What does the doctor mean when he says, "the world collapsed in timber and debris"?

The poem ‘A Doctor’s Journal Entry for August 6, 1945’ by Vikram Seth is an account of the horrific incident of bombings of Hiroshima in 1945. It is written in the form of a journal entry by a doctor. These entries were a record of the panic stricken lives that people in Hiroshima were living. The journal entries are written in a language used in daily lives. It gives a clear picture of the bombings and how no one was able to comprehend what had happened all of a sudden. The poet has made use of exaggeration to give a vivid picture. The roof, the walls and everything around had collapsed in timber and debris. Only thing visible was dust all around. The atmosphere was of horror and panic.