Page 698 - (ISC)² CISSP Certified Information Systems Security Professional Official Study Guide

transport mechanisms, such as telephone, cellular, television, audio,
radio, and network mechanisms.

There are two types of electromagnetic interference (EMI): common

mode and traverse mode. Common mode noise is generated by a
difference in power between the hot and ground wires of a power
source or operating electrical equipment. Traverse mode noise is
generated by a difference in power between the hot and neutral wires
of a power source or operating electrical equipment.

Radio-frequency interference (RFI) is another source of noise and
interference that can affect many of the same systems as EMI. A wide

range of common electrical appliances generate RFI, including
fluorescent lights, electrical cables, electric space heaters, computers,
elevators, motors, and electric magnets, so it’s important to locate all
such equipment when deploying IT systems and infrastructure
elements.

Protecting your power supply and your equipment from noise is an

important part of maintaining a productive and functioning
environment for your IT infrastructure. Steps to take for this kind of
protection include providing for sufficient power conditioning,
establishing proper grounding, shielding all cables, and limiting
exposure to EMI and RFI sources.

Temperature, Humidity, and Static

In addition to power considerations, maintaining the environment
involves control over the HVAC mechanisms. Rooms intended

primarily to house computers should generally be kept between 60
and 75 degrees Fahrenheit (15 and 23 degrees Celsius). However, there
are some extreme environments that run their equipment as low as 50
degrees Fahrenheit and others that run above 90 degrees Fahrenheit.
Humidity in a computer room should be maintained between 40 and
60 percent. Too much humidity can cause corrosion. Too little

humidity causes static electricity. Even on antistatic carpeting, if the
environment has low humidity it is still possible to generate 20,000-
volt static discharges. As you can see in Table 10.1, even minimal levels
of static discharge can destroy electronic equipment.