Preventive Physical Controls

Preventive physical controls are employed to prevent unauthorized personnel from entering computing facilities (i.e., locations housing computing resources, supporting utilities, computer hard copy, and input data media) and to help protect against natural disasters. Examples of these controls include:

•  Backup files and documentation.

•  Fences.

•  Security guards.

•  Badge systems.

•  Double door systems.

•  Locks and keys.

•  Backup power.

•  Biometric access controls.

•  Site selection.

•  Fire extinguishers.

Backup Files and Documentation

Should an accident or intruder destroy active data files or documentation, it is essential that backup copies be readily available. Backup files should be stored far enough away from the active data or documentation to avoid destruction by the same incident that destroyed the original. Backup material should be stored in a secure location constructed of noncombustible materials, including two-hour-rated fire walls. Backups of sensitive information should have the same level of protection as the active files of this information; it is senseless to provide tight security for data on the system but lax security for the same data in a backup location.

Fences

Although fences around the perimeter of the building do not provide much protection against a determined intruder, they do establish a formal no trespassing line and can dissuade the simply curious person. Fences should have alarms or should be under continuous surveillance by guards, dogs, or TV monitors.

Security Guards

Security guards are often stationed at the entrances of facilities to intercept intruders and ensure that only authorized persons are allowed to enter. Guards are effective in inspecting packages or other hand-carried items to ensure that only authorized, properly described articles are taken into or out of the facility. The effectiveness of stationary guards can be greatly enhanced if the building is wired with appropriate electronic detectors with alarms or other warning indicators terminating at the guard station. In addition, guards are often used to patrol unattended spaces inside buildings after normal working hours to deter intruders from obtaining or profiting from unauthorized access.

Badge Systems

Physical access to computing areas can be effectively controlled using a badge system. With this method of control, employees and visitors must wear appropriate badges whenever they are in access-controlled areas. Badge-reading systems programmed to allow entrance only to authorized persons can then easily identify intruders.

Double Door Systems

Double door systems can be used at entrances to restricted areas (e.g., computing facilities) to force people to identify themselves to the guard before they can be released into the secured area. Double doors are an excellent way to prevent intruders from following closely behind authorized persons and slipping into restricted areas.

Locks and Keys

Locks and keys are commonly used for controlling access to restricted areas. Because it is difficult to control copying of keys, many installations use cipher locks (i.e., combination locks containing buttons that open the lock when pushed in the proper sequence). With cipher locks, care must be taken to conceal which buttons are being pushed to avoid a compromise of the combination.

Backup Power

Backup power is necessary to ensure that computer services are in a constant state of readiness and to help avoid damage to equipment if normal power is lost. For short periods of power loss, backup power is usually provided by batteries. In areas susceptible to outages of more than 15–30 min., diesel generators are usually recommended.

Biometric Access Controls

Biometric identification is a more sophisticated method of controlling access to computing facilities than badge readers, but the two methods operate in much the same way. Biometrics used for identification include fingerprints, handprints, voice patterns, signature samples, and retinal scans. Because biometrics cannot be lost, stolen, or shared, they provide a higher level of security than badges. Biometric identification is recommended for high-security, low-traffic entrance control.

Site Selection

The site for the building that houses the computing facilities should be carefully chosen to avoid obvious risks. For example, wooded areas can pose a fire hazard, areas on or adjacent to an earthquake fault can be dangerous and sites located in a flood plain are susceptible to water damage. In addition, locations under an aircraft approach or departure route are risky, and locations adjacent to railroad tracks can be susceptible to vibrations that can precipitate equipment problems.

Fire Extinguishers

The control of fire is important to prevent an emergency from turning into a disaster that seriously interrupts data processing. Computing facilities should be located far from potential fire sources (e.g., kitchens or cafeterias) and should be constructed of noncombustible materials. Furnishings should also be noncombustible. It is important that appropriate types of fire extinguishers be conveniently located for easy access. Employees must be trained in the proper use of fire extinguishers and in the procedures to follow should a fire break out.

Automatic sprinklers are essential in computer rooms and surrounding spaces and when expensive equipment is located on raised floors. Sprinklers are usually specified by insurance companies for the protection of any computer room that contains combustible materials. However, the risk of water damage to computing equipment is often greater than the risk of fire damage. Therefore, carbon dioxide extinguishing systems were developed; these systems flood an area threatened by fire with carbon dioxide, which suppresses fire by removing oxygen from the air. Although carbon dioxide does not cause water damage, it is potentially lethal to people in the area and is now used only in unattended areas.

Current extinguishing systems flood the area with Halon, which is usually harmless to equipment and less dangerous to personnel than carbon dioxide. At a concentration of about 10%, Halon extinguishes fire and can be safely breathed by humans. However, higher concentrations can eventually be a health hazard. In addition, the blast from releasing Halon under pressure can blow loose objects around and can be a danger to equipment and personnel. For these reasons and because of the high cost of Halon, it is typically used only under raised floors in computer rooms. Because it contains chlorofluorocarbons, it will soon be phased out in favor of a gas that is less hazardous to the environment.