OSHA Soil Classification (Type A, B, C)
OSHA's three-tier system for rating how stable excavated soil is, Type A being the most stable, Type C the least, which determines what kind of protective system, sloping, benching, shoring, or a trench box, a given excavation legally requires.
Why it matters
The same trench depth can be safe or deadly depending on the soil type, since Type C soil, like loose sand or previously disturbed ground, can collapse far more easily and with far less warning than stable Type A clay. A competent person has to classify the soil correctly before deciding what protection the trench actually needs.
On a real project
A competent person evaluating a trench finds the soil has been previously disturbed and has water seeping into it, both signs that rule out classifying it as the more stable Type A, so the crew sets up a trench box rated for the less stable classification instead of relying on sloped walls alone.
Who this matters most to
A Safety Manager, acting as the jobsite's competent person, classifies soil on every excavation before crews are allowed to enter it.
Where this goes wrong
A crew assumes soil is stable Type A because the excavation looks similar to one they dug the week before, without actually testing it. The soil turns out to be unstable Type C, and the trench wall collapses under a load it was never classified to resist.