Final answer:
The grating sound heard during equal inspiration/exhalation suggests the presence of pleural friction rub, which is typically caused by inflammation of the pleura.
Step-by-step explanation:
The grating sound heard during equal inspiration/exhalation suggests the presence of pleural friction rub, which is typically caused by inflammation of the pleura (the lining of the lungs). In this case, the possible airway burns from the structure fire may have caused inflammation and irritation of the pleura. This can lead to the development of pleurisy, which can cause a grating sound during breathing. Therefore, the correct answer is C. Fluid accumulation in the small airways.