▁area . ▁Fire fig h ters ▁sometimes ▁do ▁not ▁attempt ▁to ▁protect ▁structures ▁without ▁ade qu ate ▁def ens ible ▁space , ▁as ▁it ▁is ▁less ▁safe ▁and ▁less ▁likely ▁to ▁succeed . ▁ ▁C riteria ▁A ▁first ▁concept ▁of ▁def ens ible ▁space ▁for ▁most ▁fire ▁ag encies ' ▁primary ▁goal ▁of ▁fuel ▁reduction ▁is ▁a ▁recommended ▁or ▁required ▁def ens ible ▁space ▁around ▁a ▁structure ▁to ▁extend ▁for ▁at ▁least ▁ ▁in ▁all ▁directions . ▁A ▁second ▁concept ▁of ▁def ens ible ▁space ▁is ▁" f uel ▁reduction ." ▁This ▁means ▁plants ▁are ▁select ively ▁th inned ▁and ▁pr un ed ▁to ▁reduce ▁the ▁comb ust ible ▁fuel ▁mass ▁of ▁the ▁remaining ▁plants . ▁The ▁goal ▁is ▁to ▁break ▁up ▁the ▁more ▁continuous ▁and ▁dense ▁un inter rupted ▁layer ▁of ▁veget ation . ▁A ▁third ▁concept ▁of ▁def ens ible ▁space ▁is ▁" f uel ▁lad der " ▁management . ▁Like ▁r ungs ▁on ▁a ▁lad der , ▁veget ation ▁can ▁be ▁present ▁at ▁varying ▁height s ▁from ▁ground cover ▁to ▁trees . ▁Gr ound ▁fuel ▁" r ungs ", ▁such ▁as ▁d ried ▁grass es , ▁can ▁transmit ▁fire ▁to ▁shr ub ▁r ungs , ▁which ▁then ▁transmit ▁up ▁tree ▁branch ▁r ungs ▁into ▁the ▁tree ▁can opy . ▁A ▁burning ▁tree ▁produces ▁em bers ▁that ▁can ▁blow ▁to ▁new ▁areas , ▁spread ing ▁and ▁so ▁making ▁it ▁more ▁difficult ▁to ▁control ▁a ▁wild land ▁fire . ▁One ▁guid eline ▁is ▁for ▁a ▁typical ▁separation ▁of ▁three ▁times ▁the ▁height