The more liquid the soil, the more you need to protect yourself against cave-in. Changing weather conditions Hardpacked soil can become soupy and unstable after rain. Trenches which are safely sloped or shored in dry weather can become deathtraps when it's wet. Thawing soil can also become unstable quickly. Heavy loads in area Don't park heavy equipment next to a trench.
Every trench is a possible trap for hazardous atmospheres.
When in doubt, test and ventilate.