Environmental Health News

Conference Highlight: The Art & Science of Safe Tunneling

Return to Spring/Summer 2013 issue

Course participants tour the State Route 99 tunnel boring machine at Alaska Way

Course participants tour the State Route 99 tunnel boring machine at Alaska Way.


Elizabeth Sharpe.

More than a century ago, a tunnel deep in the Cascade Mountains opened, linking the Great Northern Railway between Minneapolis and Seattle in an attempt to avoid problems on the original line caused by heavy winter snowfalls. The earth was dug out with a steam-powered mucking shovel aided by crews of workers with hand shovels. Ventilation was later added to the original tunnel because it had a build-up of fumes from train locomotives. Recent years have seen increasing sophistication in the equipment and methods used to build and safeguard tunnels for transportation and other purposes. Considerations involved in constructing safe tunnels have also grown.

The art and science behind tunneling construction safety was the focus of a course offered at the University of Washington, May 29–30, and sponsored by our Northwest Center for Occupational Health & Safety.

“The purpose of this course was to discuss the scientific basis for health and safety best practices, learn about regulations, and provide an opportunity for owners, contractors, regulators, and health and safety professionals to talk about strategies for building tunnels in the safest way possible,” said Course Director Nicholas Reul, a postdoctoral fellow in the department and physician in the Occupational and Environmental Medicine Clinic at Harborview Medical Center.

More than 125 people participated in the course, which included a tour of the State Route (SR) 99 tunnel boring machine. The machine—which is nearly as tall as a five-story building—will burrow two miles along the waterfront. The SR 99 tunnel corridor will replace the aging Alaska Way Viaduct.

Speakers addressed dangers and necessary precautions in tunneling, among other topics. “A fair number of tunnels cave in, catch fire, blow up, and kill people,” said Stephen Hart, a safety engineer for the Mining and Tunneling Unit of California’s Department of Occupational Safety and Health. In his long career in the industry, there have been 57 worker fatalities in California. Hart presented on the need for regulations, more frequent inspections, and updated standards.

Use of tunnel boring machines puts some workers under pressurized conditions, similar to conditions faced by deep-sea divers. Decompression sickness or “the bends” can result in injury, even death, if not treated quickly. According to John Freiberger (Duke Center for Hyperbaric Medicine and Environmental Physiology), fatality from pressure can occur between 26.4 and 32.4 pounds per square inch gauge. Dive tables for deep-sea divers set limits on exposure to pressure and ascent speed. In tunneling, similar tables are available and hyperbaric or decompression chambers are required on site to treat decompression illness.

The risks also include workers’ exposure to diesel exhaust, carbon monoxide, and silica in soil and rock. Senior Lecturer Martin Cohen and Professor Emeritus Michael Morgan talked about regulations, sampling methods, and controls to better protect workers.

The pending release of a one-hour safety training video for workers involved in tunnel construction (H.O.L.E. - Hazard Observation & Labor Education) was also announced. The video was created by Associated General Contractors of Washington, Anita Johnson (Sound Transit), Mike Warren (Northwest Laborers-Employees Trust Fund), and Integrity Safety Services and funded by the Washington State Department of Labor & Industries Safety & Health Investments Projects (SHIP).

Return to Spring/Summer 2013 issue