Excavation and trenching

0:00 Intro

Excavation and trenching, for the CHST exam. Every rule and number here is cited to its primary source, on screen.

0:09 Learning objectives

In this lesson, you'll learn to: state the depth thresholds that trigger each rule, explain the competent person's inspection duties, classify soil and match it to a maximum slope, and apply slope math to size a cut.

0:25 Two depths to memorize

Two depth thresholds drive most exam questions here. Protection is required, except entirely in stable rock, or under 5 feet with no sign of cave-in per a competent person. At 4 feet or more, trench egress is within 25 feet of lateral travel.

0:48 Underground installations

Test first if deeper than 4 feet and a hazardous atmosphere could be expected. Underground utilities come in three stages. Before opening, estimate locations and contact owners. No reply in 24 hours (unless law requires longer), or no exact location? Proceed with caution, using detection equipment or other acceptable means.

1:16 Competent person duties

Approaching them, determine the exact location by safe and acceptable means. While open, protect, support or remove them as necessary. The competent person carries the inspection duty. Inspect daily: before work starts and as needed throughout the shift. Also inspect after every rainstorm or hazard-increasing occurrence.

1:44 Appendix A soil classification

All these inspections apply when exposure can be reasonably anticipated. If hazards are found, remove exposed employees until precautions are taken. The competent person also monitors water removal equipment. A competent person classifies each deposit, using at least one visual and one manual analysis. 5 tsf or greater, but never if fissured, vibrated, previously disturbed, or in certain layered or other less-stable conditions. 5 tsf, or granular soil like angular gravel and silt.

2:31 Table B-1

5 tsf or less, sand or gravel, or submerged or freely seeping soil. A layered system takes its weakest layer, unless a more stable layer lies under a less stable one. Default: no steeper than 1½ to 1. Otherwise Table B-1 gives the steepest slope under 20 feet deep. Stable rock may be vertical. Type A is three-quarters to one, Type B one to one, Type C one and a half to one.

3:01 Worked example: slope

Short-term, open 24 hours or less, Type A at 12 feet or less may be one-half to one. Over 20 feet, a registered professional engineer designs it. Run equals depth times the horizontal part of the slope.

3:19 On the job

Type B is 1 to 1, so run equals depth times 1. 8 feet times 1 is 8 feet per side. 5 is 12 feet. Weaker soil means a flatter slope. You're the CHST on a utility job. Overnight rain hit an open trench over 5 feet deep. First, the competent person inspects after the rainstorm, before work starts.

3:47 Common exam traps

If a hazard is found, exposed employees are removed until precautions are taken. Over 5 feet, and not entirely in stable rock, the exemption is gone: a protective system, plus egress within 25 feet of lateral travel. Now, six traps that catch people on exam day. One: under 5 feet is exempt only with no sign of cave-in. Two: trench egress starts at 4 feet, within 25 feet of lateral travel.

4:23 Recap quiz

Three: inspect before work, as needed, and after every rainstorm. Four: a competent person classifies soil. Five: short-term Type A, 12 feet or less deep, may be one-half to one. Six: with distress, cut back at least one-half to one flatter. Question 1. Maximum simple slope, Type C under 20 feet deep? A: three-quarters to one. B: one to one. C: one and a half to one. D: one-half to one. C. Type C is one and a half to one, 34 degrees. Question 2. A 6-foot trench in sound soil, not stable rock. A: protection required. B: exempt if no cave-in sign. C: exempt, under 8 feet. D: no egress. A. The exception covers only excavations under 5 feet, or stable rock. Question 3. Owners cannot locate lines in 24 hours; law requires no longer. A: wait indefinitely. B: proceed with caution, detection equipment. C: dig unprotected. D: skip the request. B. Proceed with caution, using detection equipment or other acceptable means. Want to see where you stand on every CHST domain? com.

25 questions, free, no card. You get a readiness score for each CHST domain.