Numerous new clean agents have replaced halon 1301, the original clean agent, during the last decade and a half. Currently, NFPA 2001 lists 13 separate clean agents that are suitable for use in spaces that are either normally occupied, or normally unoccupied.1 During the 1970s and 1980s, halon 1301 was the only clean agent available. One simply determined if a clean agent was preferred for a given application. If so, halon 1301, as the only clean agent available, was automatically selected for use.
Today, with potentially 13 different clean agents to choose from, a fire safety solution using a performance-based engineering selection process is very beneficial to help ensure that the optimal clean agent for the given application is selected. Performance-based fire protection analysis and design is a process that involves determining key performance goals and objectives that a fire protection system must accomplish. This process increases the reliability and effectiveness of a system so designed. The system will be more cost effective and is more likely to satisfy the needs of the system owner and other interested parties.
This paper discusses the key elements that should be included in such a process, when applied to the selection of a clean agent.
PERFORMANCE-BASED FIRE PROTECTION ANALYSIS & DESIGN
The SFPE Engineering Guide to Performance-Based Fire Protection Analysis and Design2(the Guide) offers an excellent performance-based engineering methodology that can easily be adapted to the process of selecting clean agents. The Guide defines performance-based design as follows:
An engineering approach to fire protection design based on (1) agreed upon fire safety goals and objectives, (2) deterministic and/or probabilistic analysis of fire scenarios, and (3) quantitative assessment of design alternatives against the fire safety goals and objectives using accepted engineering tools, methodologies, and performance criteria.
Performance-based analysis and design offers a number of benefits over other design methods, including maximized value, reliability, and effectiveness. The process of performance-based analysis and design, as detailed in the Guide, includes the generic steps listed below (Note: Italics are added to relate the steps specifically to the task of selecting an optimum clean agent).
Step 1: Define the project scope.
(Selection of a clean agent for the specific application.)
Step 2: Identify the project goals and prioritize them.
(Relative to the optimal clean agent for the specific application)
Step 3: Define the project objectives.
(Relative to the clean agent)
Step 4: Develop the performance criteria.
(Relative to the clean agent)
Step 5: Develop design fire scenarios.
(Plausible for the given situation)
Step 6: Develop trial designs.
(Select clean agent candidates that are potentially suitable)
Step 7: Evaluate and modify the trial designs.
(Identify the clean agents with the most suitable characteristics)
Step 8: Select the final design
(Identify the single clean agent with the optimal characteristics)
WHAT ARE CLEAN AGENTS?
Clean agents are volatile or gaseous fire extinguishants that are electrically nonconductive and leave no residue upon evaporation. They were developed and commercialized in direct response to the phase out of halon 1301 initiated by the Montreal Protocol. The Montreal Protocol was adopted into U.S. law through the Clean Air Act of 1990. Clean agents are addressed in NFPA 2001, as well as several international standards. By definition, carbon dioxide is not a clean agent, and therefore is not a subject of this article.
Clean agents are categorized in two chemical groups: halocarbon and inert. Halocarbon clean agents extinguish fire by a combination of chemical and physical mechanisms. The predominant mechanism is a function of the specific chemical compound. Nine halocarbon agents are currently listed in NFPA 2001.
Halocarbon agents that contain bromine and iodine extinguish fire predominantly by chemical means, breaking the chain reaction necessary for a fire to continue. Halocarbon agents that do not contain bromine and iodine, including those that contain fluorine, extinguish fires predominantly by physical means. They extract heat from the flame reaction zone by a combination of heat of vaporization, heat capacity, and the energy absorbed by the decomposition of the agent.
Inert clean agents extinguish fire by reducing the flame temperature below levels necessary to support a continuous combustion process. This is accomplished by simultaneously reducing the oxygen concentration and raising the heat capacity of the atmosphere surrounding the flame. Four inert agents are currently listed in NFPA 2001.
CLEAN AGENTS ARE USED IN SYSTEMS
Clean agents are applied to a fire by means of a clean agent system. Most fire safety solutions involving clean agent systems are a total flooding type, which are configured to flood a specific volume surrounding the fire, thereby establishing a design concentration of agent in air that is capable of extinguishing the fire. Some clean agent fire safety solutions are local application type, which discharge clean agent directly on the burning fuel to extinguish the fire.
