Before yesterday , 19 firefighters assigned to wildfires had died on duty this year , said Tracey Powers , spokeswoman for the National Interagency Fire Center in Boise .
Before Sunday , 19 firefighters assigned to wildfires had died on duty this year , according to Tracey Powers of the National Interagency Fire Center in Boise .
a sequence of measurements of some quantity taken at different times often at equally spaced intervals