Information Circular 9477 

Mining Roof Bolting Machine Safety:
 

A Study of the Drill Boom Vertical Velocity
 

By Dean H. Ambrose, John R. Bartels, August J. Kwitowski, Raymond F. Helinski,

 Sean Gallagher, Ph.D., Linda J. McWilliams, and Thomas R. Battenhouse, Jr. 

DEPARTMENT OF HEALTH AND HUMAN SERVICES
 

Centers for Disease Control and Prevention
 

National Institute for Occupational Safety and Health
 

Pittsburgh Research Laboratory
 

Pittsburgh, PA
 

May 2005 
ORDERING INFORMATION 

Copies of National Institute for Occupational Safety and Health (NIOSH)
 

documents and information
 

about occupational safety and health are available from
 

NIOSH–Publications Dissemination
 

4676 Columbia Parkway
 

Cincinnati, OH 45226–1998


 FAX: 513–533–8573

 Telephone: 1–800–35–NIOSH 

(1–800–356–4674)

 E-mail: pubstaft@cdc.gov

 Web site: www.cdc.gov/niosh 

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.
 

DHHS (NIOSH) Publication No. 2005–128
 
CONTENTS
 

Page 

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

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

Background ................................................................................... 4
 

Research . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 
 

Study population ............................................................................. 5
 

Model validation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 
 

Experimental design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 
 

Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 
 

Data analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 
 

Frequency and cross-tabulation analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 
 

Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 
 

Variables investigated . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 
 

Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 
 

Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 
 

Frequency analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 
 

Fixed variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 
 

Conditional variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 
 

Random variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 
 

Data sets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 
 

Cross-tabulation analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 
 

Seam height versus random variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 
 

Subject versus random variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 
 

Work posture versus random variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 
 

Drilling behavior versus random variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 
 

Bolting behavior versus random variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 
 

Boom speed versus fixed, conditional, and random variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 
 

Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 
 

Logistic regression analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 
 

Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 
 

Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 
 

Model 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 
 

Model 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 
 

Model 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 
 

Model 4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 
 

Model 5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 
 

Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 
 

Survival analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 
 

Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 
 

Variables investigated . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 
 

Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 
 

Survival analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 
 

Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 
 

Results of forward selection process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 
 

Risk model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 
 

Boom speed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 
 

Boom direction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 
 

Drilling behavior . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 
 

Work posture/seam height combinations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 
 

Bolting behavior . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 
 

Anthropometry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 
 

Operator location . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 
 

Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 
 

Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 
 
CONTENTS–Continued
 

Page 

Other research considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 
 

Acknowledgments .............................................................................. 25
 

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 
 

Appendix A.—Frequency of incidents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 
 

Appendix B.—Frequency by operator location . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 
 

Appendix C.—Frequency data sets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 
 

Appendix D.—Cross-tabulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 
 

Appendix E.—Logistic regression models for roof bolter simulation data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 
 

Appendix F.—Survival analysis tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 
 

Appendix G.—Illustrations of operator's work behaviors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 
 

ILLUSTRATIONS 

1. Artist concept of an operator caught within the boom arm and canopy ............................... 2
 

2. Actual dual boom arm roof bolting machine ................................................... 3
 

3. Full-scale wooden roof bolter boom arm setup for data collection .................................. 3
 

4. Operator close to the moving boom arm with hand on the controls .................................. 3
 

5. A roof bolter operator's work posture in an underground coal mine ................................. 4
 

6. Virtual operator contacted in the left hand (or fingers) and left leg . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 
 

7. Angular data of the original and modified viewing areas for the virtual operator ....................... 8
 

8. A view of the roof bolter model from a computer monitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 
 

9. Flowchart of NIOSH's algorithm for processing the simulation data files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 
 

A–1. Incidents by seam height . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 
 

A–2. Incidents by operator percentile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 
 

A–3. Incidents by work posture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 
 

A–4. Incidents by boom speed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 
 

A–5. Incidents by drilling behavior . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 
 

A–6. Incidents by bolting behavior . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 
 

A–7. Incidents by boom direction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 
 

A–8. Incidents by body part . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 
 

A–9. Incidents by machine part . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 
 

B–1. Incidents by operator location . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 
 

B–2. Contact incidents by operator location and body part . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 
 

B–3. Contact incidents by operator location and work posture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 
 

B–4. Contact incidents by operator location and seam height . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 
 

D–1. Contact incidents by seam height and boom direction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 
 

D–2. Contact incidents by seam height and body part . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 
 

D–3. Contact incidents by seam height and machine part . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 
 

D–4. Contact incidents by operator percentile and boom direction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 
 

D–5. Contact incidents by operator percentile and body part . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 
 

D–6. Contact incidents by operator percentile and machine part . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 
 

D–7. Contact incidents by work posture and boom direction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 
 

D–8. Contact incidents by work posture and body part . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 
 

D–9. Contact incidents by work posture and machine part . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 
 

D–10. Contact incidents by drilling behavior and boom direction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 
 

D–11. Contact incidents by drilling behavior and body part . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 
 

D–12. Contact incidents by drilling behavior and machine part . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 
 

D–13. Contact incidents by bolting behavior and machine part . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 
 

D–14. Contact incidents by bolting behavior and boom direction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 
 

D–15. Contact incidents by bolting behavior and body part . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 
 

D–16. Contact incidents by boom speed and boom direction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 
 

D–17. Contact incidents by boom speed and body part . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 
 
ILLUSTRATIONS–Continued
 

Page 

D–18. Contact incidents by boom speed and machine part . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 
 

D–19. Contact incidents by boom speed and work posture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 
 

D–20. Contact incidents by boom speed and operator percentile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 
 

D–21. Contact incidents by boom speed and drilling behavior . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 
 

D–22. Contact incidents by boom speed and seam height . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 
 

D–23. Contact incidents by boom speed and bolting behavior . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 
 

G–1. 45-in seam height and different work postures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 
 

G–2. 60-in seam height and different work postures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 
 

G–3. 72-in seam height and standing work posture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56 
 

TABLES 

1. Subject anthropometric data ................................................................ 6
 

2. Data that met the acceptance criteria ......................................................... 6
 

3. Behavior list for drilling a hole and installing a bolt ............................................. 7
 

4. Reaction times of operators used in the roof bolter model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 
 

5. Thirty-five possible simulation scenarios for each operator percentile ............................... 9
 

6. Data sets composed of conditions, operator percentile, and assigned numbering scheme . . . . . . . . . . . . . . . . . 10 
 

7. Factors that determined the number of observations (simulation executions) per seam height . . . . . . . . . . . . . 11 
 

8. Sample data output file . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 
 

9. Comparison of one contact per execution versus all contacts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 
 

10. Results of slow versus fast reaction for simulation executions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 
 

11. Hypothesized time-to-event regression model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 
 

12. Main effects risk model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 
 

13. Instantaneous relative risk estimates at specified time for each variable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 
 

A–1. Incidents by seam height . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 
 

A–2. Incidents by operator percentile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 
 

A–3. Incidents by work posture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 
 

A–4. Incidents by boom speed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 
 

A–5. Incidents by drilling behavior . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 
 

A–6. Incidents by bolting behavior . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 
 

A–7. Incidents by boom direction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 
 

A–8. Incidents by body part . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 
 

A–9. Incidents by machine part . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 
 

B–1. Incidents by operator location . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 
 

B–2. Contact incidents by operator location and body part ............................................ 32 
 

B–3. Contact incidents by operator location and work posture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 
 

B–4. Contact incidents by operator location and seam height . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 
 

C–1. Frequencies by data sets sorted by contacts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 
 

C–2. Frequencies by data sets sorted by avoid incidents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 
 

C–3. Data sets by body part and contacts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 
 

D–1. Contact incidents by seam height and boom direction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 
 

D–2. Contact incidents by seam height and body part . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 
 

D–3. Contact incidents by seam height and machine part . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 
 

D–4. Contact incidents by operator percentile and boom direction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 
 

D–5. Contact incidents by operator percentile and body part . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 
 

D–6. Contact incidents by operator percentile and machine part . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 
 

D–7. Contact incidents by work posture and boom direction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 
 

D–8. Contact incidents by work posture and body part . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 
 

D–9. Contact incidents by work posture and machine part . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 
 
TABLES–Continued
 

Page 

D–10. Contact incidents by drilling behavior and boom direction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 
 

D–11. Contact incidents by drilling behavior and body part . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 
 

D–12. Contact incidents by drilling behavior and machine part . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 
 

D–13. Contact incidents by bolting behavior and machine part . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 
 

D–14. Contact incidents by bolting behavior and boom direction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 
 

D–15. Contact incidents by bolting behavior and body part . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 
 

D–16. Contact incidents by boom speed and boom direction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 
 

D–17. Contact incidents by boom speed and body part . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 
 

D–18. Contact incidents by boom speed and machine part . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 
 

D–19. Contact incidents by boom speed and work posture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 
 

D–20. Contact incidents by boom speed and operator percentile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 
 

D–21. Contact incidents by boom speed and drilling behavior . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 
 

D–22. Contact incidents by boom speed and seam height . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 
 

D–23. Contact incidents by boom speed and bolting behavior . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 
 

E–1. Modeling the probability of a contact for slow reaction time of operator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 
 

F–1. Univariate model information (outcome slow) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 
 

F–2. Models with boom speed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 
 

F–3. Models with boom speed, boom direction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 
 

F–4. Models with boom speed, boom direction, drilling behavior . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 
 

F–5. Models with boom speed, boom direction, drilling behavior, work posture/seam height . . . . . . . . . . . . . . . . . 52 
 

F–6. Models with boom speed, boom direction, drilling behavior, work posture/seam height, bolting behavior . . . 53
 

F–7. Models with boom speed, boom direction, drilling behavior, work posture/seam height, bolting behavior, 


operator percentile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 
 

F–8. Final model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 
 

UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT 

fL footlambert in/sec inch per second 

ft foot lb pound 

hr hour msec millisecond 

in inch sec second 
 

MINING ROOF BOLTING MACHINE SAFETY:
 

A STUDY OF THE DRILL BOOM VERTICAL VELOCITY 


By Dean H. Ambrose,1

1

Safety engineer, Pittsburgh Research Laboratory, National Institute for Occupational Safety and Health, Pittsburgh, PA.
 

 John R. Bartels,2

2

Mechanical engineer, Pittsburgh Research Laboratory, National Institute for Occupational Safety and Health, Pittsburgh, PA.
 

August J. Kwitowski,3 

3

Civil engineer, Pittsburgh Research Laboratory, National Institute for Occupational Safety and Health, Pittsburgh, PA.


Raymond F. Helinski,4

4

Electronics technician, Pittsburgh Research Laboratory, National Institute for Occupational Safety and Health, Pittsburgh, PA (retired).
 

Sean Gallagher, Ph.D.,5

5

Research physiologist, Pittsburgh Research Laboratory, National Institute for Occupational Safety and Health, Pittsburgh, PA.
 

Linda J. McWilliams,6 

6

Statistician, Pittsburgh Research Laboratory, National Institute for Occupational Safety and Health, Pittsburgh, PA.
 

and Thomas R. Battenhouse, Jr.7 

7

Geosciences system analyst, Science Applications International Corp., Augusta, GA.
 

ABSTRACT 

This report examines the boom arm vertical speed for roof bolting machines to study a moving boom arm 

appendage at different speeds during different work scenarios. The goal of this study is to determine the impact 

of the appendage speed on the likelihood of the operator's hand, arm, head, or leg making contact, such as 

touching the moving appendage. The overall research goal is to reduce workers' risks to injury from exposure 

to underground mining machinery. 

Accident investigation reports from the Mine Safety and Health Administration do not usually contain 

enough information to aid in studying this problem, and lab experiments with human subjects are not feasible 

because of safety issues. As an alternative, researchers used a unique computer simulation model that uses a 

virtual human, vision tracking, and generates random virtual human motions and risky work behaviors. By 

using specialized software to simulate the computer model, researchers accurately identified potential hazards 

of tasks where it is not possible to perform experiments with human subjects. 

Results of a frequency distribution analytic approach show that, regardless of other variables, contact 

incidents were always greater when the boom was moving up, always greater on the hand, and always greater 

for the boom arm part of the machine. The reason why the subject experiences more contacts when the boom 

arm is moving up rather than down is that more risky behaviors occur during drilling and bolting when the 

boom is ascending. 

Results of a cross-tabulation analytic approach show that the 25th-percentile operators experienced more 

contacts than other operator sizes and had most of their contacts during a boom speed of 13 in/sec. The 

hand-on-boom behavior during drilling and bolting tasks experienced more contacts than other work behaviors, 

and both tasks had most of their contacts during speed 13 in/sec. The 60-in seam experienced more contacts 

than other seam heights and had most of the contacts during speed 16 in/sec. 

For univariate logistic regression models, seam height is the most important predictor of the probability of 

a contact. However, a multivariate logistic regression model predicted contacts are more likely with the bothknee work posture in the 60-in seam, a 25th-percentile operator compared to a 55th-percentile operator, and 

speeds 16 and 22 in/sec compared to 7 in/sec. 

Results of a survival analytic approach suggest that controlling the boom speed is the most important factor 

in determining the risk of an operator making contact. Based on the data collected, boom speeds greater than 

13 in/sec result in a substantial increase in risk to the roof bolter operator making contact. Speeds less than or 

equal to 13 in/sec are associated with a more modest relative risk of making contact, which represents a 

decrease in potential hazard. Virtual operator's response time has little effect on the number of contacts 

experienced. 

The mining industry can use the information in this study to reduce the likelihood that roof bolter operators 

will experience injury due to contact with a moving roof bolting machine's boom arm. 
2 

INTRODUCTION
 

The Mine Safety and Health Administration's (MSHA) 

Health and Safety Accident Classification injury database 

showed an average of 660 roof bolter operator accidents per 

year over a 5-year period (1999–2003). This makes roof bolting 

the most hazardous machine-related job in underground mining, 

representing 39% of all machine-related accidents in underground coal mines. Protecting the safety of our Nation's mine 

workers is of paramount importance; however, there are 

currently no regulations or method of determining the safe speed 

of roof bolter boom arms. Several fatalities of operators of 

underground coal mining equipment have led to an investigation 

of safe vertical velocities of a roof bolter boom arm at the 

National Institute for Occupational Safety and Health's (NIOSH) 

Pittsburgh Research Laboratory (PRL). MSHA established a 

roof bolting machine committee with members from the West 

Virginia Board of Coal Mine Health and Safety, NIOSH, and 

roof bolter manufacturers. The committee's objective was to 

identify hazards and recommend solutions. The data collection 

effort involved analysis of MSHA accident data, visits to 

underground mines to interview experienced roof bolting 

machine operators, discussions with roof bolting machine 

manufacturers, interviews with workers who were injured while 

performing roof bolting tasks, and reviews of research on roof 

bolting safety. The information-gathering and fact-finding efforts of the committee identified 10 roof bolting-related problems that may have contributed to or caused accidents while the 

operator was within the drill head or boom pinch-point area (see 

figure 1). 

Figure 1.—Artist concept of an operator caught within the boom 

arm and canopy. 

Seven of the 10 problems presented were associated 

with moving appendages [MSHA 1994]. Emphasis was placed 

on hazards related to the movement of the boom arm of a roof 

bolting machine. A set of solutions for each problem was 

recommended to increase the safety of roof bolting operations 

[MSHA 1994]. MSHA [1994] also recommended additional 

safety measures such as reduced drill speed rate, allowing the 

operator to react and either stop machine movement or move 

clear of a closing pinch point. One major observation regarding 

this study was that there are no data on safe speeds for booms 

operating close to workers in confined environments such as an 

underground coal mine. 

This study reports the initial step to define a safe speed range 

for a roof bolter's boom arm. MSHA accident investigation reports do not usually contain scientific information to aid in 

studying interactions between a machine and its operator. In 

addition, lab experiments with human subjects are not feasible 

because of safety and ethical issues. With this in mind, NIOSH 

researchers successfully developed a computer model that uses 

UGS PLM Solutions' Jack simulation software. The model generates data by means of simulation while altering several 

variables associated with the machine and its operator. These 

include coal seam height, the operator's anthropometry, work 

posture, choice of risky behavior, and the machine's appendage 

velocity. The resulting simulation database has been studied by 

researchers to investigate appendage speeds and decrease the 

number of contacts (possible injuries) to the miner by improving 

machine designs or operating procedures. Researchers believe 

that such simulations, treated with advanced statistical procedures such as logistic regression and survival analysis, 

provide very useful tools to evaluate the hazards of tasks where 

it is not possible to perform experiments with human subjects. 

The model contains a virtual mine environment that includes 

roof bolter (figure 2) and operator models and experimentally 

mimics the virtual human and machine actions that can cause a 

contact. In this report, when operator limbs and a roof bolter 

appendage in the computer model interact and result in touching, the event is defined as a contact. Simulations of the model 

enable researchers to generate a database of contacts between a 

machine and its operator. 

Three-dimensional computer simulations provide machine 

designers and safety analysts with a way to evaluate contact 

hazards concerning operator/machine interaction. Anthropos, 

Jack, Ramsis, and Safework are commercial software tools that 

digitally model humans for ergonomic analyses and work 

performance evaluations. NIOSH's simulator uses a roof bolting 

machine and biomechanical human models that execute on Jack 

(version 1.2) simulation software. Computer simulations enable 

the study of multiple mine environments (i.e., seams of different 

heights), motions of workers (represented by virtual humans), 

and different work scenarios (e.g., various drilling and bolting 

tasks, work postures, and risky work behaviors). These studies 

would be dangerous and time- and cost-prohibitive if they were 

conducted in the field. 

One of the most difficult problems in using a computer 

simulator that generates human motions is trying to determine 

whether the model in the simulator accurately represents the 

actual mechanical system. The uncertainty and randomness inherent in a machine operator's tasks can be compared to 

someone drinking a beverage from a cup. Lifting the cup to 

one's mouth and placing it back onto the table exhibits some 

random variation in its motion path, and one could easily 
 

3 

visualize the path of that motion. To model this random motion, 

the sequence of someone drinking a beverage from a cup would 

recur until the cup is empty. Each motion path would differ 

slightly even though the motions basically look alike. Likewise, 

in the case of a machine operator, the operator's work behaviors, 

motions of each behavior, and motion paths associated with 

each motion behavior will have some degree of randomness 

despite the basic task sameness. Through careful study, 

researchers successfully incorporated within the roof bolter 

model the randomness of the operator's motion and path 

variance within that motion. This factor of randomness gives 

NIOSH's simulator the capability to realistically represent the 

operator's motions and work behaviors while executing any 

machine task. Ambrose [2000, 2001, 2004] and Volberg and 

Ambrose [2002] discuss in detail the development of random 

motions used in the roof bolter model. 

Figure 2.—Actual dual boom arm roof bolting machine. 

(Photograph courtesy of J. H. Fletcher & Co., Huntington, WV.) 

Before collecting final simulation data, researchers used test 

results by Bartels et al. [2001, 2003] on the roof bolter model to 

validate and ensure that parameter assumptions made for the 

computer-based simulation conform to actual field practice. 

Training videos, in-mine observations and videos, and working 

with a bolter manufacturer and experts helped to determine 

actual bolting practice. Studies by Bartels et al. [2001, 2003] 

verified the operator's response times, task motions, and field of 

view relative to the roof bolter's boom arm. Human subject tests 

with a full-scale working mockup of a roof bolter boom arm 

(figure 3) were used to collect motion data that helped determine 

parameters for building valid and credible models. 

Figure 3.—Full-scale wooden roof bolter boom arm setup for 

data collection. The mannequin illustrates motion sensor 

locations. The roof 

bolter model requires input data that closely matches an actual 

machine operating characteristics (e.g., dimensions and speeds) 

as well as data that accurately reflect physical characteristics of 

the operator, such as how close to the moving boom arm he or 

she is to reach machine controls and insert the drill steel or bolt 

into the drill head (figure 4).

Figure 4.—Operator close to the moving boom 

arm with hand on the controls. 

 Researchers obtained these data by 

using a motion tracking/capturing system using experienced 

United Mine Workers of America (UMWA) miners as subjects. 

The subjects performed prescribed tasks on the mockup that 

mimic bolting practices that did not include risky behaviors as 

described in this report. Researchers found no differences between test subjects' actual bolting practice and recommended 

practice (according to roof bolting training materials). During 

human subject data collection, risky behaviors invalidated a test 

session, resulting in rerunning the test. 

Experiments in other industries have provided some evidence for resolving safe machine appendage speeds for reducing 

potential hazards. Industries using robots exhibit concern for 

guidelines for robotics safety. Etherton [1987] reports that 

10 in/sec is a speed whereby humans could recognize and react 

to a perceived hazard in the system. In addition, the Occupational Safety and Health Administration (OSHA) [1987] reports 

that robot speeds for teach-and-repeat programming sessions are 

required to be slow. The current standard of the American 

National Standards Institute recommends that this slow speed 

should not exceed 10 in/sec. However, Karwowski et al. [1992] 

report that test subjects with respect to the potential hazards 

from a moving robot arm similarly perceive the range of slow 

speeds of robot motion from 8 to 16 in/sec. Their study suggests that the safe slow speed of robot motions for teaching and 

programming purposes lies somewhere between 10 and 8 in/sec, 

and for safe reduced speed of robot motions redefines the 

current recommendation of 10 in/sec. Moreover, the U.S. 
 

4 

Department of Energy [1998] states that because the teacher can 

be within the robot's restrictive envelope, mistakes in programming can result in unintended movement, so a restricted speed 

of 6 in/sec is required on any part of the robot. This slower 

speed would minimize potential injuries to a teacher if 

inadvertent action or movement occurred. 

