In a complete metric space that is equipped with a doubling measure and supports a Poincaré inequality, we study strict subsets, i.e. sets whose variational capacity with respect to a larger reference set is finite. Relying on the concept of fine topology, we give a characterization of those strict subsets that are also sets of finite perimeter, and then we apply this to the study of condensers as well as BV capacities. We also apply the theory to prove a pointwise approximation result for functions of bounded variation. Theorem 1.1. Let D ⊂ X and let E ⊂ X be a bounded set of finite perimeter with I E ⊂ D. Then cap 1 (I E , D) < ∞ if and only ifCap 1 (I E 1 \ fine-int D) = 0.Moreover, then cap 1 (I E , D) ≤ C a P (E, X) for a constant C a that depends only on the doubling constant of the measure and the constants in the Poincaré inequality. * 2010 Mathematics Subject Classification: 30L99, 31E05, 26B30.