Fire Prevention, Detection, and Suppression

Training and awareness programs for staff are critical to prevent fires and minimize the loss of life in the event of fire.

Many jurisdictions require organizations to train their staff on fire prevention and emergency evacuation procedures including responding to fire.

In the United States, this is required by the regulations of the Occupational Safety and Health Administration (OSHA). In the European Union (EU), Directive 89/654/EEC places similar workplace requirements and expectations on employers. This training would help employees identify unsafe conditions and may include training on the use of handheld extinguishers and other actions to reduce the impact of a fire.

Fire code in most jurisdictions generally requires fire alarm systems in commercial spaces.

While protecting the people in an organization is the primary goal, the effect of fire on businesses can be devastating. Data centers generally have additional requirements placed on them to address their unique fire dangers.

Understanding fire suppression requires a layered approach to the prevention, detection, and suppression of fire.

These three activities each need to be assessed at the building, room, and enclosure (rack) level in a data center. Different controls may be appropriate for each circumstance.

Prevention is the most important part of decreasing the likelihood and impact of fire in any space. Adherence to building codes, reduction of fire load (paper, clutter, waste, flammable, or hazardous materials), and regular inspections form the basis of any fire prevention program. Data centers would likely establish policies that prohibit smoking and limit flammable equipment (such as wood furniture and storage of flammable liquids such as paint and cleaning supplies).

If prevention fails, detection of the fire is essential. Proper sensors, placed appropriately, provide sufficient warnings at the building, room, and rack levels and will identify potential fire events before they cause significant damage.

Traditional spot-type smoke detectors use ionization or photoelectric cells. lonization detects smoke by measuring electrical current between two charged plates as air passes between them. Photoelectric cells measure changes in light due to smoke particles. Newer spot-type smoke detectors use several types of sensors, including both ionization and photoelectric, and also detectors for carbon monoxide, heat, and flame to provide a broader range of detection and minimize false alarms. These are increasingly used in data centers and server rooms.

Aspirating sensors, by contrast, are continually breathing in a small amount of the air surrounding the sensor, which can be placed anywhere in a room or its HVAC ducts and plenum spaces. These Very Early Smoke Detection Apparatus (VESDA) systems are often integrated into the return air systems in a room. These extremely sensitive detectors are often coupled with sensors in the plenum space beneath the raised floors supporting the racks and cabinets. Their sensitivity allows the sensor to provide different levels of alarm—a | low level might trigger an annunciator or warning light, where a higher level of smoke detection would initiate the full suppression system.

Finally, many vendors are providing preengineered fire suppression systems in their racks and cabinets. These systems can isolate more precisely and locate the source of the fire, and the suppression can be focused on the affected area. This reduces the impact of suppression on systems located near the event.

As shown in the figure, fire can be characterized in five general types or classes (note that class letters vary by country):

• Class A: ordinary combustible solids like paper, wood, plastic
• Class B: flammable liquids
• Class C: electrical fires
• Class D: flammable metals
• Class K: commercial cooking equipment

Ordinary Combustibles

Flammable Liquids

Electrical

Flammable Metals Paper, Wood

Petroleum Products

Energized Equipment

Magnesium Lithium

Commercial Cooking Commercial Cooking Equipment Equipment

Figure: Fire classes (U.S.-based National Fire Protection Assoclation)

These distinctions are useful when selecting a suppression method since different methods are effective on certain types and ineffective (or dangerous on others. For data centers and general office spaces, the primary concerns are classes A, B, and C. For these types of fires, there are two general approaches to suppression systems: water-based and gas-based suppression systems.