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By Root 3070 0

(EMI) and radio frequency interference (RFI) are two additional environmental considerations. Motors, lights, and other types of electromechanical objects cause EMI, which can cause circuit overload, spikes, or electrical component failure. Making sure that all signal lines are properly shielded and grounded can minimize EMI. Devices that generate EMI should be as physically distant from cabling as is feasible because this type of energy tends to dissipate quickly with distance.

Figure 6.7 shows a motor generating EMI. In this example, the data cable next to the motor is picking up the EMI. This causes the signal to deteriorate, and it might eventually cause the line to be unusable. The gray area in the illustration is representative of the interference generated by the motor.

RFI is the by product of electrical processes, similar to EMI. The major difference is that RFI is usually projected across a radio spectrum. Motors with defective brushes can generate RFI, as can a number of other devices. If RF levels become too high, it can cause the receivers in wireless units to become deaf. This process is called desensitizing, and it occurs because of the volume of RF energy present. This can occur even if the signals are on different frequencies.

Figure 6.8 demonstrates the desensitizing process occurring with a wireless access portal (WAP). The only solutions in this situation would be to move the devices farther apart or to turn off the RFI generator.

FIGURE 6.7 Electromagnetic interference (EMI) pickup in a data cable

FIGURE 6.8 RF desensitization occurring as a result of cellular phone interference

Project TEMPEST

TEMPEST is the name of a project commenced by the U.S. government in the late 1950s. TEMPEST was concerned with reducing electronic noise from devices that would divulge intelligence about systems and information. This program has become a standard for computer systems certification. TEMPEST shielding protection means that a computer system doesn’t emit any significant amounts of EMI or RFI. For a device to be approved as a TEMPEST, it must undergo extensive testing, done to exacting standards that the U.S. government dictates. Today, control zones and white noise are used to accomplish the shielding. TEMPEST-certified equipment frequently costs twice as much as non-TEMPEST equipment.

Fire Suppression

Fire suppression is a key consideration in computer-center design. Fire suppression is the act of actually extinguishing a fire versus preventing one. Two primary types of fire-suppression systems are in use: fire extinguishers and fixed systems.

Fire Extinguishers

Fire extinguishers are portable systems. The selection and use of fire extinguishers is critical. Four primary types of fire extinguishers are available, classified by the types of fires they put out: A, B, C, and D. Table 6.1 describes the four types of fires and the capabilities of various extinguishers.

TABLE 6.1 Fire Extinguisher Ratings

Several multipurpose types of extinguishers combine extinguisher capabilities in a single bottle. The more common multipurpose extinguishers are A-B, B-C, and ABC.

The recommended procedure for using a fire extinguisher is called the PASS method: Pull, Aim, Squeeze, and Sweep. Fire extinguishers usually operate for only a few seconds—if you use one, make sure you don’t fixate on a single spot. Most fire extinguishers have a limited effective range of from three to eight feet.

A major concern with electrical fires is that they can reoccur quickly if the voltage isn’t removed. Make sure you remove voltage from systems when a fire occurs.

Most fire extinguishers require an annual inspection. This is a favorite area of citation by fire inspectors. You can contract with services to do this on a regular basis: They will inspect or replace your fire extinguishers according to a scheduled agreement.

Fixed Systems

Fixed systems are usually part of the building systems. The most common fixed systems combine fire detectors with fire-suppression systems, where the detectors