This report documents NIOSH's success in achieving its 

expected outcome to examine the speed range of a roof bolter 

boom arm for different workplace scenarios and compare statistically which scenarios are most likely to cause contacts 

(possible injuries) to miners. 

BACKGROUND
 

Roof bolting is one of the most basic functions and most 

dangerous jobs in underground coal mining. Roof bolts are the 

main method of roof support in mines, which is essential to 

ventilation and safety. After miner crews remove a section of 

the coal seam, roof bolting machine operators install bolts (steel 

rods) to secure areas of unsupported roof from caving in. 

A bolter crew's typical work sequence includes tramming and 

positioning the machine, general preparation and setup, drilling 

a hole, and installing a bolt. General preparation is a 

miscellaneous category that includes setting up temporary roof 

supports, scaling, handling ventilation material, performing a 

methane check, handling supplies, emptying the dust box, and 

examining the workplace. Drilling bolt holes involves inserting 

the drill steel in the chuck, adding extension steels if necessary, 

changing the bits, drilling the hole, and removing the steel. Bolt 

installation involves making up bolt assemblies, inserting resins 

in the hole if necessary, bending bolts, inserting bolts into the 

hole, aligning the bolts, raising bolts, and spinning to mix resin 

or torque the installed bolt. The sequence repeats until the assigned area of the roof is secure and then the machine trams to 

a new location. 

Roof bolting may be regarded as a fairly structured and 

repetitive work situation. Although there is an established work 

cycle, it is commonly altered due to external influences, 

including variability in geology, interruption by coworkers and 

supervisors, machine malfunctions, variability of supplies, etc. 

The roof bolter operator is under constant production pressure 

to install as many bolts in one 8-hr shift as necessary to keep up 

with coal-cutting operations while remaining vigilant to all of 

the possible dangers. Consequently, roof bolting work in a 

newly exposed roof area involves even greater risk from the yet 

unsupported and unknown conditions. 

The roof bolter operator does his or her job in a confined 

environment (see figure 5) in a limited working height, e.g., 

45 in, and in close proximity and in low visibility to a moving 

drill head mounted on a boom arm 72 in long. 

Figure 5.—A roof bolter operator's work posture in an 

underground coal mine. 

This restricted 

work environment can force the operator in awkward postures 

for tasks that require quick reactions to avoid being contacted by 

moving machine parts. Restricted visibility due to a protection 

canopy and low lighting conditions further complicate the task. 

Moreover, roof bolters work in a newly exposed roof area; 

consequently, there is greater risk from the unsupported and 

unknown conditions. 

The range of the operator location is about 20 to 38 inches 

from the boom arm because of the restricted work space or work 

posture when performing the bolting tasks. This range of 

distance brings the operator close to the boom arm while it is 

moving. Subsequently, this closeness allows the operator to 

easily reach the controls and perform tasks that require handling 

the drill steel and bolt that attaches to the drill head located at 

one end of the boom arm. 

One major observation regarding the study by MSHA [1994] 

was that there are no data on safe speeds for booms operating 

close to workers in confined environments such as an 

underground coal mine. To address this problem, the main 

question that needs to be answered is: What range of boom 

speeds minimizes the roof bolter operator's chances of contact 

or possible injury without sacrificing job performance? This 

question becomes even more important in light of potential rules 

being discussed by MSHA on improving the design of roof 

bolters. The information needed to answer the question is— 

• When does the operator see the moving boom arm and 

drill head during the bolting operation? 

• How frequent are the contacts between the operator and 

moving machine appendages? 

• What are the distances between the operator's hands, arms, 

legs, and head and the moving boom arm and drill head during 

each of the operator's job tasks? 
 

 

5 

• How do changes in various work postures, such as 

kneeling on one knee, kneeling on two knees, or standing, 

impact the previous three questions? 

To answer these questions effectively, a sufficient number of 

studies must be done to collect data on contacts and variables 

that influence them. A contact means the boom arm touches the 

operator's hand, arm, head, or leg (figure 6). 

Figure 6.—Virtual operator contacted in the left hand 

(or fingers) and left leg. 

 A contact does not 

necessarily mean an injury. However, a severe injury or fatality 

can occur if the operator makes contact while in a drill head or 

boom arm pinch-point area. MSHA accident investigation 

reports do not usually contain enough information to aid in 

studying this particular problem, and lab experiments with 

human subjects are not feasible because of safety issues. 

Therefore, a computer simulation model approach was used as 

the primary means to generate and collect the data during boom 

arm movement [Ambrose 2000]. 

Previous studies by Klishis et al. [1993a,b] on worker job 

performance and machinery and work environment identified 

miners' risks and hazard exposures while bolting. More than 

two dozen bolting-related problems (including specific human 

behaviors) were recognized as potential situations that could 

lead to injury or expose workers to injury. Approaches to avoid 

these situations were suggested and applied at mining operations 

to evaluate specific problems in roof bolting tasks. Turin et al. 

[1995] conducted a human factors analysis of hazards related to 

the movement of the drill head boom of a roof bolting machine. 

Seven short-term recommendations to increase the safety of roof 

bolting operations were developed: use a dead-man interlock 

device to cut off power to the controls when the operator is out 

of position, place fixed barriers at pinch points and other 

dangerous areas, provide better control guarding, reduce the 

fast-feed speed, use automatic cutoff switches for pinch points 

and other dangerous areas, redesign the control bank to conform 

to accepted ergonomic principles, and use resin insertion tools 

and resin cartridge retainers. 

RESEARCH
 

STUDY POPULATION 

The study population used in the simulation software for any 

virtual human model can cover the 5th through 95th percentile 

for males and females. Using the wide-range capability of Jack 

software to scale the operator's anthropometry, researchers made 

three virtual operators that conformed to 25th-, 55th-, and 92ndpercentile males (table 1). The three virtual human models were 

chosen to match closely to human subject data that were collected for model verification/validation and to study the target 

population, which is 99% male. Since the goal of the lab tests 

was not to duplicate the entire simulation population but only to 

verify that the simulation model represents an accurate picture 

of the roof bolter model, a small sample of 12 human subjects 

from the local UMWA office was tested. Two female miners 

were study volunteers that represented 20th- to 30th-percentile 

male operators. Table 1 provides information on the height, 

weight, age, and sex for the 12 subjects used in the motion 

studies. The optimum viewing area tests used 12 subjects from 

NIOSH-PRL since no special mining skill was involved and no 

anthropometry data were needed. 

MODEL VALIDATION 

Two different methods to validate the model were chosen. 

The first method was the traditional face validity evaluation by 

roof bolter manufacturers and users. A questionnaire was developed and distributed to manufacturers, bolter operators, and 

mine inspectors. The responders were shown two animations 

that showed an operator performing roof bolting tasks: one was 

the virtual operator produced from the motion-capture data, the 

other was the virtual operator created from the model. The respondents were asked to compare aspects of the animations 

without knowing which motion source was shown in the animation by scoring on a scale from 4 being good to 1 being poor. 

The virtual operator produced from the motion-capture data 

scored an average of 2.55, the virtual operator created from the 

model scored an average of 2.34, and the average difference in 

questionnaire scoring was 0.64. Verification of the validity of 

the model was first implied when 14 of 15 responders agreed 

that the simulation animations did not differ significantly from 

the animations of human operators. 
 

6 

Table 1.—Subject anthropometric data 

Subject Height, 

in 

Weight, 

lb 

Age, 

years 

Sex Operator 

percentile 

Percentile 

interval 

virtual25 ..... 66.4 159.4 — male 24 20–30 

virtual55 ..... 70.0 172.4 — male 54 50–60 

virtual92 ..... 71.8 187.0 — male 91 90–95 

human 1 . . . . . 71.0 187.2 47 male 84 80–90 

human 2 . . . . . 68.7 135.8 54 male 51 50–60 

human 3 . . . . . 69.4 177.7 41 male 61 60–70 

human 4 . . . . . 69.2 179.5 44 male 58 50–60 

human 5 . . . . . 70.4 185.9 49 male 79 70–80 

human 6 . . . . . 71.9 194.0 49 male 92 90–95 

human 7 . . . . . 66.5 169.8 53 female 24 (male) 20–30 

human 8 . . . . . 66.4 168.5 47 female 24 (male) 20–30 

human 9 . . . . . 69.7 183.9 50 male 63 60–70 

human 10 . . . . 71.8 198.2 47 male 91 90–95 

human 11 . . . . 69.3 183.0 44 male 59 50–60 

human 12 . . . . 68.3 174.9 48 male 49 40–50 

The second method compared the motions generated by the 

simulation with motion data collected on human subjects. 

Although the predictions of the model could not be directly 

compared, the accuracy of the movements used to generate 

"contact data" could be. The aspects of operator movements determined to be critical were the range of motion of operators and 

variation in those movements. 

Two sets of simulation data were generated from motion data 

of the knee and standing work postures. The first used virtual 

operators with anthropometric measurements identical to those 

of the 12 human subjects tested. Here, the data were compared 

on a subject-to-subject basis. The second set used operators 

generated from Jack software in seven different anthropometric 

sizes. Researchers compared data to an average of the human 

subjects within a 10th- percentile range, e.g., the Jack-generated 

55th-percentile operator was compared to the average of the 

subjects in the 50th-60th percentile range. 

The human subject movement data tended to vary greatly 

from individual to individual, making it impractical for a direct 

comparison of each individual's exact path of movement. Because the amount of movement and the variation of movement 

were the primary concerns, the comparisons were made between 

the statistical ranges by using standard deviation of movement. 

Researchers developed two sets of test data to verify the model. 

One set compared Jack-generated operators' motions in each of 

the anthropometric size ranges with human subject data averaged for that range ("average" operator). The other set 

compared an individual test subject's motions with a simulation 

using that subject's anthropometry ("human subject" operator). 

The criterion for acceptance of the simulation data was less than 

1.6-in difference from the human subject data, the static positional accuracy of the motion-tracking system with the 

resolution settings used. 

Table 2 shows the percentage of range of motion data by 

using standard deviations that met the acceptance criteria. 

Table 2.—Data that met the acceptance criteria 

Percent met Work posture Condition criteria 

Both knees . . . . . . . .60-in seam average operator . . . . 71.43 

60-in seam human subject Both knees ........ 63.54
 operator .................... 

Right knee . . . . . . . .60-in seam average operator . . . . 71.07 

60-in seam human subject Right knee . . . . . . . . 62.29
 operator .................... 

Standing . . . . . . . . . .72-in seam average operator . . . . 69.64 

72-in seam human subject Standing .......... 72.66
 operator ....................
 

Starting position . . . .Average operator . . . . . . . . . . . . . 80.35 
 

Starting position . . . .Human subject operator . . . . . . . . 72.22 


 Overall average . . — 70.40 

 The 

simulations run using average operators (generated from Jack 

software 25th-, 45th-, 55th-, 65th-, 75th-, 85th-, and 92ndpercentile persons) showed a greater percentage of standard 

deviation values that met the acceptance criteria. This would be 

expected since averaged standard deviation values were used as 

the input data for the simulation. In general, the percentage of 

agreement was good in relation to modeling a scenario with the 

complexity of roof bolting. 

To assess the performance of the model, Bartels et al. [2003] 

report in detail the lab experiments and results that compared 

movements of the virtual human in the model to those of their 

test subject counterparts. The report also discusses the evaluation of human motion and response time data to duplicate 

accurately the skills and experience involved in operating 

mining equipment. 

EXPERIMENTAL DESIGN 

The roof bolting operation was broken down into specific 

tasks. Klishis et al. [1993b] observed the tasks and the amount 

of time spent on each task. The task list provided a guide in 

developing the experimental design for lab human subject tests 

and motion scenarios for the computer simulations. 

Early phases of roof bolter model development used input 

parameter values that were guesses to allow development to 

progress. Consequently, limited lab experiments were necessary 

to determine input parameters (e.g., accurate field of vision, 

human response in roof bolting postures, human motion 

envelopes of body appendages, and initial work starting 

postures) for the roof bolter model and to validate the model and 

simulations. 

The computer model generates and collects contact data 

between the machine and its virtual operator while recording 
7 

predictor variables, such as the seam height, the operator's 

starting positions, operator work postures, risky work behaviors, 

anthropometry, and the machine appendage velocity. Data 

collected by the roof bolter model consist of counting the 

number of contacts and recording the time when a contact 

happens. 

Collected data were recorded to a file for each simulation 

scenario execution. The first line in the file contained information on the seam height, work posture, boom arm speed, 

operator anthropometry, and operator work behaviors. Furthermore, the following information was recorded every 0.03 sec to 

the file: 

• Simulated time(s) 

• The operator's initial distance (in) from the boom arm 

• The boom arm distance (in) from a reference point on the 

floor level 

• Distance calculations (in) between eight viewing area 

reference points and a reference point on the boom arm to help 

determine when the operator sees the boom arm 

• A number marking sequential contacts between limbs and 

machine appendage was recorded for each simulated frame. 

The computer model contains seven variables having different levels. The seam height (three levels) consisted of 45, 60, 

and 72 in to accommodate the operator's work posture (four 

levels): right knee, left knee, both knees, and standing. Human 

subject motion tests provided data that defined models of virtual 

humans whose percentile interval ranged from the 24th to the 

92nd. The operator's final anthropometry (3 levels+) conformed 

to 25th-, 55th-, and 92nd-percentile males. Researchers also 

collected operator's starting locations from the human subject 

motion test data and calculated unique starting location values 

for each subject as a function of the seam height and work 

postures in that seam. The operator's risky behavior during 

drilling and bolt installation each had four levels. The five 

levels of the boom arm speeds—7, 10, 13, 16, and 

22 in/sec—were selected from MSHA [1994]. Researchers had 

originally planned to collect data on four speeds. Based on 

initial results from the data analysis of a four-speed database, 

researchers could not speak to the risks associated with speeds 

between 10 and 16 in/sec. Therefore, researchers included a 

fifth speed, 13 in/sec, which split the difference between two 

initial speed levels. 

A behavior motion is a series of human motions that mimics 

a specific action. Studies on worker job performance and machinery and work environment identify miners' risky work behavior 

and hazard exposures while bolting [Klishis et al. 1993a,b]. 

Researchers used this information to identify specific risky 

behaviors for the drilling operation and bolt installation (see 

table 3 and figures in appendix G). Also, researchers were interested in work behaviors occurring only when the machine 

appendage had movement; consequently, other risky behaviors 

associated with operating a roof bolter were not used. Ambrose's 

[2004] decision algorithm was integrated within the model that 

randomly selects which behavior to use for a simulation 

execution. Numerical parameters used in the algorithm came 

from the percentage of operator actions that resulted in hazard 

exposure. These parameters were based on statistical observations of bolter operator actions associated with unsafe acts 

[Klishis et al. 1993a]. 

Table 3.—Behavior list for drilling a hole and installing a bolt 

Operation Work behavior description 

Drill . . . . . Hand off the drill steel and hand off the boom arm. 

Hand on the drill steel. 

Hand on the boom arm. 

Hand on the drill steel and then hand on the boom arm. 

Bolt . . . . . Hand off the bolt or wrench and hand off the boom arm. 

Hand on the bolt or wrench. 

Hand on the boom arm. 

Hand on the bolt or wrench and then hand on the boom 

arm.

 NOTE.—Klishis et al. [1993a,b] were not specific with regard to hand 

location on the boom arm, drill steel, or wrench. In the simulations, 

researchers placed the hand on the boom arm approximately aft-end of 

the drill head and placed the hand on drill steel, bolt, or wrench 

approximately midsection of the item. 

As part of the experiment design, the operator's chance of 

avoiding a contact was also evaluated to ensure that an avoid 

incident (near-miss) would not be considered a contact. This 

required knowledge of when the operator sees the moving boom 

arm and the reaction time needed to avoid the boom arm. 

Investigators used information from Helander et al. [1987], 

Kobrick [1965], and Welford and Brebner [1980] to define a 

predetermined human response time— 250 msec (fast) and 

400 msec (slow)—to get out of the way of a moving boom arm 

once it is seen. Table 4 quantifies data to determine "fast" and 

"slow" reaction times of operators as a function of seam height, 

work posture, and operators' anthropometric data. 

Investigators originally used a viewing area for the virtual 

operator that was a cone with an oval directrix as defined by 

Humantech [2003] to experiment with the virtual human's 

vision-tracking capabilities. For acceptable viewing in reduced 

lighting conditions found in underground mines, MSHA's 

minimum lighting requirements mandate illumination levels of 

0.06 fL. The viewing area was modified from lab test results on 

human subjects that determined the optimal viewing area and 

accurate field of vision for the virtual human in underground 

mines (figure 7). 

Because investigators did not have access to the simulation 

software source code, the operator's reaction time in combination with the viewing area could not be made an integral part 

of the computer model. Consequently, when executing simulations, recorded data included time of contacts and when the 

boom arm was in and out of the operator's view. Subsequently, 

during data postprocessing of the contact database, a collision 

check algorithm compared time-pairings of when the boom arm 

was in and out of view to determine suspected avoid incidents 

(near-misses). The results provided investigators with enough 

information that identified contacts that could be avoided by the 

operator. 

The 25th-, 55th-, and 92nd-percentile operator models were 

placed in a virtual mine environment that contained a model of 
8 

Table 4.—Reaction times of operators used in the roof bolter model, milliseconds 

45-IN SEAM HEIGHT 

Right-knee Left-knee Both-knees 

Operator work posture work posture work posture 

percentile Fast Slow Fast Slow Fast Slow 

reaction reaction reaction reaction reaction reaction 

time time time time time time 

25th . . . . . . 436 736 356 656 376 676 

55th . . . . . . 401 701 366 666 397 697 

92nd . . . . . 330 630 384 684 349 649 

60-IN SEAM HEIGHT 

Right-knee Left-knee Both-knees 

Operator work posture work posture work posture 

percentile Fast Slow Fast Slow Fast Slow 

reaction reaction reaction reaction reaction reaction 

time time time time time time 

25th . . . . . . 370 670 376 676 356 656 

55th . . . . . . 333 633 392 692 353 653 

92nd . . . . . 403 703 424 724 375 675 

72-IN SEAM HEIGHT 

Standing 

Operator work posture 

percentile Fast Slow 

reaction reaction 

time time 

25th . . . . . . 374 674 

55th . . . . . . 376 676 

92nd . . . . . 388 688 

Figure 7.—Angular data of the original and modified viewing areas for the 

virtual operator. 
 

9 

a Fletcher8

8

J. H. Fletcher & Co. was a project collaborator. Fletcher provided 

information on a roof bolting machine. The company is the largest U.S. 

manufacturer of roof bolting equipment. 

 roof bolter boom arm assembly. When using the 

virtual mine environment, simulations were executed on each 

percentile operator while performing 1 of 35 possible scenarios 

(table 5). 

Table 5.—Thirty-five possible simulation scenarios for each operator percentile 

Scenario 

Seam height, in Work posture Boom speed, in/sec 

45 60 72 Right 

knee 

Left 

knee 

Both 

knees Standing 7 10 13 16 22 

1 ...... 8 8 8

2 ...... 8 8 8

3 ...... 8 8 8

4 ...... 8 8 8

5 ...... 8 8 8

6 ...... 8 8 8

7 ...... 8 8 8

8 ...... 8 8 8

9 ...... 8 8 8

10 ..... 8 8 8

11 ..... 8 8 8

12 ..... 8 8 8

13 ..... 8 8 8

14 ..... 8 8 8

15 ..... 8 8 8

16 ..... 8 8 8

17 ..... 8 8 8

18 ..... 8 8 8

19 ..... 8 8 8

20 ..... 8 8 8

21 ..... 8 8 8

22 ..... 8 8 8

23 ..... 8 8 8

24 ..... 8 8 8

25 ..... 8 8 8

26 ..... 8 8 8

27 ..... 8 8 8

28 ..... 8 8 8

29 ..... 8 8 8

30 ..... 8 8 8

31 ..... 8 8 8

32 ..... 8 8 8

33 ..... 8 8 8

34 ..... 8 8 8

35 ..... 8 8 8

For example, simulation scenario 17 (in table 5) is one 

observation for any percentile operator who performs bolting 

tasks in a seam height of 60 in, on the left knee, and with a 

boom arm operating at a speed of 7 in/sec. The scenarios consisted of various combinations of the seam height, work posture, 

and boom arm speed. Researchers did not simulate the standing 

work posture in the two lower seam heights. Also, the knee 

work postures were not simulated in the highest seam height. 

When simulating any scenario, each simulation execution 

represented one observation, and information for that 

observation was recorded to one data file. 
10 

Table 6 shows how the simulation executions were organized 

into test series called data sets. The test series helped researchers with distributing the work in gathering data from 

simulation executions. Data sets were developed by using all of 

the simulation scenarios reflected in table 5. A data set contains 

a fixed seam height, boom arm speed, operator work posture, 

and anthropometry. Furthermore, data sets were also used to 

help show results in frequency data analysis. 

Conditions1 

4507R ..... 

Table 

Operator 

percentile 

25th 

6.—Data sets composed of conditio

Execution's 

assigned Conditions1 

number range 

0000 0049 6007R ...... 

ns, operato

Operator 

percentile 

25th 

Execution's 

assigned Conditions1 

number range 

1800 1849 7207S ...... 

r percentile, and assigned numbering scheme 

Operator 

percentile 

25th 

Execution's 

assigned 

number range 

3600 3649 

55th 0050 0099 55th 1850 1899 55th 3650 3699 

4507L ..... 

92nd 

25th 

0100 

0150 

0149 

0199 6007L ...... 

92nd 

25th 

1900 

1950 

1949 

1999 7210S ...... 

92nd 

25th 

3700 

3750 

3749 

3799 

55th 0200 0249 55th 2000 2049 55th 3800 3849 

4507B ..... 

