United States
Environmental Protection
Agency
Office of Health and
Environmental Assessment
Washington DC 20460
Research and Development
EPA/600/S8-85/010 Mar. 1989
&EPA Project Summary
Development of Statistical
Distributions or Ranges of
Standard Factors Used in
Exposure Assessments
E. Anderson, N. Browne, S. Duletsky, J. Ramig, and T. Warn
This summary provides information
on how to calculate human exposure
to toxic substances and ranges of
values for body weight, skin surface
area, and ventilation rates.
Percentile distribution of body
weight were computed from the
Second National Health and Nutrition
Examination Survey (NHANES II) data
base computer program. Distribu-
tions of skin surface areas were
similarly calculated from NHANES
height and weight data by applying
regression equations.
Insufficient data precluded the
development of distributions of
ventilation rates. Activity pattern
information is presented to permit
the calculation of time-weighted
average ventilation rates.
This Project Summary was devel-
oped by EPA's Office of Health and
Environmental Assessment, Wash-
ington, DC, to announce key findings
of the research project that is fully
documented in a separate report of
the same title (See Project Report
ordering information at back).
Introduction
Using standard factors in exposure
assessments promotes consistency
among various exposure assessment
activities in which the Environmental
Protection Agency (EPA) is involved.
Consistency with respect to common
physical, chemical, and biological
factors, to assumptions about typical
exposure situations, and to the presen-
tation of the possible ranges of estimates,
enhances the comparability of results and
encourages gains in state-of-the-art
exposure assessment techniques.
Current practice for estimating human
exposures typically involves the
assumption of average values for such
factors as body weight, liquid con-
sumption, and respiration rates. The full
report presents statistical distributions or
ranges of values for these factors.
Where sufficient data are available,
percentile distributions are developed.
Where insufficient data precluded the
development of statistical distributions,
ranges of values were compiled from
measurements reported in the literature.
In a few instances, unpublished data
obtained through correspondence with
researchers have been used to develop
ranges or distributions. All data, including
these unpublished data, are presented in
the Appendices of the full report. A
glossary of terms is also presented.
Body Weight
Published percentile distributions for
body weight for men and women and
male and female children are based
primarily on data gathered in the first
National Health and Nutrition Examination
Survey during 1970 and 1974. The
source of data used in this study is the
more recent, second National Health and
Nutrition Examination Survey , NHANES
II, for which published percentiles are not
yet available.
NHANES II was conducted on a
nationwide probability sample of ap-
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proximately 28,000 persons, aged 6
months to 74 years, from the civilian,
noninstitutionalized population of the
United States. The survey started in
February 1976 and was completed in
February 1980. The sample was selected
so that certain population groups thought
to be at high risk of malnutrition (persons
with low incomes, preschool children and
the elderly) were oversampled.
NHANES II provides information on
20,322 interviewed and examined indi-
viduals.
Weight was measured with a scale that
mechanically prints weight to quarter-
pound intervals directly onto the
permanent record.
In the full report, percentiles (and their
standard errors) of the distribution of
body weight have been computed from
the NHANES II data using the computer
program QNTLS.
Surface Area of the Human
Body
Two approaches can be used to
determine the surface area (SA) of the
body: direct measurement of the skin
area or estimating the SA by geometrical
approximation.
Several direct measurement tech-
niques have been used to measure SA,
including direct coating, triangulation,
and surface integration.
The coating methods consist of
coating either the whole body or specific
regions with a substance of known or
measured area. In some instances the
pieces of coating were placed on cross-
section paper and the area measured by
counting the squares covered. In others,
the areas of the pieces of coating were
calculated by weighing the coating or
weighing duplicates cut from a substance
of uniform thickness. Triangulation
consists of marking the area of the body
into geometric figures then calculating
the figure areas from their linear dimen-
sions. Surface integration is performed
by running a planimeter over the body in
parallel strips of equal width. The SA is
calculated by adding the areas of all the
strips measured. Directly measuring
body SA by any method described
above is a difficult and time consuming
task. Consequently, existing direct
measurement data are limited.
