Recommendations for Testing

Radar-Based Collision Warning

Systems on Heavy Equipment

Department of Health and Human Services

Centers for Disease Control and Prevention

National Institute for Occupational Safety and Health

RI9657

REPORT OF INVESTIGATIONS/2002
Report of Investigations 9657

Recommendations for Testing Radar-Based Collision

Warning Systems on Heavy Equipment

Todd M. Ruff

U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES

Centers for Disease Control and Prevention

National Institute for Occupational Safety and Health

Spokane Research Laboratory

Spokane, WA

May 2002
This document is the public domain and may be freely copied or reprinted.

Disclaimer: Mention of any company or product does not constitute endorsement by NIOSH.

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DHHS (NIOSH) Publication No. 2002-135
CONTENTS

Page

Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Introduction ................................................................................... 2

Determining effective test targets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Test targets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Test description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Test results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Radar system 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Radar system 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Conclusions and recommendations for targets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Effect of body type on radar detection ............................................................... 9

Test description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Test results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Radar system 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Radar system 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Recommendations for testing systems on heavy equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Initial evaluations on heavy equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Considerations for radar systems in a production setting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Appendix: Test procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

ILLUSTRATIONS

1. Small trihedral corner reflector attached to PVC pipe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

2. Approximate radar cross-section patterns for different reflectors with relative magnitudes of reflected signal . . 3

3. Radar system mounted on dolly for testing ...................................................... 4

4. A test sphere with diameter of 36 cm (14 in) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

5. Ninety-one centimeter (36 in) in diameter weather balloon coated with conductive paint .................. 4

6. Test manikins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

7. Radar system 2 and heavy manikin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

8. Radar system 2 and foam manikin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

9. System 1: Detection zones for person, corner reflector, and small sphere . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

10 System 1: Detection zones for person and large sphere . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

11. System 2: Detection zones for person, corner reflector, and small sphere . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

12 System 2: Detection zones for person and large sphere . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

13. Low mounting configuration for tests to compare people . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

14. High mounting configuration for tests to compare people . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

15. Determining detection zone for person 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

16 Determining detection zone for person 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

17. Detection zones for persons 1, 2, and 3 and system 1 mounted low . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

18. Detection zones for persons 1 and 2 and system 1 mounted high (15° tilt) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

19. Example of differences in inner detection ranges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

20. Detection zones for persons 1 and 2 and system 1 mounted high (25° tilt) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

21. Detection zones for persons 1 and 2 and system 2 mounted low . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

22. Detection zones for persons 1 and 2 and system 2 mounted high (15° tilt) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

23. Detection zones for persons 1 and 2 and system 2 mounted high (25° tilt) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT

cm centimeter ft foot

GHz gigahertz ft2 square foot

kg kilogram gal gallon

km/h kilometer per hour in inch

m meter lb pound

m2 square meter % percent

ms millisecond ° degree

TABLES

Page

1. Test subjects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

2. Human physical dimensions in SAE J833 ....................................................... 9
RECOMMENDATIONS FOR TESTING RADAR-BASED COLLISION

WARNING SYSTEMS ON HEAVY EQUIPMENT

By Todd M. Ruff

ABSTRACT

Researchers at the National Institute for Occupational Safety and Health are investigating technologies that

could be used to detect objects, small vehicles, and pedestrian workers that may be in the blind areas of haulage

equipment used in mining and construction. A detection system that warns the equipment operator that there

is an obstacle nearby could prevent collisions and save many lives each year. One popular technology for

collision warning systems is radar. Several different types of radar have been tested in the laboratory and on

mining equipment. Early in the study, questions arose concerning the best way to test radar systems. Many

factors affect the performance of radar, including the size, shape, and composition of the object that is to be

detected; the height of the radar antenna(s); and the relative motion of the radar system and/or object. This

report discusses several different test procedures and test targets and recommends methods to determine how

effective a radar system will be in detecting a person near heavy equipment.
2

INTRODUCTION 

Researchers at the National Institute for Occupational Safety

and Health (NIOSH) are investigating technologies that could

be used to detect objects, small vehicles, and pedestrian workers

that may be in the blind areas of large mining equipment. A detection system that warns the equipment operator that there is an

obstacle nearby could prevent collisions and save many lives

each year.

One popular technology to accomplish this is radar. There

are several commercially available radar systems designed to

monitor the blind areas around many types of vehicles. In this

study, NIOSH researchers were interested in protecting workers

around large haulage equipment used in surface mining and

construction. Tests using several different types of radar systems have been conducted on several sizes of off-highway

dump trucks (Ruff 2000, 2001). The purposes of these tests

were to evaluate the effectiveness of each radar system in

detecting objects and people and to determine best practices for

installing the systems. 

The detection zone of a radar system depends on many factors, including (1) the type and configuration of the radar antenna, (2) the size, shape, and composition of the object being

detected, and (3) the mounting height and tilt angle of the radar

antenna. These last two factors are variables that can be controlled by users. In the early stages of these evaluations, several

issues with test procedures required some experimentation with

radar mounting locations and different test objects to establish

a standard test method. 

The most common accidents involving collisions with mining or construction equipment involve pedestrian workers or

smaller passenger vehicles. A radar system used to warn of

collisions should be very good at detecting these two objects.

The question then arose, “What should be used as a standard test

object during evaluations of radar systems?” When comparing

a radar system’s ability to detect a person or a small vehicle, detecting a person will be more difficult due to a person’s smaller

size and greater variability. Thus, the ability of a system to detect a person is an important characteristic to evaluate. Many

objects can be used to simulate a person, so the focus of the first

task was to determine the best test object to use when defining

the radar’s detection zone for a person. 

