I'm in awe of tunnels. How do they construct giant tubes under mountains, lakes, rivers and oceans? How long does it take? How many people are needed to build a tunnel and what are their jobs? Why don't workers suffocate when they're working underground? And why go below ground? The quick answer: because life above ground is congested.

May 4-15, 2014 is North American Occupational Safety & Health Week (NAOSH). To celebrate and increase awareness of occupational safety and health to workers around the world, we're profiling the Detroit-Windsor Tunnel, the only vehicular underwater tunnel that crosses international borders (the United States and Canada) in the entire world ? providing a rapid North American commerce conduit.

"The Detroit-Windsor tunnel is an immersed tube which is constructed by digging a big trench on the river or sea bottom, then placing a tunnel structure on the bottom of the trench segment by segment, connecting these segments together to form a completed tunnel, then filling the trench to cover the new structural tunnel," explained consultant and historian Harvey A. Parker.

While they're not architecturally elegant like bridges, tunnels are fascinating in their engineering and the dangers that lurk underground.

In the 1870s, ground was broken for a tunnel under the Detroit River, but a pocket of hazardous gas ended the project when workers were 135 feet out under the river. This gas leak made workers so sick that none of them would work again, so the project was scrapped. Ever hear the expression "canary in a coal mine?" Tunnel builders also sent canaries down to detect underground gases. Invented in 1815 by Sir Humphry Davy, Davy lamps provided a test for the presence of gases such as methane and hydrogen sulfide. If flammable gas mixtures were present, the flame of the Davy lamp burned higher with a blue tinge. Using shovels and rail cars to remove the earth, workers known as "muckers" or "sand hogs" would work eight hours in a tunnel, and then spend four hours decompressing ? otherwise they'd get what divers refer to as "the bends." Cave-ins and flooding were not uncommon.

Can you imagine that kind of backbreaking labor in cold, dark and confined spaces? Bottom line? Tunnel building is hot, dirty, and dangerous work.

Despite the opinion of scientific experts that anyone using the tunnel would die of carbon monoxide poisoning, a Windsor Salvation Army Captain, Fred W. Martin, pursued the dream of a Detroit-Windsor tunnel which was "fueled" by the growth of the automotive industry. In 1926, a New York engineering firm determined that a tunnel would be both feasible and profitable, which enabled Martin to secure financial backing from a group of Detroit bankers.

This was a major engineering endeavor for its time. Probably the most dramatic part of the tunnel's design and construction was the fabrication, launching, towing, and sinking of 9 enormous steel tubes ? the underground section of the tunnel.

Key Facts:

• Tunnel construction began in 1927.
• The tunnel was completed in 1930.
• The tunnel is jointly owned by the cities of Windsor, Ontario and Detroit, Michigan.
• The tunnel is 5,160 feet in length and cost $23,000,000 to construct.
• More than 500 laborers were employed during its construction.
• The tunnel rests 75 feet below the surface of the Detroit River.
• About 12,000 vehicles pass through the tunnel daily. So that drivers and workers are breathing in fresh air, 1.5 million cubic feet of fresh air is pumped into the tunnel every minute.

Tunnel Construction and Visual Communications   

There are two separate phases for signage during construction and post construction. During construction there are more hazard signs such as electric shock, falling rock, and exit locations. Safety equipment locations and standard OSHA signs are required. Depending on the type of tunnel there is some signage in fluid (sewer, water) conveyance tunnels. For transit and highway tunnels there are signs identifying firefighting equipment, exit locations, distance to exits, and call boxes for fire police emergency.

Russell is a senior engineer manager with Parsons Brinckerhoff (PB), with more than three decades of experience in the design, inspection, evaluation, and rehabilitation of tunnels, underground structures and deep foundations, including Portland, Oregon's light rail tunnel under the zoo. To do a better job with safety and visual communications, we need to study more about human cognition, networking and how important information gets sent and comprehended, Also, more tunnel projects around the world are really multi-language worksites. This means that signage and communication has to be in many languages.

So what's happening in the world of tunneling today?

• Tunnels are getting bigger (larger diameter)
• Hard rock and soft ground tunnel-boring (TBM) technology
• Advanced tunnel waterproofing systems
• Work has been done to understand fire in tunnels ? both train and vehicular ? and this has resulted in changes to design.
• Advances in grout materials and technology allow contractors to make the ground stronger and less permeable
• When water is a problem, either pumps or and well systems work to keep the ground dry.
• Remote-controlled pipe-jacking operations provide continuous support to the excavation face by applying mechanical or fluid pressure to balance groundwater and earth pressures.
• 3D laser scanners and other networked sensor systems quickly survey and evaluate underground conditions and stability

Driven by commerce, culture, and cost, tunnels all over the world are underway. The most exciting tunnels are crossing continents and powering through the Swiss Alps. While each new project seems to grow in price and complexity, engineers and designers are also working to improve safe conditions for workers by installing high-visibility lighting, energy efficient ventilation systems, electricity, and elevators.

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