The Important "Adjacent Area"

When it comes to the topic of excavation safety there is a specific meaning for the term “adjacent area”. Picture the area around an excavation that is equivalent to the depth. That is the “Adjacent Area”.?In the world of excavation safety that area is sacred. But that doesn’t mean we can’t put anything there or can’t work in that area, it just means we have to respect that area and observe some very real limitations and safety concerns.

The reason that there is not much discussion about this important topic even though it is referenced in several places in the standard and in tabulated data, is that it is defined in the OSHA Excavation Standard in only one place. That place is Appendix C (Timber Shoring) in subpart P. Since most people do not have a need to use timber shoring, they find no need to consult that part of the standard. But the “adjacent area” is truly a significant concept.

The “Adjacent Area” is described in Appendix C because there is a tight limit on how much of a surcharge load can be placed in the adjacent area when using Appendix C to construct a timber shoring system. It may come as a surprise that Appendix C only allows a two-foot-high spoil pile (or 20,000 lbs. of equipment) in this adjacent area. The reason is that the surcharge loading in the adjacent area results in increasing pressure on the installed shoring system. In other words, the downward pressure of the surcharge loads adds to the lateral earth pressure on a protective system. Too much lateral load can cause a timber shoring system (or any protective system) to fail.

Note that some manufacturer’s tabulated data for shoring or shield equipment has a limit of a three-foot-high spoil pile or a limit of 36,000 lbs. in the adjacent area.

The adjacent area is also referred to as the “area of influence” and there are other important considerations. For example, in 1926.651 (a) Surface Encumbrances, it states that all surface encumbrances must be supported or removed to safeguard employees. This regulation is directed at trees, boulders or any structure that is in the adjacent area which might become unstable and fall into the excavation. We could add sidewalks, walls, utility poles, signs and sign bases, vaults, etc. to this list. So, if someone is wondering if they should be concerned about either the weight or stability of an object near the excavation, a simple test is to check to see if the object is within the adjacent area.

There is an additional item of concern with regard to this topic, and that has to do with underground utilities that might be located within this adjacent area. For example, if we excavate in an area and there is a parallel utility within the adjacent area, we have to take special precautions to make sure that the existing underground installation is not going to move. One way to do that is by installing shoring equipment with the excavation process to maintain pressure on the trench walls to prevent any soil movement.

Finally, remember that there are times when job circumstances require the expertise of a registered professional engineer. One of these situations could include challenges in the adjacent area such as surcharge loads that exceed the limits of a particular protective system, or if there are structures which could be damaged or compromised. This is one reason why the designated competent person needs to be able to recognize existing and predictable hazards and should be adequately trained in safe excavation work including the application of appropriate protective systems. This is also an example when the services of a trench safety representative could offer practical guidance when selecting an adequate protective system.

For more information on this and other excavation safety issues we refer the reader to “Trench and Excavation Safety By the Book”. It is available for only $39.00 at www.trenchandexcavationsafety.com