. 2 below). An evidential breath tester

is considered to be satisfactory if paired comparisons of blood and breath alcohol concentrations,

taken over many subjects, yield a correlation coefficient of at least 0.95. Furthermore, since it has been recognized that breath alcohol readings tend to be biased toward lower values than blood

alcohol concentration, a limiting value of -22 percent has been set: that is, the breath alcohol concentration must not be less than 78 percent of the value for blood alcohol concentration. These procedures are acceptable, but have the following undesirable features:

• It is impractical to obtain a sample of human subjects that (a) is representative of the drinking driver population, and (b) is large enough to account for physiological variability

among individuals yet at the same time small enough to manage within the limits of available laboratory resources.

• Federal guidelines require that experimental data be obtained without human

experimentation whenever possible.

• Medical monitoring of intoxicated subjects is increasingly difficult to obtain.

There are obvious advantages to the replacement of human subjects with a mechanical system

that is essentially an operational equivalent to the human subject for this purpose, and whose

performance is more reproducible. Of course, human breath cannot be faithfully reproduced in every respect. Nonetheless, the key physical parameters relevant to breath alcohol content measurement can be closely modeled and simulated. It is the purpose of this report to characterize relevant breath parameters and to describe the Breath Alcohol Sample Simulator (BASS) that was

developed by the Transportation Systems Center (TSC) as a means of reproducing accurate equivalents of human breath. The report discusses measurements made on human subjects to establish values for parameters that the BASS must accommodate, and the demonstration of the

validity of the BASS as a replacement for human drinking subjects with different levels of alcohol

content.

2
2. PARAMETERS TO BE MODELED BY A SAMPLE SIMULATOR

It is necessary to understand the essential features of the human respiratory system in orfJer to consider the effects of the presence of alcohol and to characterize those attributes which can be measured, modeled, and simulated. A more complete treatment than the summary discussion below can be found in any standard text on human physiology.

The airways of the respiratory system include (a) the alveolar sacs within the lungs and (b) the upper respiratory tract (URT), which consist of the oro-nasal cavity, pharynx, larynx, trachea,

bronchi, and bronchioli. Where blood vessels contact the alveoli, the surface-to-volume ratio is much higher than that in the remainder of the respiratory system. Consequently, the alveoli-blood

interface is the primary locus for active gas exchange between blood and breath, with relatively

little exchanged elsewhere. Here, then, almost all alcohol exchange takes place. All components of the entire respiratory system are covered with watery mucus that plays an important role in establishing the alcohol content of expired breath. As air laden with alcohol vapor, carbon dioxide, or other gases passes through the system, some molecules are dissolved into the surface moisture. At any given moment, during a breathing pause, stationary air in the URT

contains alcohol vapor tending toward equilibrium with the watery film. Following an inhalation, alcohol deposited in the watery film during the previous expiration is mixed with other gases

present. A single expiration at this time manifests an alcohol concentration much lower than that found in the alveoli. However, if the mucus of the URT becomes saturated with respect to alcohol—as would occur with rebreathing exhaled breath several times—the expired breath reaches an alcohol concentration comparable to that deep in the system. The effect of a single (i.e., non-rebreathed) expiration is production of an asymmetric alcohol concentration profile over time;

figure 1 shows typical mass spectrometer traces of forced human exhalations, using ions from

a) INTOXICATED HUMAN SUBJECT

(ETHYL ALCOHOL)

BREATH ALCOHOL SAMPLE SIMULATOR

(ETHYL ALCOHOL)

FlcUHK 1. Typical mass speclromeler profiles (concentration \'s. time). (Ion specimen monitored: for ethanol mass 31, for carbon dioxide mass 44. Concentration units are arbitrary). Note: Failure of CO, concentration to return to base line

after completion of exhalation is an artifact of instrumental set-up.
either ethyl alcohol or carbon dioxide as expired air indicators. The absorption-desorption process underlying this profile is described in more detail elsewhere [2,7,8]. The air-to-blood and air-to-water partition coefficients for ethyl alcohol have been determined

[2,9]. In vitro measurements yielded the partition ratios shown below (in terms of volume of air containing the same amount of alcohol as one volume of liquid in equilibrium with air):

Temperature Liquid/air volume ratio

Blood 37° 1/1692

(Pulmonary blood temperature)

34° 1/2033

(Average single breath temperature)

Water 37° 1/2128

34° 1/2538

In vivo measurement of the alcohol concentration of the end portion of expired breath for single breath [2] and rebreathed breath [2,6,10] yield the following ratios:

Average breath temperature Blood/air volume ratio Smgle breath 34 °C 1/2300

Rebreathed breath 34°-36 °C 1/2100

These data indicate that, even in the alveoli, alcohol vapor is in equilibrium with surface

water, rather than blood. (That the rebreathed temperature does not reach 37 °C is related to the

fact that the data were not obtained at 100% relative humidity, i.e., inspiration of dry 37 °C air cools URT by evaporation of surface water.) The single breath ratio obtained for a given individual varies according to the pattern of breathing prior to sampling, ambient temperature and the volume expired. The National Safety