92nd 

25th 

0250 

0300 

0299 

0349 6007B ...... 

92nd 

25th 

2050 

2100 

2099 

2149 7216S ...... 

92nd 

25th 

3850 

3900 

3899 

3949 

55th 0350 0399 55th 2150 2199 55th 3950 3999 

4510R ..... 

92nd 

25th 

0400 

0450 

0449 

0499 6010R ...... 

92nd 

25th 

2200 

2250 

2249 

2299 7222S ...... 

92nd 

25th 

4000 

4050 

4049 

4099 

55th 0500 0549 55th 2300 2349 55th 4100 4149 

4510L ..... 

92nd 

25th 

0550 

0600 

0599 

0649 6010L ...... 

92nd 

25th 

2350 

2400 

2399 

2449 4513R ...... 

92nd 

25th 

4150 

4200 

4199 

4249 

55th 0650 0699 55th 2450 2499 55th 4250 4299 

4510B ..... 

92nd 

25th 

0700 

0750 

0749 

0799 6010B ...... 

92nd 

25th 

2500 

2550 

2549 

2599 4513L ...... 

92nd 

25th 

4300 

4350 

4349 

4399 

55th 0800 0849 55th 2600 2649 55th 4400 4449 

4516R ..... 

92nd 

25th 

0850 

0900 

0899 

0949 6016R ...... 

92nd 

25th 

2650 

2700 

2699 

2749 4513B ...... 

92nd 

25th 

4450 

4500 

4499 

4549 

55th 0950 0999 55th 2750 2799 55th 4550 4599 

4516L ..... 

92nd 

25th 

1000 

1050 

1049 

1099 6016L ...... 

92nd 

25th 

2800 

2850 

2849 

2899 6013R ...... 

92nd 

25th 

4600 

4650 

4649 

4699 

55th 1100 1149 55th 2900 2949 55th 4700 4749 

4516B ..... 

92nd 

25th 

1150 

1200 

1199 

1249 6016B ...... 

92nd 

25th 

2950 

3000 

2999 

3049 6013L ...... 

92nd 

25th 

4750 

4800 

4799 

4849 

55th 1250 1299 55th 3050 3099 55th 4850 4899 

4522R ..... 

92nd 

25th 

1300 

1350 

1349 

1399 6022R ...... 

92nd 

25th 

3100 

3150 

3149 

3199 6013B ...... 

92nd 

25th 

4900 

4950 

4949 

4999 

55th 1400 1449 55th 3200 3249 55th 5000 5049 

4522L ..... 

92nd 

25th 

1450 

1500 

1499 

1549 6022L ...... 

92nd 

25th 

3250 

3300 

3299 

3349 7213S ...... 

92nd 

25th 

5050 

5100 

5099 

5149 

55th 1550 1599 55th 3350 3399 55th 5150 5199 

4522B ..... 

92nd 

25th 

1600 

1650 

1649 

1699 6022B ...... 

92nd 

25th 

3400 

3450 

3449 92nd 5200 5249 

3499 

55th 1700 1749 55th 3500 3549 

92nd 1750 1799 92nd 3550 3599 

1

The first two digits represent seam height (in). The second two digits represent boom arm speed (in/sec). The letter represents work posture 

as follows: R = right knee; L = left knee; B = both knees; S = standing. 

Table 7 summarizes the factors (per seam height) that were 

used to generate observations (data files) that made up the 

research database. Note that the database represents the equivalence of actual field observations of roof bolting work in 

underground coal mines for a period of 12.15 eight-hour shifts. 

The 8-hr shift data were calculated using information from an 

unpublished time study of a roof bolter cycle time that installed 

4-ft bolts with a dual-boom bolter equipped with an automatic 

temporary roof support system. The roof bolter equipment in 

the time study was the same machine model and bolt length used 

in the simulation. 

MEASUREMENTS 

Virtual human models that matched closely to human subject 

data collected for model verification/validation were given 

specific instructions as to how to perform the bolting tasks for 

each of the simulation scenarios. In each condition, the virtual 

operator was required to work in the starting posture throughout 

the tasks. Three kneeling postures were used in the two lower 

seam heights. The standing posture was used in the unrestricted 

(high) seam. The standing postures for the two taller operators 

were flexing more toward the right side and forward to 

accommodate the workspace and proper right-hand alignment 

with the machine controls. This posturing was also observed 

during lab tests that collected human subject motion data for 

validating the model. The random starting position between the 

operator and boom arm were based on seam height and the 

operator's work posture according to results from human subject 

lab tests. Each virtual operator faced perpendicular to the long 

side of the boom arm, and the machine controls were always to 
11 

the operator's right. The virtual operator grabbed the tools (drill 

steel, bolt, or wrench) with the right hand, passed the tool off to 

the left hand, and grabbed them with both hands to finish setting 

the tool in the drill head and/or hole in the mine ceiling (mine 

roof). 

Table 7.—Factors that determined the number of observations (simulation executions) 

per seam height 

Factors Observation Seam Boom Work Simulation totals height, in Operators speeds postures executions 

2,250 . . . . . . . . 45 3 5 3 50 

2,250 . . . . . . . . 60 3 5 3 50 

750 . . . . . . . . . 72 3 5 1 50 

Overall - 5,250 — — — — — 

Table 8.—Sample data output file 

CONF=1 SEAM=2 POST=3 SPED=1 SUBJ=1 BEHD=1 BEHB=1 

time OPL V1 V2 V3 V4 V5 V6 V7 V8 BAM LPB LPD LAB LAD LLB LLD RLB RLD HDB 

0.03 54. -4. 38. 5. 63. 28. 58. 32. 20. 19. 0. 0. 0. 0. 0. 0. 0. 0. 0. 

0.06 54. -4. 38. 5. 63. 28. 58. 32. 20. 19. 0. 0. 0. 0. 0. 0. 0. 0. 0. 

0.10 54. -4. 38. 5. 63. 28. 58. 32. 20. 19. 0. 0. 0. 0. 0. 0. 0. 0. 0. 

0.13 54. -4. 38. 5. 63. 28. 58. 32. 20. 19. 0. 0. 0. 0. 0. 0. 0. 0. 0. 

0.16 54. -4. 38. 5. 63. 28. 58. 32. 20. 19. 0. 0. 0. 0. 0. 0. 0. 0. 0. 

0.20 54. -4. 38. 5. 63. 28. 58. 32. 20. 19. 0. 0. 0. 0. 0. 0. 0. 0. 0. 

0.23 54. -4. 38. 5. 63. 28. 58. 32. 20. 19. 0. 0. 0. 0. 0. 0. 0. 0. 0. 

First line and columns of data file (coded) Subsequent lines and columns in data file 

CONF - machine control configuration time - simulated time, sec 

 1=piano key controls OPL - operator's distance from the boom arm, in 

SEAM - seam height V1 through V8 - reference points on the vision cone whose values are 

1=45 in; 2=60 in; 3=72 in used to determine if the boom arm is seen by the operator 

POST - work posture BAM - to determine boom arm movement, a distance is measured 

1=right knee; 2=left knee; 3=both knees; 4=standing between a floor reference point and boom arm reference, in 

SPED - boom arm speed LPB through HDB - a numerical marking that indicates if a contact 

1=7 in/sec; 2=10 in/sec occurred between an operator limb and machine appendage. "1" 

3=16 in/sec; 4=22 in/sec means contact; "0" means no contact. 

5=13 in/sec LPB / LPD = left palm with boom / with drill head 

SUBJ - operator's anthropometry LAB / LAD = left forearm with boom / with drill head 

1=25th; 2=55th; 3=92nd LLB / LLD = left leg with boom / with drill head 

BEHD - operator's behavior during the drilling task RLB / RLD = right leg with boom / with drill head 

1=none; 2=hand on drill HDB = head with boom arm 

3=hand on boom; 4=hand on both 

BEHB - operator's behavior during the bolting task

 1=none; 2=hand on bolt

 3=hand on boom; 4=hand on both 

Figure 8.—A view of the roof bolter model from a 

computer monitor. 

Once the preparation for the drilling or bolt installation task 

was completed, the right hand was positioned on the appropriate 

lever that controlled the boom arm's vertical movement. Boom 

arm speed was the same ascending and descending. During the 

boom arm movement, the left hand's motion would be one of 

four possible risky work behaviors as defined in table 3. At no 

time during boom arm movement was the virtual operator 

positioned in a pinch-point area of the drill head or boom arm. 

When the virtual operator and machine interacted and 

resulted in touching, the event was defined as a contact. 

Researchers were interested in contacts occurring only when the 

machine appendage was moving. Furthermore, the model 

included random operators' motions before and after the boom 

arm appendage moved [Ambrose 2004]. These motions helped 

to improve motion accuracy through random positioning of the 

arm and hand just before or after appendage movement. Also, 
 

 

 

 

12 

these motions made the overall model (figure 8), when 

simulated, look visually realistic. 

Data were collected according to the organized data sets 

(table 5). Three separate computers were used in the datagathering phase of the study. Using different computers did not 

influence simulation outcomes because a copy of the simulation 

model executed perfectly on all computers. No changes or 

modifications to the model were necessary for any of the 

computers used in data collection. The data collection phase 

took 5 months to complete. 

Researchers had each of the 5,250 simulation executions 

stored in separate data files. One data file contained lines of 

information identified by a timeframe. The number of 

timeframes varied because the length of a simulation execution 

changed due to one or more of the following: boom speed, 

seam height, or risky work behavior. A timeframe constitutes 

one line of data in the output file, except for the first line in the 

file, which describes each simulation scenario. Table 8 shows 

several lines of a data file. The table also includes definitions 

for line and column descriptors. 

DATA ANALYSIS
 

Results of this analysis of roof bolter simulations provide 

information that could be quite helpful in making recommendations to reduce the likelihood that roof bolter operators 

get injured from contact with a moving boom arm. Researchers 

believe that the use of such simulations, treated with frequency 

and cross-tabulation and advanced statistical procedures such as 

logistic regression and survival analysis, provide extremely 

useful tools to evaluate potential hazards of tasks where it is not 

possible to perform experiments with human subjects. 

NIOSH contracted with Science Applications International 

Corp. (SAIC), Augusta, GA, to assist in the data-postprocessing 

phase of the research. SAIC postprocessed data from 5,250 

simulation executions with the aid of a customized software 

program whose algorithm followed the flow diagram in figure 9. 

SAIC generated the final database by developing a customized 

program based on NIOSH's algorithm that detailed sequences 

for examining the simulation results. NIOSH analysts used 

SAIC's final database for this portion of the study. 

The resulting database contains information representing 

variables that could influence predictions of contact incidents 

between the operator's body parts and the moving boom arm and 

drill head. The determinations of contact incidents for each 

simulation execution resulted in four possible occurrences: 

• A contact between the machine and the operator for a 

person with both slow and fast reactions. 

• A contact between the machine and the operator for a 

person with only slow reactions. 

• An avoid incident (near-miss) where a contact occurred in 

the simulation, but postanalysis determined that the operator 

saw the bolter boom arm and had fast enough reactions to get 

out of the way of (avoid) the contact. 

• A complete simulation execution where no contacts or 

avoid incidents occurred (none). 

A simulation execution would continue to completion even 

though it was possible for a single simulation to have multiple 

contacts and avoids. The presence of multiple incidents in a 

single simulation execution meant that data analysis could be 

done on either a data set containing avoids and all contacts (all 

of the contacts) or one incident per simulation execution 

(one run/one contact). Consequently, researchers made two 

separate sets of data from the initial postprocessed database. 

Table 9 compares the two sets of data. This comparison 

showed that the source of contact incidents and the relationship 

of the variables associated with the incidents did not differ 

significantly for the two. The one run/one contact data set was 

also considered by researchers to more accurately represent the 

real-world situation, as an operator would most likely stop or 

at least pause after being struck with a moving machine 

appendage. The one run/one contact data set also lent itself to 

other types of data analysis techniques such as logistic 

regression and survival analysis. 

Analysis also shows that the reaction time of the operator did 

not significantly affect the outcome of the simulation (table 10). 

The number of contact incidents for an operator with slow 

reactions differed from those for an operator with fast reactions 

by less than 1% in both data sets. The results were as expected 

insofar as there was a difference. There was a reasonable 

difference in reaction times between fast and slow operators 

obtained from reaction time tests on our human subjects. 

However, the speculation as to why a small difference in 

contacts might be reflected in the speed range of the boom being 

studied is that if the operator with fast reactions could not get 

out of the path of the boom, the slower operator certainly would 

not either. Also, depending on the stimulus, small differences 

were found in some reaction time test cases in the literature 

search. Moreover, literature reviews were not helpful with 

whole-body reaction of the upper torso and limbs in confined 

spaces, which was a concern in our research. 

The following sections contain frequency and crosstabulation, logistic regression, and survival analyses. All 

analyses were conducted using only the occurrences for the 

operator with slow reactions that included one contact per simulation executions (one run/one contact). Frequency analysis is 

the simplest method to observe how different categories of 

values are distributed in the sample database. Customarily, if a 

data set includes any categorical data (e.g., seam height, 

appendage speed, work posture, etc.), then one of the first steps 

in the data analysis is to compute a frequency table for those 

variables. Cross-tabulation is a combination of two (or more) 

frequency tables arranged such that each cell in the resulting 

table represents a unique combination of specific values of 

cross-tabulated variables. Thus, cross-tabulation allows researchers to examine frequencies of observations that belong to 
13

 Figure 9.–Flowchart of NIOSH’s algorithm for processing the simulation data files. 
14 

specific categories for more than one variable. By examining 

these frequencies, researchers can identify relationships between 

cross-tabulated variables and provide information on trends to 

use other statistical approaches for the database. 

Logistic regression is a technique used for relating one or 

more independent variables to an outcome variable, which follows a binomial rather than a normal distribution. This model 

is useful for identifying risk factors related to the presence or 

absence of a condition. Researchers used the logit (logistic) 

transformation of p (the probability of an event or nonevent) as 

the dependent variable. Complex numerical algorithms are generally required to fit the parameters of the model. 

Survival analysis is a statistical technique that allows researchers to determine factors that influence both whether an 

event occurs (for example, contact between the boom and 

operator) and the time until that event occurs. In the present 

situation, this event might represent contact between the boom 

of the roof bolter and the worker operating the machine at some 

point in the period of a simulation execution. Since several 

variables (such as boom speed, work posture, worker behaviors, 

etc.) were varied in the simulations, survival analysis can be 

used to evaluate which of these factors were most important in 

terms of predicting an event (contact), as well as whether certain 

work behaviors, postures, or other factors might actually protect 

a worker from experiencing a contact. 

Presenting various approaches to data analysis was part of the 

research objective, and each analysis technique used the same 

database. However, we do not recommend comparing results 

from each approach because of the differences in underlying 

mathematics, the computational details, and expected outcomes. 

Table 9.—Comparison of one contact per execution versus all contacts 

Reaction One run/one contact All contacts Variable time Avoid incidents Contacts Avoid incidents Contacts 

Seam height, in . . . . . . . . . . Slow . . . . . 45>60>72 60>45>72 60>45>72 60>72>45 

Fast . . . . . . 45>60>72 60>45>72 60>45>72 60>72>45 

Operator percentile . . . . . . . . Slow . . . . . 92>55>25 25>55>92 25>55>92 25>55>92 

Fast . . . . . . 55>25>92 25>55>92 25>55>92 25>55>92 

Work posture1 . . . . . . . . . . . . Slow . . . . . L>B>R>S B>R>L>S L>B>R>S B>R>S>L 

Fast . . . . . . L>B>R>S B>R>L>S L>B>R>S B>R>L>S 

Boom arm speed, in/sec . . . . Slow . . . . . 10>13>7>22>16 16>22>13>10>7 10>13>7>16>22 16>22>7>13>10 

Fast . . . . . . 10>13>7>22>16 16>22>7>10 10>13>7>16>22 16>22>7>13>10 

Drilling behavior2 . . . . . . . . . Slow . . . . . B>D&B>N>D B>D&B>N>D B>D&B>N>D B>N>D&B>D 

Fast . . . . . . B>D&B>N>D B>N>D&B>D B>D&B>N>D B>N>D&B>D 

Bolting behavior3 . . . . . . . . . Slow . . . . . N>B>BT>BT&B B>N>BT&B>BT B>N>BT&B>BT B>BT&B>N>BT 

Fast . . . . . . B>N>BT>BT&B B>N>BT&B>BT B>N>BT&B>BT B>BT&B>N>BT 

Boom direction4 . . . . . . . . . . Slow . . . . . D>U U>D D>U U>D 

Fast . . . . . . D>U U>D D>U U>D 5 Body part . . . . . . . . . . . . . . . Slow . . . . . H>L>A>HD H>L>HD>A H>L>A>HD H>A>L>HD 

Fast . . . . . . H>L>A>HD H>L>HD>A H>L>A>HD H>A>L>HD 

Side6 . . . . . . . . . . . . . . . . . . . Slow . . . . . L>R>HD L>HD>R L>R>HD L>HD>R 

Fast . . . . . . L>R>HD L>HD>R L>R>HD L>HD>R 

Machine part7 . . . . . . . . . . . . Slow . . . . . B>D B>D B>D B>D 

Fast . . . . . . B>D B>D B>D B>D 

1

L = left knee; R = right knee; B = both knees; S = standing.
 

2

B = hand on boom; D = hand on drill steel; D&B = hand on drill steel then on boom; N = none.
 

3

B = hand on boom; BT = hand on bolt; BT&B = hand on bolt then on boom; N = none.
 

4

D = down; U = up.
 

5

H = hand; L = leg; A = arm; HD = head.
 

6

L = left; R = right; HD = head.
 

7

B = boom; D = drill head.
 

Table 10.—Results of slow versus fast reaction for simulation executions 

All contacts One contact per simulation 

Frequency Percent Cumulative 

percent 

Cumulative Frequency Percent percent 

SLOW OPERATOR 

Avoid . . . . . 2,777 27.02 27.02 755 14.38 14.38 

Contact . . . . 5,798 56.42 83.45 2,750 52.38 66.76 

None . . . . . . 1,701 16.55 100.00 1,745 33.24 100.00

 Total . . . . 10,276 100.00 — 5,250 100.00 — 

FAST OPERATOR 

Avoid . . . . . 2,768 26.94 26.94 799 15.22 15.22 

Contact . . . . 5,807 56.51 83.45 2,706 51.54 66.76 

None . . . . . . 1,701 16.55 100.00 1,745 33.24 100.00

 Total . . . . 10,276 100.00 — 5,250 100.00 — 
15 

FREQUENCY AND CROSS-TABULATION ANALYSIS 

Method 

Variables Investigated 

The model used three types of predictor variables: (1) fixed 

variables were used as input for simulation setup, (2) conditional 

variables were randomly selected within the computer model 

and then fixed before executing the simulation, and (3) random 

variables were "values" that changed during the simulation 

execution. The fixed variables were: 

•	 Roof bolter boom arm speed.—The boom speeds used 

were 7, 10, 13, 16, and 22 in/sec. When the boom arm 

moved up or down for drilling or bolting, one selected 

speed was maintained for all events throughout the 

simulation execution. 

•	 Seam height.—The area in which the operator had to 

perform the roof bolting procedure is defined as the 

distance from the floor to the top of the coal seam or roof, 

which may go beyond the top of the coal seam. The 

specific heights used were 45, 60, and 72 in. 

•	 Operator's posture while performing the roof bolting 

tasks.—The work postures used were kneeling on the 

right knee, kneeling on the left knee, kneeling on both 

knees, and standing. The one selected work posture was 

maintained throughout the simulation execution. 

•	 Operator's anthropometry.—The operators' percentiles 

were grouped within the general population as 

determined by height. The percentile size operators used 

were 25th, 55th, and 92nd. 

The conditional variables were: 

•	 Operator's behavior during the drilling phase of the 

simulation.—Drilling behavior was randomly selected 

before beginning the simulation. The operator could 

place his hand on the drill steel, place his hand on the 

boom arm, place his hand on the drill steel then the boom 

arm, or the hand would not be placed on any of the 

machine parts. 

•	 Operator's behavior during the bolting phase of the 

simulation.— Bolting behavior was randomly selected 

before beginning the simulation. The operator could 

place his hand on the bolt, place his hand on the boom 

arm, place his hand on the bolt then the boom arm, or the 

hand would not be placed on any of the machine parts. 

•	 Operator's location.—The operator would be randomly 

positioned with respect to the bolter at the beginning of 

the simulation. The operator location is defined as the 

distance from a reference point on the boom arm to a 

reference point in the small of the operator's back. At no 

time during boom arm movement was the operator 

positioned in pinch-point areas of the drill head or 

boom arm. 

The random variables were: 

•	 Boom arm direction (up or down).—This is the direction 

in which the boom arm was moving when an incident, 

either a contact or an avoid incident, occurred. The 

direction could only be one of two directions, up or 

down, and if the boom arm was not in motion the incident 

would not be used. 

•	 Body part (hand, arm, leg, and head).—This is the part 

of the operator involved in an incident. The parts of the 

body that could potentially be struck by the moving boom 

arm were the hand, arm, leg, or head. 

•	 Machine part (boom arm and drill head).—This is the 

part of the bolting machine assembly that could strike the 

operator. The only moving parts used for this simulation 

were the boom arm and drill head. 

Data 

Frequency and cross-tabulation analyses included 5,250 

simulation executions. Of the simulations examined, 2,750 

exhibited contact between the boom and the operator. 

