For those who don't already know...
Sometimes Ifrit will overlap Searing Wind, meaning he will cast it on one healer, then cast it again on the other healer before the first one expires.
If this happens the healer who got Searing Wind FIRST! will stop exploding even if you still have the debuff, so you can move back to the middle and free up space for the other healer who just got Searing Wind.
Hope this helps.