Catechism of the Catholic Church §1483 — excerpt
In case of grave necessity recourse may be had to a communal celebration of reconciliation with general confession and general absolution. Grave necessity of this sort can arise when there is imminent danger of death without sufficient time for the priest or priests to hear each penitent's confession.
This translation is under copyright, so only the cited words are quoted here. Follow the link for the full text. Translation: English translation of the Catechism of the Catholic Church, 2nd ed. (Libreria Editrice Vaticana), as posted at vatican.va.
Also cites: CIC, can. 962 #1 · CIC, can. 961 # 2 · CIC, can. 961 # 1