Of course, one option is to use an actual person for a test

object, rather than an object that simulates a person. The second

task then involved determining how a radar system’s detection

zone differed according to the size of person detected. These

data were then used to determine a size range for a test person

to ensure that the detection zone did not vary significantly when

someone else conducted the same tests with a different person.

Finally, NIOSH researchers tested several different radar systems on many types of dump trucks. Observations were made

regarding the variables involved when systems were mounted on

actual heavy equipment and the effects of these variables on the

detection zone and the reliability of the radar system. Some of

the most significant variables involved (1) whether the engine

was running or not, (2) whether the equipment was moving or

stationary, and (3) the mounting location and orientation of the

radar antenna. A summary of these observations and recommendations is included in this report along with a recommended

test procedure.

DETERMINING EFFECTIVE TEST TARGETS

One obstacle that a collision warning system must detect is

a person working near the equipment. To evaluate the effectiveness of a radar system in detecting a person, either the

detection characteristics for an actual person must be evaluated

or the detection characteristics of some object that accurately

represents a person must be evaluated.

NIOSH researchers needed to find out what object would

most accurately simulate the presence of a human, realizing that

the most effective test target may turn out to be an actual

person. To this end, the detection zones for several test targets

were compared with the detection zone for an actual person

using two different types of radar systems.

TEST TARGETS

Several test targets are commonly used to evaluate radar

systems. Of these, corner reflectors and metallic spheres were

evaluated because they are frequently used in radar testing and

calibration. A test manikin has also been suggested as a test

target by the Society of Automotive Engineers (SAE), which

recommends the use of either a person or a manikin in a

kneeling position to evaluate the detection zone of a collision

warning system (SAE 1999). To show the potential for discrepancies depending on manikin composition, we compared

the detection ranges for two types of manikins. Finally, in previous NIOSH tests, researchers used an actual person to determine the reliable detection zones for people, so the results

from test objects are compared to the results for a person. 

Trihedral corner reflectors are often used as a standard test

target for evaluating radar (figure 1). The dimensions of the

metallic reflector determine how much of the radar’s signal is

reflected back to the antennas. This reflection characteristic is

also referred to as radar cross section (RCS) and depends on the

composition, size, and shape of the object, as illustrated in

figure 2. These dimensions must be calculated so that the RCS

of the reflector equals the RCS of a person. A trihedral corner

reflector with dimensions of 8.4 cm (3.3 in) on each side has

been proposed in preliminary standards. The reflector must be
3

Figure 1.—Small trihedral corner reflector attached to PVC pipe.

Figure 2 —Approximate radar cross-section patterns for different reflectors with relative magnitudes of reflected signal (U.S.

Dept. of the Navy, 2001).

attached to the end of a long plastic pole, which allows it to be

positioned inside the radar beam while allowing the person

holding it to remain outside the radar beam (tests must be

conducted to assure that the plastic pole is not detected by

itself). An advantage to this method is that the reflector is

easily purchased or constructed, and it represents a repeatable

target size. Also, with a proper pole or other rigging, it is

theoretically possible to determine the vertical dimensions of a

radar beam. One disadvantage is that a corner reflector is

extremely directional, i.e., the amount of signal reflected back

to the radar depends on the reflector’s orientation (figure 2).

Another disadvantage is the potential for radar signal reflection

from the person holding the plastic pole.

Another standard test target is a metallic sphere. Again, the

diameter of the sphere must be such that it reflects an amount of

radar signal equivalent to what a person would reflect. According to Skolnik (1990), the RCS for an adult male ranges between 0.4 and 1.2 m2

 (4.3 and 12.9 ft2), depending on radar

frequency. After talking with radar system manufacturers, we

used an estimate of 0.8 m2

 (8.6 ft2) for the RCS of a man in a

standing position. This resulted in a metallic sphere with a diameter of 1 m (39 in). The sphere must also be attached to

some type of rigging or a plastic pole to allow the person holding it to remain outside the radar beam. Depending on the

weight of the sphere, this may not be practical. Standard metal

spheres constructed for radar calibration tests are available.

However, for the size required in this application, the sphere

would weigh approximately 26 kg (57 lb) and cost almost

$5000. This is definitely not practical, so other options were investigated. Theoretically, both the vertical and horizontal beam

dimensions can be determined using a sphere, and the magnitude of the reflected signal does not depend on orientation

(figure 2). 

The SAE standard for evaluating collision warning systems

(SAE 1999: Discriminating Back-Up Alarm System standard

J1741) allows the use of person or an anthropomorphic dummy

or manikin. The manikin is to be the size of a small person (5th

percentile female), as defined by SAE standard Human Physical

Dimensions J833 (1989), dressed in a long-sleeved shirt and

long pants, and placed in a kneeling position in the detection

zone. No other specifications are given, which may result in

variations in test results due to the different materials that are

used in manikin construction. Sophisticated manikins, like

those used in automobile crash tests, contain more metal parts

than those used in department stores, for example, and this

difference may affect detection, especially for radar. Also,

while a manikin may be practical for initial evaluations, we suspect that these tests must be confirmed using a test object that

more closely approximates the RCS of a human.

NIOSH researchers have been evaluating radar systems

using a human test subject in a standing or walking position.

An advantage to this is that the test results accurately represent

the detection characteristics of an actual person and do not

introduce the possible discrepancies associated with inanimate

objects. The time requirements for tests using a person are

short,

and the detection zone is easily determined by simply walking

within the area of interest and recording the zone in which reliable detection occurred. A disadvantage to this method is that

a person’s height may slightly affect the results, depending on

the mounting configuration of the radar antenna. Also, this

method is effective in determining horizontal dimensions of the

detection zone, but not vertical dimensions. 