Most clean agent fire safety solution systems are arranged for automatic operation, some for manual operation. Clean agent systems are comprised of several integrated subsystems, or components, as shown below.
- Clean agent extinguishant
- Agent storage
- Agent distribution
- Agent enclosure (total flooding systems)
- Fire detection, notification, control
- Auxiliary controls (HVAC shut down, power interruption, etc.)
The process of performance-based analysis and design can be applied to each of the above subsystems. In so doing, the process would be applied to the system as a whole resulting in an optimized system that possesses a high level of quality.
This paper focuses on the application of the process of performance-based analysis and design to the first subsystem listed above the selection of the clean agent.
PERFORMANCE-BASED CLEAN AGENT SELECTION
STEP 1: DEFINE THE PROJECT SCOPE
The project scope defines the boundaries of the performance-based analysis or design. This paper deals with the selection of a clean agent, and that is what the project scope would be.
Project Scope: Select the optimum clean agent for the specific application under consideration.
If the scope of the project were more complex, it would be advisable to identify all of the stakeholders and solicit their input in defining the project scope. Developing a consensus of the stakeholders relative to the project scope will improve the quality and overall acceptance of the results. The Guide defines stakeholder as “one who has a share or interest in an enterprise. Specifically, an individual (or representative) interested in the successful completion of a project.”
A list of stakeholders typical to a clean agent system design project might include, but not necessarily limited to, the following:
- Business owner (end user)
- Design team
- Authorities having jurisdiction (building, fire, insurance)
- Construction team (construction manager, general contractor, subcontractors)
- Clean agent and system manufacturers
STEP 2: IDENTIFY AND PRIORITIZE THE PROJECT GOALS
There are three general goals, one or more of which is commonly assigned to most fire protection analysis or design projects: 1) prevent loss of life or serious injury due to fire or its effects; 2) minimize loss of property due to fire or its effects; 3) minimize interruption of business operations due to fire or its effects (also referred to as mission preservation).
All three of these general goals are applicable to most projects that consider the use of clean agents; however, the third goal is usually the predominant one. Clean agents, for example, are widely used to protect operations that utilize computerized electronic data processing, telecommunications, and broadcasting equipment. It is paramount to keep interruptions to such operations to an absolute minimum in the event of a fire. Preserving the mission is critical. Accomplishing this goal will usually also substantially achieve the second goal. The first goal, protecting people, is always important. For many clean agent applications, such as those mentioned above, the expected fires are relatively low-energy fires that are not likely to threaten the occupants in the immediate surrounding areas before they are able to escape safely.
- Minimize interruption of the company’s business operations where such interruption would harm a customer’s business, harm a customer’s relationship with the company, harm the company’s brands, or otherwise prevent accomplishment of the mission.
- Prevent loss of life or serious injury to building occupants and emergency responders.
- Minimize damage to the company’s physical assets.
STEP 3: DEFINE THE PROJECT OBJECTIVES
This step involves identification of the stakeholder objectives to meet the project goals. The various stakeholders might define these objectives in different terms; however, they should be clear and agreed to by all stakeholders. For example, the company may state a Goal #1 objective to limit interruption of telecommunication operations to no more than 4 hours. The insurance stakeholder may state a Goal #1 objective to limit interruption of telecommunication operations to no more than 24 hours. By selecting a final limit of 4 hours, both stakeholders are satisfied.
Once the consensus stakeholder objectives have been identified, the design engineer translates them into concise design objectives. Design objectives are stated in terms that can be subsequently quantified in fire protection engineering terms and used to develop specific performance criteria.
Feasible stakeholder objectives related to the selection of a clean agent are listed below in bold text. The translation of each stakeholder objective to a design objective is shown in italics.
Goal #1 Objectives:
- Limit interruption of all critical telecommunications operations to no more than 4 hours.Limit damage to all critical equipment from a fire, fire effects, and suppression effects to one, or several, individual components that can be replaced or restored to full service in less than 4 hours.
