Ceilings of rooms and circulation spaces (but not including protected stairways) may incorporate thermoplastic lighting diffusers if ALL of the following provisions are observed:
a. The surfaces of the void space above the suspended ceiling comply with the general provisions that apply to the space below the suspended ceiling
b. TP(a) diffusers can be used without restriction
c. TP(b) diffusers are restricted as detailed below.
Read More