Aspirating Fire Detection in Data Centers
Technology provides early smoke detection and streamlined testing and maintenance
Fire is the second-leading cause of failure (after power issues), according to a 2015 Capitoline survey, and the risk is increasing as greater power densities (20-plus kW per rack) are housed in more confined spaces.
When a fire does occur, the downtime can be catastrophically expensive.
“Because data centers are so critical to business operations today and so costly in terms of service disruption and reputational damage when there is downtime, the goal is to detect fires as early as possible at the incipient stage before it becomes a fire fighting exercise,” said Steven Joseph, director of market development - Mission Critical division at Xtralis.
However, a dilemma occurs when data center owners try to meet prescriptive fire safety regulations designed to protect humans, not assets. After all, most data centers are staffed by very few people.
Given the sheer size (which can encompass hundreds of thousands of square feet) and how densely packed with hot, power-intensive electronics these environments can be, the focus needs to be on achieving high-performance, 24/7 uptime, along with asset preservation.
Data Center Smoke Detection Challenges
“As a result of maximizing server power in the smallest available space, present day data centers often have unusually high heat densities of more than 300 W per square foot,” said Joseph.
He added that data centers contain ample sources of fuel (plastics, circuit boards, and insulated jacketing for wires) and that mechanical equipment, such as HVAC systems with moving parts, fans, bearings or belts, can start a fire from friction.
Mounting spot smoke detectors on ceilings is increasingly becoming insufficient to alert data centers of a fire risk before an outage or serious service disruption is triggered. One significant reason is that most data centers direct large volumes of air to cool equipment, and spot detectors wait for smoke to accumulate at their sensing chamber.
“In the beginning stages of a fire, smoke has very little buoyancy because it doesn’t have much heat,” Joseph said. “Combined with the strong airflow for cooling, it will not have the thermal lift needed to reach the ceiling. Air mixing from cooling also dilutes any smoke accumulation in the space. So, the smoke migrates with the airstream away from the ceiling.”
According to Joseph, structural barriers near the ceiling such as HVAC ducts and fully loaded cable trays can also obstruct smoke from reaching detectors.
The industry’s practice to contain server aisles (which directs air to cool equipment within a designated aisle rather than the entire space) is also complicating traditional spot-type smoke detection.
“When traditional smoke detectors are installed within contained hot aisles, the high heat temperatures reached in the hot aisle can, in some cases, exceed the listed range of traditional smoke detectors, which renders them unsuitable,” Joseph said. “The problem is that our codes and standards are written to predominantly address life safety, not necessarily asset protection. But from a data center owner’s perspective, asset and business continuity protection is a key goal.”
Fortunately, the International Code Council (ICC) accepts alternative, performance-based designs that allow for “alternate materials and methods” that offer equivalent or superior fire safety performance. In terms of enhancing fire safety, this often involves scientific calculations and engineering as well as computer fire modeling. With this approach, a design is considered acceptable if the fire engineering calculations demonstrate that it meets the measurable performance criteria set at the start of the process.
“Many data center owner/operators that rely on a design-build approach to meet the prescriptive life safety requirements are finding out the hard way that they may not get the very early detection and asset protection they require due to structural and environmental constraints,” Joseph said. “So they need to supplement this with a performance-based fire detection system that meets their asset preservation and business continuity objectives.”
One way that data center owner/operators are achieving asset protection and business continuity goals is with advanced aspirating smoke detection technology. The technology enables earlier detection and a swift response by detecting very small concentrations of smoke particulate, potentially before smoke becomes visible or a fire begins to flame and burn. Newer generation aspirating technologies are better suited to discriminate against dust, which can minimize false alarms.
Some aspirating detection systems can identify and monitor smoke density by individual sampling pipes that allow a single zone to be divided into four separate sectors.
In case of fire, this capability this allows responders to more accurately target the affected area. Systems like this also provide several programmable alarm thresholds that enable a swift escalating response, which can help to stop a fire and minimize potential damage before a fire suppression release.
Ease of maintenance
Even with these benefits, one of the primary advantages of an aspirating smoke detector system is its ease of maintenance, inspection, and servicing.
Aspirating systems do not require testing at each sample hole. Instead, tests can be conducted at the central unit and at benchmark test points, which can be can be conveniently located at ground level, outside of secured areas.
And although aspirating detection systems cost more than traditional spot smoke detectors on a one-to-one basis, they can end up costing less than conventional options overall.
“When total costs, including operational expenditures like testing and maintenance are included, aspirating systems often come out ahead,” said Joseph.
For more information, visit www.xtralis.com.