This is a basic template with the purpose of including all arguments / table variables to make it easily known which values can be accessed.
gameevent.Listen( "flare_ignite_npc" )
hook.Add( "flare_ignite_npc", "flare_ignite_npc_example", function( data )
local entindex = data.entindex // The Entity:EntIndex() of the ignited NPC.// Called when a flare sets an NPC on fire.end )