Council has established a ratio of 1/2100 as a firm upper limit when converting single breath

alcohol levels to blood alcohol concentration. Application of this ratio (instead of 1/2300) to breath alcohol testing provides a generous margin in favor of the accused in drunk driver proceedings. In other words, any lower ratio (such as 1/2300) would yield higher estimates of blood alcohol concentration. As is shown in figure la, the expired breath profile can be viewed as a sequence of three

distinct sections in terms of the relative alcohol concentration and the rate of change: a small

initial portion (io-'t) low in alcohol, but with rapidly changing concentration; an intermediate

portion {ti,-t\,2) with slowly changing concentration; and a final portion (fi/2-0 in which a steady

state of the highest concentration has been reached. It will be seen in section 4 that the last quarter of the total volume of expired breath is appropriate for determining the "highest"

concentration (alveolar alcohol concentration). Since the vital capacity^ of most adults lies between

2 and 6 liters (L) [7], not more than 500 mL of the final portion of an expired breath should be

retained for analysis to ensure that the breath tester sampling system will be applicable to all individuals, including those with the smallest vital capacities.

Given the objective of accurate assessment of alcohol concentration in the deep respiratory

system and in view of the asymmetry of the time profile of alcohol concentration of expired air, the optimal measuring device should be designed to discard the first portion of expired breath,

retaining only the last portion for analysis. It is similarly obvious that an artificial breath sample must be generated in a controlled sequence to produce an appropriate time-concentration profile at a prescribed flow rate for a specified volume. The volumes of (simulated) breath that are discarded

Vital capacity is the maximum volume of air which can be exhaled by a person following a maximal inhalation.

4
and retained will then depend on the flow rate. At constant delivery pressure, flow rate is in turn determined by the flow resistance of the breath tester; if that flow resistance is high, resultant high flow pressure undesirably induces a backward flow of air and compression of the air. A backflow, related to turbulence and system geometry, causes mixing of the air delivered

earlier and later, thus diluting the analyzed portion and biasing the measurement of alcohol concentration on the low side. The direction of bias results from compression, which increases the

density. In the normal operation of most breath testers, the collected breath sample volume

expands upon reverting to atmospheric pressure before analysis; hence the apparent alcohol concentration is less than the actual [8]. (This effect is discussed further below.) To avoid backflow

and compression effects, it is desirable to design EBT's with low flow resistance. In sum, the volume, flow rate, flow pressure, and temperature of the expired air during the

collection process are the key parameters which affect the measured value of alcohol concentration. The following section discusses the characteristics of the sample simulator

developed by TSC to model these parameters.

3. BASS DESIGN OBJECTIVES

The BASS is a mechanical device that can objectively produce an intended substitute for human breath; its purpose is to test the sampling performance capability of an EBT. The

appropriate breath sample for an EBT is that portion of the exhalation that contains an adequate

amount of the undiluted portion of expired alveolar air. Since the measured alcohol concentration depends strongly on the parameters discussed in the last section, each parameter requires control, the degree of which depends on the relationship of that parameter to alcohol concentration. A

sampling simulator incorporating and properly controlling the required functional parameters

should then satisfy the objectives.

The requisite functional parameters and their relationships to the alcohol concentration in the breath sample collection process are discussed in the following sections. Human physiology varies with individuals and also with time in the same individual, hence any given functional relationship

is based on statistical averages. In those cases where choices were necessary, a conservative approach was used in the sense that assigned values would result in an estimated BAG on the low

side, thus affording greater protection for a driver accused of drunkenness.

Temperature

The average temperature of expired breath is 34 °C. The temperature coefficient for partition of alcohol in the temperature range from 20°-40 °C is about 6 percent per degree. Control of temperature to within ±0.1 "C is required in order to produce samples with ethanol vapor

concentrations that meet the requirements of the NHTSA Standard for Calibrating Units [5]. Volume and Time

The volume of breath measured after deep inspiration and forced exhalation (vital capacity) varies among individuals from about 2 to 6 L [7], and may take an adult, depending on age, sex, and physical condition, from 6 to 17 seconds (s) (see sec. 4) to deliver into currently available EBT's. To be able to simulate the undiluted expired alveolar air contained within the last quarter

portion of the breath, the BASS must accommodate total volumes equivalent to the full range of

vital capacity (2 to 6 L) and deliver the sample over times of 6 to 17 s.

5
Flow Rate and Pressure

According to the Poseuille equation for laminar flow in a pipe, the flow rate, Q (volume per

unit time), is related to the pressure drop from the inlet to the outlet, A/>, by

Q = ^p

where r is the radius and / is the length of the pipe through which the fluid flows and ju, is the

viscosity of the fluid. Since the flow resistance is inversely related to the pressure drop, it follows

that 8]U.// TTr* is the flow resistance. If the latter is a constant, the flow rate is directly proportional

to the pressure drop. If the pressure drop is to be minimized while keeping the flow rate constant, the flow resistance must be lowered. This may be accomplished by reducing the length or increasing the radius of the flow pipe, or by doing both. Physiologically, the flow resistance is about 3.3 cm HjO-s/L in normal breathing through the

oro-nasal cavity fll]. For a flow rate of 1 L/s, which corresponds to 6 L of air delivered in 6 s, the pressure drop is only about 3.3 cm H^O. A BASS whose output is open to the atmosphere

should therefore have a flow resistance of 3.3 cm HjO-s/L to assure that the simulator delivers simulated breath to an EBT without inducing error. The effect of the delivery pressure into EBT's

will be discussed in section 4.

