Iowa Code § 808.6: Forcible execution.

1. The officer may break into any structure or vehicle where reasonably necessary to execute the warrant if, after notice of this authority and purpose the officer’s admittance has not been immediately authorized. The officer may use reasonable force to enter a structure or vehicle to execute a search warrant without notice of the officer’s authority and purpose in the case of vacated or abandoned structures or vehicles.

2. The officer executing a search warrant may break restraints when necessary for the officer’s own liberation or to effect the release of a person who has entered a place to aid the officer.