A furnace wall in which there are open spaces around the brick as a result of firebrick shrinkage, is __________.

Correct Answer: Option C — loose and should be repaired

Refractory shrinkage creates open spaces and gaps in furnace walls, compromising structural integrity. Under standard marine boiler maintenance guidelines per 46 CFR, loose brickwork must be promptly repaired or repointed to prevent hot gas bypassing and subsequent casing damage.