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Underground Construction (Tunneling) - OSHA Standards

John Poullain, P.E.


Course Outline

This one-hour online course provides general guidelines for recognizing the potential hazards of underground construction of tunnels and chambers and the methods taken to prevent or reduce exposure to the hazards. Topics include the OSHA standards for safety and protection from underground hazards such as reduced natural ventilation and light, difficult access and egress, exposure to air contaminants, fire, flooding and explosion. The text discusses steps to provide safe operation of hoists and cranes and for drilling and blasting underground. Where and how often site and equipment inspections should be performed are discussed. 

This course includes a multiple-choice quiz at the end, which is designed to enhance the understanding of the course materials.

Learning Objective

At the conclusion of this course, the student will have reviewed the following topics:

Intended Audience

This course is intended for engineers, construction managers, and safety inspectors.

Benefit to Attendees

The student will become familiar with OSHA safety standards for underground excavation and understand potential hazards such as hazardous air, fire and explosion and the importance of providing access and egress from excavations. OSHA standards cover protective methods used to shield workers from underground hazards. The importance of excavation preplanning, site and equipment inspections, site safety and safety equipment are also discussed.

Course Introduction

The course is based on an OSHA underground construction publication, which covers standards written to provide a safe work site. Underground excavations are recognized as one of the most hazardous of construction operations. They are inherently unstable and pose several serious hazards to workers, which include mainly excavation failures such as cave-ins, subsidence, fires, explosions and hazardous air. Other excavation hazards include falls, falling debris and materials or construction equipment and unhealthful atmospheric conditions.

Existing soils at the site may be unstable due to excess clay, expansive clays, silts, fine sands, gravels, voids, or high watertables. Problem soils may be encountered such as loess, hydraulic fills and tailings which have collapsing or low-density structures, and when saturated from ground water have large decreases in volume and loss of strength.  

Planning underground excavation work must be given careful attention. Hazards such as vehicular traffic, vibration from moving construction equipment near to shafts, surface drainage, water tables, utilities, inhalation of toxic fumes and changes in the weather have to considered and planned for to prevent costly delays or contract changes later for remediation of problems. Control of traffic may have to be planned for and the work site may have to be tested for low oxygen, hazardous or toxic gases. Motors or construction equipment may be running or storage tanks or pipes may have leaked, saturating the soil. Surface water should be controlled by sloping drainage away from ingress and egress shafts.

Factors, which affect stability of excavations, are the types of soil, depth of cut, subsidence of soil and surcharges. Using maximum allowable slopes and/or benching and shoring or shielding systems provides protection from cave-ins and other hazards. Spoil material from an excavation must be properly placed in order to maintain excavation stability. The weight of spoil material can cause cave-ins or fall onto workers in an excavation. Spoils may have to be hauled somewhere else temporarily if there is insufficient space or ROW at the work site.

Course Content

This course is based on the OSHA publication 3115-06R “Underground Construction (Tunneling)” (2003 Edition, 30 pages), PDF file.

The link to the those document is:

“Underground Construction (Tunneling)”, OSHA publication 3115-06R

Please click on the above underlined hypertext to view, download or print the document for your study. Because of the large file size, we recommend that you first save the file to your computer by right clicking the mouse and choosing "Save Target As ...", and then open the file in Adobe Acrobat Reader. If you still experience any difficulty in downloading or opening this file, you may need to close some applications or reboot your computer to free up some memory.

Course Summary

In order to keep an underground excavation safe and free from accidents it is vital to recognize the potential hazards. Their causes and selection of protection systems are discussed along with standards for site control, requirements for ventilation, illumination, and air monitoring and drilling and blasting underground. The importance of pre-job planning, the minimum amount of site inspections and having safety equipment and rescue personnel available at the work site is discussed. 

Related Links

For additional technical information related to this subject, please refer to:

http://www.cdc.gov/niosh/topics/trenching
National Institute for Occupational Safety and Health (NIOSH) information and guideline publications for web training, case studies for actual accidents and their prevention. 

http://www.buildsafe.com/resource/trench/trench.htm  
Information and resources for excavation safety and hazards, accident analysis and alerts from NIOSH, Construction Safety Council and the construction industry.

Quiz

Once you finish studying the above course content, you need to take a quiz to obtain the PDH credits.

DISCLAIMER: The materials contained in the online course are not intended as a representation or warranty on the part of PDH Center or any other person/organization named herein. The materials are for general information only. They are not a substitute for competent professional advice. Application of this information to a specific project should be reviewed by a registered architect and/or professional engineer/surveyor. Anyone making use of the information set forth herein does so at their own risk and assumes any and all resulting liability arising therefrom.