For inert gas clean agents, what are the maximum discharge times to achieve 95 percent of the minimum design concentration for flame extinguishment?

• A. 120 seconds for B; 60 seconds for A/C
• B. 30 seconds for B; 60 seconds for A/C
• C. 60 seconds for B; 90 seconds for A/C
• D. 60 seconds for B; 120 seconds for A/C

Answer: (D)

The main idea is how quickly an inert gas clean agent must discharge to reach a safe, effective level for extinguishment, while still protecting occupants. The 95 percent of the minimum design concentration is used as the practical target to ensure the flame is suppressed promptly without overdosing the space.

For inert gas systems, agent categories reflect how readily the gas disperses. Category B agents generally mix and spread more quickly, so the standard allows a shorter maximum discharge time—60 seconds—to reach 95% of the MDC. Category A/C agents have slower or more complex dispersion, so a longer maximum discharge time—120 seconds—is permitted to ensure the 95% MDC is achieved uniformly throughout the space.

Thus, the correct pairing is 60 seconds for the B category and 120 seconds for the A/C category. Shorter or longer times outside these limits could either fail to reach extinguishing concentrations in time or introduce unnecessary risk during discharge.