Avoiding the Smell of Burning Data
Information technology has become an important and integral part of our daily lives. As a result, most organizations today have a primary data center, which accommodates the computing, data storage and networking equipment that are critical to operations and communication. Since the strategic importance of information technology in business depends on uninterrupted use, data centers require a superior fire protection, security and backup power infrastructure.
Due to significant financial losses that can follow business interruption, the importance of fire protection cannot be overemphasized. Data centers and information technology equipment—on which these businesses depend—are particularly vulnerable to the effects of fire. Therefore, fire protection engineers should consider the following when designing systems for data centers: location of the data center; fire detection methods; fire suppression methods; equipment, utilities and materials; and housekeeping.
Fires originating within data centers will always represent a serious threat to these facilities' reliability and uptime. Even though data center fires are relatively infrequent, their effects can result in considerable loss of revenue, data and, ultimately, customers.
The typical fire types found within data centers are Class A and C fires. Class A fires involve ordinary combustibles, such as wood, paper, certain plastics, rubber and cloth, while Class C fires involve energized electrical equipment. A study performed by NFPA indicates that the majority of fires originating within data centers are Class C fires involving electrical distribution equipment. Additionally, according to FM Global, Class A fires in data centers are typically caused by arson.
Both NFPA and FM Global indicate that electricity is the main ignition source causing fires within data centers. This demonstrates that even electrical equipment installed in accordance with all applicable codes and standards can still experience failure modes that potentially result in ignition.
According to NFPA, electric wires and cable insulation was the material ignited in one-third of the fires reported for its study. However, the property damage due to these fires was limited, since two-thirds of them were confined to the object of origin. Furthermore, per FM Global, arson is one of the leading causes of fires in data centers, as measured by loss amounts. To reduce the possibility of initiating a large fire and increase the chance that a fire protection system will be capable of controlling or extinguishing the fire, it was concluded that ordinary combustible and plastic materials should be limited within data centers.
The equipment found within data centers is mainly vulnerable to the heat conditions, steam and combustion products accompanying a fire. Here are some possible scenarios:
Elevated temperatures in excess of 120°F may damage computer equipment such as magnetic tapes (above 125°F), hard disks (above 125°F) and equipment components (above 174°F).
Corrosive combustion byproducts such as zinc chloride (ZCl) solution, hydrogen fluoride (HF) and hydrogen bromide (HBr) may damage electronic components.
Soot particles may form an insulating layer on equipment, which may impact contacts.
Conductive soot may lead to electrical shortening.
A trend within the information technology industry is a decrease in floor space and an increase in more compact and powerful computer systems. Consequently, more heat is being generated and the number of potential ignition sources is increasing, which increases the possibility of fire development. This trend is also making it more difficult to protect data centers against fire and its products of combustion, since equipment and electrical cabling are more densely packed. Additional challenges associated with fire protection within data centers need to be addressed when choosing fire protection strategies:
The vulnerability of information technology equipment.
Access problems associated with raised floors and ceiling voids.
High airflow conditions/smoke dilution, which makes detection more difficult.
Restricted access, which makes maintenance more difficult.
An ideal setting
Another consideration is location. According to FM 5-32 and NFPA 75, data centers should be in non-combustible buildings and should not be located adjacent to, below or above areas or other structures where hazardous processes are located. Additionally, data centers should not be located in basements. If a basement is the only option, precautions should be taken to facilitate smoke venting and to prevent flooding from interior and exterior sources that can occur, including a fire on an upper floor. FM recommends that data centers should not be located in multi-story buildings, especially unsprinklered buildings. The large area above or below the computer system floor creates a far greater probability of damage due to an exposure fire than in a single-story building.
Experience with fires affecting data centers has demonstrated that the fire often starts in areas outside of the data center. The fire and its related products can enter the data center if the center is not adequately separated from other areas of the building by sealed and rated walls. According to NFPA 75, data centers should be separated from all adjacent occupancies by at least one-hour fire-resistive rated walls having 45-minute opening protection and all penetrations protected by a material having the same fire-resistive rating as the penetrated wall. However, it is recommended to increase the rating of the perimeter walls to two hours where adjacent walls are already rated two hours or greater.
FM Data Sheet 5-32 recommends more stringent separation requirements and suggests that data centers should not be directly connected to any supporting areas. However, if it is connected, the wall separating the data center from adjacent areas should have a fire-resistive rating of at least one hour with one-hour rated openings and penetration seals. Both NFPA 75 and FM 5-32 recommend that the wall separating the data center from the adjacent occupancies should extend from the structural floor to the structural floor above.
Given IT equipment's high vulnerability to fire damage, early detection within data centers is extremely important. The probability of a devastating fire can be significantly reduced by choosing the correct fire detection system.
Fire detection can be achieved by both heat and smoke detection. Automatic sprinklers, which are mandatory throughout, and heat detectors are commonly found within data centers. However, these devices are ineffective at the incipient fire stage (i.e., before a damaging amount of smoke is present). Consequently, both NFPA 75 and FM 5-32 require an approved smoke-actuated fire detection system in the following areas of a data center:
The ceiling level throughout the data center;
Below raised floors containing cables;
Above suspended ceilings and below raised floors when these areas are used to recirculate air to other portions of the building.
Smoke detectors, identified by their operating principle, are either ionization or photoelectric. Ionization smoke detectors are quicker to respond to flaming fires, since they respond to relatively small particles. Photoelectric smoke detectors, on the other hand, provide a faster response to smoldering fires, since they respond to relatively large particles.