Body SA can be estimated using
geometric methods by assuming the
parts of the body resemble geometric
solids, then calculating the surface area
of the solids based on a few
measurements of length and circum-
ference. For example, the SA of the trunk
may be estimated by measuring the
length from the groove of the neck to the
tip of the coccyx and taking circum-
ferences just under the arms, at the level
of the pubis.
A linear method has been proposed in
which estimates are made on the
principle that the surface area of the
parts of the body are proportional, rather
than equal, to the surface area of the
solids they resemble, so that estimates
of SA made from lengths and circum-
ferences need to be corrected by con-
stants obtained from direct measure-
ments of SA.
Several formulae have been proposed
for estimating body SA from measure-
ments of other major body dimensions.
Generally, the formulae are based on the
principles that body density and shape
are roughly the same and that the
relation of SA to any dimension may be
represented by the curve of central
tendency of their plotted values or by the
algebraic expression for the curve. Most
formulae for estimating SA relate height
to weight. The first such equation derived
can be expressed by:
SA = KW 2/3
where SA is surface area in square
meters, W is weight in kilograms, and K
is a constant. While the equation has
been criticized because the specific
gravities of human bodies are not equal
and because the surface area per unit
volume differs for individuals with
different body builds, it gives a
reasonably good estimate of SA.
A formula that has found wide
acceptance and use is:
SA = a0 H3-, Wa2
where SA is surface area in square
meters, H is height in centimeters, and
W is weight in kilograms. The value of an
(0.007182), a, (0.725), and a2 (0.425)
were estimated from a sample of only
nine individuals for which SA was directly
measured.
More recently, values of the model
parameters were solved for the rela-
tionship between SA and height and
weight by multiple regression analysis.
The least squares best fit for this
equation yielded the following values for
the three coefficients: an = 0.024265, a-|
= 0.3964, and 82 =0.5378. The result is
this equation for estimating surface area:
SA = 0.024265 H° 3964 W° 5378
expressed logarithmically as:
In SA = In 0.024265 + 0.3964 In H
0.5378 In W.
The coefficients for this equation agr
remarkably with those obtained in earl
measurements.
A graphical method has been propos
whereby SA could be read from
diagram relating height and weight
surface areas. However, it does not gi
an explicit model for calculating SA. T
graph was developed empirically bas
on 252 cases, 127 of which were fr(
401 direct measurements report
earlier. In the other 125 cases the SA w
estimated using the linear method.
Several investigators who have work
in determining body surface area ha
reported their results in terms of surfa
areas (SA) of different parts of the bo
as well as total surface area. T
literature contains SA of body parts b(
as direct measurements and
estimates. Data on body part SA ha
been reported for both sexes, for seve
ethnic groups, and for ages ranging frc
newborn to elderly.
This study presents the largest sint
group of direct measurements made
any SA investigator, involving a balanc
sample of individuals according to s
age group, and compares the results
Japanese measurements with Germa
and Americans, however, only averag
for each age group and sex a
presented, which limits the usefulness
the data for determining ranges
percentages for each body part or regie
Our recent study proposed a hum
skin surface model based on a geomet
method of estimating SA. Various bo
dimensions for a "50th percentile ma
were used with a mensuration formula
geometric solids to calculate the SA
the geometric solid most closely relat
to the body part. The results were
ported as a percentage of total !
associated with each body part, whi
shows the author's comparison of I
model with three earlier publish
methods.
Available direct measurement d«
were analyzed using the Statistic
Processing System (SPS) softwe
package to generate equations tt
calculate SA as a function of height a
weight. These equations were then us
to calculate SA distributions of the U
population with NHANES II height a
weight data using the computer progn
QNTLS.
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Ventilation Rates
Pulmonary ventilation data and activity
pattern data permit the calculation of
time-weighted average ventilation rates.
Pulmonary ventilation is the mass
movement of gas in and out of the lungs.