TEST DESCRIPTION 

To determine the difficulties and effectiveness of each type

of target, a test was conducted to determine the detection zones

of the targets for two different radar systems that were made for

heavy equipment. System 1 operates at approximately 13 GHz,

and system 2 at approximately 6 GHz. The detection zones for

the various objects were then compared to the detection zone for

an upright (standing) person to determine whether the object

was an accurate representation of a person.

The test area was a flat, empty, asphalt parking lot with

dimensions of approximately 24 m (80 ft) wide by 46 m (150 ft)

long. The radar system was mounted on a handcart (dolly)
4

Figure 3.—Radar system mounted on dolly

for testing.

Figure 4.—A test sphere with diameter of 36 cm (14 in).

Figure 5.—Ninety-one centimeter (36 in) in diameter weather

balloon coated with conductive paint.

approximately 114 cm (45 in) high, powered by a car battery,

and placed at one end of the parking lot (figure 3). A grid was

laid out in front of the radar system with spacing between points

of 0.76 m (2.5 ft).

First the detection zone for a person was determined by

having a NIOSH researcher walk within the area of interest.

The points at which the person was consistently detected by the

radar were marked on the ground and recorded on a graph. A

more detailed description of the test procedure can be found in

the appendix.

Next, the corner reflector was tested. The reflector had dimensions of 8.4 cm (3.3 in) on each side and was mounted on

the end of a 3-m (10-ft) long polyvinyl chloride (PVC) pipe

(figure 1). The person holding the pipe then walked near, but

not in, the detection zone for the person. The reflector was held

out in the zone, and the points at which it was detected were

marked on the ground and recorded on a graph. Several reflector orientations and heights were tested at each grid point to

ensure accurate recording of the detection zone.

Two different reflective spheres were tested. The first sphere

was made from easily obtained materials and was simple to construct. A 36-cm (14-in) in diameter playground ball was covered in aluminum foil, and the foil was secured using foil tape.

The ball was then attached to the end of the PVC pipe using

string (figure 4).

Because 36 cm (14 in) is too small to represent a person

accurately and the foil did not provide a smooth surface, another

larger sphere was needed to approximate the RCS of a person.

One idea was to construct an approximation of a metallic sphere

from a weather balloon spray-painted with conductive paint.

The balloon had a final diameter of 91 cm (36 in). (It could

have been inflated larger than this, but then it would not have fit

through doors.) The 91-cm (36-in) size is a close approximation

of the RCS of a person; however, the reflectivity of the

conductive paint was not known. The balloon was then hung on

the end of the PVC pipe (figure 5). Constructing this test target

was fairly simple; however, the conductive paint is quite expensive ($400/gal). Care must also be taken in order to ensure

that the paint does not peel off because of deflation or

expansion or rough treatment during the test. 

Each sphere was tested by placing it in the potential

detection zone and recording the point where it was consistently

detected. The PVC pipe theoretically allowed only the sphere

to be detected. The spheres were placed near the ground and as

high as 2.1 m (7 ft) to ensure accurate recording of the detection

zone.

Finally, two different manikins were tested to show the effects

of manikin composition on the radar detection range. The first

model (figure 6, left) is a crash test dummy similar to the newer

Hybrid III 5th percentile female (the model number was not

available). It is composed of a steel and aluminum frame with

a vinyl skin (heavy manikin). The second manikin (figure 6,
5

Figure 6.—Test manikins.

Figure 7.—Radar system 2 and heavy manikin.

Figure 8.—Radar system 2 and foam manikin.

right) is a model used in accident reconstruction and is available

from Atlanta Legal Photo Services (model 2047).1

 It is composed of a wire frame surrounded by a foam body (light

manikin). 

Only radar system 2 was available at the time of the manikin

tests, so results may vary depending on the radar system. Our

tests were conducted with the manikin in a sitting position

because (1) the version of the SAE standard available to us at

the time of the tests required the manikin to be in a sitting

position, (2) it is impossible to put some manikins in a kneeling

position, and (3) only the height for a sitting manikin is

specified in the standard. (Results may vary slightly between

kneeling and sitting due a difference in height). Each manikin

was placed in a sitting position at various points directly in front

of the radar along the centerline to determine the reliable

detection range (figures 7 and 8). The height from the ground

to the top of the manikin’s head was 81 cm (32 in). Comparing

the detection range of sitting manikins along the centerline was

sufficient to show the effects of differing compositions. 

TEST RESULTS

Radar System 1

Figure 9 shows the detection zones as recorded for a person,

the trihedral corner reflector, and the 36-cm (14-in) in diameter

sphere. The person used for this test was a NIOSH researcher

who was 190 cm (6 ft, 3 in) tall and weighed 84 kg (185 lb).

Test results using a different person may vary slightly

(discussed below). The results show that the person had the

largest detection zone, the corner reflector’s detection zone was

smaller, and the zone for the 36-cm (14-in) sphere was smaller

yet. 

Some difficulties were encountered when testing the corner

reflector. Many times, while trying to find a detection point, it

was not possible for the person to stay out of the detection zone.

Thus, at many points within the potential detection zone, the

person had to lift the pipe and reflector and move it out of the

detection zone to determine if he were being detected. This was

a time-consuming process. Also, detection of the corner

reflector was sporadic and depended on orientation. The corner

reflector had to be moved, tilted, and turned several times at

each potential detection point to verify detection or no

detection. Detection also depended on reflector height. With

all these variables, many times the reflector was not detected in

the same place twice. Repeatability was difficult to establish,

and the outline sketched on the plot in figure 9 is a best

estimate.

