You can analyze it by infrared spectroscopy and elemental analysis.  

Ref: 

Study on preparation and fire-retardant mechanism analysis of intumescent flame-retardant coatings

Jun-wei Gu; Jun-wei Gu;Guang-cheng Zhang;Guang-cheng Zhang;Shan-lai Dong

Shan-lai Dong;Qiu-yu Zhang;Qiu-yu Zhang; Jie Kong;Jie Kong

Surface and Coatings Technology 01/2007; DOI: 10.1016/j.surfcoat.2007.03.020

I think you can use TPP apparatus to expose the test sample and then observe the changes using material analysis approaches, such as SEM, and the above suggested by Maddali. You can also use cone calorimeter to expose the sample.

Dear Maddali,

I appreciated your kinds

Dear Yehu Lu,

I appreciated your kinds