When must the atmosphere in an excavation be tested before workers enter, and what is the OSHA oxygen deficiency level?

1. Never; trenches always have safe air
2. When a hazardous atmosphere exists or could reasonably be expected (for example near landfills or stored chemicals) in excavations greater than 4 feet; oxygen below 19.5% is deficient
3. Only in excavations shallower than 2 feet
4. Only if the soil is classified as stable rock