As mentioned earlier, the 36-cm (14-in) sphere was thought

to be too small for this application. Figure 9 confirms this and

shows that the detection zone was much smaller than that for a

person. Also, it was difficult to establish the detection zone of

1

Mention of specific products or manufacturers does not imply endorsement

by the National Institute for Occupational Safety and Health.
6

the sphere without walking into the detection area, thus causing

erroneous results. Detection depended on height with this sphere,

but not orientation. This test was conducted more quickly than

for the corner reflector, and we decided to pursue further tests

with the weather balloon that approximated a larger sphere.

Figure 10 compares the detection zone for a person with the

zone for the balloon. The detection zones are roughly the same

size. A few difficulties were seen in using the balloon , e.g., its

detection depended on height. The zone was enlarged in a few

places near the radar system if the balloon was raised 1.5 to 1.8 m

(5 to 6 ft) off the ground. The results shown in figure 10 were for

the balloon at roughly 1 m (3.3 ft) off the ground. Also, as the

day progressed and the temperature rose, the balloon expanded,

causing the conductive paint to crack and peel. While it was

relatively simple to construct the reflective balloon with the correct equipment, a balloon may not be practical as a standard test

target. 

Radar system 1 was not available when the tests of the manikins were conducted. See the next section for the results using

radar system 2. 

Radar System 2

A second radar system built by a different manufacturer was

tested to verify the results of previous tests. Figure 11 compares

the detection zones for a person, the corner reflector, and the

small sphere. The same difficulties were seen in these tests, and

the differences in the detection zones for the various targets were

significant. The detection zone for the small foil-covered sphere

was, as expected, much smaller than the detection zone for a

person. The detection zone for the corner reflector was also smaller than that of a person. Figure 12 compares the detection zones

for a person and the large balloon. Again, the zones are similar

with the exception that the sphere was detected 61 cm (2 ft)

farther away than the person.

The tests of the manikins consisted of finding those distances

at which the manikin was detected directly in front of the radar

system (figure 7). Using the heavy manikin and a radar mounting

height of 114 cm (45 in), the manikin was detected between 3.8

and 5.3 m (12.5 and 17.5 ft). It was not detected anywhere else

along the centerline. The light manikin was not detected at any

position.

This test was conducted again with the radar mounting height

at 74 cm (29 in) to determine if the poor detection was due to the

manikin sitting underneath the radar beam. For this test, the

heavy manikin was detected between 0.76 and 7.6 m (2.5 and 25

ft). The light manikin was only detected at one point and that was

directly in front of the radar at a distance of 0.76 m (2.5 ft). A

final test was conducted with a small person in the same sitting

position to compare the detection range between manikins and

people. The person was detected from 0 to 7.6 m (25 ft), which

was a very similar result to that for the heavy manikin.

CONCLUSIONS AND RECOMMENDATIONS FOR

TARGETS

Test results show that trihedral corner reflectors are difficult to

use as test targets. Detection of a corner reflector is highly dependent on the angle and orientation of the reflector relative to the

incident radar signal. Moderate variations in the orientation of the

reflector can result in its not being detected in areas where

detection would be expected. The most practical method of

testing a corner reflector is to mount it on a plastic pole so that a

person can walk outside the potential detection zone while

holding the reflector inside the zone. However, it is sometimes

difficult to tell if the person is actually causing the alarm rather

than the reflector. A less practical means of positioning the reflector would be to use rigging or lines that extended well outside

the detection zone and that could be adjusted by a person or by

moving the radar system. This would solve the problem of false

detections of the person, but causes many other difficulties. 

If a person is not used as the test target, the next best thing is

a metallic sphere with a diameter of at least 91 cm (36 in).

Unfortunately, a metallic sphere of this size is not affordable or

practical for these tests. An approximation of a sphere using a

weather balloon or rubber ball coated with conductive paint is

feasible, but not very durable.

If a manikin is to be used as a test target, as recommended in

the SAE standard, it must have a RCS similar to that of a human

of the same size. In these limited tests, a high-quality crash test

dummy that contains a steel and/or aluminum frame was a close

representation of a human. However, this type of manikin is very

expensive. The less expensive and lighter foam manikin used in

these tests was not an accurate representation of a human and can

not be used to evaluate radar. It may be feasible to use a foam

manikin with clothes in evaluating other types of technology, such

as ultrasonic or infrared sensors, but further tests are needed to

verify this.

The SAE standard calls for the manikin or person to be in a

sitting or kneeling position; however, most of our other tests

involving people were conducted with the person standing. A

standing person was used because walking through the detection

zone is more practical and safer than sitting, especially when

testing systems on actual equipment. Also, the most common

position for a human on a work site and near equipment will be

either standing or walking, not sitting. It is legitimate to require

the detection of a sitting or crouching person, but this would be

a most extreme case, much like detecting a person lying down.

It is difficult for a radar system to detect a sitting person yet

ignore rocks and ruts on the ground. These tradeoffs and safety

concerns forced researchers to evaluate the most common

position of a person near the equipment, which would be the

standing position.
7

Figure 9.—System 1: Detection zones for person, corner reflector, and small sphere.

Figure 10.—System 1: Detection zones for person and large sphere.

It was concluded that to determine a radar system’s reliable

detection zone for a person, an actual person should be used as

the test target. However, this raised the question of what effects

body type or height might have on the radar’s detection zone.

This is the subject of the next section.
8

Figure 11.—System 2: Detection zones for person, corner reflector, and small sphere.

Figure 12.—System 2: Detection zones for person and large sphere.
9

Figure 13.—Low mounting configuration for tests to compare

people.

Figure 14.—High mounting configuration for tests to compare

people.

