It is increasingly recognised that all complex buildings should be covered by a relevant and up to date fire strategy. This is particularly the case for special infrastructures such as process plant buildings (for e.g. power stations). These buildings contain a number of risk areas, each of which requires an appropriate and specialised level of evaluation. A fire strategy should consider eight key elements (fire safety factors), all of which are relevant to their fire safety and protection. The fire safety elements are the basis for the determination of a new semi-quantitative methodology of the evaluation of the Fire Risk Index assessment. The methodology contains a number of checks appropriate for different industrial areas, graphical tools and calculation procedures. The process allows the comparison of an actual fire strategy against a pre-determined baseline strategy. The case study for an exemplar industrial boiler house is used to illustrate the proposed methodology.