
We address the problem for fire blocking by constructing a wall $\zeta$ whose shape is a spiral. This is considered the best strategy in the case of a single firefighter is constructing the wall with a finite construction speed $\sigma$: the barriers which satisfy this bound on the construction speed are called admissible. We prove a sharp version of Bressan’s Fire Conjecture \cite{Bressan_conj} in this case, i.e. when admissible barriers are spirals: namely, there exists a spiral-like barrier confining the fire in a bounded region of $\R^2$ if and only if the speed of construction $\sigma$ is strictly larger that a critical speed $\bar \sigma = 2.61…$. The existence of confining spiral barriers for $\sigma > \bar \sigma$ is already known, while we concentrate on the negative side, i.e. if $\sigma \leq \bar \sigma$ no admissible barrier blocks the fire.