EFFECT OF BODY TYPE ON RADAR DETECTION

To better understand the effects of body size on the detection

zone for a given radar system, researchers compared the detection zones for three different-sized people. The same two

radar systems were used for these tests. However, other variables were introduced in order to consider the effects of

different-sized mining equipment. These variables involved

mounting height and downward tilt of the radar antenna.

Several different configurations were tried and compared.

TEST DESCRIPTION

These tests were conducted in the same parking lot as previous tests. For each radar system, three different mounting

configurations were tested. The first configuration consisted of

mounting the radar on a test frame at a height recommended by

the manufacturer (approximately 114 cm [45 in]). The radar

unit was not tilted at this height, but pointed straight out into the

detection area (figure 13). The second mounting configuration

had the radar at a height of approximately 264 cm (104 in) with

15° downward tilt (figure 14). The third configuration was at

the same height, but with a 25° downward tilt. (The measurement of tilt angle is shown in figure 14.) The higher mounting

location is similar to what would be needed if the radar were

mounted near the light bar of a large off-highway dump truck.

In initial tests, three test subjects were used, and their physical attributes are listed in table 1. However, after the first few

tests it was apparent that body weight was not a significant factor, and only persons 1 and 2 were used thereafter. All the persons tested were wearing cotton pants, a cotton shirt or jacket,

and leather shoes. (Metal items such as glasses, belt buckles,

and watches were removed at first, but then allowed after we

determined that these items had no effect on the dimensions of

the detection zone.) 

The test subjects were chosen on the basis of their size differences. We wanted to use test subjects that were close to the

5th percentile female and 95th percentile male as described in

the SAE standard J833–Human Physical Dimensions (1989).

In this standard, the dimensions and weights of small (5th percentile female), medium, and large (95th percentile male) humans are given (table 2). Note that a medium person’s attributes are not the same as the average U.S. height and weight,

which is 160 cm (5 ft 3 in) and 61 kg (135 lb) for an adult female and 175 cm (5 ft 9 in) and 73 kg (162 lb) for an adult male

(Droste and Dye, 1994).

The reliable detection zone for each person was determined

by having one person walk toward the radar unit and place a

marker where reliable detection began and where it ended (figures 15 and 16). After the edges of the detection zone were

marked, the zone was recorded on a graph. Then the next person repeated the test. For more details, see the appendix.

Table 1.—Test subjects

Person Gender Height (with shoes) Weight, kg (lb) 

1 Female 160 cm (5 ft 3 in) 50 (110)

2 Male 190 cm (6 ft 3 in) 84 (185)

3 Male 190 cm (6 ft 3 in) 120 (265)

Table 2.—Human physical dimensions in SAE J833

Height (with shoes) Weight, kg (lb)

Small (5th percentile

 female)

 155 cm (5 ft 1 in) 48 (106)

Medium (halfway between

 the two)

 170 cm (5 ft 7 in) 73 (161)

Large (95th percentile male) 188 cm (6 ft 2 in) 96 (212) 
10

Figure 15.—Determining detection zone for person 1.

Figure 16.—Determining detection zone for person 2.

TEST RESULTS

Radar System 1

The first radar system was mounted level at 107 cm (42 in)

high on the test frame. The detection zones for persons 1 and

2 were determined first. Person 3 was then tested to determine

if body weight would affect the detection zone for the radar

system. The detection zone for all three persons is shown in

figure 17 and was the same for all test subjects. Based on this

result, person 3, being the same height as person 2, was no

longer used in the tests.

The next test of system 1 was at a height of 267 cm (105 in)

and a tilt angle of 15° downward. The detection zones for persons 1 and 2 are shown in figure 18. The outer range of the system was 7.6 m (25 ft) for both test subjects; however, the inner

range did differ by 1.5 m (5 ft) because of the difference in the

test subjects’ heights. Figure 19 illustrates this effect. It shows

that the outer range is not expected to change because

approximately the same amount of the person’s body is in the

radar beam regardless of the person’s size. The inner range

varies because the shorter person is walking underneath the

beam at a distance further from the radar. Note that the width

of the left side of the detection zone varied by 0.76 m (2.5 ft) for

each person. The exact cause of this is unknown, and the test

subject’s size could not be proven as the cause.

The last test of system 1 was at a height of 262 cm (103 in)

and a tilt angle of 25° downward. The detection zones for persons 1 and 2 are shown in figure 20. The outer range of the system was 6.9 m (22.5 ft) for both test subjects, and the inner

range differed by only 31 cm (12 in). This difference was expected because of the steeper beam angle for a 25°-radar tilt

angle. Also of significance was the large change in overall detection zone dimensions for both people when comparing the

low mounting position with the high mounting position. 

Radar System 2

The second radar system was mounted level at 114 cm

(45 in) high on the test frame. The detection zones for persons

1 and 2 are shown in figure 21 and are essentially identical. The

outer range at this height was 8.4 m (27.5 ft), and detection

occurred all the way up to the front of the radar unit.

The next test of system 2 was at a height of 267 cm (105 in)

and a tilt angle of 15° downward. The detection zones for persons 1 and 2 are shown in figure 22. The outer range of the

system was 7.9 m (26 ft) for both test subjects; however, the

inner range did differ by 0.76 m (2.5 ft) because of the difference in the test subjects’ heights. The width of the detection

zone did not vary at the outer detection ranges, but began to narrow slightly as test subject 1 walked under the radar beam. 

The last test of system 2 was at a height of 267 cm (105 in)

and a tilt angle of 25° downward. The detection zones for persons 1 and 2 are shown in figure 23. The outer range of the system was 7.9 m (26 ft) for both test subjects; however, the inner

range still differed by 0.76 m (2.5 ft) because of the difference in

the test subjects’ heights. Again, the width of the detection zone

did not vary at the outer detection ranges but began to narrow

slightly as the smaller test subject walked under the radar beam.