Results 

Frequency Analysis 

A table of incidents was compiled for fixed, conditional, and 

random variables used in the simulation in order to determine 

their effect on the operator (contacts between the operator and 

the machine). The results of the tabulation of incidents by 

variable showed which variables played the largest role in the 

occurrences of potential contacts to operators. The variables 

that were associated with the greatest number of contacts and 

avoid incidents are presented. The following appendices in this 

report contain charts and tables for frequency analysis: 

appendix A, "Frequency of Incidents"; appendix B, "Frequency 

by Operator Location"; and appendix C, "Frequency Data Sets." 

Fixed Variables 

As shown in table A–1, the 60-in seam height had the most 

contacts, 59% of the total number of contacts and 25% of the 

avoid incidents. Table A–2 shows that the anthropometry did 

not show a large difference for any one size individual, but the 

25th-percentile operator had 40% of the total contact incidents. 

Table A–3 shows that the work posture on both knees had the 

greatest number of contact incidents compared to other postures 

(32% of the total contacts). Table A–4 shows that all boom arm 

speeds resulted in contact incidents; the faster speeds (16 and 

22 in/sec) accounted for 43% of the total contacts. 
 

 

16 

Conditional Variables 

Data in tables A–5 and A–6 show that the hand-on-boom 

behavior for drilling or bolting had more contacts than any other 

drilling or bolting behavior. Table B–1 showed three locations 

with increased contact incidents: 21.7, 29.9, and 30.3 in. 

Further sorting of operator location indicated that the increase 

at 21.7 in was associated with increased head incidents with the 

operator on both knees in a 60-in seam height (see tables B–2 to 

B–4). The increase in incidents at 29.9 and 30.3 in were associated with the operator in a standing position and an increase 

in contacts with the hand (see tables B–2 and B–3). 

Random Variables 

Table A–7 shows the boom arm upward direction had 

significantly more contacts (76% of the total) and fewer avoid 

incidents (37% of the total) than the down direction. Table A–8 

shows the hand was involved in 67% of all contact incidents. 

Table A–9 shows the boom arm was the closest moving 

machine part to the operator and accounted for 80% of all 

contact incidents. 

Data Sets 

Frequency analysis was done on the data sets described in 

table 6. The data set for each simulation execution was a predetermined set of the variables assigned for a set of 

50 simulation executions. An example of this would be 45R07, 

which defines the set of conditions for a 45-in seam height, with 

the operator on the right knee and the boom arm speed set at 

7 in/sec. Examining the data sets in tables C–1 and C–2 confirms trends seen when the results for the individual variables 

were analyzed. Examples of this analysis show: (1) data sets 

6022B and 6016B (60-in seam height with the operator on both 

knees) had the most contacts, (2) data sets 4510L and 4510B 

(45-in seam height with the operator on both knees) had the 

most avoid incidents, and (3) the hand for data set 7207S and 

the head for data set 6022B had the most contacts. 

Cross-tabulation Analysis 

A cross-tabulation of incidents was compiled for selected 

variables used in the simulation in order to determine their effect 

on contacts between the operator and machine. The results of 

the tabulation of contact incidents by variable showed which 

variables played the largest role in the occurrences of potential 

contacts to operators (see appendix D). 

Seam Height Versus Random Variables 

In comparing seam heights against boom direction, body 

part, and machine part (tables D–1 to D–3), the following 

relationships were identified. Regardless of seam height, contact 

incidents were always greater on the hand, always greater for 

the boom arm part of the machine, and always greater when the 

boom arm was moving up. The greatest number of contacts was 

always associated with the 60-in seam. The greatest number of 

contacts occurred for the 60-in seam with the boom moving up 

(46% of all contacts), the 60-in seam with contact on the hand 

(32% of all contacts), and the 60-in seam with contact made 

with the machine boom (47% of all contacts). The fewest 

number of contacts occurred for the 72-in seam with the boom 

moving down and the 45-in seam with contact made with the 

drill head. Zero contacts occurred with the operator's leg at a 

45-in seam height and with the operator's head at a 72-in seam 

height. 

Subject Versus Random Variables 

In comparing subjects against boom arm direction, body part, 

and machine part (tables D–4 to D–6), the following relationships were identified. Regardless of subject size, contact 

incidents were always greater when the boom was moving up, 

always greater on the hand, and always greater for the boom part 

of the machine. The greatest number of contacts was always associated with the 25th-percentile size, and the fewest number of 

contacts always occurred with the 92nd-percentile size. The 

greatest number of contacts occurred for the 25th-percentile size 

with the boom moving up (29% of all contacts), occurred on the 

hand (27% of all contacts), and involved the machine boom 

(31% of all contacts). The fewest number of contacts occurred 

for the 92nd-percentile size with the boom moving down, 

occurred on the arm, and involved the drill head. 

Work Posture Versus Random Variables 

Analysts identified several relationships when comparing 

work posture against boom direction, body part, and machine 

part (see tables D–7 to D–9). Regardless of posture, contact incidents were always greater when the boom was moving up, 

always greater on the hand, and always greater for the boom part 

of the machine. The greatest number of contacts occurred for 

the both-knee work posture with the boom moving up (27% of 

all contacts), the right-knee posture with contact made with the 

hand (18% of all contacts), and the both-knee posture with 

contact made with the machine boom (25% of all contacts). The 

fewest number of contacts occurred for the standing posture 

with the boom moving down and for the standing posture with 

contact made with the drill head. Zero contacts occurred for the 

cases involving the operator's head in the right-knee, left-knee, 

and standing work postures and for those involving the 

operator's leg in the both-knee posture. 

Drilling Behavior Versus Random Variables 

Analysts identified several relationships when comparing 

drilling behavior against boom direction, body part, and machine part (see tables D–10 to D–12). Regardless of drilling 

behavior, contact incidents were always greater when the boom 

was moving up, always greater on the hand, and always greater 

for the boom part of the machine. The greatest number of 
 

 

 

 

17 

contacts occurred for the hand-on-boom behavior with the boom 

moving up (42% of all contacts), occurred on the hand (41% of 

all contacts), and involved the machine boom (45% of all 

contacts). The fewest number of contacts occurred for the 

hand-on-drill-steel behavior with the boom moving down, 

hand-on-drill-steel behavior with contact on the arm, and handon-drill-steel-behavior involving the drill head part of the 

machine. 

Bolting Behavior Versus Random Variables 

Analysts identified several relationships when comparing 

bolting behavior against boom direction, body part, and machine 

part (see tables D–13 to D–15). Regardless of bolting behavior, 

contact incidents were always greater when the boom was 

moving up, always greater on the hand, and always greater for 

the boom part of the machine. The greatest number of contacts 

occurred for the hand-on-boom behavior with the boom moving 

up (26% of all contacts), occurred on the hand (27% of all 

contacts), and involved the machine boom (32% of all contacts). 

The fewest number of contacts occurred for the hand-on-bolt 

behavior with the boom moving down, the hand-on-boomthen-bolt behavior with contact on the arm, and the hand-on-bolt 

behavior with contact made with the drill head. 

Boom Speed Versus Fixed, Conditional, and Random Variables 

Analysts identified several relationships when comparing 

boom speed against boom direction, body part, and machine part 

(table D–16 to D–18). Regardless of boom speed, contact 

incidents were always greater when the boom was moving up, 

always greater on the hand, and always greater for the boom part 

of the machine. The greatest number of contacts occurred at the 

16 in/sec speed for the following: boom moving up (17% of all 

contacts), hand part of the body (16% of all contacts), and the 

boom part of the machine (18% of all contacts). The fewest 

number of contacts occurred for the 10-in/sec speed with the 

boom moving down, the 7-in/sec speed involving contact with 

the arm, and the 22-in/sec speed involving contact with the drill 

head. 

Analysts identified several relationships when comparing 

boom speed against work posture, subject, drilling behavior, 

bolting behavior, and seam height (tables D–19 to D–23). For 

all boom speeds, the work posture on both knees had the 

greatest number of contacts and the standing posture had the 

fewest number of contacts. The greatest number of contacts 

occurred for the 16-in/sec speed with the work posture on both 

knees; the fewest number of contacts occurred for the 22-in/sec 

speed while standing. Regardless of boom speed, the 25thpercentile sizes had the greatest number of contacts while, 

regardless of speed, the 92nd-percentile size had the fewest 

number of contacts. The greatest number of contacts occurred 

for the 13-in/sec speed at the 25th-percentile size. The fewest 

number of contacts occurred for the 10-in/sec speed at the 92ndpercentile size. Regardless of boom speed, the 60-in seam 

height had the greatest number of contacts. The 72-in seam had 

the fewest number of contacts for all speeds except 10 in/sec, 

where the 45-in seam had the fewest. The greatest number of 

contacts was associated with the 16 in/sec speed at the 60-in 

seam height. The fewest number of contacts was for the 

10-in/sec speed at the 45-in seam height. Regardless of boom 

speed, the hand-on-boom drilling behavior had the most 

contacts and, regardless of speed, the hand-on-boom bolting 

behavior had the most contacts. Regardless of speed, the 

hand-on-drill-steel drilling behavior had the fewest number of 

contacts and, regardless of speed, the hand-on-bolt bolting 

behavior had the fewest number of contacts. For the drilling 

behaviors, the greatest number of contacts was for 13 in/sec and 

hand on the boom; the fewest number of contacts was for 

13 in/sec and hand on the drill steel. For the bolting behaviors, 

the greatest number of contacts was for 13 in/sec and hand on 

the boom; the fewest was for 10 in/sec and hand on the bolt. 

Summary 

The frequency-fixed variable analyses showed the following: 

•	 The faster boom speeds of 16 and 22 in/sec combined 

accounted for the greatest number of contacts (43% of the 

total). 

•	 The seam height of 60 in had the most contacts, with 59% 

of the total number of contacts and 25% of the avoid 

incidents. 

•	 A work posture on both knees had the greatest number of 

contact incidents compared to other postures (32% of the 

total contacts). 

•	 The 25th-percentile individual had slightly more contact 

incidents than the other size individuals. 

The frequency-conditional variable analyses showed the 

ollowing: 

•	 42% of all contacts occurred for the hand-on-boom 

behavior when the boom was moving up. 

•	 41% of all contacts occurred for the hand-on-boom 

behavior with contact made with the hand. 

•	 45% of all contacts occurred for the hand-on-boom 

behavior with contact made with the machine boom. 

The frequency-random variable analyses showed the 

ollowing: 

•	 The hand was the closest body part to the moving boom 

arm and was involved in 67% of all contact incidents. 

•	 The boom was the closest moving machine part to the 

operator and accounted for 80% of all contacts. 

•	 Regardless of other variables, contact incidents were 

always greater when the boom was moving up. 

The cross-tabulation/fixed-variable analyses showed the 

ollowing: 

•	 Regardless of boom speed, 92nd-percentile-sized operators 

experienced fewer contacts than other operator sizes. 

•	 Regardless of boom speed, 25th-percentile-sized operators 

experienced more contacts than other operator sizes. 

f

f

f
 

18 

The cross-tabulation/fixed-random-variable analyses showed 

the following: 

•	 46% of all contacts occurred in the 60-in seam with the 

boom moving up. 

•	 47% of all contacts occurred in the 60-in seam and 

involved the machine boom. 

LOGISTIC REGRESSION ANALYSIS 

Method 

An initial approach to the modeling of the roof bolter 

simulation data used logistic regression analysis. This statistical 

procedure is often used to investigate the relationship between 

a binary or dichotomous response (outcome variable) and a set 

of predictor variables (or covariates). For a binary response 

model, the response, Y, can take on one of two possible values, 

denoted for convenience by 1 or 0.

§ p · 

logit () p	 log  ̈  ̧ D E  c  ̈  ̧ x (1)

© 1 p1 

where x is a vector of explanatory variables, 

p = Pr(Y = 1 | x), 

 is the intercept parameter, 

and 1 is the vector of slope parameters. 

Odds ratio (OR) estimates are computed from the parameter 

estimates. The OR is defined as the ratio of the odds for those 

with the response factor variable (x = 1) to the odds for those 

without the response factor variable (x = 0). The OR is obtained 

by exponentiation of the value of the parameter associated with 

the response factor. It indicates how the odds of an event 

change as, for example, a dichotomous response factor changes 

from 0 to 1. For instance, an OR of 2 means that the odds of an 

event when the response factor variable x = 1 are twice the odds 

of an event when x = 0. The linear logistic regression models in 

this study were fit by the method of maximum likelihood. In a 

very general sense, the method of maximum likelihood 

estimation yields values for the unknown model parameters, 

which maximizes the probability of obtaining the observed set 

of data. 

For the roof bolter simulation data, the outcome contact 

variable was coded as "contact" (Y = 1) versus "avoid + no 

contact" (Y = 0). The predictor variables or covariates 

considered in this analysis were restricted to only those that 

remained static during a simulation execution. These included 

(1) seam height, (2) boom speed, (3) anthropometry, (4) work 

posture, and (5) a work posture/seam height combination. Work 

posture/seam height combination was used because the higher 

seam height used only one posture—standing. The logistic 

regression analysis modeled the probability of a "contact" as a 

function of this set of covariates [Pr(Y = 1 | x)]. The analysis 

included 5,250 simulation executions, and 52% of the 

simulations exhibited a contact between the boom and the 

operator. All models used data generated for an operator with 

slow reaction time in order to be consistent with the other 

analytical techniques used in this report. 

Initially, researchers produced univariate logistic regression 

models (models with only one predictor variable or covariate). 

A final main effects multivariate model that included all of the 

covariates tested in the univariate models was generated. The 

method of reference cell coding was used for all of the 

covariates (SAS version 8.0). A covariate was considered to be 

significantly related to the outcome when the p-value of the 

Wald test was <0.05. All models had a statistically significant 

main effect for the covariate(s). This analysis investigated no 

interactions terms. R2 value, based on the likelihood ratio chisquare for testing the null hypothesis that all the coefficients are 

zero, was calculated for all of the models. This R2 is a 

generalized coefficient of determination that measures 

predictive power (it cannot be interpreted as a proportion of 

variance explained by the covariates). The results of the logistic 

regression analysis are presented in appendix E. 

Results 

Model 1 

For this model, the covariate under consideration was seam 

height. The reference group was seam height equal to 45 in. 

For 60 in compared to 45 in, the likelihood of a contact was 

almost seven times greater (OR = 6.96). For 72 in compared to 

45 in, the likelihood of a contact was six times greater (OR = 

6.33). The R2 was equal to 0.24, which is the largest value 

shown for any of the univariate models. Thus, for these logistic 

regression models, seam height is the most important predictor 

of the probability of a contact. 

Model 2 

The predictor variable in this model was boom speed. 

A boom speed of 7 in/sec was the reference level. The contact 

difference between 10 in/sec and the reference group was less 

likelihood of a contact. ORs of approximately 1.35 and 1.19 

were found for 16 and 22 in/sec, respectively, compared to 

7 in/sec. There was no significant effect found at 13 in/sec. 

Model 3 

Anthropometry was the covariate entered in this model. 

A virtual human model that represented an operator conforming 

to the 55th percentile was chosen as the reference group. At the 

25th percentile, an operator would be 1.65 times more likely to 

be contacted, whereas at the 92nd percentile an operator would 

be less likely to be contacted (OR = 0.69). 
 

 

 

19 

Model 4 

In this model, the predictor variable was work posture, with 

standing being the reference level. Being on the right knee, the 

left knee, or both knees, an operator would be less likely to be 

contacted (OR = 0.36, 0.35, and 0.60, respectively). 

Model 5 

This model represented a multivariate model. A multivariate 

analysis is a more comprehensive modeling of the data. In a 

multivariate logistic regression model, each estimated 

coefficient provides an estimate of the log odds adjusting for all 

other variables included in the model. For this model, a problem 

occurred when seam height and anthropometry were included 

simultaneously. A linear combination occurred because the 

cells were empty for standing in 45- and 60-in seam heights and 

kneeling in 72-in seam heights. To handle this situation, a new 

variable was created that combined both seam height and work 

posture. "Standing/72 in" was considered the reference level, 

with the other categories being "right knee/45 in," "right 

knee/60 in," "left knee/45 in," "left knee/60 in," "both 

knees/45 in," and "both knees/60 in". For this new variable, the 

only OR that showed significant contact compared to 

"standing/72 in" was "both knees/60 in" (OR = 2.05). In this 

model, a 25th-percentile operator would be about two times 

more likely (OR = 1.93) to be contacted compared to the 55thpercentile reference level. Boom speeds of 16 and 22 in/sec 

were approximately 1.5 and 1.26 times more likely, 

respectively, of involving a contact compared to 7 in/sec. 

In order to incorporate the predictor variables that were 

dynamic over the course of a simulation execution, it was 

necessary to use a modeling approach that took into account the 

element of time. Survival analysis (e.g., Cox regression) was 

the next step used for the modeling of the roof bolter simulation 

data. 

Summary 

• Compared to seam height of 45 in, the likelihood of a 

contact was nearly seven times greater in a seam height of 60 in 

and six times greater in a seam height of 72 in. 

• The odds of a contact between a boom speed of 13 in/sec 

and 7 in/sec, the reference group, were not significant. 

• ORs of approximately 1.35 and 1.19 were found for boom 

speeds of 16 and 22 in/sec, respectively, compared to 7 in/sec. 

• A 25th-percentile operator is 1.65 times more likely to be 

contacted than a 55th-percentile operator. A 92nd-percentile 

operator is less likely to be contacted (OR = 0.69) than a 55thpercentile operator. 

• Comparing work postures/seam heights, the operator has 

about the same likelihood of a contact when on the right knee, 

left knee, or both knees. 

• For the multivariate model (comparing standing posture, 

7 in/sec boom speed, and 55th-percentile operator), significantly 

higher ORs were found: 2.05 for "both knees/60 in," 1.5 for 

16 in/sec and 1.26 for 22 in/sec, and 1.93 for the 25th-percentile 

operator. 

SURVIVAL ANALYSIS 

The following describes the results of a survival analysis on 

the simulations presented in this report. Some of the 

information presented regarding the methods and results of the 

survival analysis are somewhat technical. However, a summary 

at the end of this section describes the major findings of the 

survival analysis for those not interested in the technical aspects 

of the analysis. 

Method 

Variables Investigated 

Several variables believed to be important in influencing 

whether and when a contact might occur were investigated. 

These include boom speed, drilling and bolting behaviors, boom 

direction (up or down), work posture/seam height combinations 

(e.g., worker on right knee in 45-in seam), operator location, and 

anthropometry (worker size). The dependent (or the outcome) 

variable was the time to an event (i.e., boom making contact 

with the worker) occurring. 

Except for operator location, which was entered as a 

continuous variable, all variables in the model were entered as 

dummy variables using a referent (or comparison) condition 

against which all other levels of the variable were judged. The 

following list identifies the referent conditions for all 

independent variables for which dummy coding were used. 

• Boom speed: 7 in/sec 

• Drilling behavior: hand not touching boom or drill steel 

• Bolting behavior: hand not touching boom or bolt 

• 	Work posture/seam height combination: standing in 72-in 

seam 

• Anthropometry: 25th-percentile worker 

• Boom direction: boom not moving upwards 

• 	Operator location: distance from operator's back to boom 

is 23 in 

Data 

Researchers examined 5,250 cases involving possible contact 

between the boom arm and the operator. A number of cases 

involved no contact between the operator and the boom while 

the boom was not moving. As a result, the survival analysis 

comprised 3,517 cases. Of this total, 2,750 cases involved 

unintentional contact with a moving boom arm (considered an 

"event" in the survival analysis). The balance (767 cases) 

consisted of censored observations or cases where unintentional 

contact between the boom arm and operator occurred throughout 

the simulation execution. 
20 

Survival Analysis 

A Cox regression model (time-to-event regression analysis) 

was conducted to evaluate the factors influencing the time when 

contact was made to the worker. Table 11 shows the hypothesized time-to-event regression model. Analysts used a forward 

selection procedure in developing the model. In each step, 

variables were selected for inclusion on the basis of the Akaike 

Information Criterion (AIC), i.e., the model whose variable 

resulted in the lowest AIC was selected at each successive step 

of the model-building process. The model-building process 

ceased when the lowest AIC for a step was greater than the 

lowest AIC obtained in the previous step. 

A primary assumption of the time-to-event regression model 

was that the hazard proportions associated with the model's 

variable comparisons did not differ significantly with respect to 

time during the period of analysis. This assumption was 

checked for all variables at the univariate stage of the modelbuilding process. If the assumption was not tenable, the interaction between the variable and the natural logarithm of time 

was included in the model whenever that variable was entered 

into the regression models. A final check of the proportional 

hazards assumption was performed once the final model was 

determined. 

Probabilities that risk ratios were significantly different 

from 1 were calculated using the Wald statistic for covariates 

with one degree of freedom. Probabilities for variables with 

multiple degrees of freedom were obtained by subtracting the 

log likelihood for the reduced model from the full model and 

obtaining a chi-square with the appropriate degrees of freedom. 

Alpha levels were set at 0.05 for all cases. Results for each step 

of the survival analysis are presented in appendix F. 

Results 

Results of Forward Selection Process 

Variables entered earlier in the model-building process are 

considered more influential for predicting the time-to-event 

(contacts) than those entered later. The following list shows the 

order in which variables were entered into the model: 

1. Boom speed 

2. Boom direction 

3. Drilling behavior 

4. Work posture/seam height combination 

5. Bolting behavior 

6. Anthropometry (operator percentile) 

7. Operator location 

Tables F–1 to F–7 contain results of the analyses in the 

development of the main effects model. These tables reveal that 

the first five variables included in the model violated the 

proportional hazards assumption. This indicates that the hazard 

associated with a contact occurring was not constant over the 

period of the analysis, but that the hazard changed over time. 

Thus, in the final model (table F–8), these variables included 

interaction terms with the natural logarithm of time to properly 

assess the associated risks throughout the period of the 

simulation. 

