/execute @e[type=ArmorStand,name=flame,score_c_min=60] ~ ~ ~ summon FallingSand ~ ~ ~ {TileID:51,Time:1,Motion:[0.0,1.0,0.0]}
The execute command makes an entity (in this case an armor stand "type=ArmorStand", with 'flame' as name "name=flame" and with a score called 'c' settled at 60 or more "score_c_min=60") summon a falling sand in his position (~ means the relative position of an entity) with the id of a fire block ("TileID:51", 51 is fire's numeric id) and with an up-motion ("Motion:[0.0,1.0,0.0]", each 0.0 represents a relative coordinate-motion).
/scoreboard players add @e[type=ArmorStand,name=flame] c 1
adds one ("1") to the scoreboard of all armor stands (type=ArmorStand) called flame (name=flame)
/scoreboard players set @e[type=ArmorStand,name=flame,score_c_min=61] c 0
sets to 0 the scoreboard of all the armor stands ("type=ArmorStand") called flame ("name=flame") with the scoreboard settled to 61 or more ("score_c_min=61")
/execute @e[type=ArmorStand,score_c_min=1,score_c=1] ~ ~ ~ scoreboard players set @e[type=FallingSand,r=1] c 1
makes all the armor stands ("type=ArmorStand") with the scoreboard called c settled to 1 ("score_c_min=1,score_c=1") set the scoreboard 'c' of all the falling sands in the range of a block to 1
/execute @e[type=FallingSand,score_c=1] ~ ~ ~ kill @a[r=1]
makes all the falling sands with the score 'c' set to 1 kill all the players in the range of a block ("r=1")
/scoreboard objectives add c dummy
adds a scoreboard (c) which can be modified only with commands
/summon ArmorStand ~ ~-3 ~ {NoGravity:1b,Small:1b,Invisible:1b,CustomName:"flame"}
summons an armor stand three blocks under the command block (~ represents relative coords). This armor stand doesn't fall ("NoGravity:1b") is small ("Small:1b"), is invisible ("Invisible:1b") and is named flame ('CustomName:"flame"')
PLACE THIS COMMAND THREE BLOCKS HIGHER THAN WHERE YOU WANT TO PLACE THE FLAME-GENERATOR