Also note that, while the overall dimensions did change, the

difference in detection zones between low mounting and high

mounting were not as significant as when using system 1.

CONCLUSIONS

Based on these limited tests, the following conclusions can

be made for these two radar systems.

• A person’s height does not affect the maximum range or

outer dimensions of the detection zone.

• A person’s height does affect the dimensions of the detection

zone for radar systems mounted higher than approximately 1.8

m (6 ft) above the ground, but only at locations near the radar

unit where the test subject begins to walk under the radar beam.

The difference in the dimensions of the inner detection zone did

not exceed 1.5 m (5 ft) for the configurations and people tested.

However, if a person is in a crouching or sitting position, the

inner detection zone dimensions could vary significantly when
11

Figure 17.—Detection zones for persons 1, 2, and 3 and system 1 mounted low.

Figure 18.—Detection zones for persons 1 and 2 and system 1 mounted high (15° tilt).

compared to the same person standing. 

• In general, a person’s height did not affect the width of the

detection zone, except at close-in ranges where the test subject

began to walk under the radar beam.

• In our limited tests, body weight did not appear to have a

significant effect on the detection zone of a radar system.

• Mounting height and tilt angle do affect the dimensions of

the detection zone. This effect is not the same for every radar

system.

• Small metal items on the test subject, such as glasses,

watches, or jewelry, do not appear to affect the dimensions of

the detection zone.
12

Figure 19.—Example of differences in inner detection ranges.

Figure 20.—Detection zones for persons 1 and 2 and system 1 mounted high (25° tilt).
13

Figure 21.—Detection zones for persons 1 and 2 and system 2 mounted low.

Figure 22.—Detection zones for persons 1 and 2 and system 2 mounted high (15° tilt).
14

Figure 23.—Detection zones for persons 1 and 2 and system 2 mounted high (25° tilt).

RECOMMENDATIONS FOR TESTING SYSTEMS ON HEAVY EQUIPMENT

Based on the above test results and other tests conducted on

surface mining and construction equipment, the following

general recommendations are made concerning the evaluation

and implementation of radar-based collision warning systems.

Most manufacturers will provide a data sheet or description of

the detection characteristics of their radar system; however, it is

important to verify the operation of the radar system on the

actual equipment on which it will be used. Information on false

alarm rates, mounting locations, and detection zones for a person and a smaller vehicle will be critical in making a decision

on the effectiveness of a collision warning system prior to final

installation on equipment used in actual production.

INITIAL EVALUATIONS ON HEAVY EQUIPMENT

• Radar systems should be mounted at approximately chest

height for the best detection. Justification: This height allows

the best detection of a standing person because a significant portion of the body is within the radar beam, even at close distances. Lower mounting heights may result in false alarms from

detecting the ground. Higher mounting locations will require

the radar antenna to be tilted downward in order to improve

close-in detection. This decreases the maximum range of the

radar detection zone and may increase false alarms.

• After installing a collision warning system according to the

manufacturer’s instructions, the equipment should be moved in

reverse (or forward for front-mounted sensors) in an area with

no obstacles or people to determine if false alarms occur. The

ground surface should be typical of actual working conditions.

Justification: Tests have shown that false alarms may result

from the detection of rotating tires or other components of the

equipment itself. Also, some systems malfunction because of

the vibration of the equipment, shocks from shifting gears, or

braking suddenly. False alarms may also be generated from the

detection of irregularities in the ground surface such as ruts or

rocks. After conducting these tests, adjustments to system settings and the mounting configuration may be necessary. If these

adjustments do not eliminate false alarms, the system may not

work on that particular piece of equipment or in that particular

environment.

• The reliable detection zone for a person should be determined by having a person walk toward the stationary, but

running, equipment. Justification: A person walking into the

blind area of a stationary machine is a common hazardous

condition, and the system must be able to detect this. Tests

have shown that an actual person should be used to conduct

these tests because other test objects, such as radar reflectors or

manikins, may have different detection characteristics. It is also

recommended that several, close-in detection points be tested

with the person in a crouching position so that the limitations of

the radar in detecting a sitting or crouching person can be

understood and conveyed to equipment operators. The
15

equipment should have the engine running to verify that

vibration will not affect operation of the radar.

• The reliable detection zone for a person should be verified by

moving the equipment toward a stationary standing person.

This must only be done at test grid points where it is safe, i.e.,

points that provide sufficient stopping distance when the person

is detected or when the person or spotter indicates that detection

has not occurred where expected. Radios must be used so that

the person can communicate with the equipment operator, and

a spotter must be in an area where the operator can see hand signals. These tests should be conducted with the person standing

so that his or her movement is not restricted. Justification:

Tests have shown that the detection zone for some radar

systems decreases in size when the equipment moves toward the

person as a result of vibration or speed sensitivity. 

• A person of average height (175 cm ±8 cm [5 ft 9 in ±3 in])

should be used to determine the detection zone for a person.

The person should wear clothing typical of that work site.

Justification: The detection zone does not change significantly

for persons of slightly differing heights. However, the zone

may be different for persons on two extremes of height, i.e., a

160-cm (5-ft, 3-in) person versus a 190-cm (6-ft, 3-in) person.

Testing with an average-sized person will give a good

indication of system performance. 

