When raising steam on an idle boiler and the steam pressure has risen to about 5 pounds more than the pressure of the boiler already on the line, you can __________.

Correct Answer: Option D — put the boiler on the line

When raising steam on an idle boiler, it can be safely cut into the main steam line when its pressure exceeds the active header pressure by approximately 5 psi. This differential ensures smooth paralleling without reverse flow.