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Therefore, selecting a fire suppression system should be given the attention it deserves. This tip discusses classes of fire and suppression system options, and will help you decide what's best for your data center disaster recovery plan.
Types of fires
To better understand fire suppression systems capabilities and limitations, it's important to understand the types of fires they are designed to suppress. In North America, there are five fire classes:
- Class A: Fire with combustible materials as its fuel source, such as wood, cloth, paper, rubber and many plastics
- Class B: Fire in flammable liquids, oils, greases, tars, oil-base paints, lacquers and flammable gases
- Class C: Fire that involves electrical equipment
- Class D: Fire with ignitable metals as its fuel source
- Class K: Fire with cooking materials such as oil and fat at its fuel source
No matter where your data center is located, fire can be considered a potential disaster. Data center environments are typically at risk to Class A, B or C fires. It goes without saying that a data center should not be built in a facility exposed to the risk of ignitable metal fires (e.g., magnesium) or anywhere near a kitchen.
If a fire does occur in a data center environment, it's important to suppress that fire as quickly as possible. Here are the most common fire suppression systems currently installed in data centers and the pros and cons of each:
Water sprinklers: The most common fire suppression systems in business environments (and often found in the server rooms, especially in smaller IT environment) are water sprinklers. Water sprinklers are usually present in the server room because server rooms are usually developed using existing office space already fitted with water sprinklers. This basic system essentially consists of a grid of water pipes equipped with fusible heads that melt over a certain temperature to allow pressurized water to escape and spray over a specific radius.
Pros:
- Low installation costs because it's often already existent in commercial and office space
- Low cost of operation as it requires no pricey agent reload
- Once activated, provides fire suppression until the system is shut off
Cons:
- Limited to Class A fire suppression
- Subject to accidental discharge if a head or pipe is broken
- Requires significant cleanup regardless of the event that triggered the discharge
- Will cause significant water damage to IT equipment and surrounding finishes or materials
Pre-action water sprinklers: Pre-action water systems are essentially the same as a water sprinkler system except they require at least two alarm conditions to be activated. In other words, an accidental activation will not cause the system to discharge. Rather, an event triggering an alarm must be followed by a second event confirming a fire condition (i.e., a broken sprinkler head alone would not cause system discharge unless smoke or heat is also detected) before system discharge takes place. This confirmation mechanism defines the term "pre-action."
Pros
- Prevents accidental discharge
- Low cost of operation as it requires no pricey agent reload
- Conventional water sprinkler systems can be converted to pre-action systems
- Once activated, provides fire suppression until the system is shut off
Cons
- Limited to Class A fire suppression
- More costly than a conventional water sprinkler system
- Requires significant cleanup following a system discharge
- Can be zoned, but discharge sometimes takes place at the entire zone level
- Will cause significant water damage to IT equipment and surrounding finishes or materials
Gaseous agent fire suppression systems
The most sophisticated fire suppression systems use a combination of pre-action controls and a "clean" gaseous agent to extinguish fires. Gaseous agent fire suppression systems are typically stored in tanks and once the system is activated, gas is piped to the designated areas by zones and discharged through special overhead nozzles. There are numerous options available ranging from the discontinued Halon systems to clean agents such as Novec 1230 (also known as Sapphire).
Halon systems were common in mainframe environments and were designed to quickly suppress fires. While these systems can still be recharged today using existing reserves or Halon recovered for systems being replaced, the EPA mandated that production of Halon 1301 be halted by December 31, 1993, due to the known harmful effect of the gas on the ozone layer and adverse effects on the health of people exposed to the chemical following a discharge.
Pros
- Very effective suppressant for Class A, B and C fires
- No significant damage to IT equipment following a discharge
Cons
- Harmful to people and the environment
- Agent no longer in production
- Requires space for agent storage tanks
- Requires moderate residue cleanup following a discharge
- More costly than a conventional water sprinkler system
Halon replacement gas agents
There are a number of options for the replacement of Halon fire suppression systems. Different, non-corrosive, total flooding gases that are safe for use in occupied spaces are now available. They have different fire suppression capabilities and much like their predecessor, they are stored in tanks and distributed by pipes to protected zones and discharged through special nozzles in the event of a fire. Some of the most common gas agents include:
Inergen (IG-541)
- Inergen is a mixture of inert gases, (52% nitrogen, 40% argon and 8% carbon dioxide) and is effective on Class A, B and C fires
FM-200 (HFC-227)
- Effective on Class A, B and C fires
FE-13
- Effective on Class B fires only
FE-25
- Effective on Class A fires only
FE-227
- Effective on Class A and B fires only
Sapphire (Novec 1230)
- Effective on Class A, B and C fires
Pros
- Usually no cleaning is required following a discharge
- No significant damage to IT equipment following a discharge
- Many gas agents are effective on Class A, B and C fires
- No known adverse effects on people and environmentally friendly
Cons
- More costly than a conventional water sprinkler system
- Requires space for agent storage tanks
- Fire suppression capacity is limited to the amount of gas agent stored for the volume of the room
Other fire suppression consideration for your data center
From a cost perspective, the most economical of these fire suppression systems are the traditional water sprinkler systems, followed by the pre-action system and finally the gas agent system, which has the same attributes as a pre-action systems, with the added cost of the gas agent and appropriate storage tanks.
There are a few other elements to consider when selecting a fire suppression system; this depends mostly on local codes and insurance policies. For example:
Emergency power off (EPO): When a water sprinkler system is used, it may be required by your local electrical code to install an EPO switch that cuts power to the main data center electrical feed and to the output of the UPS to ensure no IT equipment is powered on in the presence of water.
Backup for gas agent fire suppression: Some insurance companies now require that even if a gaseous agent fire suppression system is installed, it must be backed up by a pre-action or conventional water sprinkler system which, as mentioned earlier, will keep going until the main water valve is shut off. Many insurers consider it possible that a fire may keep burning even following the complete discharge of the gas agent reserve which would leave a facility with no backup fire suppression.
Overall, regardless of which option you choose, every data center disaster recovery plan should come equipped with a fire suppression system that best suits their data storage environment as well as their budget.
About this author: Pierre Dorion is the data center practice director and a senior consultant with Long View Systems Inc. in Phoenix, Ariz., specializing in the areas of business continuity and DR planning services and corporate data protection.
This was first published in June 2010