Decreasing demand and reduced budgets are driving changes to traditional crewing methods in the UK Fire and Rescue Service. Using an integration of two years' operational data within a novel framework, this paper assesses the impact of alternative crewing on operational effectiveness in one UK FRS. Changes in crewing patterns were implemented without substantial impact on overall operational effectiveness, but there may be a risk to wider operational resilience. The Overall Effectiveness of Fire Operations (OEFO) assessment tool can inform FRS decision making in an authentic way allowing stakeholder confidence in the outcomes, whilst being timely and not too complex or costly to evaluate. The OEFO approach is an important contribution to practice through its ability to assess public services at a time of challenging reform and demonstrates alterations can be made to crewing patterns to better match demand provided there is consideration of the potential wider impact.