|Clean Agent Design Requirements Continue to Evolve|
Issue 57: Clean Agent Design Requirements Continue to Evolve
By Jeff L. Harrington, P.E., FSFPE
Clean agents were originally advanced as "halon
alternative options”. Prior to the Montreal Protocol and the U.S. Clean
Air Act of 1990,2 Halon 1301 and carbon dioxide (CO2)
were the two gaseous agents in predominant use in fixed, total-flooding
extinguishing systems. Halon 1301 had an advantage over CO2
for normally-occupied spaces because it did not adversely affect humans
at design concentrations necessary to extinguish fires. CO2 was a common choice for total-flooding, normally-unoccupied spaces and local applications.
Life with CO2 and Halon 1301 was simple. Each agent had its own NFPA design and installation standard: NFPA 123 for CO2 and NFPA 12A4
for Halon 1301. In each of these standards, only one agent was
addressed. Then, Halon 1301 was phased out of production in response to
the new environmental protection regulations. Not one, but many new
agents were developed to replace Halon 1301.
NFPA 20015 was the new standard created to
address the halon alternative agents, dubbed "clean agents”. NFPA 12A
was used as a template to create the new NFPA 2001. To accommodate a
growing number of new clean agents, NFPA 2001 evolved into a document
with more complexities and a broader scope than NFPA 12A.
For example, new science was adapted and applied to
develop guidelines for each new clean agent to provide safety to humans
that might be exposed to the minimum design concentration. Refinements
in the cup burner apparatus and test procedure were also implemented to
provide more accurate determinations of minimum extinguishing
concentrations for Class B fuels and more uniformity between test
laboratories. The safety factor applied to the minimum extinguishing
concentration to determine the minimum design concentration was
increased from 1.2 to 1.3 for Class B fuels. Furthermore, a new standard
test method was implemented to determine the minimum extinguishing
concentration for Class A fuels with surface burning.
NFPA 2001 continues to evolve. The 2012 edition of NFPA was acted on by NFPA at its Association Technical Meeting in June 2011, and issued with an effective date of August 31, 2011. This latest edition contains numerous revisions, three of which will be detailed in this article. These revisions are:
Supervision of Electric Actuators in Place
Electric actuators are routinely removed from the discharge and
selector valves that they control to facilitate periodic testing. It is
not uncommon for one or several of the electric actuators to remain
unattached after the testing work has been completed. This leaves the
clean agent system in an impaired state, with no indication that it is
This revision to the standard is intended to require clean agent
system manufacturers to provide a means to supervise the attachment of
electric actuators to the discharge or selector valve that they control,
and to give them time to develop the necessary technology and
manufacturing processes to implement it.
Modification of Class A Minimum Design Concentration Safety Factor
The committee’s intent in making this change was to provide a method
of determining the minimum design concentration for Class A surface fire
hazards that was hardware-independent for all agents.
Increase in Class C Fire Hazard Safety Factor
The committee recognized that Class C fire hazards might have
characteristics different from Class A surface fire hazards, and that
some of these differences could influence the minimum extinguishing
concentration and, therefore, the minimum design concentration.
A Fire Protection Research Foundation report6 showed that
there is both theoretical and empirical support for the notion that
Class C fire hazards require a higher quantity of clean agent to
reliably extinguish them than corresponding Class A fire hazards. The
report outlines the fundamentals for an appropriate test method and
apparatus that could be used for determining the appropriate minimum
extinguishing concentration for Class C fire hazards for each clean
agent. In February 2009, the Fire Protection Research Foundation
conducted a workshop devoted to the subject of this project to review
the report and develop direction for the next steps. A summary of this
workshop was published.7
This recent work, coupled with several years of evaluation by the
committee, resulted in a change in the 2012 edition of NFPA 2001
regarding the method of determining the minimum design concentration for
Class C fire hazards. The standard now states, in Section 126.96.36.199, that
the minimum design concentration for Class C fire hazards shall be the
minimum extinguishing concentration, as determined from 188.8.131.52,
multiplied by a safety factor of 1.35.
The clean agent industry continues its work to develop a test
protocol and test apparatus for determining minimum extinguishing
concentrations for Class C fire hazards.
Jeff L. Harrington is with Harrington Group, Inc.
2nd Quarter 2012 - Date Line 2012: Issues and Future Directions for Water Mist Fire Protection Systems
2nd Quarter 2010 - Fire Protection in an Environmentally Sustainable World
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