Iban Blast is a combat spell that is unlocked after completing the Underground Pass quest. It can inflict up to 25 Hitpoints of damage (up to 27 with the Occult necklace, or 31 with Occult necklace and Slayer helmet (i) while on task). To cast the spell, the player also needs to wield Iban's staff.
The spell can be cast a total of 120 times with the staff before it must be recharged. This can be extended to 2,500 cast with an Iban's upgraded staff. One charge is consumed per cast against monsters, and two charges are consumed per cast against other players.
As of 21 August 2014, Iban's staff (and its upgraded counterpart) are both able to auto-cast Iban Blast.
Note that elemental staves cannot be used to cast Iban blast. A Tome of Fire can be used, however, and will not consume any of the Tome of Fire's charges.