Inert Gas discharge time 1

[ZDR1985]

Hi guys,

I am just a bit confused on this, so someone in here could enlighten me please. What is the difference between the two statements below from NFPA-2001 (Standard on Clean Agent Fire Extinguishing System).


Distribution System Section
5.7.1.1.2* For inert gas agents, the discharge time required to
achieve 95 percent of the minimum design concentration for
flame extinguishment shall not exceed 60 seconds for Class B
fuel hazards, 120 seconds for Class A surface fire hazards or
Class C hazards, or as otherwise required by the authority having
jurisdiction.

Nozzles Section
6.4.1.2* The maximum permitted time to extinguish a fire
with an inert gas agent shall be 30 seconds.

Thank you.

 

[stookeyfpe]

Section 6.4.1.2 requires a sufficient number of nozzles be provided for the volume of the design compartment to cause the fire to be extinguished within 30 seconds. The amount of agent to accomplish this is dependent on the fire hazard classification of the design fuel. Because many agents extinguish fires by oxygen exclusion (or dilution), a certain design concentration will be specified by Section 5.7.1.1.2, which are based on the selected extinguishing agent. As a result, Section 5.7.1.1.2 requires the volume of agent discharged be at least 95% of the design concentration within 1 or 2 minutes, again based on the fire hazard classification of the fuel.

The logic I've employed is the fire extinguished fairly rapidly and a minimum design concentration ensures the atmosphere of the compartment remains at a concentration to prevent reignition. This provides time for emergency responders to investigate the compartment, determine the fire is extinguished, and remove the fuel that contributed to the fire.