Risk Model 

Based on the results of the forward selection Cox regression 

analyses, a main effects risk model was developed (table 12). 

The coefficients in this model helped to evaluate the relative risk 

of experiencing a contact at different points during the 

simulation executions and showed the degree of influence for 

each variable in the model while controlling for the effects of all 

other covariates. For example, if one wanted to know the relative risk of a contact for a worker bolting with the boom moving 

up at 16 in/sec at time 25 (compared to reference conditions), 

one would simply insert a "1" for each term containing a z2 and 

z7, a "25" for each term with ln (time) included, and a "0" for all 

other variables. The result would be that such a worker would 

have a chance of experiencing a contact that was 33.25 times the 

referent condition. 

Table 13 shows the instantaneous relative risk of experiencing a contact for all model variables at different times in the 

simulation process. Each estimate of risk of experiencing a 

contact represents the increase (or decrease) in the chance of a 

contact occurring at a particular time assuming that the specified 

variable is present and that the influencing factor is judged 

against the referent condition. The following sections detail the 

implications of the relative risk model in terms of the 

independent variables examined. 

Boom Speed 

Boom speed was the most influential variable in terms of 

explaining the time to an event (contact) occurring. Increases in 

boom speed resulted in increased chance of a contact throughout 

the period of the simulation. Thus, based on the data collected 

in this simulation analysis, boom speeds greater than 13 in/sec 

result in a substantial increase in chance that the roof bolter 

operator would be contacted, while speeds less than or equal to 

13 in/sec are associated with a more modest hazard level. 

Boom Direction 

Relative risk of being contacted for the boom moving in an 

upward direction (compared to downward or no movement) 

were greatest at the beginning of the task and decreased with 

time. Early in the task, upward movement of the boom resulted 

in a threefold increase in the chance of a contact. At the 

midpoint of the simulation (time = 25), the relative chance was 

still more than twice the referent condition. This change in the 

hazard reflects the fact that conditions where the boom is 

moving upward occur earlier, on average, than situations where 

the boom is moving downward. Thus, the risk of being 

contacted associated with upward boom movement tend to be 

seen earlier in the simulation rather than later. In general, 
21 

chances of a contact were greater for upward compared to 

downward boom movement. 

Drilling Behavior 

Analysts found hand placements when drilling to result in 

significant increases in the chance of a contact occurring early in 

the simulation, with decreasing chances observed as the 

simulation time increased. This chance of being contacted profile 

reflects the fact that the drilling phase of roof bolting occurs early 

in the task, and chance of a contact associated with this activity 

would be seen early in the simulation. Having the hand on the 

drill steel then the boom resulted in the greatest increase in 

chances of being contacted compared with the hand being on 

neither the drill steel nor the boom. Having the hand only on the 

boom was associated with an only slightly less chance of a contact 

than having the hand on the drill steel then boom, but a greater 

chance than when having the hand on the drill steel. 

 

Table 11.—Hypothesized time-to-event regression model 

§ E 1 1 2 2 3 3 4 4 5 5 6 6 7 7 8 8 9 9 10 10 11 11 z  E z  E z  E z  E z  E z  E z  E z  E z  E z  E z · ht | z h t | zexp ̈  ̧ 0  ̈  ̧  E z  E z  E z  E z  E z  E z  E z  E z  E z © 12 12 13 13 14 14 15 15 16 16 17 17 18 18 19 19 20 20 1 

 k = coefficients for variables used in the model; z11 = posture/seam: left knee/45 in; 

z1 = boom speed 10 in/sec; z12 = posture/seam: left knee/60 in; 

z2 = boom speed 13 in/sec; z13 = posture/seam: both knees/45 in; 

z3 = boom speed 16 in/sec; z14 = posture/seam: both knees/60 in; 

z4 = boom speed 22 in/sec; z15 = bolting behavior: hand on bolt; 

z5 = boom moving upwards; z16 = bolting behavior: hand on boom; 

z6 = drilling behavior: hand on drill steel; z17 = bolting behavior: hand on bolt then on boom; 

z7 = drilling behavior: hand on boom; z18 = 55th-percentile worker; 

z8 = drilling behavior: hand on drill steel then on boom; z19 = 95th-percentile worker; and 

z9 = posture/seam: right knee/45 in; z20 = operator location (in). 

z10 = posture/seam: right knee/60 in; 

 

Table 12.—Main effects risk model 

h(t | z) h 0 (t | z) exp(2.300 
 z 1 1.173
 z 1 
ln(time)  3.698 
 z 2 1.971
 z 2 
ln(time)  3.890 
 z 3 

2.299 
 z 3 
 ln(time)  4.234 
 z 4  2.649 
 z 4 
ln(time)  2.995 
 z 5  0.668 
 z 5 
ln(time)  3.906 
 z 6 

1.142 
 z 6 
ln(time)  4.978
 z 7 1.428
 z 7 
 ln(time)  5.282 
 z 8 1.465
 z 8 
 ln(time)  9.236 
 z 9 

3.927 
 z 9 
 ln(time)  6.049 
 z 10  2.291
 z 10 
 ln(time)  9.470 
 z 11  3.959 
 z 11 
ln(time)  6.002 
 z 12 

2.274 
 z 12 
 ln(time)  9.014 
 z 13  3.743
 z 13 
 ln(time)  2.539 
 z 14 1.137 
 z 14 
ln(time)  0.675 
 z 15 

0.341
 ln(time)  0.250 
 z 16  0.230 
 z 16 
 ln(time)  0.241
 z 17  0.268 
 z 17 
ln(time)  0.047 
 z 18 

0.243
 z  0.170 
 z ) 19 20 

z1 = boom speed 10 in/sec; z11 = posture/seam: left knee/45 in; 

z2 = boom speed 13 in/sec; z12 = posture/seam: left knee/60 in; 

z3 = boom speed 16 in/sec; z13 = posture/seam: both knees/45 in; 

z4 = boom speed 22 in/sec; z14 = posture/seam: both knees/60 in; 

z5 = boom moving upwards; z15 = bolting behavior: hand on bolt; 

z6 = drilling behavior: hand on drill steel; z16 = bolting behavior: hand on boom; 

z7 = drilling behavior: hand on boom; z17 = bolting behavior: hand on bolt then on boom; 

z8 = drilling behavior: hand on drill steel then on boom; z18 = 55th-percentile worker; 

z9 = posture/seam: right knee/45 in; z19 = 95th-percentile worker; and 

z10 = posture/seam: right knee/60 in; z20 = operator location (in). 
 

 

22 

Work Posture/Seam Height Combinations 

Table 13 shows a number of interesting relationships related 

to the effects of work posture and seam height. First, all 

restricted posture/seam combinations increase the chance of a 

contact to the worker (or decrease the time-to-event) compared 

to a standing posture in a 72-in seam. However, this effect is 

particularly pronounced in the 45-in seam, with very high 

chances of being contacted observed in this low seam height. 

These results clearly show the increased threat of contact to the 

operator as seam heights diminish. However, the kneeling 

postures used also seem to affect the time to an event occurring. 

Within each seam height, the greatest chance of a contact was 

associated with kneeling on the right knee. Kneeling on the left 

knee had a slightly less chance of a contact, while kneeling on 

both knees had the lowest chance. These findings indicate 

possible recommendation to change work posture that might 

significantly reduce the chance of workers making contact with 

the boom of the roof bolter machine. 

Table 13.—Instantaneous relative risk estimates at specified time for each variable 

Variable Time = 15 Time = 25 Time = 35 Time = 45 

Boom speed, in/sec:

 10 . . . . . . . . . . . . . . . . . . . . . . . . . . . 

 13 . . . . . . . . . . . . . . . . . . . . . . . . . . . 

 16 . . . . . . . . . . . . . . . . . . . . . . . . . . . 

 22 . . . . . . . . . . . . . . . . . . . . . . . . . . . 

Boom moving up . . . . . . . . . . . . . . . . . 

Drilling behavior:

 Hand on drill steel ............... 

 Hand on boom ................. 

 Hand on drill steel then on boom . . . 

Work posture/seam height:

 Right knee/45 in ................ 

 Right knee/60 in ................ 

 Left knee/45 in ................. 

 Left knee/60 in ................. 

 Both knees/45 in ................ 

 Both knees/60 in ................ 

Bolting behavior:

 Hand on bolt ................... 

 Hand on boom ................. 

 Hand on bolt then on boom ....... 

Operator percentile:

 55th . . . . . . . . . . . . . . . . . . . . . . . . . . 

 92nd ......................... 

Operator location, in . . . . . . . . . . . . . . . 	

2.40 

5.15 

10.34 

18.89 

3.27 

2.25 

3.03 

3.73 

4.05 

1.18 

3.48 

1.18 

3.08 

1.72 

0.78 

0.70 

0.62 

1.05 

1.29 

.017*OPLOC 	

4.37 

14.10 

33.45 

73.14 

2.33 

1.26 

1.47 

1.77 

30.10 

3.75 

26.40 

3.73 

20.77 

3.06 

0.64 

0.62 

0.54 

1.05 

1.29 

.017*OPLOC 	

6.49 

27.37 

72.49 

178.38 

1.85 

0.86 

0.91 

1.07 

112.80 

8.12 

100.02 

8.01 

73.22 

4.50 

0.59 

0.56 

0.48 

1.05 

1.29 

.017*OPLOC 	

8.72

44.92

129.20

347.11 

1.58 

0.64

0.64

0.75 

302.63

14.47

270.52

14.20

187.60

5.98 

0.54

0.54

0.46 

1.05

1.29 

.017*OPLOC 

Bolting Behavior 

Coefficients for bolting behaviors were all less than 1, indicating a protective effect. This is because the bolting task is 

done late in the simulation. Any contact due to these bolting 

behaviors will happen relatively late in the simulation sequence, 

resulting in a longer time-to-event. 

Anthropometry 

Model coefficients suggest that larger (92nd-percentile) 

workers have about a 25% increased chance of experiencing a 

contact (or being contacted more quickly) compared to smaller 

(25th-percentile) workers. Average size workers (55th-percentile) enjoy an obvious reduction in the chance of making 

contact, about 5% lower than for small-size workers. 

Operator Location 

The negative coefficient for the operator location variable 

(a continuous variable) shows that the greater the distance between the operator and the boom, the less likely the operator will 

be to experience a contact (or the longer it will take for a contact 

to occur). Compared to the referent condition where the operator's 

back is 23 in from the boom, moving an additional 9 in away will 

reduce the relative risk by 31%. The maximum operator location 

distance studied, 38 in, reduced the relative risk by 50% compared 

to the referent. Although moving the operator farther away from 

the boom decreases the chance of a contact, it should be noted that 

this could also make the operator's job more difficult. For 

example, greater strength demands would be required to handle a 

bolt or drill steel farther from the body. However, this data 

analysis suggests that bolter operators should position themselves 

as far away from the boom as possible, and this will not 

compromise their ability to perform the bolting task. 

Summary 

One of the main interests in performing this survival analysis 

was to determine the impact of boom speed on the chance of 

experiencing a contact in these simulations of roof bolter 

activities. Results show that boom arm speed was the most 

influential factor in terms of affecting the chance of a contact 

occurring and the time at which such a contact might occur. 
 

 

 

 

23 

Moreover, results of this analysis show that there is a significant 

increase in the risk of being contacted at the two highest boom 

speeds, 16 and 22 in/sec, compared to the lower speeds 

(13 in/sec or less). The former were associated with a marked, 

and perhaps unacceptable, increase in the risk of being 

contacted, whereas the risk for the latter was much more 

modest. From the current analysis, one can conclude that boom 

speeds above 13 in/sec entail significant chance of being 

contacted. Speeds that are 13 in/sec or below result in a much 

lower exposure to being contacted, which represents a decrease 

in potential hazard. 

Covariates such as operator work behaviors (placing the hand 

on the boom, drill steel, or bolt), work posture and seam height 

combinations, boom direction, operator location, and worker 

anthropometry were also significant factors in the time-to-event 

regression analysis. Workers were more likely to experience a 

contact when the boom was moving in an upward direction, 

especially early in the roof bolting task. Kneeling work postures 

generally resulted in increased risk of being contacted compared 

to standing in a 72-in seam. Kneeling on the right knee 

within each seam height entailed the greatest chance of a 

contact. Positioning of the workers farther from the boom 

resulted in a lower risk of being contacted; however, this could 

also impact the workers' ability to perform the roof bolting task. 

Larger workers were 25% more likely to make contact with the 

boom, whereas smaller workers were about 5% less likely to 

make contact. Drilling behaviors such as placing the hand on 

the boom or drill steel resulted in a greater chance of a contact, 

while bolting behaviors (occurring later in the bolting cycle) 

increased the time when the event occurred. 

It should be noted that this survival analysis was developed 

using a main effects model only. It is possible that the factors 

examined in this report have interactive effects (for instance, 

boom speed could have more of an impact on the chance of 

being contacted when certain work postures are adopted). The 

large number of simulations, computational demands of running 

Cox regression models and of checking proportional hazard 

assumptions, and the large number of interactions (120) made 

analysis of these interactions impractical given the time 

constraints involved. 

CONCLUSIONS
 

NIOSH researchers successfully developed a computer 

model that generates contact data by means of simulation while 

exercising the model with several variables associated with the 

machine and its operator, such as coal seam height, the 

operator's anthropometry, work posture and choice of risky 

behavior, and the machine's appendage velocity. The resulting 

simulation database contains 5,250 observations. The database 

represented the equivalence of actual field observations of roof 

bolting and corresponds to a work period of 12.15 eight-hour 

shifts. 

Analysts used data only on the occurrences for the operator 

with slow reactions that included one incident per simulation 

execution (one run/one contact). Researchers on this project 

believe the use of such simulations, treated with statistical 

procedures such as frequency, cross-tabulation, logistic regression, and survival analysis, provide extremely useful tools 

to evaluate the hazards of tasks where it is not possible to 

perform experiments with human subjects. Results of this analysis could help in making recommendations that reduce the 

likelihood that roof bolter operators experience injuries due to 

contact with a moving boom. 

Analysis shows that the reaction time of the operator did not 

significantly affect the outcome of the simulation. The number 

of contact incidents for an operator with slow reactions differed 

from those for an operator with fast reactions by less than 1% in 

both data sets. There was a reasonable difference in reaction 

times between fast and slow operators obtained from reaction 

time tests on our human subjects. As to the reason for the small 

difference in contacts, researchers speculate that in the boom 

speed range studied, if the operator with fast reactions could not 

get out of the path of the boom, the slower operator certainly 

would not either. 

Results from frequency distribution analyses showed: 

• The seam height of 60 in had the most contacts (59% of the 

total number of contacts), and the seam height of 45 in had 75% 

of the avoid incidents. 

• The 25th-percentile individual had 7% more contacts than 

the 55th-percentile and 13% more than the 92nd-percentile. 

• The one-knee work posture had 49% of the total number of 

contact incidents, the posture on both knees had 32%, and the 

standing posture had 19%. 

• The faster boom speeds of 16 and 22 in/sec combined 

accounted for the greatest number of contacts (43% of the total). 

• The hand-on-boom behavior for both drilling and bolting 

tasks accounted for most of the contacts. 

• The boom-up direction had the most contacts (76% of the 

total number of contacts). The boom-down direction had 63% 

of the avoid incidents. 

• The hand was the closest body part to the moving boom 

arm and was involved in 67% of all contacts. The leg was the 

second most contacted body part (15% of all contacts). 

• The boom was the closest moving machine part to the 

operator, accounting for 80% of all contacts. 

• Regardless of other variables, contact incidents were always 

greater when the boom was moving up, always greater on the 

hand, and always greater for the boom arm part of the machine. 

The reason why the subject experiences more contacts when the 

boom arm is moving up rather than down is that riskier behaviors 

occur during drilling and bolting, when the boom is ascending. 

Results regarding boom speed from cross-tabulation analyses 

showed: 
 

24 

• Regardless of boom speed, the boom-up direction had 

more contacts than boom-down. 

• The boom-up direction had most of its contacts at the two 

higher boom speeds: 22% at speed 16 in/sec and 21% at speed 

22 in/sec. 

• Regardless of boom speed, the operator's hand had more 

contacts than the other body parts. 

• The hand had most of its contacts during speed 16 in/sec 

(24%) and 13 in/sec (21%). 

• The boom arm had more contacts than the drill head and 

had most contacts during speeds 16 and 22 in/sec. 

• The both-knee work posture had more contacts than the 

other postures and had most contacts (23%) during speed 

16 in/sec. 

• 25th-percentile operators had more contacts than other 

operator sizes and had most of their contacts (22%) during speed 

13 in/sec. 

• Regardless of boom speed, the hand-on-boom behavior 

during drilling and bolting tasks had more contacts than other 

work behaviors. 

• Drilling tasks had most of their contacts (24%) during 

speed 13 in/sec. Bolting had most contacts (22%) during the 

same speed. 

• The 60-in seam had more contacts than the other seam 

heights and had most of the contacts (22%) during speed 

16 in/sec. 

Logistic regression analyses showed: 

• Compared to a seam height of 45 in, contacts occurred 

nearly seven times more often in a 60-in seam height and six 

times more often in a 72-in seam height. 

• The odds of a contact between a boom speed of 13 and 

7 in/sec, the reference group, were not significant. 

• ORs of approximately 1.35 and 1.19 were found for 16 and 

22 in/sec, respectively, compared to 7 in/sec. 

• A 25th-percentile operator had a likelihood of making 

more contacts (1.65) than a 55th-percentile operator. 

• A 92nd-percentile operator had a likelihood of making 

fewer contacts (0.69) than a 55th-percentile operator. 

• Comparing work postures/seam heights, about the same 

likelihood of a contact occurred when the operator was on the 

right knee, left knee, or both knees. 

• For the multivariate model (comparing standing posture, 

7-in/sec boom speed, and 55th-percentile operator), significantly 

higher ORs were found: 2.05 for both knees/60 in, 1.5 for 

16 in/sec and 1.26 for 22 in/sec, and 1.93 for the 25th-percentile 

operator. 

Results of a survival analytic approach showed: 

• Controlling the boom speed is the most important factor in 

determining the chance of an operator making contact. 

• Boom speed was the most influential variable for 

explaining the time to an event (contact) occurring. 

• Increases in boom speed resulted in increased chance of a 

contact throughout the period of the simulation. 

• The chance of being contacted at the higher boom speeds 

(16 and 22 in/sec) was generally two to four times greater than 

at 13 in/sec and four to eight times greater than at 10 in/sec. 

• A boom arm speed greater than 16 in/sec resulted in a 

substantial increase in the chance of the boom making contact 

with the roof bolter operator. 

• Boom speeds less than or equal to 13 in/sec resulted in a 

smaller chance of being contacted, which represents a decrease 

in potential hazard. 

OTHER RESEARCH CONSIDERATIONS
 

The process of performing 5,250 simulations and subsequent 

analyses required a considerable effort. Automating the simulation software and integrating data management with data 

analysis can enhance the virtual-reality simulation method. 

Software automation can decrease the time required to produce 

simulations and permit more time for data analysis. The integration of data management and data analysis can increase 

efficiency and permit an extensive examination of available 

information. For instance, a central database could streamline 

software automation by providing a queue of requested simulations, real-time monitoring of active simulations, and archived 

data from completed simulations. Simple data analysis interfaces could query data directly from the database and allow 

researchers to update calculations as data become available. In 

addition, enhanced data analysis interfaces would trigger 

calculations within the database or initiate iterative computations on a remote system; this would increase the efficiency of 

repetitious analyses and permit an unparalleled degree of 

exploratory data analysis. Individual researchers could use 

interfaces tailored to their specific roles. Virtual-reality 

simulations provide a wealth of information that is unavailable 

through conventional investigations. These automation, data 

management, and data analysis enhancements could efficiently 

represent this information and allow investigators to draw 

insightful conclusions regarding health and safety issues. 

Analysts answered this study's question concerning boom 

speed by using the most appropriate statistical techniques 

available. Other factors such as drilling behavior, bolting 

behavior, boom direction, work posture/seam height combination, operator location, and anthropometry showed significant influence on the chance of an operator making contact. 

Using analytical techniques, an examination of the database 

would uncover significant interactions between these factors 

should they exist. 

Researchers recommended a study to increase the safety for 

bolting machine operators during lateral boom swing operations. 
 

 

 

 

 

25 

This research has been approved and is currently underway. 

Boom swing usually occurs when the operator is repositioning 

the boom arm to a new bolt insertion location. It requires that 

the operator properly actuate the right control(s) and then 

reposition his/her body in coordination with the moving boom 

arm. In low seam heights, operators may perform boom swings 

from kneeling positions, which hinders their ability to avoid 

contact with the boom arm. Observation of boom swing shows 

that even experienced operators have a tendency to actuate the 

boom swing control in the direction opposite from what is 

intended. The fundamental issue is which boom swing speed(s) 

maximize the operators' chances of escaping injuries while still 

allowing the operators to perform bolting functions effectively. 

Like the vertical boom arm study, this work will use primarily 

motion capture and computer simulation/modeling technologies 

to evaluate human motions while operating a bolting machine in 

various postures. Expected outcomes include lateral boom 

swing velocities, possible control, and procedural modifications 

to minimize inadvertent control actuation. 

ACKNOWLEDGMENTS
 

The authors gratefully acknowledge the following colleagues 

at the NIOSH Pittsburgh Research Laboratory: Joseph P. 

DuCarme, Mary Ellen Nelson, Albert H. Cook, George F. 

Fischer, Albert L. Brautigam provided technical expertise in the 

design and fabrication of the roof bolter mockup and platform, 

and the associated electrical and hydraulic control systems. 

E. William Rossi provided technical support in operating the 

motion tracking and data collection system. Mary Ellen Nelson, 

Albert H. Cook, and Mary Ann Rossi assisted in the lab human 

subject tests. 