Due to the increasing importance of early warning, the sale of photoelectric smoke detectors has increased significantly in recent years; 75% of smoke detectors sold worldwide in 2001 were of the photoelectric type. This trend, according to the 19th Edition of the NFPA Fire Protection Handbook, is a result of the performance advantage of photoelectric smoke detectors in detecting smoldering fires and their ability in detecting flaming fires when the fire is not in close proximity.
In addition to operating principles, there are also two categories of smoke detector in terms of response time: early-warning smoke detectors and very-early-warning smoke detectors. Early-warning smoke detectors are the traditional ceiling-mounted, spot-type detectors of the ionization or photoelectric type, while very-early-warning smoke detectors are of the air-sampling type.
Air-sampling smoke detection systems using the cloud-chamber principle are recommended within data centers due to the high airflows created by HVAC systems, smoke dilution caused by turbulent airflows and the importance of detecting a fire in the incipient stage and of avoiding false alarms.
These systems constantly sample the air from multiple points throughout the environment, and if any smoke particles are present, a cloud will be formed within a sensing chamber and a photoelectric light-scattering detector will respond if a predetermined threshold value is exceeded. The value of air-sampling smoke detection systems is also recognized by NFPA 75 and FM 5-32 and is recommended in areas where the loss expectancy to fire and/or smoke is very high.
VESDA (produced by Vision Systems) is one of the more commonly used air-sampling smoke detection systems today. It provides very early warning by detecting smoke particles in the incipient stage of a fire. The system can be provided with multiple alarm trigger points ranging from 0.0015% to 6% per ft. obscuration, which allows it to be used within clean, dusty, dirty or smoky environments. Due to its sensitivity, VESDA is unaffected by high airflows and can overcome smoke dilution, and the frequency of nuisance alarms with the system is relatively low.
The correct strategy
The likelihood of business interruption within mission critical facilities such as data centers can be significantly reduced by applying the correct fire protection strategies. It is recommended that owners and insurers of data centers follow the guidelines provided by NFPA 75 and FM 5-32 when designing for fire protection. Additionally, very early warning smoke detection systems and clean agent total flooding systems are recommended for all mission critical data centers, so that a fire can be detected and suppressed in its incipient stage.
Next month the authors will discuss fire suppression methods, including total flooding systems and clean agents, water mist systems and pre-action sprinkler systems.
Facts and Figures
Data center fire protection consideration 1:
• Smoke control . According to FM 5-32, an automatic smoke control system is recommended for rooms where smoke damage from an exposure fire can result in significant loss.
Data center fire protection consideration 2:
• Fire alarm system and control panel . According to NFPA 75 and FM 5-32, a fire alarm control panel should supervise all provided smoke and heat detection systems. A control panel should also be provided for a pre-action sprinkler system, if such sprinkler system is provided.
Data center fire protection consideration 3:
• Utilities . As indicated in the statistical analyses performed by FM and NFPA, the main ignition source found within computer centers is electricity, and the main material ignited is electric wires and cable insulation. Consequently, both NFPA 75 and FM 5-32 provide requirements for the electrical system and equipment (e.g., UPS, wires, cables, etc.) serving data centers.
Data center fire protection consideration 4:
• Water detection and temperature/humidity control . According to FM 5-32, independent and separate HVAC systems should be provided for data centers, and these rooms should be at a positive pressure relative to adjacent areas. A means for emergency shutdown should be provided, since such systems may exhaust suppression agents. Alarm signals indicating abnormal temperatures and humidity should also be provided. Additionally, it is recommended by FM 5-32 to provide liquid detection in data centers housing critical systems.
Data center fire protection consideration 5:
• Housekeeping . Per NFPA 75 and FM 5-32, only computer equipment and support equipment should be permitted within the data center. All ordinary combustibles should be kept outside the areas that contain the computer systems. Furthermore, the space beneath the raised floor should not be used for storage purposes and abandoned cables should not be allowed to accumulate.
The importance of fire protection of computer equipment and its facilities was first recognized by the computer industry during the late 1950s. Since then, two design standards specifically intended for computer equipment and facilities have been developed:
NFPA 75 Protection of Information Technology Equipment.
FM Data Sheet 5-32 Electronic Data Processing Systems.
Following a request for standardization of fire protection recommendations by the computer industry during the late 1950s, the National Fire Protection Assn. (NFPA) began developing the first standard applicable for electronic computer systems. This standard was officially adopted at the 1962 NFPA Annual Meeting and is today know as NFPA 75 Protection of Information Technology Equipment. NFPA 75 comprises the recommended best practices for information technology equipment and equipment areas. The intent of this standard is to identify recommended guidelines for the protection of such equipment/areas from damage by fire and thereby limit the likelihood of business interruption.
FM Data Sheet 5-32 was developed by FM Global and includes loss prevention recommendations for computer equipment and systems. Similar to NFPA 75, the intent of FM 5-32 is to provide organizations with guidelines to protect computer equipment, systems and areas against damage caused by fire, water, power loss, humans, etc.
The following list of standards provides additional guidelines for the fire protection systems and equipment recommended by NFPA 75 and FM 5-32:
NFPA 2001 Standard on Clean Agent Fire Extinguishing Systems
NFPA 12A Standard on Halon 1301 Fire Extinguishing Systems
NFPA 12 Standard on Carbon Dioxide Extinguishing Systems
NFPA 13 Standard for Installation of Sprinkler Systems
NFPA 750 Standard for Water Mist Fire Protection Systems
NFPA 10 Standard for Portable Fire Extinguishers
NFPA 72 National Fire Alarm Code
NFPA 70 National Electrical Code
NFPA 90A Standard for the Installation of Air-Conditioning and Ventilating Systems
NFPA 220 Standard on Types of Building Construction