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:

1. Requirement to supervise in-place actuators
2. Class A surface fire hazard design concentration safety factor modification
3. Class C fire hazard design concentration safety factor increase

Supervision of Electric Actuators in Place
The standard now requires [Section 4.3.4.1 and 4.3.4.2] that electric actuators on agent storage container discharge valves and selector valves be supervised in place. Their removal must cause an audible and visible indication at the system releasing control panel. The standard also states that these requirements shall become effective on January 1, 2016.

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 impaired.

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 previous (2008) edition of NFPA 2001, Section 5.4.2.4, required that a safety factor of 1.2 be applied to the minimum extinguishing concentration to determine the minimum design concentration for Class A surface fire hazards. This has been revised in the 2012 edition to require the minimum design concentration for Class A surface fire hazards to be the greater of 1.2 times the minimum extinguishing concentration determined according to Section 5.4.2.2, or the equivalent of the minimum extinguishing concentration for heptane as determined according to Section 5.4.2.1.

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 minimum design concentration for a Class C fire hazard, in previous editions of NFPA 2001, was required to be at least the same as for a Class A surface fire hazard for any given clean agent. There were no other requirements pertaining to Class C fire hazards.

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 5.4.2.5, that the minimum design concentration for Class C fire hazards shall be the minimum extinguishing concentration, as determined from 5.4.2.2, 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.

1. The 1987 Montreal Protocol on Substances that Deplete the Ozone Layer, United Nations Environment Programme, Nairobi, 1987.
2. Title VI - Stratospheric Ozone Protection, Clean Air Act, S.1630.ENR, U.S. Senate, Washington, DC, 1990.
3. NFPA 12, Standard on Carbon Dioxide Fire Extinguishing Systems, National Fire Protection Association, Quincy, MA, 2011.
4. NFPA 12A, Standard on Halon 1301 Fire Extinguishing Systems, National Fire Protection Association, Quincy, MA, 2009.
5. NFPA 2001, Standard on Clean Agent Fire Extinguishing Systems, National Fire Protection Association, Quincy, MA, 2012.
6. Linteris, G., "Clean Agent Suppression of Energized Electrical Equipment Fires", Fire Protection Research Foundation, Quincy, MA, January 2009.
7. Clean Agent Suppression of Energized Electrical Equipment Fires, Workshop Held in Conjunction with SUPDET 2009: Fire Protection Research Foundation, Quincy, MA, February 24, 2009.

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