Alcohol Concentration

The expirogram shown in figure la shows a typical profile of breath alcohol concentration. A

sample simulator must generate a sample with an alcohol concentration profile with increasing

levels of alcohol concentration, attaining a final concentration plateau comparable to the level of

the final concentration in the breath profile. However, the latter portion of the simulation will be

adversely affected if flow resistance in the breath tester induces high delivery pressure. This

problem will be addressed in the following section.

4. TSC BREATH ALCOHOL SAMPLING SIMULATOR

Design Approach

Typical asymmetric breath alcohol profiles (as shown in fig. la) can be approximated (as in

fig. Ic) by arranging several commercial simulators in parallel, their exit tubes all connected to a common manifold. By switching air through the several simulators in an appropriate sequence, a

series of profile steps, joined together, will produce a single profile. The resultant overall profile can be shaped as desired by adjusting the amount of alcohol in the individual simulators and by

regulating the times of switching. This design approach was followed in constructing the BASS, a block diagram of which is shown in figure 2.

Assembly and Operation

The elements of BASS construction are shown in figures 3 through 6 (pressure gage is not shown). Figure 3 shows the operation of the device. A 7-L air-driven floating piston and cylinder

assembly delivers air through the three temperature controlled alcohol solution reservoirs. The

output mixture of alcohol and air is passed into the breath test instrument being evaluated. The following discussion identifies by manufacturer and model the equipment used in fabricating the prototype BASS unit. However, mention of an item or manufacturer in no way

constitutes an endorsement of the products by either the NBS or the DOT Transportation Systems

Center. Any equipment which meets the functional requirements described herein may be used to construct a breath alcohol sample simulator.

6
PRESSURIZED #3 OUTPUT

TO COMP

AIR SUPPLY

#1 OUTPUT

#2 OUTPUT

OUTPUT

m AIR FROM COMP AIR SUPPLY

AIR FROM PISTON PRESSURE

VALVE OPEN S VALVE CLOSED

FuiUKK 3. Breath alcohol sample simulator operating diagram.

7
INDICATOR ROD

TO RESERVOIRS ASSEMBLY, PRESSURE GAGE, ETC.

COMPRESSEDAIR SUPPLY

15"

3/4" 1

FLOATING PISTON

6-15/16" DIA,

7"-

.RING SEALS 12]

-7/16"

VENT

Fl(;iil<K 4. BASS construction. Air supply assembly.

8
o

cc

C9

cc O Q_

— V7 \

9
10
The cylinder assembly is shown in figure 4 and reservoir assembly in figure 5. Input and

output solenoid valves (Model 53C18HN14-2, Valcor Engineering, Kenilworth, NJ) are automatically controlled so that air passes through each solution at the proper time and for the proper duration. The wiring diagram for the control of the solenoid valves and the timers is shown

in figure 6. A typical output alcohol profile is shown in figure Ic. Concentration step heights are determined by alcohol concentrations in solutions 1, 2, and 3, contained in the three reservoirs,

respectively. (Solutions are replaced frequently to compensate for alcohol depletion on use.) Step

widths are determined by relay timer (Model W21LMASOX-2, Magnecraft Electric Co., Chicago,

IL) settings, which control the solenoid valves. Timers are individually adjustable from 1 to 12 s. Heaters, thermo-regulators, and stirrers used in the solution reservoirs were taken from MKII

Simulators, Smith and Wesson Electronics, Springfield, MA, the shafts of which were extended. Air diffusers (double) were taken from Model 999 Air Pump, Lew Childre and Sons, Inc., Foley, AL. Precision thermometers were used to monitor temperature. Working pressures are variable from 0 to 500 cm H2O (0-200 in H2O). Although maximum human delivery pressures correspond

to only about 160 cm HjO (64 in H2O) [11], higher working pressures are needed to overcome the high flow resistance of the air diffusers.

If convenient, sample volumes delivered into breath testers can be measured at the breath

tester vent port, which is connected to a 9 L recording vitalometer. If the breath tester vent port is not accessible, the unit under test can be placed in an air tight glove box of sufficient size to provide at least 15 cm (6 in) clearance between the sides and top of the interior surfaces of the glove box. The glove box should have internal outlets for 110 V ac power, or connections for dc

power as appropriate for the instrument under test and a transparent viewing window that allows observation of all controls and displays of the breath tester. The output of the BASS is connected

to the input of the breath tester through an air tight feed through. A fitting is installed in a wall of

the glove box, to which the 9 L recording vitalometer is connected. The sample volume delivered

to the breath tester is then measured directly as the volume of air displaced from the glove box.

