Fire Protection in Mission-critical Facilities
Fire-protection technology for mission-critical facilities has long been a standard consideration for most engineering, IT, and facilities professionals. Whether as simple as portable extinguishers or as complex as high-sensitivity smoke detection coupled with clean-agent suppression systems, fire protection is a must.
Historically speaking, mission-critical facilities (MCFs) have required an elevated level of fire protection due to two factors:
- MCFs comprise a collection of high-value assets, typically electronics, that have significant monetary value and are often even more valuable operationally. The cost of replacement and downtime associated with damage to these assets can be astronomical.
- MCFs inherently involve a greater level of risk than most commercial space because of the presence of both a constant ignition source (electricity) and a plentiful supply of fuel (generally plastics as in printed circuit boards).
These facilities have different fire protection requirements. Traditionally, systems have been sought that provide the greatest level of protection for the least cost. The level of protection provided can be loosely evaluated using two standards:
- extinguishing fire rapidly and effectively
- minimizing damage to the protected assets.
Fire Protection EvaluationAnalyzing a facility is the first step in evaluating potential fire protections schemes. Three factors should be considered:
- Analysis of facility. In new construction, particular requirements such as tightly sealed windows/doors and venting if necessary should be examined (see below for discussion of various clean agents). In older facilities being outfitted with a suppression system, room integrity is of critical importance. Most local fire protection contractors can assist in a determination of room integrity for a given facility.
- Hazard analysis. It is most important to differentiate between class A (common combustibles such as plastics and fabrics) and class B (flammable liquids) hazards. Most MCFs contain only class A hazards, but a thorough review of the hazards in a space will reveal other risks. AHJs and system manufacturers can provide additional guidance in this area.
- Overall risk assessment. A thorough risk assessment leads to an understanding of the potential harm of an incident and the likelihood that it will occur. A risk matrix helps determine how a given facility should be categorized (see figure 1).
Protection StrategyIt is natural to compare the cost and effectiveness of fire protection strategies when determining how to protect a facility (see figure 2).
- A pre-action sprinkler system is water based and incorporates several operations in order to minimize the risk associated with accidental discharge and water damage. With a pre-action system, a significant level of heat is required to activate the system. While the level of risk associated with false discharges or damaged heads is low, the level of protection to the assets is still based on heat detection and water discharge. Use of water-based systems should be considered as part of the overall risk profile within the MCF.
- Waterless/clean agent systems are typically gas based and offer a system of detection, control, and suppression. Early fire detection sends a signal to a control panel that provides a countdown prior to agent discharge (typically 30 seconds) to allow for occupants to evacuate and for other preparations (e.g., mechanical door closures, automatic dampers, etc.) to activate.
Waterless Fire Protection Systems - An OverviewIn developing a waterless fire protection scheme, additional choices and further evaluation are necessary. The suppression system is made up of a multitude of components from valves, piping, nozzles, cylinders, and the suppression agent itself. It is important to recognize the importance of the agent, as well as the system as a whole, and how the agent is delivered to the protected space.
Halon 1301 is the suppression agent by which all others are compared. Halon is exceptional at extinguishing fires, and its safety for both people and the protected space is outstanding. However, the Montreal Protocol banned the production of Halon 1301 and led the industry to develop a number of Halon alternative agents.
These alternatives include: (Brand names are used due to their universal recognition. Many different chemical formulas, names, and other designations can be used for each of these compounds. See figure 3 for additional designations.
- FM-200 is the brand name for the compound HFC-227ea, or heptafluoropropane. FM-200 is a hydro-fluorocarbon (HFC) compound and is the most widely used and recognized halon alternative on the market today. FM-200 extinguishes fires through the absorption of heat and does not significantly reduce the oxygen concentration within the space. An FM-200 discharge does not leave a residue or harm people or equipment in the protected space. The extinguishment times and storage space required are very similar to Halon (see figure 4). Concentrations for FM-200 use are typically between 6.25 and 8 percent by volume.
- FE-13 is also an HFC compound and is a lesser used, niche agent. FE-13 has several unique characteristics, including a very low boiling point that allows it to vaporize when discharged at very low temperatures) and a high vapor pressure (allows the discharge to be quite energetic). These two features make FE-13 a good choice for low-temperature applications (both storage and protected space) as well as particularly high ceiling applications. Concentrations for FE-13 use are typically around 20 percent by volume.
- FE-25 is a newly available Halon alternative. FE-25 had long been used for unoccupied spaces, but it is now applicable to all traditional occupied space applications through the use of physiologically based pharmacokinetic (PBPK) modeling. PBPK is a simulation methodology used to predict human response and blood stream absorption in the exposure to these types of compounds. The two major standards organizations that establish guidance for use of these systems (ISO and NFPA) have both adopted the PBPK method for the determination of toxicology thresholds at which these agents may be used safely in an occupied space. Prior to the adoption of the PBPK model, FE-25 had a use concentration slightly above the first threshold of toxicology, called the no adverse effect level (NOAEL). Presently, use concentrations are slightly below the thresholds determined using the PBPK methodology. The compound is also an HFC and extinguishes fire in much the same mechanism as both FM-200 and FE-13. Concentration for FE-25 use is typically between 8.0 and 9.0 percent by volume.
- Novec 1230 fluid is the newest clean agent on the agent market. Novec 1230 fluid is a Fluorine-based compound but is not an HFC. Novec 1230 fluid extinguishes fire by absorbing heat and thus does not reduce oxygen concentrations within the protected space, similar to all three HFC compounds mentioned above. Novec 1230 fluid has both zero ozone depletion potential and an extremely short atmospheric lifetime, which contributes to its low global-warming potential. Novec 1230 is a good selection in applications with end users who are particularly sensitive to environmental factors. The concentration for Novec 1230 fluid use is typically between 4 and 6 percent by volume.
- Argonite is different from the other agents in that it is a blend of naturally occurring gases, not a Fluorine-based compound. Argonite is an inert-gas compound. Argonite is a 50/50 blend of Argon and Nitrogen. Argonite reduces oxygen in the protected space so that combustion cannot sustain itself. This oxygen reduction does not, however, preclude using Argonite in an occupied space because the oxygen concentration is reduced to a point at which combustion cannot be sustained but human safety is maintained for a short exposure. Argonite systems require dedicated venting systems because the quantity of agent is significant in order to reduce oxygen levels sufficiently.
- Inergen is also a blend of naturally occurring gases, similar to Argonite. Inergen is a blend of approximately 40 percent Argon, 52 percent Nitrogen, and 8 percent Carbon Dioxide (CO2). The added CO2 in Inergen serves one primary purpose. CO2 increases the breathing rate in humans. In a reduced-oxygen atmosphere, it is helpful to increase breathing rates, to take in more oxygen. Inergen is also subject to venting requirements as mentioned above for Argonite. Typical use concentrations for both Argonite and Inergen are 35 to 40 percent by volume, resulting in an oxygen concentration of between 12 and 14 percent.
ConclusionFire protection for mission-critical facilities can be a complex and daunting topic. It is best to break up the task into several topics and begin to create manageable assignments out of each one.
- Understand the value of the facility in question. Value can be defined in a number of ways from asset value to operational value to historical or sentimental value.
- Evaluate the level of risk in the facility in question. What has been done to mitigate these risks? What can be done? What should be done in order to adequately protect against a potential hazard, including fire, in the facility?
- Investigate the options available from water-based systems to waterless systems and determine what is right for a facility and its business. Understand the unique and varying levels of protection from each option. It is the business owner’s responsibility to fully understand what each system will provide.