Today we are going to look at how fire detection systems can be used in Data Centers to prevent catastrophic loss and damage; we will focus on Very Early Smoke Detection Systems, (VESDA – Very Early Smoke Detection Alarm).
Without an efficient and safe environment, there is no way to be assured of business continuity. To be assured that the environment is efficient and safe in the data center and other mission-critical spaces, we depend upon environmental monitoring of all sorts.
In our data centers we constantly monitor for:
- Equipment Failure
- Out of capacity equipment
- Increased power consumption
- HVAC Operation
- Water Leakage
Effective fire monitoring is crucially important, as the effect on computer equipment of exposure to smoke is dramatic. The pictures below show short circuits cause by smoke induced corrosion. The sooner we can stop smoke being created, the less chance we get this kind of damage.
Another thing to keep in mind is the cost of active fire fighting suppression costs you during the initial purchase and every time you use and need to refill it. Recently an accidental discharge at one of my sites (caused by a badly installed detector) cost me $140k to refill the gas cylinders, and that is for a small site.
The bigger costs may however be hidden:
- The safety risks caused by dumping the suppressant – whether it be water near high voltages or the burning of the new breed of gaseous agents
- The downtime caused by damage to the equipment
- And the cleanup time and costs involved.
As the power density in our data centers rises, so does the fire risk Fire risk is becoming more likely, because:
We are reaching the limits of physics in terms of heat removal with air – better methods are inevitable but even when implemented will only present new failure modes
- Inefficient or improper planning – equipment loads are increased without managing risk
- Introduction of unplanned fuel sources
- Use of closed actively cooled and hot aisle containment cabinets also presents new risks – if these cabinets are not actively monitored they can be allowed to generate a large fire before breaching the cabinet and being detected by the open area fire detection system
Properly installed, very early smoke detection systems are crucial to the successful operation of modern data centers.
- Time to investigate and understand the threat
- Time to prepare staff and visitors
- Time to stage the response and avoid the cost of nuisance alarms
- Time to investigate options for control of the fire
- Time to transfer data and processes to redundant systems
- Time to evacuate
- Time to suppress the fire
- Time to ensure business continuity
The unique environments within Telecom and Data Center facilities present a challenge to both early and reliable fire detection. Detection is made difficult because of smoke dilution in the large open spaces and because of high velocity airflow and scrubbing of the air at each air change. Detection performance may be unreliable because of the unpredictable airflows and the physical location of detectors in areas of difficult access is also a challenge. Areas of particular difficulty are:
- Under floor spaces
- Ceiling spaces
- Between racking
- Beam Pockets
- In equipment cabinets
There are two main types of fire detectors; one is the point detector and the other the ASD pipe detector. The first, the point detector suffers from a few basic problems:
- Low Sensitivity – they are designed for detection of fires in the later stages of combustion and are passive units.
- They present some impedance to the flow of air and smoke into the detection chamber (UL268 requires use of an insect and lint mesh)
- They are not able to report the blockage of the chamber (without flow sensing)
- They are prone to nuisance alarms
- Not able to filter out or discriminate between sources of nuisance alarms (ASD systems filter many unwanted sources of nuisances alarms through the pipe network and the filter)
- Few use good software algorithms to do dust discrimination
- Do not maintain performance
- Reduce sensitivity over time
- Allow optics to become contaminated (without a clean air bleed)
The ASD pipe detector has a number of significant advantages over the point detector to the point that most modern data centers use ASD pipes, the first is that they are typically 1000 times more sensitive than a conventional point detector and a number of features of VEWSD make them Tolerant of air dilution and high airflow. In fact, in many cases the detectors are placed in areas of high airflow, such as across HVAC return air vents. VEWSDs actively draw air samples containing the smoke to a central detector. These detectors monitor airflow and ensure a consistent airflow rate. If any changes in airflow are detected, this will be reported and blockages can be investigated. A good VEWSD protects the Optics of the detector, for a longer life and absolute calibration-free smoke detection.
VEWSD monitors the entire progression of a fire – easily detecting fire long before smoke is visible and long before any other forms of detection. Clearly the best time for detection is the incipient stage, the point where damage is minimized and response options maximized, and it is here where VEWSD affords you a critical advantage.
Note that to provide complete protection, VEWSDs offer a fourth alarm, Fire 2, which is typically programmed to release suppression.
Air movement caused by the HVAC systems interferes with the normal dispersion of smoke making its detection by conventional passive point-type technologies more difficult and unpredictable. Air movement, filtering, and the introduction of clean air during the air conditioning cycle will all cause smoke dilution and make the task of detection more difficult.
The cooling effects of air conditioning decrease the temperature of the smoke plume. This impairs the performance of heat detectors. It also means that the smoke is less buoyant and travels not to the ceiling where conventional detectors are installed, but straight to the HVAC return air vent.
Good HVAC systems are designed to collect all air from the room and efficiently transport it to the return air vent – so why not take advantage of that and place detection there. Placing sample holes at the return air vent provides first line of protection. This really only works for ASD systems as conventional point detectors do not work well in the high airflow.
Using ASD is usually more cost effective, because sample holes can be positioned as required by standards (such as on the ceiling) as well as where the smoke will go when the HVAC is active. One detector can often be used for both applications.
The Hot Aisle recommends the use of external cool air to reduce the cost of cooling (free air or fresh air cooling). Fresh air presents a number of real risks – the external air can be contaminated and threaten equipment operation – it should therefore be monitored.
The picture above shows the location of ASD pipes around the fresh air intake vent.
There are a number of areas that require smoke detection but are difficult to access for installation and maintenance:
- Under floors
- In ceiling space
- Beam pockets that impede normal airflow
- Above racking
- In underground cable tunnels
- Within equipment cabinets
One ASD detector with multiple sampling pipes can be installed rather than multiple point detectors. Most fire codes recommend an increase in the number of point (spot) type detectors as the air change rate increases, however, there is no such restriction on ASD sample holes.
The floor void, and sometimes ceiling void, of data center Facilities usually contains large quantities of electrical cabling. This creates a significant fire risk, thus, such areas must be protected. Air Sampling Detection (ASD) is well suited to such areas since the detector can be positioned either inside or outside the protected area where it is more convenient for service and maintenance personnel.
The photo below highlights the large quantity and high density of cables located under a Telecommunication facility floor, and the inherent risk with the increase in heat density. If a fire event were to happen, a fire would spread extremely quickly.
With the introduction of fully enclosed cabinet solutions (contained hot aisle) for the protection of blade servers, there is a need for dedicated detection within the enclosure. Alternatively smoke will not be detected until a fire has breached the cabinet. In cabinet sampling allows much earlier detection of small amounts of smoke that might otherwise remain undetected and slowly contaminate the expensive systems within. ASD is proven to be reliable in the high airflows within these cabinets and offers a number of communications options for automated response to any risk.
The square or rectangular cavities created by the beams are known as ‘Inter-beam Spaces’. Joists, arranged in parallel, will divide the ceiling into long trenches rather than Inter-beam Spaces. Each has different requirements.
The Current US National Fire Protection Authority (NFPA) 72 code recommends that, for ceiling heights and beam depths equal or greater than 3.7 m and 300 mm respectively, every compartment (inter-beam space) should contain its own smoke detection point. Using CFD modeling, proven by research with NFPA, it has been proven the superiority of ASD in these difficult environments. This means either a point detector in every inter-beam space or an Air-sampling Smoke Detection (ASD) system sample hole in every inter-beam space. ASD is more cost and performance effective.