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Excavation, Trenching JeShoring Safety and the OSHA Excavate .> Standard - ... Page 1 of 3 <br /> a <br /> CHAPTER ER FOUR. PROTECTIVE SYSTEMS <br /> Protective systems are methods of protecting workers from cave-ins of material that can fall or roll into an <br /> excavation,or from the collapse of nearby structures.As mentioned in earlier chapters, if an excavation is <br /> less than 5 feet deep, OSHA does not require a protective systems unless the competent person sees <br /> signs of a potential cave-in.(It is important to remember that a wall collapse in a trench four and 1/2 <br /> feet deep can still have serious results!)For trenches between 5 feet and 20 feet deep, shoring and <br /> sheeting,shielding, sloping and benching are all acceptable protective measures. It is up to the <br /> planners of the construction project and the competent person on site to determine which systems will <br /> work best. If an excavation is greater than 20 feet deep,a registered professional engineer must <br /> design the protective system. <br /> Shoring systems are structures of timber, mechanical,or hydraulic <br /> systems that support the sides of an excavation and which are <br /> designed to prevent cave-ins. Sheeting is a type of shoring system <br /> that keeps the earth in position. It can be driven into the ground or <br /> work in conjunction with a shoring system. Driven sheeting is most <br /> frequently used for excavations open for long periods of time.Another <br /> type of sheeting, in which plates or shoring grade plywood (sometimes <br /> -- called Finland form)is used in conjunction with strutted systems such <br /> as hydraulic or timber shoring. These strutted systems are also <br /> referred to as active systems.The most frequently used strutted <br /> system involves aluminum hydraulic shores which are lightweight, <br /> re-usable and installed and removed completely from above ground. <br /> A shield, also known as a trench <br /> box, is another common protective <br /> system used by contractors.Trench boxes are not designed to prevent <br /> cave-ins, but rather serve to"shield"workers within the structure <br /> should a cave-in occur. This is an excellent choice when placing ` <br /> continuous installations, as in pipe laying The box is placed in the <br /> trench and dragged along with the progress of the work.A few <br /> important points about shields: <br /> • Personnel should be out of the box and above ground when the <br /> shield is being moved.You could be caught between the k <br /> moving box and fixed object(s); <br /> ' • The top of the shield should extend at least eighteen (18) <br /> inches above the level of any materials that could cave or roll <br /> into the trench; <br /> • Some shields are designed to be stacked, one on top of another. Never stack shields that are not <br /> designed for that purpose, and do not stack shields from different manufacturers, as they may not <br /> be compatible. <br /> • The forces of a cave-in can literally push a box sideways,causing a crushing hazard. After a box is <br /> positioned for the work,the voids between the box and the trench wall should be filled with <br /> excavated material to prevent displacement caused by a cave-in. <br /> • Shielding should always be used according to manufacturer's tabulated data. <br /> With both shoring and shielding,workers are only protected as long as they stay within the confines of <br /> the system. <br /> Sloping and benching are another means of protecting workers from cave-in hazards. Sloping is a <br /> http://www.afscme.org/health/excav05.htm 8/25/2005 <br />