by Dr. Mark L. Robin, Technical Services Consultant, DuPont Fluoroproducts
What is a Class C fire? What materials does it involve?
|DuPont Fire Extinguishants are safe and effective for use in areas where sensitive electronic equipment and people are present.
NFPA Standard 10 defines Class C fires as those that, "involve energized electrical equipment."
A Class C fire actually involves Class A (solids, cellulosic materials) or Class B (liquids, gases) materials and energized electrical equipment.
For example, a fire involving a power cable that is energized (i.e., has current flowing through the wire during the fire) is considered a Class C fire.
In this case, the insulation on the wire, a Class A material, is burning (the copper wire itself is noncombustible) as an electrical current flows through the wire.
If the current is removed, the situation is considered a Class A fire.
What governing body determines the industry standard for design concentration amounts of clean agent fire extinguishants? How is this determined?
In the U.S. and countries that require compliance with National Fire Protection Agency (NFPA) standards, NFPA 2001 Standard on Clean Agent Fire Extinguishing Systems, outlines minimum requirements for total flooding clean agent fire extinguishing systems.
NFPA 2001 (2004 edition) Section 5.4 contains requirements for Class A, B and C fires, including design concentration levels.
For Class A fires, the NFPA requires that the extinguishing concentration be determined by tests that are part of a listing program.
As a minimum, the listing program must conform to UL 2166 Standard for Halocarbon Clean Agent Extinguishing Systems or UL 2127 Standard for Inert Gas Clean Agent Extinguishing Systems, both of which contain a number of large-scale fire tests that are employed to determine the extinguishing concentration.
The minimum design concentration for Class A fires is specified in NFPA 2001 as the extinguishing concentration times a safety factor of 1.2.
For Class C fires, NFPA 2001 requires that the minimum design concentration be at least that for a Class A surface fire.
Why the recent uncertainty about the optimum concentration amounts of clean agent necessary to extinguish Class C fires?
|Recently there has been uncertainty about the optimum concentration amounts of clean agent necessary to extinguish Class C fires.
The Fire Suppression Systems Association (FSSA) Class C working group and the NFPA 2001 Technical Committee recently evaluated a series of studies that were developed over the past several years by various corporations and industry organizations.
Based on their results, the authors of these studies concluded that Class C fires might require minimum design concentrations higher than those employed for Class A fires.
Consequently, the NFPA 2001 Technical Committee recommended increasing the minimum design concentration for Class C hazards from the current level (1.2 times the Class A minimum extinguishing concentration) to 1.6 times the Class A minimum extinguishing concentration.
This proposed increase, included in Comment ROC 2001-61a, is being challenged by several members of the fire suppression industry.
As a result, Comment ROC 2001-61a will be the subject of a floor vote at the NFPA meeting in June 2007.
Subsequent to the NFPA 2001 Technical Committee's proposal in Comment ROC 2001-61a, new research results have been published which seriously challenge the conclusions of the studies reviewed by the committee.
The FSSA has also reviewed these recent results, reversed its prior decision, and is now opposed to changing Class C requirements based on these new studies by DuPont and Fike Corporation.
The DuPont/Fike study concludes that current minimum Class A design concentration levels may be sufficient for the protection of Class C hazards.
Any increases will result in unnecessary cost to the industry and to customers.
The conclusions stem, in part, from a careful review of the fire tests on which Comment ROC 2001-61a is based, which were flawed in the use of materials and in the test conditions employed.
In addition, field experience does not justify Comment ROC 2001-61a.
Over the past 15 years in which clean agent systems have been in use, there have been no documented examples of a failure of any clean agent system to extinguish a Class C fire.
Therefore, DuPont and Fike, as well as FSSA, believe that Comment ROC 2001-61a should not be adopted.
What factors make the cited studies flawed?
The cited studies were flawed in the materials and the test conditions employed, which were not representative of real world hazards.
For example, many of the tests involved energized nichrome wire wrapped around a piece of polymethylmethacrylate (PMMA) as a means of evaluating cable fires.
In a real world scenario, however, nichrome is never used for power conduction (copper is used in 99.99 percent of applications) and PMMA is never employed as electrical insulation for power cables.
Instead, materials such as PVC and PE are typically used as cabling insulation.
Other studies did not involve energized circuits of any form or they examined extraordinary configurations, such as nichrome wires in ethylene flames.
Here again, the relationship to real world applications is highly questionable.
In short, the configurations of these tests are not representative of the types of Class C fires that might actually occur.
Another flaw in several cited studies was a lack of reproducibility.
Reproducibility is critical to establishing and reinforcing the validity of a premise, such as increasing design concentrations.
How did the DuPont/Fike testing method differ from previous tests? What were the key conclusions of those tests?
DuPont and Fike employed materials and conditions representative of real world Class C hazards, including copper wire for power conduction, and PVC, polyethylene and other plastics commonly employed for cabling insulation. The results of these tests indicate that the current Class A minimum design concentrations may be sufficient for the protection of Class C hazards. Prior tests by Hughes Associates, Inc., which also employed representative materials and conditions, yielded the same conclusions.
The FSSA has reviewed the cited work and the recent findings from DuPont and Fike, and agrees that Comment ROC 2001-61a should not be adopted.
If NFPA votes in favor of Comment ROC 2001-61a, what will that mean for the industry and for customers?
Approval of Comment ROC 2001-61a will increase design concentrations for Class C hazards by at least 33 percent.
Class C hazards represent a large portion of clean agent applications, resulting in a significant impact on clean agent extinguishant manufacturers, as well as their customers.
Specifically, clean agent system costs would increase by more than 33 percent due to the increased amounts of clean agent required.
The industry would experience higher costs associated with shipping and handling of this additional agent.
More storage space would also be necessary to hold the new systems with higher design concentrations.
What can industry advocates do to help take action?
A Notice of Intent to Make a Motion (NITMAM) has been filed to reject Comment ROC 2001-61a.
This will result in a floor vote on the comment at the NFPA meeting, which will be held during the NFPA World Safety Congress in Boston, Mass., June 3-7, 2007.
As NFPA members prepare to vote, they should understand the recommended changes that are part of Comment ROC 2001-61a and how the proposed increase will impact them and their customers.
They should also consider whether the results of the cited studies and the 15 years of field experience support the increase.
More information is available:
» Presentation on Suppression of Class C Fires at Suppression and Detection Research and Applications Conference (SUPDET) 2007
» NFPA Web site
About the Author
Dr. Robin is a technical services consultant for the DuPont Fluoroproducts business based in Wilmington, Delaware.
Dr. Robin has more than 20 years experience in the area of fluorine chemistry and 15 years of experience in the fire suppression industry.
Dr. Robin's efforts in these areas have been described in 24 U.S. patents, more than 60 publications, and numerous scientific presentations.
Dr. Robin has also been extensively involved in the development, testing and approval of halon alternatives, including hydrofluorocarbon (HFC)
and inert gas clean extinguishing agents. Dr. Robin has participated on numerous fire suppression related committees including National Fire
Protection Agency (NFPA) 2001 and (International Standards Organization) ISO 14520. Additionally, Dr. Robin is also the recipient of the 2005
U.S. EPA Stratospheric Ozone Protection Award, presented for his efforts in the development of halon replacements and international standards
regulating their use.