I'd like to array an arrow block along a polyline with equal spaces for a fire evacuation route.  How can this be done?

No problem, use the MEASURE command.  Create a block with the tip of the arrow being the base point for insertion.  Make the arrow about ten feet long with the tip facing to the right.  Call it ARROW.  Draw your fire evacuation route as a continuos polyline.  Issue the MEASURE command and use the command line Block option.  Type ARROW for the block name prompt and set a distance, between fifty and one hundred feet, depending on the length of the polyline.  Your arrow block will be distributed along the polyline.  You may have to rotate a few of the insertions to get everything to look just right.