Alternatively, the volume delivered can be calculated from initial and final pressure readings

of the BASS as follows: the number of moles of gas, n, delivered by the apparatus, at a constant temperature, T, is

n(f)-n{i) = An =

RT

LnRT = A ipv) = pfJfPfi = p'^-.

(2)

(3)

pf are initial and final driving cylinder pressures,

and are initial and final volumes,

p is ambient atmospheric pressure,

V is volume delivered, corrected to atmospheric pressure, and

R is the universal gas constant.

Since v-=TTr-h-\-V^ (volume of reservoirs) and v^=Trr^{h-d)+V„=^v~'nT^d where r is

cylinder radius, h is cylinder height, and d is piston displacement.

TTr [P-Pf) h +

TTr

,

(4)

11
neglecting air in the lines and valves. Converting in the second term from gage pressure to absolute pressure, volume delivered becomes

V, \

{p. -p) r + ~ + ^^P" -p + pj) ^

(5)

where Pq=' \ atmosphere (406.79 in water).

Determination of Sampling Parameters

As discussed earlier, physiological principles and the variability of human capability in delivering breath for determination of alcohol content, indicate that five parameters must be

considered. These are: temperature of sample; alcohol concentration profile; pressure drop or

delivery pressure; delivery time; and delivery volume. From the last three variables, two important

parameters (viz, delivery rate and flow resistance) can be obtained. The following discussion provides an evaluation of each of them in relation to the alcohol content of the sample.

Concentration-Time Profile

The typically measured asymmetric time profile of alcohol concentration, characterized by an

early, sharp rise followed by a gradual leveling, is simulated by the BASS in the form of stepwise

variations in alcohol concentration. We have found that this permits more precise and reproducible

time-concentration control than can be obtained by continuous changes; hence, air samples can be

controlled more accurately.

Human subjects participated in tests to obtain data and time-concentration profiles for expired breath. The subjects did not ingest alcohol and were not intoxicated, removing the element

of risk from the test program and eliminating the need for medical supervision.

As can be seen in figures la and lb, the CO, concentration profile is similar to that for alcohol. Consequently, the COj concentration in the expired breath of the test subjects was

monitored and analyzed continuously to serve as an indicator of the percentage of that gas in alveolar air. A total of 19 human subjects participated in the test program; their ages, sex, and other

characteristics are summarized in table 1 along with test results. This limited sample should not be

considered as definitively representative of the entire driving population—and certainly not of the subset of drunk drivers. Rather, the aim was to identify and calibrate physiological (and, to some

extent, behavioral) variability in collecting breath samples, along with estimating the values over which pertinent EBT sampling parameters may be expected to range. The ultimate aim, of course,

is to establish the effective ranges for the simulator to ensure that it produces the characteristics of simulated breath that ar^ needed for the evaluation of EBT's. The human breath sampling tests were conducted with simple laboratory surrogates for actual EBTs. Three polyethylene tubes [(0.635 cm o.d.X 0.437 cm i.d.) (1/4 in X 11/64 in)] were used to produce the resistance appropriate for simulating breath tester sample simulation. The pressure drops measured for actual EBT's were duplicated by varying the length of the polyethylene tubing.

Thus, a 97 cm tube length has a flow resistance that corresponds to the lowest value achieved by any of the EBT's measured; a tube length of 230 cm produces the greatest observed EBT flow

resistance. The simple geometry of the tubes obviously did not exactly reproduce the flow

characteristics of actual breath testers. Nevertheless, this laboratory device did make it possible to determine relationships between "alcohol" content and the various flow parameters which were

investigated.

To obtain data for this investigation, two side arms were attached to the tube inlet: one was

attached to a capacitance manometer, the other to the differentially pumped inlet of a mass

spectrometer for real time analysis of expired air CO2 content (which represented alcohol). Each

12
subject was asked to empty his or her lungs a number of times into each simulated tester without

special coaching. Results are shown in table 1, from which the parameters of interest here can be

evaluated. A statistical description of the results for time and concentration is summarized in table 2.

