To limit the probability that combustible wall and ceiling finishes will be used in an underground walkway, which could lead to fire growth and the spread of fire, which could lead to harm to persons.
To exempt interior wall finishes in underground walkways from the application of Sentence 3.1.13.2.(1), which would otherwise allow finishes with flame-spread ratings up to 150, on the basis that noncombustible finish materials are needed in these locations to protect persons during evacuation.