Which hazard severity category represents a complete loss of the ability to accomplish the mission?

The hazard severity category that represents a complete loss of the ability to accomplish the mission is indeed Category I. This categorization indicates the most critical level of risk where the impact on mission objectives is severe enough that it would result in the total failure to achieve the desired outcome. In such scenarios, the mission cannot proceed due to the gravity of the hazard involved.

Category I is characterized by an immediate and detrimental effect on operational capability, which often necessitates immediate and robust risk management measures to avoid catastrophic outcomes. Recognizing this level of risk helps prioritize resources and actions to address the most significant threats to mission success. By understanding the implications of Category I hazards, personnel can take appropriate steps to mitigate risks and ensure operational readiness.