The fire inspector of every municipality with a population of 500,000 or more shall investigate the cause, origin, and circumstances of every fire occurring in the municipality and shall especially investigate whether it was the result of carelessness or design. Such an investigation shall be begun within 2 days, not including Sunday, of the occurrence of a fire. The fire inspector shall keep in his office a record of all fires occurring in the municipality, together with a record of all the facts, statistics, and circumstances, including the origin of the fire and the value and ownership of the property destroyed, which may be determined by the investigations provided for by this Division 9. This record shall be open to public inspection at all times.