Multiple casualty incident
In a multiple casualty incident, there are a large number of victims, but the appropriate local leadership, including the incident commander if the Incident Command System has been invoked, has determined that local resources are adequate to deal with the incident. For example, if there were a multiple-car accident with twelve seriously injured victims, ad there was only one local hospital that could handle no more than 6 urgent trauma cases would have to its mass casualty incident procedures. If, however, there were 4 hospitals able to accept up to 6 casualties, proper distribution of victims, would keep the event as a multiple casualty incident.
A facility, when it expects multiple casualties still within its resources, may go into a modified emergency response. For example, it might stop all elective surgical operations that have not already begun, to leave room for emergency surgery. Personnel in the hospital would be asked to extend their shifts of duty, and off-duty personnel would be called to come in. Once it knows its capacity has been reached, or will be reached when ambulances arrive, it may tell the emergency services dispatcher to put it on "divert", sending it no additional cases.
The hospital would be likely to alert both its physical security personnel and its public affairs staff, so order is kept when victims and families start arriving, and there is a systematic way to keep them both informed and out of the way.