How we did it
To examine which communities are most vulnerable to deadly electrical fires, the Journal Sentinel pieced together data from a number of government databases, including city property records, building violations data and national fire incident data.
First, reporters used the National Fire Incident Reporting System (NFIRS), a database of fire department responses maintained by the U.S. Fire Administration since 1976, to isolate the 8,000-plus residential structure fires reported in the city of Milwaukee from 2009 to 2019. To determine whether a fire had suspected electrical origins, the Journal Sentinel looked for electrical-related codes in two categories — factors contributing to ignition and equipment involved in ignition — the same methodology used by the National Fire Protection Administration. The Journal Sentinel used any additional details available within the database and from the Milwaukee fire and police departments and the Milwaukee County Medical Examiner’s Office to weed out fires that may have been electrical in nature but likely caused by tenant error such as placing a towel over a space heater or lint buildup in a clothes dryer.
Reporters then merged the fire data with the City of Milwaukee’s master property file to determine which neighborhoods had higher rates of electrical fires. To examine if electrical fires affected renters more frequently than owners, reporters used the same database to identify whether the parcel was owner-occupied at the time of the fire.
The NFIRS database has several limitations noted in the story, notably that reporting is voluntary. Despite reporting improvements over the past 10 years and the Milwaukee Fire Department’s reassurance that the department attempts to report all incidents to the database, the Journal Sentinel found that many fires still go unreported. In addition, reporters found that officials fail to deeply investigate the cause of many fires and simply classify them as “undetermined,” further undercounting the true incidence of electrical fires.