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Clean Agent Suppression of Energized Electrical Equipment Fires

Published

Author(s)

Gregory T. Linteris

Abstract

The NFPA 2001 standard on the use of clean agents for the suppression of fires arose from the phase-out of Halon 1301. Standard methods exists for specifying the amount of clean agent required for Class A and Class B fires, but the recommendation for Class C fires (those involving energized electrical equipment) defaults to the Class A values. While this may be appropriate for some Class C fires, there is concern that higher agent concentration may be necessary if energy is added to the fire by the electrical source. A number of test methods have been proposed to determine the amount of agent required to suppress fires in energized electrical equipment; however, there has been no broad agreement on a test method to include in NFPA 2001 for Class C fires. The present project was sponsored by the National Fire Protection Association Research Foundation to address the need for a standard test to be included in NFPA 2001 for Class C fires. The goals of the project are to understand the fire threats occurring in energized electrical equipment, and suggest a test protocol which can properly estimate the amount of agent required to suppress fires in those situations. As a first step, phone interviews were conducted with members of the technical panel and with the sponsors of the present project. These representatives, as well as other expert sources recommended by them, provided information on the likely fire threats expected in the field. Detailed case studies were supplied by FM Global. Detailed notes of the conversations as well as summaries are provided, and the data provided served as one source for definition of the threat. In order to illustrate the relevant parameters necessary to consider in fires over solid materials with added energy, a thorough literature review was performed. Topics included materials flammability and fire suppression, with the latter broken down into: a theoretical description of fire suppression, flow-field effects, effects of heat addition on suppression, and suppression of flames over condensed-phase materials. A major resource was the previous work to develop standard tests for suppression of fires in energized electrical equipment. By analyzing these in detail, and considering the relevant physics of the suppression process outlined in the review section, the desired properties of a standard test were developed, and the range of values of the most important parameter (the flux of added energy) was estimated. Major findings of the report are listed below. 1. Added energy to a burning material will affect the minimum extinguishing concentration of suppressant, and the effect is relatively independent of the energy source (e.g., resistive heating, radiative heating, conduction, preheating of the material, etc.) as long as the energy is added to the burning surface. 2. For tests which have been proposed to simulate fires in electrical equipment, the magnitude of the estimated external heat flux is similar to that which can be obtained with radiant heating experiments. 3. In the different tests which have been proposed to simulate the suppression of flames in energized electrical equipment, the suppressant concentration measured with the different tests agreed with each other reasonably well (when enough information was provided to do a comparison). 4. Many of the test methods previously proposed do not combine the relevant parameters in ways which produce the most conservative (yet plausible) test. 5. A test based on an external radiant heat flux source, a large sample (10 cm x 10 cm) in a chimney, and realistic materials is a good starting point for a test procedure. 6. Two radiant flux levels in the proposed test method are suggested: a.) an incident flux of 20 kW/m2 as a lower limit, representing the heat input without any electrical augmentation, but with an adjacent flame on similar burning material, which can enhance the burning; b.) an incident
Citation
Technical Note (NIST TN) - 1622
Report Number
1622

Keywords

Fire suppression, Class C fires, Halon replacements, Clean agents

Citation

Linteris, G. (2009), Clean Agent Suppression of Energized Electrical Equipment Fires, Technical Note (NIST TN), National Institute of Standards and Technology, Gaithersburg, MD, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=901395 (Accessed May 27, 2024)

Issues

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Created January 1, 2009, Updated February 19, 2017