T Mii.i': 1 . It,rt'dfli sit iii/)/r iij It It lit an siihjftl

lei't Sex A (re I n he f '« I'l I'l ('. JC 1

1 K 41 2.5 A 6.9 0.8 2.0 14 1 1 69 86 15 B 8.6 0.8 1.8 18 16 75 86 14 C 7.5 0.6 1.7 14 12 59 86 1 1

2 M 44 4.8 A 13.2 1.9 4.7 62 38 76 94 25

B 14.4 1.1 4.5 53 36 69 94 25 C 16.0 2.2 3.8 44 34 73 93 20

3 F 28 2.8 A 5.1 1.0 1.8 13 12 63 89 14 B 8.8 1.1 1.4 16 13 61 86 14 C 9.8 1.2 2.3 18 15 57 83 15

4 M 40 5.0 A 15.1 1.3 4.6 16 27 60 85 20 B 19.5 1.4 4.6 28 14 53 88 17 C 21.1 1.6 4.5 29 20 60 95 20

5 F 27 1.8 A 10.4 0.8 0.9 63 85 14 B 14.0 1.0 1.6 1.0 0 65 84 16 C 11.3 1.1 1.8 1.0 0 59 83 15

6 M 46 3.3 A 8.9 2.2 2.7 49 50 76 95 29 B 10.0 1.6 2.7 35 44 83 90 33 C 9.4 1.4 2.7 36 41 69 93 23

7 M 35 4.6 A 13.3 1.8 3.8 55 27 64 87 28 B 14.0 1.3 4.2 54 28 63 86 22 C 17.9 1.1 3.9 51 20 59 86 22

8 M 60 4.0 A 7.8 1.3 3.1 23 15 73 93 22

B 12.4 1.1 3.1 22 17 53 88 17 C 16.1 1.1 3.1 26 16 53 85 20

9 M 46 4.3 A 8.1 1.1 4.3 59 38 54 76 19 B 11.8 1.5 4.4 66 42 64 93 14 C 13.5 1.3 4.3 70 44 59 88 16

10 M 34 4.8 A 10.9 0.4 4.0 27 0 58 85 17 B 11.5 0.8 3.5 40 6 39 89 18 C 11.5 0.7 2.8 40 12 48 90 15

11 M 36 3.6 A 7.6 0.9 3.1 44 27 70 90 20

B 12.0 1.2 3.1 44 44 73 88 24 C 12.6 1.1 3.0 33 44 67 89 23

12 M 53 3.1 A 5.5 0.8 2.7 72 17 80 95 20

B 9.3 1.3 2.7 80 25 69 90 21 C 8.6 1.2 2.9 81 22 70 90 20

13 M 43 6.0 A 12.0 1.4 4.4 41 0 69 n 1 1 Qlo B 18.7 2.7 4.9 54 5 70 88 17 C 19.7 1.9 4.6 55 0 54 86 18

14 M 47 4.0 A 8.4 1.0 3.6 48 32 56 80 13 B 9.9 1.4 3.6 56 29 55 88 17 C 13.0 1.5 3.7 74 35 57 83 18

15 M 44 5.1 A 7.5 0.8 4.1 76 26 56 91 17 B 9.4 1.1 3.9 88 26 68 89 19 C 10.5 1.2 3.9 95 26 62 86 21

13
T\H1.K I. Breath sample of human subject (continued)

jert Sex Age VC Tube t J Pi c,

16 M 56 5.2 A 12.1 0.9 3.9 30 35 60 86 18 B 16.1 1.5 3.6 15 22 58 89 19

1 4 6 2 4 0.4- 12 35 47 82 j7

17 M 50 4..-} A 11.1 1.4 4.1 - 69 94 16 B 14.4 1.6 3.9 60 94 15

/'

I

I .oR o t 9'^ 1 4.

18 M 47 .5.1 A 7.4 1.1 3.2 51 32 67 89 18 B 9.3 1.2 2.7 52 38 56 83 18 C 10.5 1.1 2.6 52 29 61 89 18

19 M 38 4.0 A 7.4 1.2 2.8 43 42 52 85 14 B 8.0 1.4 3.6 42 51 50 86 14 C 8.7 1.2 2.7 43 45 57 86 14

42.9 4.0

o- 8.73 1.10

A 97 cm tube B 164 cm tube C 230 cm tube VC Vital capacity

I Exhalation time h Time for exhalation concentration to reach "knee" in curve

V Exhalation volume

P, Initial delivery pressure

Pf Final delivery pressure CJC, Ratio COo concentration at "knee" to final concentration Ratio CO, concentration at midpoint of exhalation to final concentration

c, Final COj concentration Mean value

cr Standard deviation

14
T^llli, 2. Hunuin siilijerl exhaliilion /iiirdnicters n — 19

1 Q P. cm HoO

I'l cm H ,0

CJC, C„JC,

Tube s s L Us (mmHg) (mmHg) % Arb. units

25.4 1 l.,5 A 9.4 1.2 3.4 0.36 (47..5)

11.1

(47.5)

7.2

65 89 19

cr 2.8 0.4 1.0 .... (20.7)

28.3

(13.5)

13.0

8.5 5.3 4.6

B 12.2 1.3 3.3 0.27 (52.9)

11.2

(24.3)

7.4

62 88 19

a 3.4 0.4 1.0 ....

