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Pre-action Dry Pipe. The advantages of the two computer-controlled systems previously described are diminished by the high cost of these systems, and many companies are unwilling to incur the cost. However, the mechanical nature of a sprinkler system provides for a less costly and less technologically advanced alternative. The pre-action dry pipe system includes the master control valve principle from the prior system, but it retains the same lead ballast sprinkler heads that have been in use for decades.

Control over the master valve may be through mechanical or microprocessor technology, although the way it works is unchanged. An inert gas is kept in the overhead pipes at all times to prevent corrosion and to provide a means for monitoring system integrity. If a pipe or connection were to fail, the system pressure would drop, triggering an alarm.

Maintaining pressure is also important because it works to keep the lead ballast properly positioned in the sprinkler heads. After a pressure failure, the sprinkler heads must be checked to ensure that they will function as expected in an emergency. The pre-action system normally controls pressure by pumping the inert gas out as water is released into the system such that the pressure is kept effectively constant.

Chemical Fire Suppression Systems

Computer systems in the not too distant past were much more susceptible to damage from a sprinkler system discharge than they are today. Engineers developed a number of alternative systems using dry chemicals or gases to suppress fires, although only two of those systems made any significant penetration into the market. The two chemicals providing a foundation for these alternatives are Halon and carbon dioxide.

Halon. The chemical compound Halon was developed by DuPont in response to the need for a non-lethal fire suppression chemical. Its formulation includes items that make Halon part of the chlorofluorocarbon (CFC) family. Halon is an ozone-depleting chemical, as are most members of the CFC family, and is already banned in several countries around the world.

The United States has signed at least one agreement that will affect the legality and availability of Halon after the year 2000. DuPont and other chemical companies are working constantly to develop alternative chemicals that do not have the same ozone-depleting potential (ODP) as Halon that can be deployed by using the same delivery systems. If a complete infrastructure replacement ends up being needed, many companies plan to change back to a water-based system.

Carbon Dioxide. This naturally occurring gas does not promote combustion and will prevent or extinguish a fire if present in sufficient levels in the atmosphere of a room or area. Unlike Halon, carbon dioxide is generally harmful to humans if present in sufficient levels to be effective as a fire suppression agent. Many companies that had selected carbon dioxide for their data centers have changed to Halon, although there are carbon dioxide systems that continue to be used.

Common Elements of Chemical Fire Suppression Agents. Halon, carbon dioxide, and other chemical fire suppression agents have a number of common elements or issues that include the following:

Atmospheric Concentration. Chemical fire suppression agents are consistently based on the idea that reducing or eliminating the available oxygen in the protected area puts out fires. Experience and testing has supported the validity of that idea. The volume of the data center must be determined very accurately so that the delivery system, quantity of the selected chemical agent, and configuration are properly installed.

Data Center Seal Integrity. The data center must be designed or modified so that its doors close automatically and that the HVAC system capacities are sufficient. If the data center doors do not close automatically, a risk is certain, particularly if the computer operators or any other persons who are evacuating the room do not take the time to ensure that the doors are fully closed. Most chemical systems discharge their contents very quickly under very high pressure. If the doors are not closed tightly, it is very likely that they will be forced open.

The opened doors increase the effective volume of the data center to include all of the adjacent areas. The increased actual volume reduces the concentration of the chemical agent, probably below effective levels, and the fire continues to burn. It is unreasonable to include sufficient extra quantities to cover an additional area because the extra amount could be 300 to 400 percent more than the original. And even ignoring the financial considerations, releasing all the chemical into the original room volume, assuming it was sealed, could blow doors or windows out and create the problem it was intended to solve.

System Delay. Almost every system has a built-in delay from the time it is activated until the contents are discharged. This delay has several objectives:

  It permits personnel to evacuate, which is essential if the chemical agent is harmful or fatal.
  It provides time to confirm the problem and abort if needed.
  It provides time for any other emergency procedures appropriate to the situation.

The IT executive is likely to have a choice regarding the length of the delay, and it is a matter that deserves consideration. The number of people normally in the data center, the chemical agent chosen, the speed with which a fire might spread, and other parts of the business that might be harmed are some of the most important considerations in setting the delay. The executive should also consult internal risk management and external insurance personnel, assuming that there is some external coverage in effect related to the particular computer installation.

The risks of setting the wrong delay are clear. Too little delay time and personnel may not be able to react according to their training and emergency procedures. An incomplete evacuation may compromise the seal integrity and lead to a failure to extinguish the fire. If the delay is too long, the fire may spread beyond the ability of the chemical agent to extinguish it. The delay normally incorporates the companion feature of an abort switch.

Abort Switch. Most, if not all, chemical systems include an abort switch. The abort switch gives company personnel the chance to prevent a system discharge if they know that there is no emergency or that there is another reason that the discharge should not be permitted to take place. There are minor variations based on building codes, vendor, and company discretion, but most abort switches are deadman switches, i.e., the switch only operates as long as someone is there to press it.

Once the switch is released, the system may continue to count down from the point it had reached when the switch was pressed, or a new count may begin. This factor is very significant because these switches are routinely located inside the data center. If it is inside the data center and if the delay timer does not reset, it may leave very little time for someone to evacuate the area if he/she has pressed the abort switch to allow others to leave and are now ready to go themselves. In addition, as described earlier, if the data center door is open when the chemical system activates, the system could fail to extinguish the fire.


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