REFERENCES
 

Ambrose DH [2000]. A simulation approach analyzing random motion 

events between a machine and its operator. Warrendale, PA: Society of 

Automotive Engineers, Inc., technical paper 2000–01–2160, pp. 1–11. 

Ambrose DH [2001]. Random motion capture model for studying events 

between a machine and its operator. In: Proceedings of the Advanced 

Simulation Technologies Conference (Seattle, WA, April 22–26, 2001). San 

Diego, CA: Society for Computer Simulation International, pp. 127–134. 

Ambrose DH [2004]. Developing random virtual human motions and risky 

work behaviors for studying anthropotechnical systems. Pittsburgh, PA: U.S. 

Department of Health and Human Services, Public Health Service, Centers for 

Disease Control and Prevention, National Institute for Occupational Safety and 

Health, DHHS (NIOSH) Publication No. 2004–130, IC 9468. 

Bartels JR, Ambrose DH, Wang RC [2001]. Verification and validation of 

roof bolter simulation models for studying events between a machine and its 

operator. Warrendale, PA: Society of Automotive Engineers, Inc., technical 

paper 2001–01–2088, pp. 1–14. 

Bartels JR, Kwitowski AJ, Ambrose DH [2003]. Verification of a roof 

bolter simulation model. Warrendale, PA: Society of Automotive Engineers, 

Inc., technical paper 2003–01–2217, pp. 1–7. 

Etherton J [1987]. System considerations on robot end effector speed as a 

risk factor during robot maintenance. In: Proceedings of the Eighth 

International System Safety Conference (New Orleans, LA). Unionville, VA: 

System Safety Society, pp. 434–437. 

Helander MG, Karwan MH, Etherton J [1987]. A model of human reaction 

time to dangerous robot arm movements. In: Proceedings of the 31st Annual 

Meeting of the Human Factors Society. Santa Monica, CA: Human Factors 

Society, pp. 191–195. 

Humantech, Inc. [2003]. Ergonomic design guidelines for engineers. Ann 

Arbor, MI: Humantech, Inc. 

Karwowski W, Parsaei HR, Soundararajan A, Pongpatanasuegsa N [1992]. 

Estimation of safe distance from the robot arm as a guide for limiting slow speed 

of robot motions. In: Proceedings of the 36th Annual Meeting of the Human 

Factors and Ergonomics Society. Santa Monica, CA: Human Factors and 

Ergonomics Society, pp. 992–996. 

Klishis MJ, Althous RC, Layne LA, Lies GM [1993a]. Coal mine injury 

analysis: a model for reduction through training. Morgantown, WV: West 

Virginia University, Mining Extension Service. 

Klishis MJ, Althous RC, Stobbe TJ, Plummer RW, Grayson RL, Layne LA, 

et al. [1993b]. Coal mine injury analysis: a model for reduction through 

training. Vol. 8: Accident risk during the roof bolting cycle: analysis of 

problems and potential solutions, Morgantown, WV: West Virginia University. 

Mining Extension Service. 

Kobrick JL [1965]. Effects of physical location of visual stimuli on 

intentional response time. J Eng Psychol 4(1):1–8. 

MSHA [1994]. Coal mine safety and health roof bolting machine 

committee: report of findings, July 8, 1994. Arlington, VA: U.S. Department 

of Labor, Mine Safety and Health Administration, Coal Mine Safety and Health, 

Safety Division, pp. 1–28. 

OSHA [1987]. Guidelines for robotic safety. OSHA directive 

STD 01–12–002 (instruction pub 8–1.3). Washington, DC: U.S. Department of 

Labor, Occupational Safety and Health Administration, Office of Science and 

Technology Assessment, September 21. 

Turin FC, et al. [1995]. Human factors analysis of roof bolting hazards in 

underground coal mines. Pittsburgh, PA: U.S. Department of the Interior, 

Bureau of Mines, RI 9568. NTIS No. PB 95–274411. 

U.S. Department of Energy [1998]. Department of Energy (DOE) OSH 

technical reference. Chapter 1 – industrial robots; part 4 – work practices; 4.1 – 

safeguarding methods. [http://www.eh.doe.gov/docs/osh_tr/ch14.html]. Date 

accessed: January 2005. 

Volberg O, Ambrose DH [2002]. Motion editing and reuse techniques and 

their role in studying events between a machine and its operator. In: Proceedings 

of the Society of Computer Simulation International Advanced Simulation 

Technologies Conference (San Diego, CA, April 14–18). Vol. 34, No. 4. San 

Diego, CA: Society of Computer Simulation International, pp. 181–186. 

Welford AT, Brebner JMT [1980]. Reaction times. New York: Academic 

Press, pp. 117–123. 
26 

APPENDIX A.–FREQUENCY OF INCIDENTS 

Figure A–1.—Incidents by seam height. 

2000 

Incidents 

1500 

1000 

500 

0 

Avoid 

Contact 

None 

45-in 60-in 72-in 

Seam Height 

Table A–1.—Incidents by seam height 

Seam 

height, in Avoid Contact None Total 

45 ................. 564 606 1,080 2,250 
 

60 ................. 185 1,619 446 2,250 
 

72 ................. 6 525 219 750 


 Total . . . . . . . . . . . . . 755 2,750 1,745 5,250 
 Incidents

Figure A–2.–Incidents by operator percentile. 

1200 

1000 

800 Avoid 

600 Contact 

400 None 

200 

0 

25th 55th 92nd 

Operator Percentile 

Table A–2.—Incidents by operator percentile 

Operator 

percentile Avoid Contact None Total 

25th . . . . . . . . . . . . . . 211 1,113 426 1,750 

55th . . . . . . . . . . . . . . 259 900 592 1,751 

92nd ............. 285 737 727 1,749

 Total . . . . . . . . . . . 755 2,750 1,745 5,250 
 
27 

Figure A–3.—Incidents by work posture. 

1000 

800 

Avoid 600 

Incidents

400 Contact 

200 None 

0 

Right knee Left knee Both knees Standing 

Working Posture 

Table A–3.—Incidents by work posture 

Work posture Avoid Contact None Total
 

Right knee .......... 237 682 581 1,500 
 

Left knee . . . . . . . . . . . . 268 669 563 1,500 
 

Both knees .......... 244 874 382 1,500 
 

Standing ............ 6 525 219 750 


 Total ............. 755 2,750 1,745 5,250 
 

Figure A–4.

700 

—Incidents by boom speed. 

600 

Avoid 

d nts500 

400 

In i ec300 Contact 

200 

100 

None 

0 

7 in/sec 10 in/sec 13 in/sec 16 in/sec 22 in/sec 

Boom Speed 

Table A–4.—Incidents by boom speed 

Boom speed, 

in/sec
 Avoid Contact None Total 

7 . . .................. 147 533 370 1,050 
 

10 . .................. 223 486 341 1,050 
 

13 . .................. 157 542 351 1,050 
 

16 . .................. 106 611 333 1,050 
 

22 . .................. 122 578 350 1,050 


 Total . . . . . . . . . . . . . . . 755 2,750 1,745 5,250 
 
28 

Figure A–5.—Incidents by drilling behavior. 

2000 

Incidents1500 Avoid 

1000 Contact 

500 None 

0 

None Hand on drill Hand on boom Hand on drill 

steel steel then on 

boom 

Drilling Behavior 

Table A–5.—Incidents by drilling behavior 

Drilling behavior Avoid Contact None Total
 

None . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68 673 1,030 1,771 
 

Hand on drill steel ......................... 42 168 142 352 
 

Hand on boom ........................... 555 1,541 458 2,554 
 

Hand on drill steel then on boom ............. 90 368 115 573 


 Total . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 755 2,750 1,745 5,250 
 

Figure A–6.—Incidents by bolting behavior. 

0 

500 

1000 

1500 

None Hand on bolt Hand on boom Hand on bolt 

then on boom 

Bolting Behavior 

Incidents

Avoid 

Contact 

None 

Table A–6.—Incidents by bolting behavior 

Bolting behavior Avoid Contact None Total 

None . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 287 748 756 1,791 

Hand on bolt ........................ 146 402 289 837 

Hand on boom ...................... 220 1,042 468 1,730 

Hand on bolt then on boom ............ 102 558 232 892

 Total . . . . . . . . . . . . . . . . . . . . . . . . . . . . 755 2,750 1,745 5,250 
29 

Figure A–7.—Incidents by boom direction. 

0 

500 

1000 

1500 

2000 

2500 

Down Up 

Boom Direction 

Incidents

Avoid 

Contact 

Table A–7.—Incidents by boom direction 

Boom direction Avoid Contact Total 

Down . ................... 472 671 1,143 
 

Up . . . . ................... 283 2,079 2,362 


 Total ................... 755 2,750 3,505 
 

Figure A–8.—Incidents by body part. 

0 

500 

1000 

1500 

2000 

Leg Arm Hand Head 

Body Part 

Incidents

Avoid 

Contact 

Table A–8.—Incidents by body part 

Body part Avoid Contact Total
 

Leg . . . . .................. . . 51 419 470 
 

Arm . . . . .................. . . 38 201 239 
 

Hand . . . .................. . . 638 1,835 2,473 
 

Head . . . .................. . . 28 295 323 


 Total . .................. . . 755 2,750 3,505 
 
30 

Figure A–9.—Incidents by machine part. 

0 

500 

1000 

1500 

2000 

2500 

Boom Drill head 

Machine Part 

Incidents

Avoid 

Contact 

Table A–9.—Incidents by machine part 

Machine part Avoid Contact Total
 

Boom . . . . . . . . . . . . . . . . . . 622 2,209 2,831 
 

Drill head . . . . . . . . . . . . . . . 133 541 674 


 Total . . . . . . . . . . . . . . . . . 755 2,750 3,505 
 
31 

APPENDIX B.–FREQUENCY BY OPERATOR LOCATION
 

Figure B–1.—Incidents by operator location. 

0 

20 

40 

60 

80 

100 

120 

140 

160 

20.1 22.0 24.0 26.0 28.0 29.9 31.9 33.9 35.8 37.8 

O perator Location (in) 

Incidents 

avoid contact none 

Table B–1.—Incidents by operator location 

Operator Operator Total Total location Avoid Contact None location Avoid Contact None incidents incidents (in) (in) 

20.1 . . . . . 0 12 0 12 29.5 . . . . . . . . 47 85 88 220 

20.5 . . . . . 0 60 1 61 29.9 . . . . . . . . 48 122 90 260 

20.9 . . . . . 2 102 6 110 30.3 . . . . . . . . 48 123 137 308 

21.3 . . . . . 2 134 15 151 30.7 . . . . . . . . 54 102 121 277 

21.7 . . . . . 8 141 16 165 31.1 . . . . . . . . 54 82 108 244 

22.0 . . . . . 4 135 27 166 31.5 . . . . . . . . 42 72 104 218 

22.4 . . . . . 6 124 22 152 31.9 . . . . . . . . 29 43 87 159 

22.8 . . . . . 13 117 22 152 32.3 . . . . . . . . 19 20 53 92 

23.2 . . . . . 4 76 12 92 32.7 . . . . . . . . 9 11 31 51 

23.6 . . . . . 4 104 12 120 33.1 . . . . . . . . 5 19 12 36 

24.0 . . . . . 13 87 11 111 33.5 . . . . . . . . 0 14 8 22 

24.4 . . . . . 17 88 23 128 33.9 . . . . . . . . 0 21 10 31 

24.8 . . . . . 22 87 41 150 34.3 . . . . . . . . 0 12 12 24 

25.2 . . . . . 26 87 62 175 34.6 . . . . . . . . 0 4 8 12 

25.6 . . . . . 43 92 45 180 35.0 . . . . . . . . 0 10 16 26 

26.0 . . . . . 43 97 64 204 35.4 . . . . . . . . 0 7 11 18 

26.4 . . . . . 34 83 53 170 35.8 . . . . . . . . 0 9 12 21 

26.8 . . . . . 24 58 53 135 36.2 . . . . . . . . 0 4 11 15 

27.2 . . . . . 21 56 46 123 36.6 . . . . . . . . 0 3 9 12 

27.6 . . . . . 17 61 45 123 37.0 . . . . . . . . 0 3 5 8 

28.0 . . . . . 19 43 46 108 37.4 . . . . . . . . 0 0 5 5 

28.3 . . . . . 17 34 44 95 37.8 . . . . . . . . 0 1 1 2 

28.7 . . . . . 27 37 53 117 TOTAL . . . . 755 2,750 1,745 5,250 

29.1 . . . . . 34 68 87 189 
Figure B–2.—Contact incidents by operator location and body part. 

0 

20 

40 

60 

80 

100 

120 

20.1 22.0 24.0 26.0 28.0 29.9 31.9 33.9 35.8 37.8 

Operator Location (in) 

Contact Incidents 

leg arm hand head 

32 

Table B–2.—Contact incidents by operator location and body part 

Operator Body part Total Operator Body part Total 

location contact location contact 

Leg Arm Hand Head (in) Leg Arm Hand Head incidents (in) incidents 

20.1 . . . . 0 0 3 9 12 29.5 . . . . . . . . 0 10 75 0 85 

20.5 . . . . 0 7 20 33 60 29.9 . . . . . . . . 0 19 103 0 122 

20.9 . . . . 2 8 37 55 102 30.3 . . . . . . . . 13 7 103 0 123 

21.3 . . . . 7 6 55 66 134 30.7 . . . . . . . . 21 8 73 0 102 

21.7 . . . . 14 17 53 57 141 31.1 . . . . . . . . 16 4 62 0 82 

22.0 . . . . 20 15 65 35 135 31.5 . . . . . . . . 3 3 66 0 72 

22.4 . . . . 29 21 54 20 124 31.9 . . . . . . . . 3 5 35 0 43 

22.8 . . . . 41 11 56 9 117 32.3 . . . . . . . . 3 2 15 0 20 

23.2 . . . . 35 4 36 1 76 32.7 . . . . . . . . 5 0 6 0 11 

23.6 . . . . 52 4 48 0 104 33.1 . . . . . . . . 6 0 13 0 19 

24.0 . . . . 34 4 49 0 87 33.5 . . . . . . . . 5 0 9 0 14 

24.4 . . . . 23 4 60 1 88 33.9 . . . . . . . . 4 1 16 0 21 

24.8 . . . . 18 9 59 1 87 34.3 . . . . . . . . 1 0 11 0 12 

25.2 . . . . 16 5 62 4 87 34.6 . . . . . . . . 0 0 4 0 4 

25.6 . . . . 13 2 77 0 92 35.0 . . . . . . . . 0 1 9 0 10 

26.0 . . . . 13 0 80 4 97 35.4 . . . . . . . . 0 0 7 0 7 

26.4 . . . . 4 8 71 0 83 35.8 . . . . . . . . 0 1 8 0 9 

26.8 . . . . 6 2 50 0 58 36.2 . . . . . . . . 0 1 3 0 4 

27.2 . . . . 6 1 49 0 56 36.6 . . . . . . . . 0 1 2 0 3 

27.6 . . . . 6 0 55 0 61 37.0 . . . . . . . . 0 0 3 0 3 

28.0 . . . . 0 1 42 0 43 37.4 . . . . . . . . 0 0 0 0 0 

28.3 . . . . 0 1 33 0 34 37.8 . . . . . . . . 0 0 1 0 1 

28.7 . . . . 0 0 37 0 37 TOTAL . . . . 419 201 1,835 295 2,750 

29.1 . . . . 0 8 60 0 68 
 Figure B–3.—Contact incidents by operator location and work posture. 

0 

20 

40 

60 

80 

100 

120 

140 

20.1 22.0 24.0 26.0 28.0 29.9 31.9 33.9 35.8 37.8 

O perator Location (in) 

Contact Incidents 

right left both stand

33 

Table B–3.—Contact incidents by operator location and work posture 

Operator Work posture Total Operator Work posture Total 

location Right contact location contact Left Both Right Left Both Standing Standing (in) incidents (in) incidents knee knee knees knee knee knees 

20.1 . . . . . . . 0 3 9 0 12 29.5 . . . . . . . . 19 5 17 44 85 

20.5 . . . . . . . 0 11 49 0 60 29.9 . . . . . . . . 14 6 25 77 122 

20.9 . . . . . . . 0 12 90 0 102 30.3 . . . . . . . . 21 13 26 63 123 

21.3 . . . . . . . 0 26 108 0 134 30.7 . . . . . . . . 7 4 25 66 102 

21.7 . . . . . . . 0 27 114 0 141 31.1 . . . . . . . . 8 9 13 52 82 

22.0 . . . . . . . 5 27 103 0 135 31.5 . . . . . . . . 8 5 11 48 72 

22.4 . . . . . . . 10 44 70 0 124 31.9 . . . . . . . . 6 4 3 30 43 

22.8 . . . . . . . 22 47 48 0 117 32.3 . . . . . . . . 2 4 2 12 20 

23.2 . . . . . . . 21 37 18 0 76 32.7 . . . . . . . . 0 0 0 11 11 

23.6 . . . . . . . 38 58 8 0 104 33.1 . . . . . . . . 0 1 0 18 19 

24.0 . . . . . . . 28 59 0 0 87 33.5 . . . . . . . . 0 0 0 14 14 

24.4 . . . . . . . 31 56 1 0 88 33.9 . . . . . . . . 0 0 0 21 21 

24.8 . . . . . . . 42 38 7 0 87 34.3 . . . . . . . . 0 0 0 12 12 

25.2 . . . . . . . 38 36 13 0 87 34.6 . . . . . . . . 0 0 0 4 4 

25.6 . . . . . . . 49 29 14 0 92 35.0 . . . . . . . . 0 0 0 10 10 

26.0 . . . . . . . 51 21 25 0 97 35.4 . . . . . . . . 0 0 0 7 7 

26.4 . . . . . . . 36 27 20 0 83 35.8 . . . . . . . . 0 0 0 9 9 

26.8 . . . . . . . 32 15 11 0 58 36.2 . . . . . . . . 0 0 0 4 4 

27.2 . . . . . . . 37 7 12 0 56 36.6 . . . . . . . . 0 0 0 3 3 

27.6 . . . . . . . 46 9 6 0 61 37.0 . . . . . . . . 0 0 0 3 3 

28.0 . . . . . . . 33 8 2 0 43 37.4 . . . . . . . . 0 0 0 0 0 

28.3 . . . . . . . 26 6 2 0 34 37.8 . . . . . . . . 0 0 0 1 1 

28.7 . . . . . . . 25 4 8 0 37 TOTAL . . . . 682 669 874 525 2,750 

29.1 . . . . . . . 27 11 14 16 68 
Figure B–4.—Contact incidents by operator location and seam height. 

0 

20 

40 

60 

80 

100 

120 

140 

160 

20.1 22.0 

Contact Incidents 

24.0 26.0 28.0 29.9 31.9 

Operator Location (in) 

33.9 35.8 37.8 

45-in 60-in 72-in 

34 

Table B–4.—Contact incidents by operator location and seam height 

Operator Seam height (in) Total Operator Seam height (in) Total

location contact location contact 

45 60 72 45 60 72 (in) incidents (in) incidents 

20.1 . . . . . 0 12 0 12 29.5........
 35 6 44 85 

20.5 . . . . . 0 60 0 60 29.9........
 42 3 77 122 

20.9 . . . . . 0 102 0 102 30.3........
 59 1 63 123 

21.3 . . . . . 0 134 0 134 30.7........
 36 0 66 102 

21.7 . . . . . 0 141 0 141 31.1........
 30 0 52 82 

22.0 . . . . . 0 135 0 135 31.5........
 24 0 48 72 

22.4 . . . . . 0 124 0 124 31.9........
 13 0 30 43 

22.8 . . . . . 0 117 0 117 32.3........
 8 0 12 20 

23.2 . . . . . 0 76 0 76 32.7........
 0 0 11 11 

23.6 . . . . . 2 102 0 104 33.1........
 1 0 18 19 

24.0 . . . . . 4 83 0 87 33.5........
 0 0 14 14 

24.4 . . . . . 12 76 0 88 33.9........
 0 0 21 21 

24.8 . . . . . 20 67 0 87 34.3........
 0 0 12 12 

25.2 . . . . . 22 65 0 87 34.6........
 0 0 4 4 

25.6 . . . . . 31 61 0 92 35.0........
 0 0 10 10 

26.0 . . . . . 47 50 0 97 35.4........
 0 0 7 7 

26.4 . . . . . 47 36 0 83 35.8........
 0 0 9 9 

26.8 . . . . . 28 30 0 58 36.2........
 0 0 4 4 

27.2 . . . . . 30 26 0 56 36.6........
 0 0 3 3 

27.6 . . . . . 28 33 0 61 37.0........
 0 0 3 3 

28.0 . . . . . 23 20 0 43 37.4........
 0 0 0 0 

28.3 . . . . . 9 25 0 34 37.8........
 0 0 1 1 

28.7 . . . . . 19 18 0 37 TOTAL . . . . 606 1,619 525 2,750 

29.1 . . . . . 36 16 16 68 
35 

APPENDIX C.—FREQUENCY DATA SETS 

Table C–1.—Frequencies by data sets sorted by contacts 

Frequencies Percentages 

Conditions1 Avoid 

incidents Contacts None Total Avoid Contacts incidents None 

6022B ..... 

6016B ..... 

6010B ..... 

6007B ..... 

6007L ..... 

6022L ..... 

7213S ..... 

6013B ..... 

6022R ..... 

7210S ..... 

7216S ..... 

6016L ..... 

6016R ..... 

7207S ..... 

6010L ..... 

6013R ..... 

7222S ..... 

6013L ..... 

6010R ..... 

4516B ..... 

6007R ..... 

4516R ..... 