The volumes of inhaled and exhaled air
usually are not exactly equal; the volume
of inspired oxygen is typically larger than
the volume of expired carbon dioxide.
Pulmonary ventilation is generally
represented by the minute volume (^e),
the volume of gas expired in liters per
minute at BTPS (gas volume at normal
body temperature and ambient
barometric pressure, saturated with water
vapor). Minute volume is the product of
tidal volume (the volume of gas moved
during each respiratory cycle) and
respiratory frequency.
Minute volume is usually measured
accurately with a water-filled spirom-
eter. The spirometer uses one-way
valves to funnel expired air into a col-
lection system or alternatively, directly
into a spirometer.
There have been several formulae
proposed in the literature to calculate
minute ventilation of humans at rest from
anthropometric data.
Resting ventilation is directly related to
the resting metabolic rate. With exercise,
minute volume increases in response to
the increase in metabolic demand. There
is an abrupt increase in ventilation with
the onset of exercise, followed by a
further, more gradual increase. With
moderate exercise, the increase is due
primarily to an increase in tidal volume;
this is accompanied by an increase in
respiratory frequency when the exercise
becomes more strenuous. When exer-
cise ceases, there is an abrupt decrease
in ventilation, followed by a more gradual
decline to preexercise values.
Review of the literature failed to
identify equations that would enable the
development of statistical distributions of
minute ventila-tion at all activity levels
for male and female children and adults.
Therefore, ranges of measured values
were compiled from the available data,
which are tabulated in the full report.
Many of these measurements are from
early studies.
Most of the available minute ventilation
measurements are from studies ex-
pressing the associated activity levels in
terms of kilogrammeters per minute. In
other studies, the activity level was given
qualitatively by the type of activity (e.g.,
walking at 3 miles per hour); the asso-
ciated breathing rates were categorized
based on representative activities.
For each age-sex-activity level
category for which data were available,
minimum, maximum, and mean minute
volumes were determined. These values
were derived from both individual
measurements and reported mean
values, for which the raw data were not
presented. Weighted means were cal-
culated by assigning each individual
measurement a weight of one and each
mean value a weight corresponding to
the number of subjects the mean repre-
sented; the weighted data were then
summed and divided by the total number
of subjects. The standard deviations for
the age-sex-activity level groups were
not calculated because many of the
mean values used were reported without
any measure of distribution variance. In
addition, many groups had very few data
points, making standard statistical sum-
maries difficult to interpret. In some
cases, means were presented without the
minimum and maximum values of the
original data sets; therefore, the minima
and maxima for age-sex-activity level
groups are representative only of the
available individual measurements.
Activity pattern data may be used in
conjunction with minute volume data to
estimate ventilation rates. In addition to
providing information on exercise levels,
available activity pattern studies also
describe the amount of time spent in
different microenvironments. Such de-
tailed information is desirable if the
ambient concentration of a pollutant
differs significantly from one microenvi-
ronment to another, as may happen with
particulate filtration from the outdoor to
the indoor microenvironment.
More detailed activity pattern data are
available in the Appendices of the full
report which presents in its entirety a
document describing activity patterns for
56 population subgroups. This document
is a supplement to a report on the
application of the National Ambient Air
Quality Standard Exposure Model to
carbon monoxide. Hourly assignments to
locations, microenvironments, and activ-
ity levels are presented for each popu-
lation subgroup.
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£ Anderson, N. Browne, S. Duletsky, J. Ramig, and T. Warn are with GCA
Corporation, Chapel Hill, NC 27514,
Tom McLaughlin is the EPA Project Officer (see below).
The complete report, entitled, "Development of Statistical Distributions or Ranges
of Standard Factors Used in Exposure Assessments," (Order No. PB 85-242
667/AS; Cost: $21.95, subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Office of Health and Environmental Assessment
U.S. Environmental Protection Agency
Washington, DC 20460
United States Center for •Environm.&ntat Research
Environmental Protection Information ' Vs,:>,":"'Yi
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