Fighting Fires in Data Centers
May 01, 2007
Appeared in Building Operating Management/FacilitiesNet
Until the mid 1990s, one substance was used to protect most data and telecommunications centers from smoke and fire damage: Halon 1301. Unlike water, Halon 1301 didn’t damage equipment. What it did damage, however, was the ozone layer. The Montreal Protocol, signed in 1987, essentially spelled the end of production for Halon 1301.
Today, facility executives can choose from several other extinguishing agents when protecting data centers. Most fall into two broad categories: halocarbon agents and inert gases. Pre-action sprinkler systems also are an option. Properly installed, all are effective and have been approved for use by the National Fire Protection Association (NFPA) says Brian Fabel, director, national accounts, Orr Protection Systems. The best choice for a particular facility will depend on the system’s overall cost, the way in which the system will be used and the space available to house the extinguishing substance.
Clean Agent Halocarbons
Clean agent halocarbon gases go by several trade names, including FM200, FE-25, and FE-13. “They work by removing heat from the fire,” says Tom Wysocki, president of Guardian Services.
FM200 was the first halon replacement agent. As a result, it’s the most widely used of the halocarbon clean agents, says Jeffrey Amato, associate fire protection consultant with Schirmer Engineering. It is stored in cylinders, and, because it must discharge in 10 seconds or less, the cylinders often need to be located near the space the FM200 is protecting.
FE-13, because of its low boiling point, is particularly well-suited for environments with lower temperatures, such as offshore oil platforms. With a maximum nozzle height of 25 feet, it also is suitable in areas with high ceilings. However, the high pressure of an FE-13 system limits the amount that can be stored within the piping. In addition, compared to FM200, a greater volume of FE-13 is required to effectively suppress a fire.
The flow characteristics and required vapor pressure of FE-25, also known as HFC-125, are most similar to Halon 1301. As a result, it often can be used as a “drop-in” replacement in Halon 1301 systems and usually requires only minimal adjustments to existing piping.
NOVEC 1230, which actually is a fluoroketone, is a fire suppression fluid. It is stored as a liquid, but discharged as a gas. “It is easy to charge and handle, because you don’t have to deal with super-pressurized cylinders,” says Amato. And, because it is a liquid, it can be transported via air in bulk quantities, he says. In contrast, most clean agent gases must be shipped in pressurized cylinders, in limited quantities and by ground transport.
To some extent, the environmental impact of the agents varies. However, Fabel says that overall they have a minimal effect on the environment. “All have an incredibly low impact when compared to everyday things like autos and homes.”
Similarly, these products have been tested by the Occupational Safety & Health Administration, and found to be safe in the concentrations required to extinguish a fire. That’s not to say that the agents have no potential effect on people. What’s important to keep in mind when evaluating any possible health effects, experts say, is the way occupants of a building will be exposed to the agents.
One way to determine the safety of a particular agent is to review its no observable adverse effects level (NOAEL). This measures the concentration at which adverse effects first are noticed in laboratory animals. For instance, the NOAEL for one clean agent is 10 percent. However, that product is effective in suppressing fires at concentrations of 4 to 6 percent. That leaves a fairly large safety margin, says Bobby Patrick, senior consulting engineer with RJA Group.
Any time a fire suppression system discharges, occupants should evacuate the building. That’s true whether the suppression system uses water or clean agents. “Only trained fire response personnel should remain in a facility in which a suppression system is operating,” says John Eager, senior associate in the critical facilities group with Syska Hennessy Group.
Special requirements are involved with suppression systems installed under NFPA Standard 2001, Clean Agent Fire Extinguishing Systems. With those systems, the room is under high pressure when the clean agent is released — another reason to evacuate the room. In addition, the room in which the agent discharges should be air-tight for at least 10 minutes to maintain the concentration required to suppress the fire.
Inert gases suppress fires by lowering the oxygen concentration in the room below the level needed to sustain combustion. However, the concentrations typically are not low enough to create a danger to humans, Wysocki says.
Inergen is a mixture of three naturally occurring gases: nitrogen, argon and carbon dioxide. Inergen works by lowering the oxygen concentration below the level that supports combustion, while also increasing the carbon dioxide present in the room. This prompts occupants to breathe more rapidly, compensating for the reduced oxygen environment, Amato says.