4507B ..... 

4513B ..... 

4522B ..... 

4522R ..... 

4507R ..... 

4513R ..... 

4516L ..... 

4513L ..... 

4522L ..... 

4510B ..... 

4510R ..... 

4507L ..... 

4510L ..... 

 Total . . . . . 

0 

0 

8 

9 

3 

13 

0 

9 

10 

0 

2 

14 

5 

1 

20 

15 

3 

28 

21 

31 

30 

28 

47 

44 

35 

28 

26 

24 

26 

37 

33 

61 

50 

31 

63 

755 

136 

127 

122 

119 

119 

115 

115 

113 

111 

108 

106 

105 

105 

104 

101 

95 

92 

91 

83 

77 

77 

54 

53 

49 

49 

44 

43 

43 

37 

36 

31 

29 

27 

18 

16 

2,750 

14 

23 

20 

22 

28 

22 

35 

28 

29 

42 

42 

31 

40 

45 

29 

40 

55 

31 

46 

42 

43 

68 

50 

57 

66 

78 

81 

83 

87 

77 

86 

60 

73 

101 

71 

1,745 

150 

150 

150 

150 

150 

150 

150 

150 

150 

150 

150 

150 

150 

150 

150 

150 

150 

150 

150 

150 

150 

150 

150 

150 

150 

150 

150 

150 

150 

150 

150 

150 

150 

150 

150 

5,250 

0.0 

0.0 

5.3 

6.0 

2.0 

8.7 

0.0 

6.0 

6.7 

0.0 

1.3 

9.3 

3.3 

0.7 

13.3 

10.0 

2.0 

18.7 

14.0 

20.7 

20.0 

18.7 

31.3 

29.3 

23.3 

18.7 

17.3 

16.0 

17.3 

24.7 

22.0 

40.7 

33.3 

20.7 

42.0 

— 

90.7 

84.7 

81.3 

79.3 

79.3 

76.7 

76.7 

75.3 

74.0 

72.0 

70.7 

70.0 

70.0 

69.3 

67.3 

63.3 

61.3 

60.7 

55.3 

51.3 

51.3 

36.0 

35.3 

32.7 

32.7 

29.3 

28.7 

28.7 

24.7 

24.0 

20.7 

19.3 

18.0 

12.0 

10.7 

— 

9.3 

15.3 

13.3 

14.7 

18.7 

14.7 

23.3 

18.7 

19.3 

28.0 

28.0 

20.7 

26.7 

30.0 

19.3 

26.7 

36.7 

20.7 

30.7 

28.0 

28.7 

45.3 

33.3 

38.0 

44.0 

52.0 

54.0 

55.3 

58.0 

51.3 

57.3 

40.0 

48.7 

67.3 

47.3

— 1

The first two digits represent coal seam height (in). The second two digits represent boom 

arm speed (in/sec). The letter represents work posture as follows: R = right knee; L = left 

knee; B = both knees; S = standing. 
36 

Table C–2.—Frequencies by data sets sorted by avoid incidents 

Frequencies Percentages 

Conditions1 Avoid 

incidents Contacts None Total Avoid Contacts incidents None 

4510L ..... 

4510B ..... 

4510R ..... 

4507B ..... 

4513B ..... 

4513L ..... 

4522B ..... 

4522L ..... 

4516B ..... 

4507L ..... 

6007R ..... 

6013L ..... 

4516R ..... 

4522R ..... 

4507R ..... 

4516L ..... 

4513R ..... 

6010R ..... 

6010L ..... 

6013R ..... 

6016L ..... 

6022L ..... 

6022R ..... 

6007B ..... 

6013B ..... 

6010B ..... 

6016R ..... 

6007L ..... 

7222S ..... 

7216S ..... 

7207S ..... 

6022B ..... 

6016B ..... 

7213S ..... 

7210S ..... 

 Total . . . . . 

63 

61 

50 

47 

44 

37 

35 

33 

31 

31 

30 

28 

28 

28 

26 

26 

24 

21 

20 

15 

14 

13 

10 

9 

9 

8 

5 

3 

3 

2 

1 

0 

0 

0 

0 

755 

16 

29 

27 

53 

49 

36 

49 

31 

77 

18 

77 

91 

54 

44 

43 

37 

43 

83 

101 

95 

105 

115 

111 

119 

113 

122 

105 

119 

92 

106 

104 

136 

127 

115 

108 

2,750 

71 

60 

73 

50 

57 

77 

66 

86 

42 

101 

43 

31 

68 

78 

81 

87 

83 

46 

29 

40 

31 

22 

29 

22 

28 

20 

40 

28 

55 

42 

45 

14 

23 

35 

42 

1,745 

150 

150 

150 

150 

150 

150 

150 

150 

150 

150 

150 

150 

150 

150 

150 

150 

150 

150 

150 

150 

150 

150 

150 

150 

150 

150 

150 

150 

150 

150 

150 

150 

150 

150 

150 

5,250 

42.0 

40.7 

33.3 

31.3 

29.3 

24.7 

23.3 

22.0 

20.7 

20.7 

20.0 

18.7 

18.7 

18.7 

17.3 

17.3 

16.0 

14.0 

13.3 

10.0 

9.3 

8.7 

6.7 

6.0 

6.0 

5.3 

3.3 

2.0 

2.0 

1.3 

0.7 

0.0 

0.0 

0.0 

0.0 

— 

10.7 

19.3 

18.0 

35.3 

32.7 

24.0 

32.7 

20.7 

51.3 

12.0 

51.3 

60.7 

36.0 

29.3 

28.7 

24.7 

28.7 

55.3 

67.3 

63.3 

70.0 

76.7 

74.0 

79.3 

75.3 

81.3 

70.0 

79.3 

61.3 

70.7 

69.3 

90.7 

84.7 

76.7 

72.0 

— 

47.3 

40.0 

48.7 

33.3 

38.0 

51.3 

44.0 

57.3 

28.0 

67.3 

28.7 

20.7 

45.3 

52.0 

54.0 

58.0 

55.3 

30.7 

19.3 

26.7 

20.7 

14.7 

19.3 

14.7 

18.7 

13.3 

26.7 

18.7 

36.7 

28.0 

30.0 

9.3 

15.3 

23.3 

28.0

— 1

The first two digits represent coal seam height (in). The second two digits represent boom 

arm speed (in/sec). The letter represents work posture as follows: R = right knee; L = left 

knee; B = both knees; S = standing. 
Table C–3.—Data sets by body part and contacts 

Conditions1 Body part Total Leg Arm Hand Head 

4507B ......... 

4507L ......... 

4507R ......... 

4510B ......... 

4510L ......... 

4510R ......... 

4513B ......... 

4513L ......... 

4513R ......... 

4516B ......... 

4516L ......... 

4516R ......... 

4522B ......... 

4522L ......... 

4522R ......... 

6007B ......... 

6007L ......... 

6007R ......... 

6010B ......... 

6010L ......... 

6010R ......... 

6013B ......... 

6013L ......... 

6013R ......... 

6016B ......... 

6016L ......... 

6016R ......... 

6022B ......... 

6022L ......... 

6022R ......... 

7207S ......... 

7210S ......... 

7213S ......... 

7216S ......... 

7222S ......... 

 TOTAL . . . . . . . 

— 

— 

— 

— 

— 

— 

— 

— 

— 

— 

— 

— 

— 

— 

— 

— 

46 

41 

— 

66 

32 

— 

70 

24 

— 

43 

27 

— 

41 

28 

20 

16 

7 

26 

26 

513 

2 

1 

2 

3 

— 

6 

8 

5 

8 

8 

2 

4 

9 

1 

4 

21 

1 

2 

14 

8 

5 

17 

2 

— 

12 

2 

3 

7 

16 

6 

3 

16 

1 

23 

17 

239 

90 

48 

67 

84 

79 

71 

79 

68 

59 

90 

61 

78 

65 

63 

68 

65 

80 

64 

63 

58 

67 

58 

54 

86 

66 

76 

81 

35 

72 

90 

123 

79 

67 

64 

56 

2,474 

8 

— 

— 

3 

— 

— 

6 

— 

— 

10 

— 

— 

11 

— 

— 

42 

— 

— 

53 

— 

— 

47 

— 

— 

49 

— 

— 

94 

— 

— 

— 

— 

— 

— 

— 

323 

100 

49 

69 

90 

79 

77 

93 

73 

67 

108 

63 

82 

85 

64 

72 

128 

127 

107 

130 

132 

104 

122 

126 

110 

127 

121 

111 

136 

129 

124 

146 

111 

75 

113 

99

3,549 1

The first two digits represent coal seam height (in). The second two digits 

represent boom arm speed (in/sec). The letter represents work posture as follows: 

R = right knee; L = left knee; B = both knees; S = standing. 

37 
38 

APPENDIX D.—CROSS-TABULATION 


Figure D–1.—Contact incidents by seam height and boom direction. 

0 

200 

400 

600 

800 

1000 

1200 

1400 

45 in 60 in 72 in 

Seam Height 

Contact Incidents 

Boom up 

Boom down 

Table D–1.—Contact incidents by seam height and boom direction 

Seam 

height, in 

Boom direction 

Up Down Total 1 Summary

45 . . . . . . . . . . . . . . 361 245 606 U>D 

60 . . . . . . . . . . . . . . 1,258 361 1,619 U>D 

72 . . . . . . . . . . . . . . 460 65 525 U>D

 Total . . . . . . . . . . . 2,079 671 2,750 —
 

1

D = down; U = up. 

Figure D–2.—Contact incidents by seam height and body part. 

0 

200 

400 

600 

800 

1000 

45 in 60 in 72 in 

Seam Height 

Contact Incidents

leg 

arm 

hand 

head 

Table D–2.—Contact incidents by seam height and body part 

Seam 

height, in Leg 

Body part 

Arm Hand Head Total 1 Summary

45 . . . . . . 0 33 563 10 606 H>A>HD>L 

60 . . . . . . 339 109 886 285 1,619 H>L>HD>A 

72 . . . . . . 80 59 386 0 525 H>L>A>HD

 Total . . . 419 201 1,835 295 2,750 — 

1

H = hand; A = arm; HD = head; L = leg. 
39 

Figure D–3.—Contact incidents by seam height and machine part. 

0 

200 

400 

600 

800 

1000 

1200 

1400 

45 in 60 in 72 in 

Seam Height 

Contact Incidents

boom 

drillhead 

Table D–3.—Contact incidents by seam height and machine part 

Seam 

height, in 

Machine part 

Boom Drill head Total 1 Summary

45 . . . . . . . . . . . . . . . . . . . . . 501 105 606 B>D 

60 . . . . . . . . . . . . . . . . . . . . . 1,295 324 1,619 B>D 

72 . . . . . . . . . . . . . . . . . . . . . 413 112 525 B>D

 Total . . . . . . . . . . . . . . . . . . 2,209 541 2,750 —
 

1

B = boom; D = drill head. 

Figure D–4.—Contact incidents by operator percentile and boom direction. 

0 

200 

400 

600 

800 

1000 

25th 55th 92nd 

Operator Percentile 

Contact Incidents

Boom up 

Boom down 

Table D–4.—Contact incidents by operator percentile and boom direction 

Operator 

percentile 

Boom direction 

Up Down Total 1 Summary

25th . . . . . . . . . . . . . . . . . . . . . . 806 307 1,113 U>D 

55th . . . . . . . . . . . . . . . . . . . . . . 688 212 900 U>D 

92nd ..................... 585 152 737 U>D

 Total . . . . . . . . . . . . . . . . . . . 2,079 671 2,750 —
 

1

U = up; D = down. 
40 

Figure D–5.—Contact incidents by operator percentile and body part. 

0 

100 

200 

300 

400 

500 

600 

700 

800 

25th 55th 92nd 

Operator Percentile 

Contact Incidents

Leg 

Arm 

Hand 

Head 

Table D–5.—Contact incidents by operator percentile and body part 

Operator 

percentile Leg 

Body part 

Arm Hand Head Total 1 Summary

25th . . . . . . . . . . . . . . . . 158 117 753 85 1,113 H>L>A>HD 

55th . . . . . . . . . . . . . . . . 181 60 578 81 900 H>L>HD>A 

92nd . . . . . . . . . . . . . . . 80 24 504 129 737 H>HD>L>A

 Total . . . . . . . . . . . . . 419 201 1,835 295 2,750 —
 

1

H = hand; L = leg; A = arm; HD = head. 

Figure D–6.—Contact incidents by operator percentile and machine part. 

1000
 

Contact Incidents


800 

600 

400 

200 

0 

Boom 

Drill head 

25th 55th 92nd 

Operator Percentile 

Table D–6.—Contact incidents by operator percentile and machine part 

Operator 

percentile 

Machine part 

Boom Drill head Total 1 Summary

25th . . . . . . . . . . . . . . . . . . 841 272 1,113 B>D 

55th . . . . . . . . . . . . . . . . . . 741 159 900 B>D 

92nd ................. 627 110 737 B>D

 Total . . . . . . . . . . . . . . . 2,209 541 2,750 —
 

1

B = boom; D = drill head. 
41 

Figure D–7.—Contact incidents by work posture and boom direction. 

0 

200 

400 

600 

800 

Right knee Left knee Both knees Standing 

Working Posture 

Contact Incidents

Up 

Down 

Table D–7.—Contact incidents by work posture and boom direction 

Work posture Boom direction 

Down Up
 Total 1 Summary

Right knee . . . . . . . . . . . . . . . . . . 245 437 682 U>D 
 

Left knee . . . . . . . . . . . . . . . . . . . . 233 436 669 U>D 
 

Both knees .................. 128 746 874 U>D 
 

Standing .................... 65 460 525 U>D 


 Total . . . . . . . . . . . . . . . . . . . . . . 671 2,079 2,750 —
 

1

U = up; D = down. 

Figure D-8.—Contact incidents by work posture and body part. 

0 

200 

400 

600 

Right knee Left knee Both knees Standing 

Working Posture 

Contact Incidents

Leg 

Arm 

Hand 

Head 

Table D–8.—Contact incidents by work posture and body part 

Work posture Leg 

Body part 

Arm Hand Head
 Total 1 Summary

Right knee . . . . . . . . . . 147 28 507 0 682 H>L>A>HD 
 

Left knee . . . . . . . . . . . . 192 34 443 0 669 H>L>A>HD 
 

Both knees . . . . . . . . . . 0 80 499 295 874 H>HD>A>L 
 

Standing . . . . . . . . . . . . 80 59 386 0 525 H>L>A>HD 


 Total . . . . . . . . . . . . . . 419 201 1,835 295 2,750 —
 

1

H = hand; L = leg; A = arm; HD = head. 
42 

Figure D–9.—Contact incidents by work posture and machine part. 

0 

200 

400 

600 

800 

Right knee Left knee Both knees Standing 

Working Posture 

Contact Incidents

Boom 

Drill head 

Table D–9.—Contact incidents by work posture and machine part 

Work posture Machine part 

Boom Drill head Total Summary 1 

Right knee . . . . . . . . . . 563 119 682 B>D 

Left knee . . . . . . . . . . . . 535 134 669 B>D 

Both knees .......... 698 176 874 B>D 

Standing ............ 413 112 525 B>D

 Total . . . . . . . . . . . . . . 2,209 541 2,750 — 

1

B = boom; D = drill head. 

Figure D–10.—Contact incidents by drilling behavior and boom direction. 

0 

200 

400 

600 

800 

1000 

1200 

None Hand on drill 

steel 

Hand on boom Hand on drill 

steel then on 

boom 

Drilling Behavior 

Contact Incidents

Up 

Down 

Table D–10.—Contact incidents by drilling behavior and boom direction 

Drilling behavior Boom direction 

Up Down Total Summary 1 

None . . . . . . . . . . . . . . . . . . . . . . . 501 172 673 U>D 

Hand on drill steel ............. 133 35 168 U>D 

Hand on boom ............... 1,160 381 1,541 U>D 

Hand on drill steel then on boom . 285 83 368 U>D

 Total . . . . . . . . . . . . . . . . . . . . . 2,079 671 2,750 —
 

1

U = up; D = down. 
Figure D–11.—Contact incidents by drilling behavior and body part. 

0 

200 

400 

600 

800 

1000 

1200 

None Hand on drill 

steel 

Hand on 

boom 

Hand on drill 

steel then on 

boom 

Drilling Behavior 

Contact Incidents

Leg 

Arm 

Hand 

Head 

43 

Table D–11.—Contact incidents by drilling behavior and body part 

Body part 1 Drilling behavior Total Summary Leg Arm Hand Head 

None . . . . . . . . . . . . . . . . . . . . . . . 200 27 332 114 673 H>L>HD>A 

Hand on drill steel . . . . . . . . . . . . . 28 13 97 30 168 H>L>HD>A 

Hand on boom . . . . . . . . . . . . . . . 162 128 1,116 135 1,541 H>L>A>HD 

Hand on drill steel then on boom . 29 33 290 16 368 H>A>L>HD

 Total . . . . . . . . . . . . . . . . . . . . . 419 201 1,835 295 2,750 — 

1

H = hand; L = leg; HD = head; A = arm. 

Figure D–12.—Contact incidents by drilling behavior and machine part. 

0 

200 

400 

600 

800 

1000 

1200 

1400 

None Hand on drill 

steel 

Hand on 

boom 

Hand on drill 

steel then on 

boom 

Drilling Behavior 

Contact Incidents

Boom 

Drill head 

Table D–12.—Contact incidents by drilling behavior and machine part 

Drilling behavior Machine part 

Boom Drill head Total 1 Summary

None . . . . . . . . . . . . . . . . . . . . . . . . . 608 65 673 B>D 

Hand on drill steel ............... 111 57 168 B>D 

Hand on boom ................. 1,234 307 1,541 B>D 

Hand on drill steel then on boom . . . 256 112 368 B>D

 Total . . . . . . . . . . . . . . . . . . . . . . . 2,209 541 2,750 — 

1

B = boom; D = drill head. 
Figure D–13.—Contact incidents by bolting behavior and machine part. 

0 

200 

400 

600 

800 

1000 

None Hand on bolt Hand on 

boom 

Hand on bolt 

then on boom 

Bolting Behavior 

Contact Incidents

Boom 

Drill head 

44 

Table D–13.—Contact incidents by bolting behavior and machine part 

Bolting behavior Machine part 

Boom Drill head Total 1 Summary

None . . . . . . . . . . . . . . . . . . . 595 153 748 B>D 

Hand on bolt ............. 305 97 402 B>D 

Hand on boom ........... 870 172 1,042 B>D 

Hand on bolt then on boom . 439 119 558 B>D

 Total . . . . . . . . . . . . . . . . . 2,209 541 2,750 — 

1

B = boom; D = drill head. 

Figure D–14.—Contact incidents by bolting behavior and boom direction. 

0 

200 

400 

600 

800 

None Hand on bolt Hand on boom Hand on bolt 

then on boom 

Bolting Behavior 

Contact Incidents

Up 

Down 

Table D–14.—Contact incidents by bolting behavior and boom direction 

Bolting behavior Boom direction 

Up Down Total Summary 1 

None . . . . . . . . . . . . . . . . . . . . . . . 619 129 748 U>D 

Hand on bolt ................. 330 72 402 U>D 

Hand on boom ............... 716 326 1,042 U>D 

Hand on bolt then on boom ..... 414 144 558 U>D

 Total . . . . . . . . . . . . . . . . . . . . . 2,079 671 2,750 —
 

1

U = up; D = down. 
 

Figure D–15.—Contact incidents by bolting behavior and body part. 

0 

200 

400 

600 

800 

None Hand on bolt Hand on boom Hand on bolt 

then on boom 

Bolting Behavior 

Contact Incidents

Leg 

Arm 

Hand 

Head 

45 

Table D–15.—Contact incidents by bolting behavior and body part 

Bolting behavior Leg 

Body part 

Arm Hand Head Total 1 Summary

None . . . . . . . . . . . . . . . . . . . 141 54 454 99 748 H>L>HD>A 

Hand on bolt . . . . . . . . . . . . . 67 41 237 57 402 H>L>HD>A 

Hand on boom . . . . . . . . . . . 143 69 738 92 1,042 H>L>HD>A 

Hand on bolt then on boom . 68 37 406 47 558 H>L>HD>A

 Total . . . . . . . . . . . . . . . . . 419 201 1,835 295 2,750 —
 

1

H = hand; L = leg; HD = head; A = arm. 

Figure D–16.—Contact incidents by boom speed and boom direction. 

0 

200 

400 

600 

7 in/sec 10 in/sec 13 in/sec 16 in/sec 22 in/sec 

Boom Speed 

Contact Incidents

Up 

Down 

Table D–16.—Contact incidents by boom speed and boom direction 

Boom speed, 

in/sec 

Boom direction 

Up Down Total Summary 1 

7 . . . . . . . . . . . . . . . . . . . . . . 390 143 533 U>D 

10 . . . . . . . . . . . . . . . . . . . . . 414 72 486 U>D 

13 . . . . . . . . . . . . . . . . . . . . . 383 159 542 U>D 

16 . . . . . . . . . . . . . . . . . . . . . 461 150 611 U>D 

22 . . . . . . . . . . . . . . . . . . . . . 431 147 578 U>D

 Total . . . . . . . . . . . . . . . . . 2,079 671 2,750 — 

1

U = up; D = down. 
46 

Figure D–17.—Contact incidents by boom speed and body part. 

