Plumbing is the trade where the safety numbers are depths and distances rather than a single trigger height, and where getting one of them wrong is how a routine dig becomes a fatality. Excavations need a protective system at 5 feet under 1926.652(a)(1), unless the excavation is entirely in stable rock, or it is under 5 feet AND a competent person has examined the ground and found no indication of a potential cave-in. Both exceptions matter and both get quoted loosely. A trench needs a stairway, ladder or ramp within 25 feet of lateral travel once it is 4 feet deep under 1926.651(c)(2), and that same 4-foot depth is where atmospheric testing kicks in wherever a hazardous atmosphere could reasonably be expected, which on sewer work it always can.
Hot work is the other number set. A fire watch is required whenever appreciable combustible material sits closer than 35 feet to the point of operation. The duration is where template writers slip: general industry says the watch is maintained at least a half hour after the work stops (1910.252(a)(2)(iii)(B)), but the construction rule (1926.352(e)) gives no number at all, it says only "a sufficient period of time". This checklist states both, and treats thirty minutes as the defensible floor rather than pretending construction has a stated interval it does not have.
The document itself is a daily verification list, not a hazard analysis. That distinction matters because contractors are often told to produce "a safety document" and end up with a risk assessment that nobody reads on the morning it would help. A risk assessment scores hazards on a matrix once per project; a method statement writes out the safe-work sequence for one job. This is the short list a crew works before the first shovel, and it has a stop-work gate, so marking the trench item as an issue prints "Stop work, do not start" at the very top of the export, above the company block, rather than burying it on page two next to the tick that said the truck had a fire extinguisher.