Welcome to allnurses
Wow, that's huge. I work in Victoria, where we have mandated ratios, which vary depending on the acuity of the hospital. In tertiary acute care it's 1:4 during the day, 1:8 at night on the wards, and 1:1 in ICU.
The wards have an availability list, where ward staff can indicate that they are prepared to work extra shifts. Great in theory, rarely utilised in practice.
My hospital has pool of nurses who function as an in-house agency and are the first port of call when there's a short fall.
Failing that we use agency. If there are no agency staff and it's a weekday morning shift the charge nurse acts as resource. Sometimes the PM staff are called and asked if they can come in for the morning instead, but this is strictly voluntary. If nobody can work then we work over ratio for a couple of hous until beds can be closed, either by transferring patients out of the unit or closing beds after discharge. We never
work over the ratio for more than a shift.