' (21.0)

28.0

(13.8)

12.7

10 3.0 4.8

C 13.1 1.4 3.2 0.25 (52.4)

12.4

(23.8)

7.4

59 88 18

cr 3.9 0.5 0.8 (23.1) (13.8) 6.8 3.9 3.4

Notes: Q Average e.xhalation flow rate. 4 97 cm tube B 164 cm tube C 230 cm tube VC Vital capacity

t E.xhalation time h Time for exhalation concentration to reach "knee" in curve

u Exhalation volume

Initial deliverv pressure

p, Final delivery pressure CJC, Ratio CO., concentration at "knee" to final concentration C„JC,- Ratio CO2 concentration at midpoint of exhalation to final concentration

Final CO, concentration Mean value

cr Standard deviation

15
The total delivery time averaged 9 1/2 s (ranging from 5.1 to 15.1 s) for the low resistance simulated tester, and 13 s for the high resistance one (with a range of 7.5 to 21.2 s). The average

time-concentration profiles (from the data of table 1) are plotted in figure 7. Here, the final CO2

concentration is taken as the (100%) alveolar concentration. The two graphs in figure 7 reveal that the concentration of CO2 reaches 60 percent at the knee, t^. of the profile and 90 percent by the midpoint, 1^,2 (in time). The CO2 profile of human

breath is approximately linear from the midpoint until the maximum concentration is attained (see also fig. la). Thus, it can be seen that air expired through the low resistance simulated tester reaches a concentration of about 95 percent of that of pure alveolar air after an average of 7 1/2

s; it takes an average of 10 s to reach the 95 percent level of alveolar air when the breath is passed through the high resistance tester. In general, the process of exhalation is steady, so that the volume of exhaled air is directly proportional to the time of exhalation (i.e., the exhalation rate

16
is constant). As seen in figure 8, the total time to empty the lungs in forced expiration with low

resistance, is typically about 5.5 s. Since the 95 percent level of alveolar air is reached in three- quarters of the total time of exhalation with resistance, it may be inferred that the expired volume

for reaching the same level of alveolar air will also be approximately three-quarters of the total expired volume. Based on this logic, the last 25 percent of the total expired volume is essentially

deep lung air and provides an appropriate sample for alcohol analysis. Indeed, if the last third of

the total volume were to be selected to represent deep lung concentration, this would afford an even greater margin of protection for the suspected drunk driver.

3.6

UME

(L

o>

0

1

1

5.5

TIME (S)

FkjURK 8. Volume of exhalation vs. time.

Since the volumes of the first two steps are not as important as the last, the concentrations

for those two steps are not critical. Concentration of alcohol in each segment, as indicated in figure

7, are most appropriately 60, 90, and 100 percent, respectively, of that of deep lung

concentration. The artificial profile then becomes:

Concentration step (1) (2) (3) Volume fraction 1/3 1/3 1/3

Alcohol concentration, BAC .060 .090 .100

Pressure, Volume, and Rate of Delivery

The partial vapor pressure of alcohol over aqueous solution depends only on solution concentration and temperature; it is not influenced by total pressure. The alcohol vapor pressure

therefore remains constant when the BASS delivers compressed air at a given pressure above

atmosphere by forcing it through each diffuser into the head space of the alcohol solution

reservoir. As a result, the head space gas pressure is increased throughout the constant volume.

Releasing the head space gas and vapor mixture to a sample collector at atmospheric pressure then

allows the mixture to expand, with a resultant decrease in alcohol concentration.^ The effect, as shown in figure 9, is that the greater the delivery pressure, the more the alcohol concentration

decreases. The effect is governed by the following relationship:

C Po

c p,+^p

where C and C are, respectively, the true (i.e., original) concentration and the (apparent)

'This discussion does not apply to those breath testers which are designed to analyze the sample at delivery pressure or higher pressure.

17
o

\ i \ \ \ L_

25 50 75 100 125 150

DELIVERY PRESSURE cm H2O

(ABOVE ATMOSPHERIC)

FlCUKK 9. Effect of delivery pressure on output concentrations of commercial simulator.

concentration measured after relaxation of delivery pressure in the collected sample; A/? is the

delivery pressure above atmospheric pressure According to the specifications of the standard [4], breath alcohol concentration must be

measurable with an accuracy of ±5 percent at levels typical of testing conditions. Referring to figure 9, it can be seen that apparent concentration, C", will be 95 percent or more of actual concentration, C, only if delivery pressure is not more than 50 cm HjO above atmospheric (with a 2cr error band of approximately ±7.6 cm HjO). Thus, figure 10 depicts the air pressure above

the solution vs. the flow rate from the output solenoid valve connected directly (that is, without the intermediary tester tube) to the spirometer. Based on eq (7), intrinsic resistance of the BASS can

therefore be determined from the slope of the line, which is approximately 3 cm H20-s/L even for flow rates in excess of Q = 0.() L/s. This is comparable to human breathing resistance in normal

expiration.

The discussions below treat the implications of limiting on the delivered value, or

(equivalently) the delivery rate, with respect to EBT's.

Rewriting eq (1), the flow resistance, , for laminar flow is given by:

Rj = ^p'Q. (7)

18
/

./

0 0.5 1.0 1.5 Q(L/s

FuiURK 10. Pressure abo\ie BASS alcohol solution vs. air flow rale. Above C = 0.6, flow resistance (slope) equals 3 cm

HjO-s/L which is similar to that for human subjects (see text).

Depending on the geometry of a collecting system and on the delivery rate, the flow may not be

laminar. According to Rohrer [12], the pressure drop for non-laminar flow may be better expressed by adding a second degree term related to delivery rate:

Ap = K,Q + K,Q\ (8)

whence,

Rf = Ap'Q = + K.,Q, (9)

where and are constants for a given collecting system.