- Limit interruption of all non-critical telecommunications operations to 48 hours. Limit damage to all non-critical telecommunications equipment from a fire, fire effects, and suppression effects to equipment, or equipment components, that can be replaced or restored to full service in less than 48 hours.
- Maintain power to all critical telecommunications equipment during a fire event to minimize interruption of operations and customer services. Supply power to all critical telecommunications equipments independently from any manual or automatic emergency power off (EPO) systems. The clean agent must be capable of extinguishing fires in energized electrical equipment.
Note: This stakeholder objective is usually not an easy consensus of all stakeholders. Typically the end user and the insurance authority might be in agreement that electric power should not be interrupted to critical equipment. The building and fire code authorities might prefer automatically interrupting power to all equipment prior to application of the clean agent. After negotiations, the building and fire code authorities may agree to allow power to remain uninterrupted. The design engineer may assist in reaching consensus on this objective by offering to select a clean agent, and design the clean agent system, such that it is capable of extinguishing fires in energized electrical equipment.
Goal #2 Objectives:
- No loss of life and no serious injuries to occupants of the protected enclosure from fire or products of combustion. The smoke layer, and radiation heat flux, from all feasible and reasonably conservative design fire scenarios must not cross thresholds harmful to the occupants of the protected space before they are able to exit the space.
- No loss of life and no serious injuries to occupants of the surrounding areas from fire or products of combustion. The smoke layer, and radiation heat flux, from all feasible and reasonably conservative design fire scenarios must not cross thresholds harmful to the occupants of the areas surrounding the protected space before they are able to exit these areas to the building exterior.
- No loss of life and no serious injuries to occupants of the protected enclosure from direct exposure to the clean agent, or its decomposition products. The clean agent selected must not be harmful to the occupants of the protected space in the required design concentration, and must not produce acidic decomposition products during the extinguishing process that could be harmful to an occupant inadvertently remaining in the protected space following clean agent discharge.
- No loss of life and no serious injuries to occupants of the surrounding areas from direct exposure to the clean agent, or its decomposition products. The clean agent selected must not be harmful in the required design concentration to the occupants of the areas surrounding the protected space, and must not produce acidic decomposition products during the extinguishing process that could be harmful to occupants that remain in the building following clean agent discharge. The integrity of the enclosure construction surrounding the protected area must remain during and following clean agent discharge.
- Minimize short-term and long-term harm to the natural environment exterior to the building from the clean agent fire, or arising from the process of accomplishing final fire extinguishment. The selected clean agent must be approved for use in normally occupied spaces by the U.S. EPA’s SNAP program, and must not be targeted for reduction or phase out in the Kyoto Protocol.
Note: The end user would normally identify an objective such as this. Other stakeholders might easily reach consensus to include this objective, since it likely will not conflict with their interests. Furthermore, the United States has not ratified the Kyoto Protocol as of the writing of this article. There is no known regulatory objective in the U.S. that would result in a prohibition on the use of clean agents that contain one or more substances that are targeted by the Kyoto Protocol for control or phase-out. Some end users have set such objectives to achieve harmony with their corporation’s environmental policies. It is shown here to illustrate that environmental factors can be a strong determining factor in the process of selecting a clean agent, and should always be considered in the performance-based analysis process.
Goal #3 Objectives:
- Minimize the loss of physical assets (real and personal property) to no more than $1,000,000. Limit damage to all critical equipment from a fire, fire effects, and suppression effects to one, or several, individual components that can be replaced in less than 4 hours, or non-critical equipment components that can be replaced in less than 48 hours. Do not allow an entire piece of equipment, or equipment cabinet, or equipment rack, to be destroyed by a fire or fire effects. Limit the increase in temperature within the protected space to that which will not cause significant damage to surrounding building construction or service elements. Limit the production of the clean agent’s acidic decomposition products during fire suppression to a level that will not cause significant damage to the surrounding building construction or service elements.
STEP 4: DEVELOP THE PERFORMANCE CRITERIA
Performance criteria for the clean agent must be developed that will satisfy the design objectives (listed in Step 3) and be used to evaluate the trial designs (candidate clean agents).
Goal #1 Performance Criteria
- Extinguish the fire at or below 2 kW.3
- Limit the production of halide acids to a concentration within the protected space of 200 ppm or less.
