Department of Magical Accidents and Catastrophes

The 'Department of Magical Accidents and Catastrophes is is responsible for repairing accidental magical damage. It is located on the third level of the Ministry of Magic and houses the following offices:

Accidental Magic Reversal Squad
The Accidental Magic Reversal Squad is a squad of wizards whose job it is to reverse 'Accidental Magic,' which is normally caused by young witches and wizards who have not learned to control their magic.

For instance, the Accidental Magic Reversal Squad was sent out in Harry Potter and the Prisoner of Azkaban when Harry inflated his Aunt Marge. They were able to successfully reverse the spell, deflating her, and proceeded to modify her memory (to remove any recollection of the incident) - presumably this latter task was performed by the Obliviators, according to their duty.

Obliviator Headquarters
An Obliviator is the designation for a Ministry of Magic employee who has the task of modifying the memory of a Muggle after witnessing incidents belonging to the magic world.

They are first called so in the sixth volume, Harry Potter and the Half-Blood Prince, although the mentioned practice already appears in the previous novels. The act of memory modification can be used by any wizard, by using the spell, "Obliviate." This event, however, is frowned upon in the wizarding society; most believe that memory modification should be done by Obliviators only.

Examples of times in which a memory charm was committed include when Professor Gilderoy Lockhart attempts to erase the memories of Harry and Ron in Harry Potter and the Chamber of Secrets, and when the auror Kingsley Shacklebolt removed all memories of the secret D.A. organisation from the mind of Marietta Edgecombe, who had been in the process of betraying its secrets.

Muggle-Worthy Excuse Committee
Explains away any magical accidents or occurrences which cannot be magically cleared up or completely removed from the minds of Muggles. For example, Peter Pettigrew killed twelve muggle bystanders and tore apart a street by means of an immense explosion during his altercation with Sirius Black. The massive and obvious damage and mortality was explained away by the committee as being due to a tragic accidental explosion of the gas main.