A fire is said to "lay down," often at night, when temperatures drop and RH rises. Fires do not "lie down." It's a long-standing term in fire and means that the fire is burning less actively than it did during the day
United States Department of Agriculture USDA Forest Service, Forests and Rangelands, Glossary of Terms, National Fire Plan, Washington, D.C., USA 2012. http://www.forestsandrangelands.gov/resources/glos sary/a.shtml, (For Fr - Amer) {497}