Unsure of the date of the statements you are quoting, but Dr. Expert may be referencing the NFPA report "Intentional Fires" authored by Richard Campbell and released in July of 2017. None of the property types in the report indicate an ITEMS FIRST IGNITED above 50 percent for FLAMMABLE OR COMBUSTIBLE OR GASES, PIPING OR FILTER.
The data is derived from NFIRS reports between 2010 and 2014 and is only as good as the data input by individual departments. GIGO Theory
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