Increase fire protection safety and effectiveness with comprehensive, up-to-date requirements for clean agent systems in the NFPA Responses are provided by NFPA staff on an informal basis. NFPA : News. This paper. A short summary of this paper. Council on January 13, , with an effective date of February 9, , and supersedes all previous editions.
First Revision No. Toggle navigation M icrolinkinc. Home Extension Country Pricing. Keyword Research: People who searched nfpa Annex material discussing this new requirement is included in the Standard.
Disconnect Switch The requirement for a disconnect switch is not new. The technical committee, however, added the requirement that the switch must be located inside a lockable cabinet or require a key to operate it in order to secure the switch against unauthorized operation. It is August 22, Page 9. The disconnect switch shall interrupt the releasing circuit to the suppression system and shall cause a supervisory signal at the releasing control unit.
Reports from the field indicated that clean agent system were being installed in rooms with raised floors and the space under the raised floor was not afforded simultaneous protection. Section 5. Each volume, room and raised or sunken floor to be protected, shall be provided with detectors, piping network and nozzles. We paraphrase substantiation provided by the submitter of the original comment with which the technical committee agreed: Even if there is no air flow or cabling in the lower space, the agents will eventually leak to the low point and may prematurely cause the concentration in the room to decay.
If there happens to be a fire below the raised floor, the concentration of agent leaking downward may not be enough to develop an extinguishing concentration, and therefore, could possibly produce great amounts of products of agent decomposition. Subsection 5. NFPA 75 requires either automatic sprinkler protection or a gaseous extinguishing system to be installed under the raised floor of a data center. Gaseous systems protecting only the space below a raised floor are not uncommon.
The newly stated requirement in NFPA is below and new Annex material explains the reason for the requirement. Annex 5. NFPA 75 edition A. During and after a discharge some of the agent from the space under the raised floor will migrate into the room above the raised floor. If any fire exists in the equipment above the raised floor, the agent at a concentration below the extinguishing concentration may be exposed to the fire. If the agent were a halocarbon, considerable decomposition of the agent could occur.
Currently NFPA 75 edition states: 8. This provision has been incorrectly interpreted by some to mean that even if the entire IT room or area and subfloor area are protected by a total flood clean agent system, the subfloor must be protected separately by an automatic sprinkler system, a carbon dioxide system, or an inert agent fire extinguishing system.
If adopted, the requirement for protection of the space under the raised floor will be clarified as follows: 8. The method for determining the minimum design concentration for extinguishing fire in Class A fuels has been modified as follows: 5. The net effect of this change is the minimum design concentration for Class A fuels may not be less than the minimum extinguishing concentration for normal heptane determined from the cup burner test.
The current Class A minimum design concentrations for inert gases will not change. Designers and installers should consult with the system manufacturer to obtain the correct MDC for hazards in which Class A fires are to be extinguished with total flood clean agent systems.
Class C fuels. The edition will mandate the following minimum design concentrations for Class C hazards: 5. The requirement which will be set forth in the edition is a result of this ongoing discussion as well as debate which took place at the NFPA technical report session this June in Boston.
Designers and installers should consult the August 22, Page Deep Seated Class A. Two types of fires can occur in solid fuels: one in which volatile gases resulting from heating or decomposition of the fuel surface are the source of combustion; and another in which oxidation occurs at the surface of, or within, the mass of fuel.
The former is commonly referred to as flaming combustion, while the latter is often called smoldering or glowing combustion. The two types of fires frequently occur concurrently, although one type of burning can precede the other.
For example, a wood fire can start as flaming combustion and become smoldering as burning progresses. Conversely, spontaneous ignition in a pile of oily rags can begin as a smoldering fire and break into flames at some later point. Flaming combustion, because it occurs in the vapor phase, may be extinguished with relatively low levels of clean agents.
