According to the illustration of a typical boiler furnace rear wall, which item number would best represent "insulating block"? Illustration SG-0003
Official USCG Answer & Rule Citation
Correct Answer: Option D — 7
In standard marine boiler refractory diagrams such as SG-0003, item 7 designates the backup insulating block layer positioned behind the dense firebrick face to minimize casing heat loss.
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