• The reliable detection zone for a smaller vehicle, such as a

pickup truck, should be determined by parking the smaller vehicle at various points in the potential detection zone and moving the equipment toward it. Justification: A smaller vehicle

parked in the blind area of the equipment is a common hazardous condition, and the system must detect this. Also, previous

tests have shown that the detection range for a pickup truck can

be as much as three times greater than the range for a person

(Ruff 2000). Operators should be made aware of the potential

for significant differences in detection zones for different

objects.

CONSIDERATIONS FOR RADAR SYSTEMS IN A

PRODUCTION SETTING

Radar systems provide an alarm in the cab of the equipment

when an object or person has been detected. Existing systems

only provide an approximate distance to the object on the alarm

display, usually by activating a series of lights. The size or type

of object and the exact location of the object are not displayed.

Also, multiple objects may be detected, but the alarm display

can only provide one alarm. This may mean that an object is

being “masked” by another larger object, e.g., a person standing

between the equipment and a wall may be hit if the operator

sees the wall and thinks that it is the only cause of the alarm.

Because of the characteristics of existing radar systems, it is

recommended that the operator verify the cause of an alarm

before moving the equipment. This can be done through direct

sight, mirrors, or cameras. 

For large equipment, visual verification would require exiting the cab and walking around the equipment if no other means

are available. Mirrors could be used in some situations, but

they, too, have limited visibility and cannot provide a view directly behind the equipment. Alternatively, a camera system

that provides a view of the blind areas, including the detection

zone of the radar system, could be used to verify the cause of

any alarm. While radar is effective in detecting people and

other large objects, false or ambiguous alarms can be common.

Until radar systems are improved, a combination of radar with

video cameras is recommended for most large equipment.

ACKNOWLEDGMENTS

The following NIOSH personnel are gratefully acknowledged for their contributions to the project—Linda Noel,

secretary; Fred Biggs, mechanical engineer; and Richard

(Rusty) Miller, mechanical engineer, who assisted with determining the effects of a person’s height on radar detection;

and

Ron Backer, deputy branch chief, who helped with designing

the test procedures and test objects. The author would also like

to thank Sandy Love, Odgen Safety Systems, and Robert

Mulloy, Multispectral Solutions, Inc., for their guidance and

advice during this work.

REFERENCES

Droste, K., and J. Dye, eds. Gale Book of Averages. Gale Research, Inc.

http://www.chipublib.org/008subject/005genref/faqheight.html, 1994.

Ruff, Todd M. Test Results of Collision Warning Systems for Surface

Mining Dump Trucks. Pittsburgh: Dept. of Health and Human Services,

Centers for Disease Control and Prevention, National Institute for Occupational

Safety and Health, Spokane Research Laboratory, Report of Investigations

9652, May 2000, 44 pp.

Ruff, Todd M. Test Results of Collision Warning Systems for Off-Road

Dump Trucks – Phase 2. Pittsburgh: Dept. of Health and Human Services,

Centers for Disease Control and Prevention, National Institute for Occupational

Safety and Health, Spokane Research Laboratory, Report of Investigations

9654, Feb. 2001, 21 pp. 

Society for Automotive Engineers [SAE]. Discriminating Back-Up Alarm

System. Surface Vehicle Standard J1741, June 1999.

Society for Automotive Engineers. Human Physical Dimensions. Surface

Vehicle Recommended Practice J833, May 1989.

U.S. Dept. of the Navy. Electronic Warfare and Radar Systems Engineering

Handbook. http://ewhdbks.mugu.navy.mil, Dec. 2001.

Skolnik, Merrill I. Radar Handbook. New York: McGraw Hill, 1990,

p. 11.16.
16

APPENDIX: TEST PROCEDURE

This test procedure describes the method a system manufacturer would use for determining the characteristics of collision warning systems employed to detect obstacles near

mining and construction equipment. Final verification of detection characteristics at mine or construction sites would require the methods described earlier.

DEFINITIONS

Collision Warning System. A system consisting of a sensor

and an alarm display that detects nearby objects and provides a

warning to the equipment operator. 

Obstacle. An object that must be detected by the collision

warning system. For these tests, the obstacles should consist of

either a person or a passenger-type vehicle.

Sensor. The part of the system that senses nearby objects,

e.g., radar antenna.

Alarm Display. The part of the system located in the cab of

the equipment to provide a visual and/or audible alarm

indicating that an obstacle is in the system’s detection zone.

False Alarm. An alarm indicating the presence of an

obstacle in the detection zone of the collision warning system

when no obstacle exists, or an alarm from any object that is a

significant distance away from the expected detection zone.

Reliable Detection Zone. The area in which an obstacle is

detected 100% of the time.

Sporadic Detection Zone. The area in which an obstacle is

detected some of the time but not always, i.e., less than 100%

detection, but more than approximately 10%.

Recorded Detection Zone. A plot of the detection zones

transcribed on graph paper with a grid spacing of either 1 m or

2.5 ft.

TEST OBSTACLES

The collision warning system must detect the obstacles that

are most commonly involved in collisions, i.e., pedestrian

workers (persons) and smaller passenger/utility vehicles such as

trucks or vans.

Person 

For tests to detect a person in the detection zone of a

collision warning system, a person should stand or walk in the

area of interest near the sensor. The person should be 175 cm

±8 cm high, including shoes. 

Smaller Vehicle 

For tests to detect a smaller vehicle in the detection zone of

a collision warning system, a passenger-type vehicle that is

typical at mine sites in the geographical area should be parked

or driven in the area of interest. At a minimum, one orientation

for the vehicle should be tested in which the vehicle faces the

sensor.