0 

200 

400 

600 

7 in/sec 10 in/sec 13 in/sec 16 in/sec 22 in/sec 

Boom Speed 

Contact Incidents

Leg 

Arm 

Hand 

Head 

Table D–17.—Contact incidents by boom speed and body part 

Boom speed, 

in/sec Leg 

Body part 

Arm Hand Head
 Total 1 Summary

7 . . . . . . . . . . . 99 25 359 50 533 H>L>HD>A 
 

10 . . . . . . . . . . 90 42 300 54 486 H>L>HD>A 
 

13 . . . . . . . . . . 76 31 387 48 542 H>L>HD>A 
 

16 . . . . . . . . . . 78 47 437 49 611 H>L>HD>A 
 

22 . . . . . . . . . . 76 56 352 94 578 H>HD>L>A 


 Total . . . . . . . 419 201 1,835 295 2,750 —
 

1

H = hand; L = leg; HD = head; A = arm. 

 

Figure D–18.—Contact incidents by boom speed and machine part. 

0 

200 

400 

600 

7 

in/sec 

10 

in/sec 

13 

in/sec 

16 

in/sec 

22 

in/sec 

Boom Speed 

Contact Incidents

Boom 

Drill head 

Table D–18.—Contact incidents by boom speed and machine part 

Boom speed, 

in/sec 

Machine part 

Boom Drill head
 Total 1 Summary

7 . . . . . . . . . . . . . . . . . . . . . . 428 105 533 B>D 
 

10 . . . . . . . . . . . . . . . . . . . . . 384 102 486 B>D 
 

13 . . . . . . . . . . . . . . . . . . . . . 420 122 542 B>D 
 

16 . . . . . . . . . . . . . . . . . . . . . 496 115 611 B>D 
 

22 . . . . . . . . . . . . . . . . . . . . . 481 97 578 B>D 


 Total . . . . . . . . . . . . . . . . . . 2,209 541 2,750 —
 

1

B = boom; D = drill head. 
Figure D–19.—Contact incidents by boom speed and work posture. 

0 

100 

200 

300 

7 in/sec 10 in/sec 13 in/sec 16 in/sec 22 in/sec 

Boom Speed 

Contact Incidents

Right knee 

Left knee 

Both knees 

Standing 

47 

Table D–19.—Contact incidents by boom speed and work posture 

Boom speed, 

in/sec Right 

knee 

Work posture 

Left Both 

knee knees Standing Total 1 Summary

7 . . . . . . . . . . 120 137 172 104 533 B>L>R>S 

10 . . . . . . . . . 110 117 151 108 486 B>L>R>S 

13 . . . . . . . . . 138 127 162 115 542 B>R>L>S 

16 . . . . . . . . . 159 142 204 106 611 B>R>L>S 

22 . . . . . . . . . 155 146 185 92 578 B>R>L>S

 Total . . . . . . 682 669 874 525 2,750 — 

1

L = left knee; R = right knee; B = both knees; S = standing. 

Figure D–20.—Contact incidents by boom speed and operator percentile. 

0 

100 

200 

300 

7 in/sec 10 in/sec 13 in/sec 16 in/sec 22 in/sec 

Boom Speed 

Contact Incidents

25th-percentile 

55th-percentile 

92nd-percentile 

Table D–20.—Contact incidents by boom speed and operator percentile 

Boom speed, 

in/sec 

Operator percentile 

25th 55th 92nd
 Total Summary 

7 .................. 221 169 143 533 25>55>92 
 

10 ................. 197 158 131 486 25>55>92 
 

13 ................. 245 195 171 611 25>55>92 
 

16 ................. 233 195 150 578 25>55>92 
 

22 ................. 217 183 142 542 25>55>92 


 Total . . . . . . . . . . . . . 1,113 900 737 2,750 —
 
48 

Figure D–21.—Contact incidents by boom speed and drilling behavior. 

0 

100 

200 

300 

400

 7 

in/sec 

10 

in/sec 

13 

in/sec 

16 

in/sec 

22 

in/sec 

Boom Speed 

Contact Incidents

None 

Hand on drill steel 

Hand on boom 

Hand on drill steel then on 

boom 

Table D–21.—Contact incidents by boom speed and drilling behavior 

Boom speed, 

in/sec 

Drilling behavior 

Hand on Hand on Hand on drill steel Total None drill steel boom then on boom 

1 Summary

7 ............ 144 28 291 70 533 B>N>D&B>D 

10 . . . . . . . . . . . 120 39 268 59 486 B>N>D&B>D 

13 . . . . . . . . . . . 140 26 373 72 611 B>N>D&B>D 

16 . . . . . . . . . . . 129 38 322 89 578 B>N>D&B>D 

22 . . . . . . . . . . . 140 37 287 78 542 B>N>D&B>D

 Total . . . . . . . . 673 168 1,541 368 2,750 — 

1

D = hand on drill steel; B = hand on boom; D&B = hand on drill steel then on boom; N = none. 

Figure D–22.—Contact incidents by boom speed and seam height. 

0 

100 

200 

300 

400 

7 in/sec 10 in/sec 13 in/sec 16 in/sec 22 in/sec 

Boom Speed 

Contact Incidents

45 in 

60 in 

72 in 

Table D–22.—Contact incidents by boom speed and seam height 

Boom speed, 

in/sec 45

Seam height, in 

 60 72
 Total Summary

7 . . . .................. . 114 315 104 533 60>45>72 
 

10 . . .................. . 72 306 108 486 60>72>45 
 

13 . . .................. . 168 337 106 611 60>45>72 
 

16 . . .................. . 124 362 92 578 60>45>72 
 

22 . . .................. . 128 299 115 542 60>45>72 


 Total . . . . . . . . . . . . . . . . . . 606 1,619 525 2,750 —
 
 

Figure D–23.—Contact incidents by boom speed and bolting behavior. 

0 

50 

100 

150 

200 

250 

7 

in/sec 

10 

in/sec 

13 

in/sec 

16 

in/sec 

22 

in/sec 

Boom Speed 

Contact Incidents

None 

Hand on bolt 

Hand on boom 

Hand on bolt then on 

boom 

49 

Table D–23.—Contact incidents by boom speed and bolting behavior 

Boom speed, 

in/sec 

Bolting behavior 

Total 1 Summary None Hand on Hand on 

bolt boom 

Hand on bolt 

then on boom 

7 . . . . . . . . . . . . . 133 69 215 116 533 B>N>BT&B>BT 

10 . . . . . . . . . . . . 136 68 175 107 486 B>N>BT&B>BT 

13 . . . . . . . . . . . . 163 88 234 126 611 B>N>BT&B>BT 

16 . . . . . . . . . . . . 157 91 220 110 578 B>N>BT&B>BT 

22 . . . . . . . . . . . . 159 86 198 99 542 B>N>BT&B>BT

 Total . . . . . . . . . 748 402 1,042 558 2,750 — 

1

BT = hand on bolt; B = hand on boom; BT&B = hand on bolt then on boom; N = none. 
50 

APPENDIX E.—LOGISTIC REGRESSION MODELS 

FOR ROOF BOLTER SIMULATION DATA 

Table E–1.—Modeling the probability of a contact for slow reaction time of operator (N = 5,250) 

Model Predictor variable  SE() 4 Pr > chi-square R2 

1 ..... Seam height: 

 45 in . . . . . . . . . . . . . . . . . . 

 60 in . . . . . . . . . . . . . . . . . . 

 72 in . . . . . . . . . . . . . . . . . . 

— 

1.9403 

1.8453 

— 

0.0668 

0.0928 

1.000 

6.961 

6.330 

—

<.0001

<.0001 

0.2435

2 ..... Boom speed: 

 7 in/sec . . . . . . . . . . . . . . . . — — 1.000 —

 10 in/sec . . . . . . . . . . . . . . . 	0.1793 0.0874 0.836 0.0402 0.0087 13 in/sec . . . . . . . . . . . . . . . 0.0343 0.0873 1.035 0.6944

 16 in/sec . . . . . . . . . . . . . . . 0.3301 0.0879 1.350 0.0006

 22 in/sec . . . . . . . . . . . . . . . 0.1721 0.0875 1.188 0.0492 

3 ..... Operator percentile: 

 55th . . . . . . . . . . . . . . . . . . . 

 25th . . . . . . . . . . . . . . . . . . . 

 92nd .................. 	

— 

0.5020 

0.3731 

— 

0.0690 

0.0681 

1.000 

1.652 

0.689 

—

<.0001

<.0001 

0.0410

4 ..... Working posture: 

Standing ............... — — 1.000 —

 Right knee . . . . . . . . . . . . . 	1.0287 0.0951 0.357 <.0001 0.0456

 Left knee . . . . . . . . . . . . . . . 	1.0637 0.0951 0.345 <.0001

 Both knees ............. 	0.5132 0.0953 0.599 <.0001 

5 ..... Working posture/seam height: 

Standing/72 in .......... — — 1.000 —

 Right knee/45 in ......... 	1.8941 0.1176 0.150 <.0001

 Right knee/60 in ......... 	0.3419 0.1129 0.710 0.0024

 Left knee/45 in .......... 	2.4724 0.1274 0.084 <.0001

 Left knee/60 in .......... 0.0404 0.1161 1.041 0.7277

 Both knees/45 in ......... 	1.5904 0.1144 0.204 <.0001

 Both knees/60 in ......... 0.7179 0.1272 2.050 <.0001 

Boom speed: 0.3195 7 in/sec . . . . . . . . . . . . . . . . — — 1.000 —

 10 in/sec . . . . . . . . . . . . . . . 	0.2377 0.1007 0.788 0.0182

 13 in/sec . . . . . . . . . . . . . . . 0.0453 0.1007 1.046 0.6525

 16 in/sec . . . . . . . . . . . . . . . 0.3995 0.1015 1.491 <.0001

 22 in/sec . . . . . . . . . . . . . . . 

Operator percentile:

0.2291 0.1010 1.257 <.0233 

 55th . . . . . . . . . . . . . . . . . . . — — 1.000 —

 25th . . . . . . . . . . . . . . . . . . . 0.6553 0.0793 1.926 <.0001

 92nd .................. 	0.4859 0.0777 0.615 <.0001 
51 

APPENDIX F.—SURVIVAL ANALYSIS TABLES 

Table F–1.—Univariate model information (outcome slow) 

Variable 

Degrees 

of 

freedom 

Beta Standard 

error p-value Risk ratio 

95% 

confidence 

interval 

AIC 

Proportional 

hazards 

probability 

Operator location . . . . . . . . . . . . . 1 	.012 .002 .000 0.988 0.984–0.992 39058.426 .274 

Operator percentile:

 55th . . . . . . . . . . . . . . . . . . . . . .

2

 .016 .045 .723 1.016 0.930–1.110 

39079.482 .857 

 92nd ..................... .167 .048 .001 1.181 1.075–1.298 

Boom speed:1

 10 in/sec . . . . . . . . . . . . . . . . . .

 13 in/sec . . . . . . . . . . . . . . . . . .

 16 in/sec . . . . . . . . . . . . . . . . . .

 22 in/sec . . . . . . . . . . . . . . . . . . 

4 

.412 

.741 

1.266 

1.507 

.065 

.065 

.065 

.067 

.000 

.000 

.000 

.000 

1.510 

2.098 

3.547 

4.514 

1.330–1.714 

1.847–2.383 

3.12–4.032 

3.956–5.150 

38431.442 .000 

Boom up . . . . . . . . . . . . . . . . . . . . 1 0.832 .045 .000 2.297 2.104–2.508 38703.881 .000 

Bolting behavior:

 Hand on bolt ...............

3 

	.187 .062 .003 .829 0.734–0.937 

39035.802 .059 

 Hand on boom ............. 	.344 .049 .000 .709 0.644–0.781 

 Hand on bolt then on boom . . . 	.386 .057 .000 .692 0.619–0.774 

Drilling behavior:

 Hand on drill steel ...........

3 

.524 .087 .000 1.688 1.424–2.001 

38793.809 .000 

 Hand on boom ............. .716 .048 .000 2.046 1.862–2.248 

 Hand on drill steel then on boom .961 .067 .000 2.613 2.292–2.980 

Work posture/seam height: 6 38892.369 .000 

 Right knee/45 in ............ 	.290 .083 .000 .748 .636–.881 

 Right knee/60 in ............ 	.308 .065 .000 .735 .647–.835 

 Left knee/45 in ............. 	.577 .097 .000 .562 .464–.680 

 Left knee/60 in ............. 	.278 .063 .000 .757 .669–.857 

 Both knees/45 in ............ 	.371 .078 .000 .690 .592–.804 

 Both knees/60 in ............ .356 .061 .000 1.427 1.267–1.608 

1

Variable whose selection at this step best improves model fit as determined by Akaike Information Criterion. 

Table F–2.—Models with boom speed 

Variable 

Degrees 

of 

freedom 

Beta Standard 

error p-value Risk ratio 

95% 

confidence 

interval 

AIC 

Proportional 

hazards 

probability 

Operator position . . . . . . . . . . . . . . . . 1 	.014 .002 .000 0.986 0.982–0.990 38318.271 0.000 

Operator percentile: 2 38340.011 0.714 

 55th . . . . . . . . . . . . . . . . . . . . . . . . . .002 .045 .963 1.002 0.917–1.095 

92nd ........................ .205 .048 .000 1.228 1.118–1.349 

Boom up1 ...................... 1 0.860 .045 .000 2.363 2.719–3.486 37948.863 .000 

Bolting behavior: 3 38284.763 .000 

Hand on bolt .................. 	.236 .063 .000 .790 .698–.893 

Hand on boom ................ 	.401 .049 .000 .670 .608–.738 

Hand on bolt then on boom ...... 	.432 .057 .000 .649 .580–.726 

Drilling behavior: 3 37964.690 .000 

 Hand on drill steel .............. .583 .088 .000 1.791 1.508–2.128 

Hand on boom ................ .846 .049 .000 2.329 2.118–2.563 

Hand on drill steel then on boom . . 1.078 .067 .000 2.939 2.576–3.353 

Work posture/seam height: 6 38178.128 .000 

Right knee/45 in ............... 	.078 .086 .365 .925 .781–1.095 

Right knee/60 in ............... 	.255 .067 .000 .775 .680–.884 

Left knee/45 in ................ 	.405 .100 .000 .667 .548–.810 

Left knee/60 in ................ 	.137 .065 .036 .872 .767–.991 

 Both knees/45 in ............... 	.143 .081 .078 .867 .739–1.016 

 Both knees/60 in ............... .484 .063 .000 1.623 1.435–1.836 

1

Variable whose selection at this step best improves model fit as determined by Akaike Information Criterion. 
Table F–3.—Models with boom speed, boom direction 

Variable 

Degrees 

of 

freedom 

Beta Standard 

error p-value Risk ratio 

95% 

confidence 

interval 

AIC 

Proportional 

hazards 

probability 

Operator location . . . . . . . . . . . . . . . . 1 	.007 .002 .001 .734 .989–.997 37688.279 0.000 

Operator percentile: 2 37682.262 0.461 

 25th . . . . . . . . . . . . . . . . . . . . . . . . . .008 .045 .865 1.008 .922–1.101 

92nd ........................ .241 .048 .000 1.272 1.158–1.398 

Bolting behavior: 3 37641.491 0.000 

Hand on bolt .................. 	.256 .063 .000 .774 .685–.875 

Hand on boom ................ 	.348 .050 .000 .706 .640–.779 

Hand on bolt then on boom ...... 	.452 .057 .000 .636 .569–.712 

Drilling behavior:1 3 37123.513 .000 

 Hand on drill steel .............. .636 .088 .000 1.889 1.591–2.243 

Hand on boom ................ 1.025 .048 .000 2.788 2.536–3.064 

Hand on drill steel then on boom . . 1.266 .067 .000 3.546 3.109–4.045 

Work posture/seam height: 6 37581.826 0.000 

Right knee/45 in ............... .476 .089 .000 1.609 1.352–1.916 

Right knee/60 in ............... 	.095 .067 .159 .909 .797–1.038 

Left knee/45 in ................ .202 .102 .049 1.223 1.001–1.495 

Left knee/60 in ................ 	.018 .066 .782 .982 .864–1.117 

 Both knees/45 in ............... .047 .082 .561 1.049 .893–1.231 

 Both knees/60 in ............... .492 .063 .000 1.636 1.446–1.851 

1

Variable whose selection at this step best improves model fit as determined by Akaike Information Criterion. 

Table F–4.—Models with boom speed, boom direction, drilling behavior 

Variable 

Degrees 

of 

freedom 

Beta Standard 

error p-value Risk ratio 

95% 

confidence 

interval 

AIC 

Proportional 

hazards 

probability 

Operator location . . . . . . . . . . . . . . . . 1 	.013 .002 .000 .987 — 36928.749 .000 

Operator percentile: 2 36948.790 .806 

 25th . . . . . . . . . . . . . . . . . . . . . . . . . 	.063 .045 .165 0.939 .859–1.026 

92nd ........................ .166 .048 .001 1.181 1.074–1.299 

Bolting behavior: 3 36910.591 0.000 

Hand on bolt .................. 	.184 .063 .004 .832 .735–.941 

Hand on boom ................ 	.323 .050 .000 .724 .656–.799 

Hand on bolt then on boom ...... 	.415 .057 .000 .661 .590–.739 

Work posture/seam height:1 6 36797.873 .000 

Right knee/45 in ............... .444 .088 .000 1.558 1.310–1.853 

Right knee/60 in ............... 	.066 .068 .332 1.936 0.820–1.069 

Left knee/45 in ................ .250 .102 .014 1.284 1.051–1569 

Left knee/60 in ................ .059 .066 .372 1.060 0.932–1.206 

 Both knees/45 in ............... .181 .082 .026 1.199 1.021–1.407 

 Both knees/60 in ............... .658 .063 .000 1.930 1.705–2.185 

1

Variable whose selection at this step best improves model fit as determined by Akaike Information Criterion. 

Table F–5.—Models with boom speed, boom direction, drilling behavior, work posture/seam height 

Degrees 95% Standard Risk Variable of Beta p-value confidence error ratio freedom interval 

AIC 

Proportional 

hazards 

probability 

Operator location . . . . . . . . . . . . . . . . 1 	.006 .005 .170 .994 .985–1.003 36180.209 .492 

Operator percentile: 2 36175.668 .979 

 25th . . . . . . . . . . . . . . . . . . . . . . . . . 	.054 .046 .241 0.948 .867–1.037 

92nd ........................ .093 .049 .057 1.098 .997–1.208 

Bolting behavior:1 3 36122.493 .046 

Hand on bolt .................. 	.162 .063 .010 .850 .751–.962 

Hand on boom ................ 	.321 .051 .000 .725 .657–.801 

Hand on bolt then on boom ...... 	.428 .058 .000 .652 .582–.731 

1

Variable whose selection at this step best improves model fit as determined by Akaike Information Criterion. 

52 
Table F–6.—Models with boom speed, boom direction, drilling behavior, work posture/seam height, bolting behavior 

Degrees 95% Standard Risk Variable of Beta p-value confidence error ratio freedom interval 

AIC 

Proportional 

hazards 

probability 

Operator location . . . . . . . . . . . . . . 1 	.002 .005 .588 .998 .989–1.007 36122.228 0.762 

Operator percentile:1 2 36115.613 0.946 

 25th . . . . . . . . . . . . . . . . . . . . . . . 	.036 .046 .429 .964 .882–1.055 

92nd ...................... .112 .049 .023 1.118 1.016–1.231 

1

Variable whose selection at this step best improves model fit as determined by Akaike Information Criterion. 

Table F–7.—Models with boom speed, boom direction, drilling behavior, work posture/seam height, 

bolting behavior, operator percentile 

Degrees 95% Standard Risk Variable of Beta p-value confidence error ratio freedom interval 

AIC 

Proportional 

hazards 

probability 

Operator location1 .............. 1 	.017 .007 .011 .983 .970–.996 36114.925 0.335 

1

Variable whose selection at this step best improves model fit as determined by Akaike Information Criterion. 

Table F–8.—Final model 

h(t|z) = h0(t|z)exp(	 2.3*10in/s +1.173*10in/s*ln(time) 
	

3.698*13in/s + 1.971*13in/s*ln(time) 
	

3.89*16in/s + 2.299*16in/s*ln(time) 
	

4.234*22in/s + 2.649*22in/s*ln(time) +
 

2.995*boomup 	 0.668*boomup*ln(time) + 


3.906*handondrillsteel(drill) 	 1.142*handondrillsteel(drill)*ln(time) + 


4.978*handonboom(drill) 	 1.428*handonboom(drill)*ln(time) 
	

5.282*handonboth(drill) 	 1.465*handonboth(drill)*ln(time) 
	

9.236*Right45in + 3.927*Right45in*ln(time) 
	

6.049*Right60in + 2.291*Right60in*ln(time) 
	

9.47*Left45in + 3.959*Left45in*ln(time) 
	

6.002*Left60in + 2.274*Left60in*ln(time) 
	

9.014*Both45in + 3.743*Both45in*ln(time) 
	

2.539*Both60in + 1.137*Both60in*ln(time) +
 

0.675*handonbolt(bolt) 	 0.341*handonbolt(bolt) +
 

0.25*handonboom(bolt) 	 0.23*handonboom(bolt)*ln(time) +
 

0.241*handonboth(bolt) 	 0.268*handonboth(bolt)*ln(time) +
 

0.047*55thpercentile + 0.243*95thpercentile 	 0.170*operatorlocation)
 

53 
54 

APPENDIX G.—ILLUSTRATIONS OF OPERATOR'S WORK BEHAVIORS 

Figure G–1.—45-in seam height and different work postures: operator's hand on the boom arm, hand on the drill steel, hand off 

both boom arm and drill steel. 
55 

Figure G–2.—60-in seam height and different work postures: operator's hand on the boom arm, hand on the drill steel, hand off both 

boom arm and drill steel. 
56 

Figure G–3.—72-in seam height and standing work posture: operator’s hand on the boom arm, hand on the drill steel, hand off 

both boom arm and drill steel.