- Extinguish a fire in energized electrical equipment and prevent re-ignition for the specified hold time or at least 10 minutes.
Goal #2 Performance Criteria
- The design concentration for the clean agent for Class C fires (energized electrical equipment) must be at or below the level corresponding to a maximum 5-minute exposure time as defined in NFPA 2001.
- Extinguish the fire at or below 2 kW.3
- Limit the production of halide acids to a concentration within the protected space of 200 ppm or less.
- The negative and positive pressure changes during the discharge of the clean agent must be controllable to a magnitude of 5 psf or less.
- The clean agent must have
an Ozone Depletion Factor (ODP) of 0.00, a relatively low atmospheric lifetime
and Global Warming Potential, and must not contain HFC
STEP 5: DEVELOP DESIGN FIRE SCENARIOS
The purpose of a clean agent is to extinguish a fire. It is therefore necessary for the design engineer to analyze the possible fire scenarios that are plausible for the protected space. These are then reduced to a reasonable number and called design fire scenarios that represent the boundaries of the conditions present. Only then is it possible for the design engineer to begin evaluating possible clean agents for selection.
Possible fire scenarios should address the heat sources and fuel involved in fire ignition and growth. They should address the building construction, service equipment, and spatial relationships that might influence, or be impacted by the fire. They should address the human element, i.e., such as the number and distribution of occupants, emergency response training and commitment, and the physical and psychological condition related to self-preservation abilities.
Listed below are brief summaries of possible fire scenarios for a typical corporate data center that incorporates sophisticated electronic data processing and telecommunications equipment. It also contains some limited administrative office space for occupants with responsibilities for the operations. The operations are contained within a single room on the first floor of a two-story building of noncombustible construction. The room is fully sprinklered using a double-interlock preaction configuration. The data center room is cut off from surrounding spaces by 1-hour fire rated, full-height walls, and contains an 18-in. raised access floor, and a suspended acoustical ceiling at the 10 ft elevation. The room covers 20,000 square feet and is occupied by 18 persons during the day shift, 8 persons during the evening shift, and 3 persons during the night shift. All occupants are well-trained, full-time employees of the end user. All occupants are capable of self-preservation without assistance.
Possible Fire Scenario #1: An electric drive motor in a high-speed data storage unit overheats due to an internal failure. Insulation on the internal windings ignites, leading to a fire that spreads to adjacent combustibles inside the equipment enclosure.
Possible Fire Scenario #2: A manufacturer’s defect on a printed circuit board inside a telecommunications equipment module within an equipment rack leads to localized overheating and ignition of the board. The fire spreads to adjacent boards until it involves the entire module, then spreads until it involves the entire rack.
Possible Fire Scenario #3: Two electrical extension cords are connected to a wall outlet and extended to a nearby work desk module where four workers share its power simultaneously. The two cords are draped over the top of an open box of paper forms. Their interconnection point is only partially engaged, and is resting on top of the paper forms. The connection point overheats and ignites the box and the paper forms. Initially, this fire is a Class A surface-type fire but, if not extinguished early, has the potential to become a deep-seated Class A fire. The fire could then spread to involve the entire box of forms and begin heating adjacent racks of telecommunication components.
Possible Fire Scenario #4: An electrical fault in a power circuit within a data processing equipment enclosure results in sustained electrical arcing, which is not interrupted by the circuit fault protection device. The heat from the continuous arcing ignites cable insulation that spreads to other cables and combustible components within the equipment cabinet. If not extinguished early, this fire could spread to fully involve the original equipment cabinet, and spread to adjacent equipment and other combustibles. Ultimately, the spreading fire would have enough energy to activate the sprinkler system in the room. This is a Class C fire. It would become a Class A surface-type fire upon interruption of electrical power to the equipment involved.
The above fire scenarios are just a few representative examples of the relative large number of those possible for such an operation. The full range of possible fire scenarios must be identified, then reduced to a smaller, more manageable number of “design scenarios”, which will be used to evaluate trial designs and in selecting a final, optimized design.
Design Fire Scenario #1: Same as Possible Fire Scenario #4.