In the absence of smoldering combustion, it will stay out. Smoldering combustion is not subject to immediate extinguishment as is flaming combustion. Characteristic of this type of combustion is the slow rate of heat losses from the reaction zone. Thus, the fuel remains hot enough to react with oxygen, even though the rate of reaction, which is controlled by diffusion processes, is extremely slow. Smoldering fires can continue to burn for many weeks, for example, in bales of cotton and jute and within heaps of sawdust.
A smoldering fire ceases to burn only when either all of the available oxygen or fuel has been consumed or when the fuel surface is at too low a temperature to react. These fires are usually extinguished by reducing the fuel temperature, either directly by application of a heatabsorbing medium, such as water, or by blanketing with an inert gas.
The inert gas slows the reaction rate to the point where heat generated by oxidation is less than heat losses to surroundings. This causes the temperature to fall below the level necessary for spontaneous ignition after removal of the inert atmosphere. For the purposes of this standard, smoldering fires are divided into two classes: 1 where the smoldering is not deep seated and 2 deepseated fires.
Whether a fire will become deep seated depends, in part, on the length of time it has been burning before application of the extinguishing agent. This time is usually called the preburn time. Another important variable is the fuel configuration. While wood cribs and pallets are easily extinguished with Class A design concentrations, vertical wood panels closely spaced and parallel may require higher concentrations and long hold times for extinguishment.
Fires in boxes of excelsior and in piles of shredded paper also may require higher concentrations and long hold times for extinguishment. In these situations, heat tends to be retained in the fuel August 22, Page Radiation is an important mechanism for heat removal from smoldering fires. Duration of Protection Hold Time This is a clarification of an existing requirement. A minimum concentration of 85 percent of the Adjusted Minimum Design Concentration shall be held at the highest level of combustibles for a minimum period of l0 minutes or for a time period to allow for response by trained personnel.
It is important that the agent Adjusted Minimum Design Concentration not only shall be achieved, but also shall be maintained for the specified period of time to allow effective emergency action by trained personnel. This is equally important in all classes of fires, since a persistent ignition source e. This change makes it clear that the intent of this requirement was and is to hold 85 percent of the adjusted minimum design concentration AMDC.
The adjusted minimum design concentration may differ from the final design concentration FDC , that is, the agent concentration actually provided. Discharge Time Inert Agents When Class A surface fire or Class C fire hazards are protected by inert gas agents, the discharge time required to achieve 95 percent of the minimum design concentration may be extended to a maximum of seconds.
The approved limits for a given inert gas system must be followed. Designers and installers should seek and follow the guidance of the system manufacturer in applying the revised 5. Open navigation menu. Close suggestions Search Search. User Settings. Skip carousel. Carousel Previous. Carousel Next. What is Scribd? Explore Ebooks. Bestsellers Editors' Picks All Ebooks.
Explore Audiobooks. Bestsellers Editors' Picks All audiobooks. Explore Magazines. Editors' Picks All magazines. Explore Podcasts All podcasts. Difficulty Beginner Intermediate Advanced. Explore Documents. Uploaded by Mohammed Amin. Did you find this document useful?
Is this content inappropriate? Report this Document. Flag for inappropriate content. Download now. NFPA Edition xd. Related titles. Carousel Previous Carousel Next. Jump to Page. Search inside document. Summary of Select Changes and Additions Under Safety in Chapter 1, exposure to the discharge of clean agent during a local application discharge is discussed.
The actual concentration of agent discharged into New definitions are included in the edition of NFPA The target minimum design concentration after the Safety Factor and the Design Factors have been taken into account. NFPA Chapter 5 Design Considerations Protection of Rooms having Subfloors Extent of Protection Reports from the field indicated that clean agent system were being installed in rooms with raised floors and the space under the raised floor was not afforded simultaneous protection.
Minimum Design Concentrations Class A fuels The method for determining the minimum design concentration for extinguishing fire in Class A fuels has been modified as follows: 5.
0コメント