The one fire metric that is genuinely comparable across every Massachusetts county is the civilian fire-death rate: average annual civilian fire deaths per 100,000 residents over 2017-2018. Deaths come from the Massachusetts Department of Fire Services’ MFIRS County Profiles (civilian fire fatalities by county, reported by fire departments via MFIRS — incident-based, i.e. counted where the fire occurred; exact, un-suppressed counts including 0/1/2); population comes from the U.S. Census Bureau. The rate is a direct, reproducible calculation —(5-year deaths ÷ 5) ÷ population × 100,000— not an estimate.

The Overall Fireground Index score normalizes that rate across the 14 counties: a z-score, inverted so a lower fire-death rate yields a higher score, centered at 50and clamped to 0-100:score = clamp(50 − z × 18, 0, 100). There is no black box. The platform's multi-dimensional scoring engine is reserved for when multiple comparable metrics exist; with one comparable fire metric today, this single transparent normalization is used instead.

Where a county publishes an incident/response figure, it is shown as sourced context with its exact definition and reporting year. These counts use incompatible definitions across counties (total incidents vs. calls for service vs. unit responses, and fiscal- vs. calendar-year), so they are never normalized into a cross-county comparison — that would be misleading.

Civilian injuries, firefighter injuries, and fire dollar loss have no authoritative per-county public source, so they are shown as “Data not publicly available”with the sources investigated. Missing data reduces Data Confidence; it never blanks a county.

Massachusetts’s fire deaths here are incident-based fire-fatality counts from the Massachusetts Department of Fire Services (MFIRS, counted where the fire occurred), the same basis used for Maryland. This is the 2017–2021 window — the most recent complete, internally-validated county-level series DFS publishes (newer per-county tables are not yet available publicly), so read Massachusetts’s figures as a slightly older vintage than other states. Because other states may use a residence-based basis, scores are ranked within Massachusetts and are not a cross-state comparison.

Data Confidence communicates how much verifiable public evidence backs a county: the authority of its sources, how many public metrics exist, and how statistically reliable the outcome data is (a county with 0-2 fire deaths over five years has a real but uncertain rate). A data-rich county reads differently from a data-sparse one — and that difference is itself information. Confidence is never based on whether every county reports identically.