The Contingency Categories Framework defines the Bureau's two tiers of containment-failure contingency — TERMINUS and EXCIDIUM — and their pairing with the four Horse Protocols. It is a framework document: it defines the categories and the structure into which individual contingencies fall. The contingencies themselves, which specify the measures taken, are the CY-type documents CY-400-81 through CY-400-94, each instantiating one tier for one Horse Protocol. This document contains no contingency measures; those are held at the access level specified in §4.

This framework defines the two contingency tiers applicable to containment failure and their attachment to the Anomalous Protocols (PR-400-71 through PR-400-74). It stands in the same relation to the contingencies (CY-400-81 through CY-400-94) as SYS-100-04 (Anomalous Protocols) stands to the protocols: a specification defining a set its members instantiate. It does not itself respond to any scenario, and it does not govern contingencies authored for predicted scenarios outside the containment-failure model, which are issued as standalone CY documents.

TERMINUS. The response to an attempted or imminent containment failure — measures invoked to arrest a failure in progress before it completes. A TERMINUS contingency is triggered by an attempted breach, the violation of a containment prohibition, or an imminent-failure indicator, and is directed at preventing the failure from being realized.

EXCIDIUM. The last-resort response following a successful containment failure — measures invoked once containment has already been lost, directed at limiting the consequences of an accomplished failure rather than preventing one. EXCIDIUM is the higher tier and the graver invocation.

The distinction is operative, not gradational: the response to an attempted failure is not the same as the response to a successful one, and the two are triggered by different conditions. This is the distinction personnel below contingency-access level are required to understand (see §4).

Each Horse Protocol carries one TERMINUS and one EXCIDIUM contingency. The framework therefore defines eight members:

Contingency content — the measures specified in each CY member — is held at Site Director level and above. Personnel below that level are required only to know that the contingencies exist and that the response to an attempted failure differs from the response to a successful one.

A TERMINUS contingency is invoked under the authority designated in its member document, typically at Site Director level.

An EXCIDIUM contingency, responding to an accomplished containment failure and carrying consequences beyond the containment site, requires Bureau directorate authority and, where its member document so specifies, Ministerial authorization.