Due to the volume of Inergen required to create conditions in which a fire can’t be sustained, pressure in the room increases significantly upon its discharge. To avoid damage to the facility, pressure vents may be required, Amato says.
Which to Choose?
Does it make a difference whether a halocarbon clean agent or an inert gas is chosen as a fire suppression system within a data center? Each has its pros and cons.
For instance, inert gases require seven to eight times the storage space of chemical clean agents. In typical applications, chemical agents are used in concentrations of about 4 to 18 percent, versus 35 to 40 percent for inert gases. In addition, chemical agents can extinguish in about 10 seconds, while inert gases typically require about 60 seconds.
On the other hand, when necessary, inert gases can be piped hundreds of feet to a data center and retain their effectiveness, Wysocki says. Liquefied halocarbon gases typically can only be piped up to about 100 feet. So, if the cylinders will be stored in the basement and the agent piped up a number of stories to reach the data center, inert gas may be a better choice.
In addition, inert gases may perform more effectively in rooms that aren’t well sealed, Fabel says. And, it typically is less expensive to replace inert gases, should the system discharge, he adds.
The costs of the different systems also vary. Liquefied gases generally are more expensive than inert gases. However, more cylinders of inert gas generally are required to protect a given area, which drives up costs, Wysocki says.
A Role for Sprinklers?
Finally, it’s important to note that experts consider sprinkler systems, when properly designed, to be safe and effective in data centers. The pipes in what are known as pre-action sprinkler systems do not hold water, unlike standard sprinkler systems, says Patrick. This reduces the risk of leaks that could damage computer or telecommunications equipment.
Instead, a valve within the system is located outside the data center and keeps water from entering. In order for water to get past the valve, two events have to occur. First, a smoke detector has to let the system know that a fire is occurring; at that point, water moves into the pipes. However, the fire has to grow to a certain temperature before the valve will open and water can discharge into the room. Given that these two events have to occur before water will flow through the pipes that are located within the data center, the risk of an accidental leak is greatly reduced.
Using a pre-action sprinkler system in a data center offers several benefits not available with other systems, Patrick says. For example, according to the International Building Code, facilities that incorporate sprinkler systems can be designed to require occupants to walk further to get to an exit than is allowed in buildings without sprinkler systems. Similarly, the code allows sprinklered buildings to install walls that have a lower fire rating than that allowed in buildings without sprinkler systems. The code does not exempt buildings with data centers from these requirements.
In addition, sprinklers tend to be less expensive than clean agent systems. The piping required to bring water to the data center is similar to that required for a clean agent system. However, unlike clean agents, the water used in the sprinkler system typically is city water and doesn’t come with an extra price tag.
Ideally, buildings would include a sprinkler system throughout the facility, as well as a gaseous fire suppression system in the data or telecommunications center, Patrick says. “You get the best of both worlds.” The gaseous system likely would be more sensitive to fire, and would put any fire out before it expanded too far. However, the sprinkler system would be ready to go, in the event that a fire grew so big that it threatened the safety of the occupants and the building structure itself. And if the fire is hot enough that the sprinkler does go off, the computer equipment most likely already is sustaining damage from the heat, flames and smoke, Patrick says.
Very Early Detection
Another fire-fighting tool is what is known as a very early smoke detection apparatus (VESDA), says Eager. These consist of systems of pipes and aspirating devices that draw air from throughout the building to a central location. The systems are so finely calibrated that they detect smoke and products of combustion even when they are present in much lower levels than would be noticed by a standard smoke detection system. As a result, they’re particularly useful in detecting fires or smoke that can fester beneath the raised floors typical in data centers. These often are harder to detect, given the high air flow and cooling conditions under the raised floors.
Of course, no matter which system is installed, it’s critical that trained professionals handle the installation, and that the system be properly maintained. Given the amount of heat generated by equipment in a data or telecommunications center, fires can and do occur. When they do, both property and lives depend on the effectiveness of the fire suppression system. “The only time you find out what you’ve got is when the systems are asked to perform,” Fabel says.