excavation
trench
serious
working outside of trenchbox
instruction of employees in excavations
undermining sidewalks
loose soil or rock
daily inspection by competent person
29 CFR § 1926.652(a)(1)
29 CFR § 1926.21(b)(2)
29 CFR § 1926.651(i)(3)
29 CFR § 1926.651(j)(1)
29 CFR § 1926.651(k)(1)