Using the polyethylene tubes described earlier as surrogate breath testers, a series of laboratory tests were run to determine pressure drop as a function of varied flow rates (i.e., volume measured against time). This permits an examination of flow resistance calculated under

the assumptions of laminar or non-laminar flow, and estimation of the constant terms for the two

expressions.

According to eq (7) for laminar flow, delivery pressure (or pressure drop) should be linearly

related to flow rate. Figure 11, a plot of A/^ vs. Q for each of the three simulated testers, exhibits considerable deviation from linearity, contradicting the assumption that the flow is laminar. On the other hand, when t^p/Q vs. Q is plotted for the same data (see fig. 12), straight lines can be easily

fitted. Values of A , and K, can be estimated for each simulated tester based on the intercept on

the Y-axis and the slope of the line. The desired values are listed in the table below. Figure 13 shows a plot of A^i and A^^ a function of the length of the simulated tester tubes.

19
230 cm

0 .2 4 .6 .8 1.0 Q (L/s)

Figure 11. Deli^tTy pressure vs. flow rale ihrough tubes.

20
21
0 100 200 ' 300

LENGTH OF TUBE (cm)

FiGURK 13. KI and K , as a function of tube length.

Having established these parameter values, along with the limiting value for A/? to insure an

apparent concentration, C, within 5 percent of the actual, C, eq (8) can then be used to solve for Q

and calculate the maximum permissible delivery rate, Q^^^:

Of L -I (10)

22
Using eq (10), values for have been calculated for each of ihe three simulated testers, the derived estimates of and K.^, and three values for the |)ressure drop, A/y as [)resented in table 3. In particular, AyD = 50 cm H2O corresponds to the limiting value for assuring accuracy of measured concentration (i.e., C' = C±S%). Since the data for figure 9 showed a standard error of estimate of 13 cm HjO for A/), (),„^^ was also computed for A/3 = 37 and 63 cm H/), the latter providing slightly higher estimates of maximum flow rates. The last column of table 3 shows an

alternative assessment of maximum flow rate, (>|„,„,, based on the physiological data (summarized

in table 2) obtained from the volume and elapsed time for expiring air by the human subjects. The

values shown were computed from:

^pmax ' t-cr, (11)

that is to say, an air volume one standard deviation above average over a period of time one

standard deviation below average.

Taui.k 3

A". Tube (A/< = 37 (A/) = 50 (A/) = 63 Q »^

length, cm (cm H,0-s/L) (cm H0O/S-/L-) cm H.O) cm H_,0) cm H,0) (L/s)

97 20 144 0.44 0.52 0.60 0.67 164 30.5 218 0.3.5 0.41 0.47 0.49 230 44 310 0.28 0.34 0.39 0.43

While the BASS is capable of delivering a sample over the full range of pressure necessary to overcome the flow resistances tabulated in table 2, a comparison of the values for Q^^^^ and Q^,„y^^ suggests that the flow resistance of some present breath testers may be marginally acceptable in terms of flow rate which might be produced by individuals who are capable of above average air delivery (i.e., higher volume and/or shorter time). At the same time, it should also be noted that physiological delivery rates typically decrease significantly from high initial values to much lower ones at the end of sample delivery (see table 2, and fig. 14). Thus the values of (^|„„,„ in the table are not representative of the flow rate at the end of expiration, which are significantly lower. Nevertheless, the foregoing discussion tends to support reducing flow resistance in breath testers and, perhaps, revision of the existing standard for breath testers to encourage designers to accomplish this. To this end, a conservative recommendation for maximum allowable back

pressure for future breath testers at a delivery rate of 0.50 L/s, 6 L total volume, would be no more than 50 cm HjO. Since the effect of excessive delivery pressure is to underestimate BAG. it would not appear to be necessary to impose the above requirement on present testers, for these

testers tend to make up a progressively smaller portion of the market. A lower limit for delivery

rate is not critical and may be set more arbitrarily at about 0.20 L/s and 2 L total volume.

23
t ^ t

t = 0 s t = 8 s

FkjL'KK 14. Typical delivery pressure profile of human subject. In the example, final pressure is about 60 percent of initial pressure.

5. CONCLUSIONS AND RECOMMENDATIONS

There are large physiological differences between individuals that result in a wide range of

vital capacities and breath pressure. Ideally, the sample collection system of an evidential breath

tester should be adjustable to accommodate the exhalation characteristics of the individual that is being tested (i.e., one or more breath samples should be collected to determine the total time of exhalation and the total volume, and the discard volume then adjusted to ensure that the last third or fourth of the sample is used for analysis). Depending upon the analytical method employed by

the EBT, this may be difficult to accomplish. Further, the increased operating complexity might be

objectionable to the users of EBT's. From a practical standpoint, then, it appears at the present time, that the most reasonable approach to establishing performance standards for the breath sample collection capability of EBT's is to evaluate the ability of such devices to analyze the appropriate portion of a breath sample at the high and low ends of the vital capacity range of the U.S. adult population. That

portion of the population lying outside of the range that is selected would not be penalized by this action, if subjected to an EBT test, for in either case (unusually large or small vital capacities and

breath delivery capabilities) the measured BAG would be the same, or less than that which would

be measured if they were a member of the population range that is selected.

