Federal Lands Fire-Related Incidents Recovery and Economic Stimulus Act of 2018 or the Federal Lands FIRES Act of 2018 This bill authorizes the President to declare a federal lands wildfire disaster. Specifically, the President may make such a declaration for any wildfire: for which a request for a declaration has been made by the governor of an affected state or the chief executive of an affected Indian tribal government; that has burned 40% or more of an area that consists of federal lands; and that, in the President's determination, causes damage of sufficient severity and magnitude to warrant assistance to supplement the efforts and available resources of states, local governments, Indian tribes, and disaster relief organizations in alleviating the damage, loss, hardship, or suffering caused by the wildfire. Assistance may be provided for secondary and tertiary damages, which may not include any area more than 100 miles from the area subject to the wildfire. The Department of Housing and Urban Development may provide assistance to states, local governments, and Indian tribes for necessary expenses for disaster relief, long-term recovery, restoration of infrastructure and housing, and economic revitalization in the most impacted and distressed areas resulting from a federal lands wildfire disaster. The bill amends the Small Business Act to allow small businesses to receive economic injury disaster loans from the Small Business Administration for a federal lands wildfire disaster.