CONSULTING-SPECIFYING ENGINEER: What are the criteria for determining when to specify fire suppression in place of traditional sprinklering? RZEZNIK: The use of special suppression systems, which includes both gaseous agents and water mist systems as the primary extinguishing method, is generally dictated by the nature of what's being protected and its relative value to the owner—or to so...
CONSULTING-SPECIFYING ENGINEER: What are the criteria for determining when to specify fire suppression in place of traditional sprinklering?
RZEZNIK : The use of special suppression systems, which includes both gaseous agents and water mist systems as the primary extinguishing method, is generally dictated by the nature of what's being protected and its relative value to the owner—or to society as a whole. Suppression systems generally come into play when the threshold of acceptable loss, due to both the fire and the application of extinguishing agent, are considerably lower than that associated with sprinklers.
HOLST : Without question, sensitive environments, such as data centers or rare document storage areas, contain valuables that require a solution that will not only protect the space but also preserve its contents. Since a wet sprinkler system can destroy computer components or rare documents in a matter of seconds, a gas suppression system is preferred. But suppression systems are costly, and the owner must determine whether the components or documents in the space are worth the added cost.
BEHNKE : But don't forget the multiple advantages of clean-agent fire-suppression systems:
They are clean, which is generally defined as not leaving behind a residue or damaging the equipment as is the case with water.
They are fast, because fire suppression is normally matched with an early-warning fire-detection system with smoke, flame and even air-sampling units. And incidentally, these typically react much faster than a temperature link or bulb.
Most are occupant-friendly in that people can remain in the room while the agent is discharging. Of course, it's always best to evacuate, but that is not always an option. An obvious exception is carbon dioxide, where evacuation is mandatory due to the depletion of oxygen.
Finally, a few agents are also sustainable, meaning that they will not likely be subject to future environmental initiatives.
HOLST : It's also true that other sensitive environments, such as areas containing chemicals known to respond adversely to water, require a gas suppression system, not only to preserve the space, but also to prevent a greater fire event.
LaSALLE : And some owners and users have long-held opinions against the use of water-based systems, particularly wet-pipe sprinkler systems. Often, their objections can be traced to misconceptions about how such systems actually function. But where education and technical arguments are ineffective, special suppression systems are the most viable alternative.
CSE: Although special suppression is significantly less damaging to sensitive environments than are sprinklers, can these systems still potentially damage valuable contents?
BEHNKE : Most chemical clean agents, when they contact fire, can produce acidic byproducts that can damage sensitive equipment and materials. But these systems are paired with fast-acting detection and are required to discharge quickly in order to suppress a fire—while it is still small—and minimize the duration of agent/fire exposure.
Inert gas agents, because they do not create these harmful byproducts, can be discharged less abruptly, but are also matched with a fast-acting detection system simply to minimize the damage caused by fire itself.
HOLST : The suppression systems used today are also thoroughly tested for their effects on computer and electrical equipment and cause almost no damage when deployed in those environments.
However, real-world situations can differ greatly from ideal testing environments. New products are not rigorously tested against every other product or compound that may be found in the office place. If something is present in the room—be it a liquid, gas or solid—that was not part of the testing conditions, the gas suppression system may react negatively. In addition, materials used to design computer components change every day.
That being said, the most important item in any occupied space is the occupant, and all manufacturers test for life-sustaining capabilities in any new product. The real world, however, can throw you a curve. For example, on a recent project, we came across an old CO2 system used to protect the underfloor space in a data center. This halon-alternative system was installed at a time when halon had been banned. However, the concentration of CO2 required for this particular fire suppression system far exceeded the human tolerance to the agent, so the system had to be replaced.
RZEZNIK : The drawbacks and unintended consequences of the interaction between special suppression systems and fire need to be carefully considered when matching an agent with a specific application. Take clean agents that rely primarily on oxygen displacement. By reducing oxygen levels to a point where the space can no longer support combustion, this method can be very effective. But large volumes of these agents are required to achieve such a goal in the desired time frame. This can result in high minimum nozzle discharge pressures, potentially resulting in the rocketing of unsecured objects within the volume, creating potentially damaging projectiles—or in the instance of protecting fragile or historic fabrics, the potential for tearing.
In a similar vein, Fluorine-based halogen agents have been reported to produce localized concentrations of hydrofluoric (HF) acid. Although testing has generally concluded that HF levels are negligible, there remains the possibility for negative effects.
LaSALLE : What the research has shown is that such products are not likely to be toxic at the resultant concentrations, but elevated levels of such gases may result in damage to nearby equipment or objects and should be avoided.
CSE: What are the most common errors designers make when specifying fire-suppression systems?
LaSALLE : Errors can occur in the technical design of the systems themselves and in a failure to understand suppression system code requirements. Common examples of the former include improper piping design, miscalculating the required agent quantity and omitting interlocks with other systems. Such errors can result in inadequate agent concentrations, overpressurization of enclosures or loss of agent through openings.