TEST METHOD

Test Area

The test area should be an open space on flat terrain with a

dry sand and/or gravel base. No rocks, foliage, or debris larger

than 8 cm in diameter should be in the test area. No objects

should be within approximately 50 m in the sensing direction of

the collision warning system, i.e., 50 m of clear area should lie

behind the equipment to establish a rear sensing zone. No large

objects should be within 25 m of both sides of the collision

warning system. All personnel, except whoever is conducting

the test, should remain in an area where they will not be detected by the collision warning system.

Sensor Mounting Locations 

General testing of the collision warning system can be

performed on a mobile test stand, but to claim that the system

will work on a specific piece of equipment, the system must be

mounted and tested on that equipment. For forward sensing, the

sensor should be mounted on the front bumper or grill according

to the manufacturer’s instructions. For rear sensing, the sensor

should be mounted on the rear bumper area. If this is not

possible, as with large off-road trucks, it can be mounted near

the light bar or on the rear axle. Other locations may be

acceptable, depending on the collision warning system’s

installation instructions. 

PROCEDURE

False Alarms

Tests of the collision warning system should start with no

obstacles near the system, as defined in the section entitled

“Test Area.” With the potential detection zones totally clear,

the equipment should be moved at slow speed (less than 8 km/h)

in the direction of sensing for approximately 15 m to determine

the frequency of false alarms. If false alarms occur, the cause

of the alarms should be determined, if possible, and noted, e.g.,

“System detected the ground” or “Detected rotating tires.” The

system should then be adjusted or relocated so false alarms are

at a minimum in a clear test area. The system settings and

mounting location when false alarms are at a minimum should

be recorded. 

Obstacle Detection

The detection zones for the collision warning system should

be determined by placing the obstacle at various distances and
17

locations behind the stationary equipment (with the engine

running) according to a test grid pattern. Test points in the

potential detection zone should be defined by a grid with a

spacing of no more than 1 m between test points. Detection at

each grid point should be determined by recording whether or

not an alarm is activated when the obstacle moves toward the

sensor in a line parallel to the long axis of the equipment. For

a person, movement toward the sensor should be at a slow walking speed (less than 6 km/h). For a smaller vehicle, movement

toward the sensor should be less than 8 km/h. 

Note: The detection zone must be verified for a moving

piece of equipment by allowing the person or small vehicle to

remain stationary at several points at the far edge of the detection zone and moving the equipment slowly toward the obstacle. The equipment may continue backing for several meters,

but must be stopped before it reaches an unsafe distance to the

obstacle. Any discrepancies over 30 cm between (1) detection

zones for moving equipment and a stationary obstacle and (2)

stationary equipment and a moving obstacle must be noted. 

 The following steps summarize the test procedure for a person (for the small vehicle tests, simply substitute a vehicle for

a person). The starting position for the person should be in

front of the sensor portion of the collision warning system, but

at a distance well outside the potential detection zone.

1. Starting on the centerline of the equipment (0-m line)

and outside the detection zone, begin the test by walking toward

the sensor. Place a marker on the centerline where detection

occurs and the alarm is activated.

2. Back up until the alarm stops. Walk toward the sensor

again to verify the position of the first detection point. Repeat

this step until a consistent detection point is determined. If

there are points where the alarm is not consistent (sporadic

detection), mark the first point where this occurs with a

different-colored marker. 

3. Continue walking toward the sensor along the 0-m

centerline. Verify that the alarm remains on while walking

along the entire line. Place a marker where detection stops and

the alarm is not activated. The alarm may be activated up to the

point directly in front of the sensor. In this case, place the

marker at this point.

4. Walk out of the detection zone to the initial starting

point.

5. Move from the 0-m centerline to the next grid line

(1 m) and repeat steps 2 through 4 along this line.

6. Repeat these steps along each line until detection does

not occur at any point on the lines.

7. Move to the other side of the centerline and repeat the

above steps to determine the detection zone for that side of the

centerline.

8. Record the position of the markers as described in

section 5.

9. Verify the detection zone for moving equipment by allowing the person to stand at the points of the detection zone

farthest away from the collision warning system. Using a spotter

and radios, signal the equipment operator to move slowly forward

a few meters. Then signal the operator to move slowly in reverse.

Record the distance to the equipment when the alarm detects the

stationary person and the alarm is activated. 

10. Stop the equipment at a safe distance from the person.

Have the operator move the equipment back to the starting position. 

11. Conduct the test again for the next detection point on

the next grid line. Repeat until the outer edges of the detection

zone are verified. Record any discrepancies greater than 30 cm

between this test and the test using the stationary equipment and

walking person.

Detection Zones

The reliable detection zone should be recorded as the area in

which the obstacle is detected 100% of the time. The obstacle

must be detected and an alarm must be generated immediately

(<200 ms) after the equipment starts moving toward the stationary obstacle or after the obstacle moves toward the

stationary equipment. The sporadic detection zone should be

recorded as the area in which the obstacle is detected less than

100% of the time, but more than approximately 10% of the time.

Less than 10% detection should be considered outside both

detection zones, but may be noted as a false alarm.

RECORDING DATA

False Alarms

False alarms should be noted when testing the collision

warning system as described above in the section on “Detection

Zones.” Possible causes of any false alarms and optimum mounting configurations to minimize false alarms should be noted. 

Detection Zones

The reliable and sporadic detection zones should be recorded

on a graph with a 1-m or 2.5-ft grid that approximates the

general shape of the detection zone as seen from a top view.

The general shape of the detection zone can be estimated by interpolating between tested points. 
Delivering on the Nation’s Promise:

Safety and health at work for all people

Through research and prevention

For information about occupational safety and health topics contact NIOSH at:

1-800-35-NIOSH (1-800-356-4674)

Fax: 513-533-8573

E-mail: pubstaft@cdc.gov

www.cdc.gov/niosh

DHHS (NIOSH) Publication No. 2002-135