Back in 1964 President Vargas Works was the only place in the country which processed single base powder for the Brazilian Armed Forces. Then its industrial activity was quite strong and around 4:45 a.m. of 23rd September an intense decomposition of nearly 15 ton of that material took place in one of the production lines workshops. The consequences of this explosion were the destruction and extensive damage to the workshops around its epicenter. At that time pictures of all affected buildings were taken and their damages fully described. This led to the present work which consists in the evaluation of the TNT equivalent charge of the explosion using the concept of damage category developed by UK engineers based on the WWII damaging bombing data. (C) 2008 Elsevier B.V All rights reserved.