Timber can be made reasonably fire-resistant by

ANS:D - seasoning process

Wood is highly combustible but not inflammable i.e, in favourable circumstances, any wood may burn to ash timber is not readily ignited except in small thickness. Timber above a particular thickness, about 12mm can't support self - sustained combustion and continuous to burn only when external heat help in supplied efficient fire retardant chemicals under heat help in the production of more charcoal and water vapour some of the chemical that can be used heat help in the production of more charcoal and water vapour. Some of the chemicals that can be used are ammonium phosphate, boric acid, borax, Zinc chloride, sodium arsenate, etc. These can be applied to get a penetration of 2.5 to 4.0 by pressure treatment or soaking.

The timber surface can be coated with coal tar to make it fire-resistant. However, chemical treatment is more effective.