Structure and Summary of Excavation Safety (1926 Subpart P)

The structure of Subpart P is interesting. One doesn’t have to dig deep (pardon me) to see the degree of thought and detail which, in my opinion, shows real genius.

Here is an overview of Subpart P with a brief explanation of each section. The purpose of this venture is not so much to extol the genius of the authors, although they deserve credit for their fine work. The intent is to provide an overview which is helpful when researching a topic, and to show the synergy of each section and the whole. The genius of the authors of subpart P should naturally be apparent.

I think we would miss the profound accomplishment if we only saw Subpart P as “a collection of safety regulations for excavations”, even though in its simplicity, that is exactly what we have. So, let’s look at 1926.650, .651, and .652, and the appendices, in order to appreciate each role and the combined effect.

1926.650 contains vocabulary that is important in the regulations. This is terminology that must be understood to get the full intent of the regulations that follow. These definitions also provide insight into basic excavation safety concepts. These are not regulations, they are definitions.

Here's a quick example: Sloping, by definition, prevents cave-ins. Shoring also, by definition, prevents cave-ins. Shields, however, by definition, do not prevent cave-ins, but they protect workers from soil that does cave in. The practical applications on this subject can tend to be lengthy, but I’ll only point out that in 1926.652 (g) we are instructed to keep the shield from shifting laterally, which could present a hazard, because shields are not designed to prevent cave-ins. Preventing lateral shifting is therefore done by maintaining a tight fit between the shield structure and the face of the excavation. Some shield manufacturers specify that preventing lateral shift can be accomplished by keeping the gap between the shield wall and the face of the excavation to no more than six inches. Larger gaps should be sufficiently back filled.

This is just one of many concepts that can be explored when looking deeper into the meanings of this vocabulary collection.

1926.651 addresses hazards, but for the most part these are not focused on cave-ins. These are about other issues such as hazardous atmospheres, the dangers in wet conditions, protecting employees from the dangers of underground installations, inspection requirements, etc.

1926.652 addresses the hazard of cave-ins. It begins by answering the question “when do I need to have a protective system?” then moves on to the legal protective system options. It also includes some protective system hazard warnings, such as described in the above example of the hazard of laterally shifting trench shields.

The appendices A through F are there to assist with the requirement just mentioned in 1926.652 (a) which states that we are to have an adequate protective system.

To use Appendix B (Sloping), Appendix C (Timber Shoring), Appendix D (Aluminum Hydraulic Shoring), we must first be able to get an idea of the soil stability. That is the purpose of Appendix A. Note: Appendix A is mentioned in most (if not all) manufacturer's tabulated data. But it's important to understand that we do not use Appendix A when using manufacturer's tabulated data because OSHA says so. We use Appendix A when using manufacturer's tabulated data because the manufacturer says to. That is an important distinction because when using a manufactured system, we are to follow the manufacturer's specifications, recommendations, and limitations. That would include how to classify soil. This is also a good time to point out that C-60 soil is defined and referenced in manufacturer's tabulated data, not Subpart P Appendix A. C-60 soil classification is legitimate because it is a part of the referenced specifications, recommendations, and limitations that end users are required to follow.

Moving on to Appendix E. This appendix simply shows some drawings of alternatives to timber shoring, which dates the standard somewhat. Timber shoring usage has steadily declined over the years. As a side note, the drawing of a stacked trench shield system appears to have the top shield inverted. It looks like it is positioned upside down. By the way, that practice is legal and safe as long as all safety precautions are met. The benefit of using the top shield upside down is that it lowers the spreader position which can greatly increase the excavator reach. Again, we must follow every safety precaution when using shields or stacked shields to ensure worker safety. That is one of the benefits of a good excavation safety competent person safety class. These safety precautions are essential.

Note: I would be interested in hearing from those who find Appendix E helpful in any other way, because I don't see much here for the modern-day excavators.

Appendix F contains a flow chart which can be very helpful to understand when protective systems are required, and the legal protective system options as outlined in 1926.652.

Hopefully this has been informative in understanding the various aspects of subpart P, and how they complement and complete each other. For more information on this and other excavation safety topics, please go to www.trenchandexcavationsafety.com

That website is where you can find “Trench and Excavation Safety by the Book”. It is a comprehensive reference guide covering excavation safety. The book also contains a copy of the federal register for subpart P which is the best commentary on what the excavation safety standard is all about. This book is the ultimate study companion for those who want to understand and even dig deeper into this important safety topic. The book price is only $39.00 which makes it affordable to provide one for foremen, safety personnel, sales reps and safety trainers. Thank you