11 seriously injured people, especially children, would completely poleaxe any a&e department in the country. Even one with major trauma center status.
For example, most hospitals only have 1 paediatric trauma team on shift at any one time. That means one paeds anaesthetist, surgeon, neurosurgeon, orthopod on a pager who can drop everything & attend. Sure there will be others in site who can come, but they will be in clinic/theaters/itu etc.
Even London's biggest trauma center only has 1 ct scanner in the department.
If you more than 4ish serious casualties at a time they will be waiting for scans, and waiting for theater.
In London it is possible to coordinate the ambulances to distribute casualties accross 4 hospitals. Cardiff won't be that lucky.
It must be horrible for all concerned.