Page 429 - Trenchless Technology Piping Installation and Inspection

Planning and Safety Considerations for Trenchless Installation Methods 379

9.3 Trenchless Safety Considerations
There is no doubt that a safe project starts in the planning and design
phase. Considering trenchless projects are “engineered” jobs with more
skilled and trained workers than conventional open-cut construction,
they provide more opportunities for safe operations. Construction
traditionally has been one of the most dangerous types of work, third
after mining and agriculture.
In 1970, U.S. Congress passed the Occupational Safety and Health
Act (OSHAct). This legislation became law on April 28, 1971, and it
had a significant impact on the construction industry. According to
OSHAct, the employer has an obligation to provide a place for
employee that is free from recognized hazards and meets the OSHA
standards. The employees must comply with the rules, regulations,
and standards applicable to their type of work.
While the use of trenchless technology is steadily increasing,
many municipalities, pipeline and utility owners, continue to
award construction contracts to companies using open-trench
method; a method that potentially can be hazardous for both work-
ers and the general public. In fact, the OSHA excavation standard
was revised in 1989 because excavating is one of the most danger-
ous of all construction operations. More workers are killed or seri-
ously injured in and around excavations than in most other phases
of construction work. Once a trench is opened, it requires the use of
protective systems, such as shoring and trench boxes to prevent
cave-ins and trench collapses. The trenches for sewer, water, and
other pipelines represent the greatest concern for cave-ins because
of the excavation in urban environments. Sewer lines are typically
installed at depths of 8 to 15 ft, with some installations as deep as
40 ft. Water lines are typically installed at depths of 4 to 5 ft, and
sometimes deeper installations are normal. Gas lines, electric, tele-
phone, and other conduits and cables tend to be placed in shallow
trenches of about 2 ft deep, but most of the times they require a
minimum of 3 to 4 ft of cover, depending on the location and regu-
latory considerations.
According to data from the U.S. Bureau of Labor Statistics,
between the years of 1992 and 2002, 384 construction workers were
killed by trenching-related injuries, an average of 35 per year (see
Table 9.2). In most cases, a cave-in was the main event leading to the
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death. Depending on the soil type and moisture content, one yd of
soil can weigh between 3000 and 4000 lb.
Compared to trench excavation, trenchless safety is negatively
affected by several factors, such as
• Lack of formal safety training: Usually workers and operators
switch back and forth between jobs that may include both tra-
ditional open-cut and trenchless work. Additionally, workers