Excavation Safety Definitions and Concepts

Subpart P (Excavations) begins with some definitions. These definitions are important because they define words that one will encounter in the regulations that follow (1926.651 & 1926.652). After all, the competent person needs to understand key words in the regulations to fully understand the regulations. That’s kind of basic, right?

What is cool is that the referenced definitions go beyond just defining terminology. They also provide insight into some key concepts that are critical to understanding the world of excavation safety. Some of these concepts are subtle, others jump right off the page. Let’s look at just a couple and I encourage the reader to study the other definitions, looking for concepts and applications.

Excavation – Any man-made hole in the ground. Subpart P applies to all excavations, regardless of size or shape.

Trench – A unique excavation because it is deeper than it is wide. Interestingly, this word appears only two times in the regulations. The most consequential is the requirement that egress be provided within 25 feet of workers in trench excavations that are four feet or deeper. Putting it another way, the 25-foot rule does not apply to those excavations that are not trenches.

The important point here is not just knowing this as if it were trivial information, but understanding the reason why there are egress rules for trenches that do not apply to non-trench excavations. This issue has been discussed in previous articles, so we’ll not go into it at this time. The reader can easily find these past articles or simply contact me at [email protected]. I’ll send the article.

Three other extremely important words that are defined are sloping, shoring, and shields.

Note that in the definition of sloping and shoring it specifically says, “prevent cave-ins”. However, in the definition of shields it doesn’t say “prevent cave-in”, it says it’s a “structure that is able to withstand the forces imposed on it by a cave-in and thereby protect employees within the structure”.

One quick take-away. Shields by design do not prevent cave-ins. Used correctly, they have the strength to protect workers from soil that caves in. This means the shield must be installed in such a way that when the soil caves in and hits the shield, it doesn’t move laterally.

From the regulations in 1926.652 (g)(1)(ii) “Shields shall be installed in a manner to restrict lateral or other hazardous movement of the shield in the event of the application of sudden lateral loads.”

If the shield moves laterally, workers in the shield could be caught in between the moving shield wall and an object inside the shield. Yes, this can and has happened. Shields cannot be manufactured in a way to restrict lateral movement, so that is the responsibility of the end user. This simply means that we do not leave a large gap between the shield wall and the vertical wall of soil.

OSHA does not specify what that gap width limit should be. The direction is simply to prevent lateral shift. To prevent lateral shifting some manufacturers specify no more than a four inch or a six-inch gap. I’ve seen some tabulated data that specifies “no gap”.

It is my opinion that due to the weight of a trench shield, some believe the shield cannot be moved if hit by soil. This is a huge misconception. The moving soil will certainly cause a shield to move laterally, placing the workers in harm’s way. That is why minimizing the gap as discussed is so important. It may take a few extra minutes to fill a large gap, but it is essential to prevent said lateral shifting.

I hope that readers are encouraged to review all the definitions, looking for concepts that are educational to the end that it will help create a safer workplace.

For more information on this and other excavation safety topics please visit www.trenchandexcavationsafety.com

There you’ll find Trench and Excavation Safety by the Book. It is an excavation safety reference guide and contains a copy of the federal register. The best part is that the cost of this book is only $39.00

Keep learning my friends.