Which factor does NFPA 2001 consider when determining whether re-entry after discharge is safe?

• A. Room altitude.
• B. Agent humidity tolerance.
• C. Agent concentration decay in the space.
• D. Color of the walls.

Answer: (C)

Re-entry safety after discharge is governed by how quickly the agent concentration in the space falls to a safe level. NFPA 2001 uses the decay of agent concentration over time to determine when it’s safe to re-enter, because the remaining inhalation hazard is what matters for occupants and responders. Ventilation and room characteristics influence that decay curve, whereas factors like room altitude, humidity tolerance, or wall color do not affect the toxic hazard, so they aren’t used to decide re-entry. The crucial factor is the agent concentration decay in the space.