"From 2013 to 2015, an estimated 23,800 vacant residential building fires were reported annually in the U.S. Vacant residential building fires are considered part of the residential fire problem, accounting for 6 percent of all residential building fires, resulting in an estimated 75 deaths, 200 injuries and $785 million in property loss each year. [...] The surrounding nonvacant properties are also at risk when vacant residential buildings catch fire. It typically takes longer for vacant residential building fires to be detected, as there are no occupants to be alerted by the smell or sound of the fires or to respond to an alarm. Thus, the property loss is greater. In addition, if the fire has been intentionally set, especially with multiple ignition points, the damage can be greater, placing the lives of more individuals -- firefighters, adjacent residents, and any squatters -- in danger. Fires in vacant residential buildings have become an even greater issue over the past decade."
U.S. Fire Administration: http://www.usfa.fema.gov/
Topical Fire Report Series (January 2018), v.18 no.9