An example of the second type of error is using a clean-agent system in lieu of sprinkler protection without knowing all the code compliance implications. The major codes have relaxed requirements for such issues as exit travel distance, corridor wall fire-resistance ratings and other features when a building is fully sprinklered. If a sprinkler system is not provided as a backup, or if the designer does not pursue the necessary approvals, an owner could face delays in occupancy permits or significant cost increases to meet the requirements of an AHJ.
HOLST : A common error is not specifying and documenting the testing and commissioning of the system. For example, while individual components—circuits, for example—may be working properly, that doesn't mean the entire system will react properly in a fire situation. Often, it is assumed that the system will work, and that testing isn't necessary. But commissioning and testing of the system's ability to perform as designed is critical for the safety of occupants and contents. One crossed terminal or one untested function can cause havoc once the system is installed and the contractor is gone.
For example, during the testing phase of one of our projects, we discovered that the reporting panel for the fire-suppression system was showing the wrong room for the fire event that was occurring. The room numbers had been changed during the project construction phase, and the controls contractor was using the old numbers. If this hadn't been discovered during testing, the damage caused and time wasted could have been disastrous.
Improper selection of a fire-suppression system can be another design error. The function of the space, the type of detection system, reporting requirements and the number of panels must be decided prior to specifying the system.
Yet another common error is not thinking through the actual process of extinguishing a fire. When a sprinkler system goes off in a data center, where does the water go? Designers often forget to provide some means of draining the water. Also, what are the sequences of events that will occur from detection to extinguishment, and do they meet the requirements and expectations of the owner?
RZEZNIK : Regardless of the agent, there are two things I see that can get neglected during a total-flooding special-suppression system design: integrity of the volume enclosure and the detection system used to initiate the suppression systems. Openings into, and penetrations through, enclosure walls should be limited to those absolutely necessary to serve the space. And then required openings must be properly sealed. Finally, as an operational consideration, the seals should be easy to maintain.
As far as detection systems and associated sequences of operation, the method needs to be sensitive enough to initiate discharge early in a fire's development. However, they can't be so sensitive as to make operation of the space impractical. The system's sequence of operations should be arranged to sound pre-discharge tones, release doors, close dampers, shut down power and shut down fans. It should also perform other relevant functions in the appropriate sequence which will be specifically defined by the situation and area being protected. Owner/operator input here is critical.
Likewise, the owner or operator must be solicited for their input regarding suppression options. Individuals most familiar with the area, object or process being protected have valuable information with regard to the sensitivities of what is being protected that may not be easily noticed by the engineer tasked with implementing an overall protection plan.
CSE: How do you avoid such mistakes?
RZEZNIK : A detailed peer review with a qualified fire-protection engineer not intimately involved in the project is always a valuable quality-control tool.
HOLST : Besides testing and commissioning—and making sure it's written into the specs—be sure to review the entire process and sequence of events from detection through extinguishment with the owner.
But mostly, remember that suppression systems should be uncomplicated and logical. During a fire event, people do not always act rational—and there isn't time to look for the instruction manual. Be sure the owner has a clear set of documents and a description of the events that are set to happen.
Michael J. Rzeznik , P.E., Regional Office Manager Schirmer Engineering Corp. White Plains, N.Y.
David N. Holst , Plumbing/Fire Protection Systems Department Manager, Bala Consulting Engineers, Philadelphia
Jeffrey LaSalle , P.E., Principal, LaSalle Engineering, LLC, Hatboro, Pa.
Joseph Behnke , Manager, Technical Services Engineered Systems, Tyco Safety Products, Fire Suppression Business, Marinette, Wis.
An Eye on the Codes
As with any building system, when it comes to fire suppression systems, it's key for engineers and consultants to keep up with the latest codes.
"Fire codes and standards are constantly changing," says Joseph Behnke, manager of technical services, engineered systems, for Tyco Safety Product's fire suppression business, Marinette, Wis. "Therefore, it is important to keep abreast of the standards published by the National Fire Protection Association and pay close attention to the requirements of local AHJs."
For example, one recent change to the International Building Code requires that building officials approve the use of extinguishing systems that are proposed as an alternative to required automatic sprinkler systems, according to Jeff LaSalle, P.E., chief fire protection engineer, EwingCole, Philadelphia.
"While this has always been a tacit requirement, the IBC now explicitly states that the code official must approve such substitutions," explains LaSalle.
Yet another change to be aware of, says Michael J. Rzeznik, P.E., regional office manager, Schirmer Engineering Corp., White Plains, N.Y., is that exposure limits for halocarbon-based agents have recently been modified.
"These new limits are based primarily on physiological-based methods, as opposed to the use of observable reactions. Exposure limits based on these physiologically based pharmacokinetic (PBPK) methods have opened the door for new agents and resulted in expanded exposure concentration levels for other agents already established in the marketplace," he explains.