SC Pipelines Practice Questions - South Carolina Pipelines Contractor Examination Exam

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A 6-foot-deep pipeline trench is near a live gas main. When must the atmosphere in the excavation be tested, and at about what concentration does natural gas first become ignitable in air?

Never; trenches are always safe once they are sloped Only after a fire starts; natural gas ignites at 50 percent in air Only if the trench is deeper than 20 feet; natural gas has no LEL When a hazardous atmosphere could reasonably be expected (excavations more than 4 feet deep), before employees enter; natural-gas LEL is about 5 percent by volume

Correct Answer:

When a hazardous atmosphere could reasonably be expected (excavations more than 4 feet deep), before employees enter; natural-gas LEL is about 5 percent by volume

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