June 1, 2007
Whether you are working 4 ft or 40 ft below ground, safety should always be on everyone’s mind. Simply put, anytime you work below the earth’s surface, you are entering an area that has no compassion, has no sense of humor and does not tolerate mistakes. In this type of environment, specific steps must be followed to assure each worker is protected at all times. In many cases, modern trenchless technology techniques allow contractors the ability to stand above ground while performing work below ground. The key benefit from utilizing the various trenchless technology methodologies in the market today is the ability to inspect, install, repair, modify, remediate and replace underground utilities without the need to excavate or install an open trench. On specific jobs, however, the open trench system is used in conjunction with trenchless technology systems. In situations like this, a review of safety issues might be helpful. As anyone who works around any type of excavation knows, no matter what system you choose to use, the most important thing to have on any excavation project is a well trained “Competent Person.” OSHA defines the Competent Person as “One who is capable of identifying existing or predictable hazards in the surroundings or working conditions which are unsanitary, hazardous, or dangerous to employees, and who has authorization to take prompt corrective measures to eliminate them. The Competent Person must have specific training in and be knowledgeable about, soil analysis, the use of protective systems and the requirements of this standard.” In cases where an open trench will be utilized (such as a complex bore, pipe jacking or pipe bursting project), a well thought out “site specific trench safety plan” can greatly reduce the time the project will take to complete and add improved safety to the project. These plans are designed and stamped by state-licensed engineers who review the soil and bore logs, loads created by adjacent structures and project requirements, calculate the specifics loads the excavation may see and select a specific shoring or shielding plan for the particular project. The costs for a site specific trench safety plan can run from a few hundred dollars (most instances) to more than $20,000 in some extreme cases.
Trench Shields
The most common product used in typical open trench systems is trench shields, which are static devices used to protect workers in an excavation. Some of the advantages to using trench shields are the wide variety of sizes of pre-manufactured trench shields, a large existing national rental fleet of trench shields in most markets and industry accepted “tabulated data” that makes choosing the right trench shield for a project a simple process. In today’s complex project environment, many trenchless contractors use trench shields (also called trench boxes) to build a temporary but secure below ground work zone (for example bore pits and receiver pits). When using a trench shield in these types of applications, the length and depth of the trench must be opened and sized to match the length and depth of the trench shields to be installed. In some cases, where trench depths are below 10 ft, multiple trench shields will be stacked to achieve a properly protected excavation. Depending on the size of the trench shield(s) selected for a project, the trench shield weights may exceed the lifting capacity of the support equipment found on a typical trenchless project. In certain deep excavations, cranes may be required to lift, set and ultimately remove the trench shield(s) from the excavation. Rigging and lifting of any heavy object is always a serious safety concern. Open trenches also create various challenges in tight suburban or intercity projects in handling of the spoil excavated from the trench and staging the necessary equipment to not only secure the trench but to perform the planned work. In addition, all open trenches that are not properly shored are prone to collapse or cave in, which can create significant dangers and damage to surrounding structures and personnel. The use of large trench shield(s) can sometimes be the most difficult part of a trenchless project. As discussed above, the rigging and lifting systems required to safely move the trench shield(s) should be properly sized and designed by a qualified lifting and rigging expert. The weight of the trench shield(s) and the dangers associated with moving large steel structures can create several potentially dangerous scenarios if the proposed “lift” is not well planned and executed. One of the services a trench safety vendor should offer is assistance in product and system selection. Through discussions with the contractor and project managers, the vendor can help gather as much data as possible to evaluate the most safe and productive system for each project. While a trench safety vendor is not typically an engineering firm, and is never the ultimate responsible or deciding party as to which system a contractor should use, their expertise and experience can be beneficial to the contractor in the final decision-making process. For example, one of the most compatible systems for trenchless applications in the market today is a slide rail. In most cases, this system can eliminate many of the safety and productivity issues found when you use trench shields. A slide rail system, by design, is a modular component system that is used in place of driven tight sheeting or built in place timber shoring systems. The modern slide rail system is a “dig and push” system that allows quick installation of a typical pit or linear system in usually one day. This dig and push feature, in many cases, can greatly reduce the risk of cave in and trench collapse that is common in open trench methods. This benefit adds a great deal of safety for adjacent structures and personnel. Another benefit of a slide rail is that since the modular components of the system are designed for a wide range of applications, many unique designs can be installed quickly and usually with one reasonably sized excavator. In many instances, the individual slide rail components are lighter and easier to handle than large trench shields. When properly designed, slide rail systems offer unequalled pipe clearance and large free span work zones. Slide rail systems also offer unique flexibility when you encounter crossing utilities or unforeseen underground obstacles. Various slide rail components have been designed to allow the user to safely and quickly install protective systems around such obstacles and crossing utilities to allow the project to continue as planned with minimal disruption.
Competent Person Training
As stated earlier, the most important thing to have on any excavation project is a well trained Competent Person. To keep abreast of the many changing regulations and new products and techniques, most trench safety industry veterans strongly recommend recurring annual Competent Person training programs. There are many varying opinions on what constitutes an adequate Competent Person training class. It is generally accepted by most industry veterans that a three to four hour “tail gate” discussion type of class does not usually offer the in-depth education required to be a fully trained Competent Person and does not include the various training aids you would receive in a six- to eight-hour formal training session held in a classroom environment. In addition, many of the more progressive trench safety training firms will offer Competent Person classes in Spanish along with all necessary training aids, manuals and certificates. Safety in and around any excavation or open trench, is a complex issue. When properly researched, selected, designed and installed most trench safety products will deliver significant productivity and safety enhancements. Only by taking the time to perform an in-depth review of the entire project, securing the proper engineering assistance and surveying the many danger areas on any project can one truly achieve a safe working area. Ron Chilton is president and CEO of National Trench Safety LLC, Houston.
As published in the June 2007 Trenchless Technology Magazine