STEP 6: DEVELOP TRIAL DESIGNS
Trial designs should be developed that have the potential to achieve the performance criteria. The design fire scenarios are used to test the effectiveness of each trial design, with the results being analyzed to help narrow the trial designs to one or two that are most effective. Applying this process to the task of selecting a clean agent is relatively simple, since it involves only one of the several subsystems that are part of a complete clean agent fire extinguishing system.
Trial Design #1: Select clean agent HFC 227ea.
Trial Design #2: Select clean agent IG-541.
Trial Design #3: Select clean agent FK-5-1-12.
The three clean agent candidates identified above as “trial designs” include two halocarbon agents and one inert agent. All three have the potential to meet most if not all of the performance objectives previously developed. These three clean agents are shown for illustrative purposes only. No implication is intended that clean agents not listed are not capable of meeting some or all of the performance criteria established for this project.
STEP 7: EVALUATE AND MODIFY THE TRIAL DESIGNS
The trial designs should be evaluated to determine if they satisfy the performance criteria when challenged by the design fire scenarios. If a trial design is successful, the next trial design would be evaluated, and so on. If a trial design is not successful, it might be modified and retested, or eliminated from consideration. In this manner, all trial designs are optimized, i.e., evaluated, modified, or eliminated, until one or more acceptable designs are developed.
Trial Design #1 Evaluation: HFC 227 ea, a halocarbon agent, is understood to be an HFC compound. This violates performance criteria #5 for Goal #2. HFC 227 ea cannot be modified by eliminating the HFC compound; therefore, it is eliminated from further consideration.
Trial Design #2 Evaluation: IG-541 is an inert clean agent. It is capable of achieving all of the performance criteria for each of the goals; therefore, it is considered an acceptable candidate design. Further evaluation will be accomplished for this agent to determine if it will be selected as the final design.
Trial Design #3 Evaluation: FK-5-1-12 is a halocarbon agent. It does not contain HFC compounds, has an ODP of 0.0, and a relatively low atmospheric lifetime. It is considered an acceptable candidate design. Further evaluation will be accomplished for this agent to determine if it will be selected as the final design.
STEP 8: SELECT THE FINAL DESIGN
The acceptable designs should be further evaluated and one chosen as the final design. All performance criteria should be reviewed and compared to the capabilities of each acceptable design. Secondary criteria that are important to any stakeholder should also be evaluated in the effort to identify the design that is optimum for this particular project.
Design Candidate #2: IG-541 requires a relatively large floor area in the vicinity of the protected area for the agent storage requirements. This floor space is not available currently, and the end user is very reluctant to renovate existing space to make the necessary room for this agent storage. This is a secondary criteria, but one that is important enough to influence the decision on the optimum clean agent for this project.
Design Candidate #3: FK-5-1-12 has a storage space requirement that is immediately acceptable to the end user without requiring space renovations. Furthermore, this clean agent employed in an automatic fire extinguishing system is capable of achieving all primary performance criteria established by consensus of the stakeholders.
The performance-based analysis and design process illustrated in this article has systematically led to the selection of a single clean agent fire safety solution that is optimized for a specific project. The selected clean agent has the capability to enable all primary, and some secondary, performance criteria to be achieved, assuming that the remaining subsystems are properly designed and installed. The probability of accomplishing this to a high degree is greatly increased if the performance-based analysis and design process, as illustrated in this article, are utilized to complete the design of all remaining subsystems.
The examples used to illustrate the performance-based analysis and design process were greatly oversimplified. The reader is encouraged to review the Guide in detail, and study the many design variables that influence the performance of clean agent fire extinguishing systems using each of the available clean agents. Each of the available clean agents have performance strengths and weaknesses that, when properly evaluated, would result in the agent being an acceptable candidate for a given project.
2001, Standard on Clean Agent Fire Extinguishing Systems, 2004 Edition,
National Fire Protection Association, Batterymarch Park, MA.
2 SFPE Engineering Guide to Performance-Based Fire Protection Analysis and Design, Copyright 2000, Society of Fire Protection Engineers and National Fire Protection Association
3 Meacham, Brian J., Factors Effecting the Early Detection of Fire in Electronic Equipment and Cable Installations, Fire Technology, First Quarter 1993, Copyright @ 1993 National Fire Protection Association