A thesis from NTNU presents results of testing of four different loose wood fibre insulation materials with three different fibre structures (fibre length, thickness) and in once case a different level of PIN flame retardant (ammonium polyphosphate 4% or 9%).
In these results self-sustained smouldering combustion starts at a lower temperature in the wood fibre with higher APP, but then progresses more slowly. The author notes that APP is not typical of FRs used in cellulosic insulation material and that further work is needed to assess the impact of FRs on the start of and development of smouldering, and so on smoke emission and fire safety.
NTNU (Norwegian University of Science and Technology) thesis “The Development of Smouldering Combustion in Combustible Building Insulation Materials”, U. Jensen, January 2016, 86 pages https://brage.bibsys.no/xmlui/handle/11250/2385048