A particulate filter for a vehicle exhaust system includes a primary filter surrounded by a secondary filter and a quenching agent injection nozzle arranged upstream of the primary filter. In a normal mode, exhaust flows through the primary filter, and in a fail-safe mode or a mixed mode, at least some exhaust flows through the secondary filter and quenching agent is injected via the nozzle to cool the primary filter. The fail-safe or mixed modes may be enacted during an overload of the primary filter, for example. If engine shutdown is initiated during regeneration of the primary filter, a rate of quenching agent injection may be adjusted so that the regeneration may be completed at a safe temperature.