A reliability analysis using second-moment approximations is conducted on two types of fire-exposed, unprotected wood floors--conventional wood joist and floor-truss assemblies. A methodology is illustrated by which the probability of structural failure of a wood floor assembly can be evaluated. This probability, with the probabilities of failure of other system components, can be used in a systematic analysis that apparently is a viable approach to realistic analysis of building fire safety. The use of reliability analysis to compare relative fire safety of different floor components is demonstrated. A procedure for introducing new components into the market, based on a concept of an equal safety index calculated for a component with a proven inservice record, is discussed. (Author).