Subpart P Excavations/Definitions
Pic: Sent to me by a plumber years ago with a note---this saved a life and my company. Trenches collapse---that is what they do! Trench Shields protect---that is what they do!
Part 1 of 2
Greetings! Several weeks I concluded a few comments on "Accepted Engineering Practices". Just what it is and how OSHA would determine what it looks like should it need to do so.
Today I wish to note a few comments about "cave-in".
It may surprise you to know that the earlier version of Subpart P (1972), and its base foundation, the ANSI Excavation and Trenching Standard of 1958, did not contain a definition for "cave-in".
I think the reason may have been an assumption that everyone knows what is a "cave-in".
Our current version of Subpart P (1989), does contain a definition of "cave-in" as well as several other key concepts, such as "competent person".
In many respects, I think instructors also assume that we know what is a "cave-in". But do we?
I frequently ask this question: How much soil or rock must fall to constitute a cave-in? Most often---the one asked just stares at me.
Let's look at the definition:
Cave-in means the separation of a mass of soil or rock material from the side of an excavation, or the loss of soil from under a trench shield or support system, and its sudden movement into the excavation, either by falling or sliding, in sufficient quantity so that it could entrap, bury or otherwise injure and immobilize a person. 1926.650(b)
In the effort to squeeze what at one time was a 7-8 hour presentation into a 4 hour presentation, while the definition is mentioned---it is given little attention.
In my opinion---this may be a critical mistake and a missed opportunity to clarity an important reality.
First, but not the most important thing: Note the portion of the definition regarding "the loss of soil from under a trench shield or support system".
During the 80's, I would sometimes get asked by contractors does my literature on trench shields mention how high off the invert they could bench the shield?
It may be hard to believe, but since the standard, both the old and new, had a 5 foot mandatory requirement for a protective system to be used---some thought that the bottom five foot of a trench must be safe. Accordingly, they benched their shields 6-9 feet above the invert. Their thinking: If the standard does not require a protective system until you are five feet in depth, then your sloping begins at 5 feet (hard or compact soil) or your shield and/or support system need not be employed.
Many still think that the 5-foot rule is based on soil and/or the height of a man. Just ask the question when you are training.
In truth, the 5-foot rule was a compromise made between labor groups who wanted the mandatory rule to start at four feet---and another large group of stakeholders (cemeteries) who wanted a 6-foot rule. The 5-foot rule is a compromise!
Please see Part 2