It is recommended that the existing NHTSA standards for breath alcohol testing devices be

modified to eliminate the use of human subjects, and that the breath sample collection capability of such devices be evaluated using the BASS as the sample source. The concentration, time, and delivery volumes appropriate for this test are summarized

below:

Concentration Profile

Concentration Step 12 3

Time, % 33 1/3 33 1/3 33 1/3

Alcohol Concentration, BAC 0.060 0.090 0.100

Sample Volume and Delivery Rate

a) 2 L at 0.20 L/s

b) 2 L at 0.333 L/s

c) 6 L at 0.50 L/s

24
The use of the BASS test profiles noted above will apply only to the evaluation of the breath sampling capability of breath alcohol devices. The other tests within the NHTSA standards, such

as precision and accuracy and environmental testing would be retained without change.

The BASS test profiles have been selected to ensure that EBT's are capable of accurately

measuring the BAG of a large portion of the adult U.S. population, without placing unduly

restrictive requirements upon the manufacturers of such devices. For example, while tests with human subjects have shown that in some cases the delivery time for an individual might be as long as 17 s, a test time of 12 s at a flow rate of 0.5 L has been selected. This is a consequence of

the fact that under prolonged delivery times, the delivery rate of an indivdual decreases rapidly. It would not be realistic to require that the unit under test accommodates the 0.5 L constant flow for a period as long as 17 s.

Appendix A—References

|l| Uniform vehicle code. Available from: National (]ommis>ion on Traffic l.aws and ()rdinani-es. 52S School St.. NW..

Washington, DC 20024.

[2] Jones, A. W.; Wright, B. M.; Jones, T. P. A historical and ex()erimental study of the breath/hlood alcohol ratio. Israelstram, S.; Lambert, S., ed. Proceedings of the Sixth International (Conference on Drugs, and Traffic Safety; 1974 September 8-13; Toronto; Addiction Research Foundation of Ontario, Toronto; 197.5.

[3] Voas, R. B.; Moulden, J. V. Breath measurement instrumentations in the U.S. Tech. Note DOT HS-801 621; Washington, DC: National Highway Traffic Safety Administration; 1975 June.

(4| Evidential breath testers for alcohol content. Federal Register. 38(212): 30459-30463; 1973 November 5.

[5] Calibrating units for breath alcohol testers. Federal Register. 40(161): 36167-36171; 1975 August 19.

[6| Flores, A. L. Rebreathed air as a reference for breath alcohol testers. Report No. DOT-TSC-NHTSA-74-4; 1975

January. Available from: NTIS.

[7] Dubowski, K. M. A study of characteristics of a reliable vs. practical breath alcohol screening test. Report No. DOTTSC-NHTSA-76-4; 1975 August.

[8] Dubowski, K. M. Biological aspects of breath-alcohol analysis. Clin. Chem. 20/21: 294-299; 1974.

[9] Harger, R. N.; Raney, B. B.; Bridwell, E. G.; Mitchell, M. F. The partition ratio of alcohol between air and water. urine and blood, estimation and identification of alcohol in these liquids from analyses of air equilibrium with them. J. Biol. Chem. 183: 197; 1950.

[10] Harger, R. N.; Forney, R. B.; Baker, R. S. Estimation of the level of blood alcohol from analysis of breath, (^uarterlv

J. Studies on Alcohol. 17(1); 1956.

[11] Hildebrand, J. Anatomy and physics of respiration. Chapter 20 in Physiology & Biophysics, 20th ed.. Vol. 2, Sec. 2. Ruch, T. C; Patton. J. D.. ed. Philadelphia, PA: W. B. Saunders Co.; 1974. 297-324.

[12] Rohrer, F. Der zusammenhang der atemkrafte and ihre abhangigkeit vom dehnungszustand der atmungsorgame.

Pfliiger's Arch. f. d. ges. Physiol. 165: 419; 1916.

25

ANNOUNCEMENT OF NEW PUBLICATIONS ON

NATIONAL CRIME AND RELATED SUBJECTS

Superintendent of Documents,

Government Printing Office,

Washington, D.C. 20402

Dear Sir:

Please add my name to the announcement list of new publications to be issued on the above subjects (including this NBS series): Name

Company . Address

City State Zip Code

(Notification Key N-538)

if U.S. GOVERNMENT PRINTING OFFICE: 1981 —340-997 '1720


U.S. DEPARTMENT OF COMMERCE

National Bureau off Standards

Washington, O.C. S0234

OFFICIAL BUSINESS

Penalty for Private Use. S300

POSTAGE AND FEES PAIO

U.S. DEPARTMENT OF COMMERCE

COM-215

U.S.MAIL

3rd Class

\