We study the structure of certain classes of homologically trivial locally C * -algebras. These include algebras with projective irreducible Hermitian A-modules, biprojective algebras, and superbiprojective algebras. We prove that, if A is a locally C * -algebra, then all irreducible Hermitian A-modules are projective if and only if A is a direct topological sum of elementary C * -algebras. This is also equivalent to A being an annihilator (dual, complemented, left quasi-complemented, or topologically modular annihilator) topological algebra. We characterize all annihilator σ-C * -algebras and describe the structure of biprojective locally C * -algebras. Also, we present an example of a biprojective locally C * -algebra that is not topologically isomorphic to a Cartesian product of biprojective C * -algebras. Finally, we show that every superbiprojective locally C * -algebra is topologically * -isomorphic to a Cartesian product of full matrix algebras.