As the title says, the fire trail from the spellbook should not burn your teamates or yourself. This is because the fire can burn your teamates, and i have been griefed before using this. Also, the fire trail very often backfires as you end burning not only your enemies but also yourself.
I think it would be good when the player who uses the spell book gets fire protection for 5 sec. but every teammate is maybe to much and can get to op.