CompTIA Security SY0-601 Exam: Basics of Physical Security Controls

Objective: Explain the importance of physical security controls.

Topics:
- bollard
- access control vestibule
- closed-circuit television (CCTV)
- Faraday cage
- air gap
- protected cable distribution
- hot aisle
- cold aisle
- secure data destruction

Perimeter Security
When planning security for network scenarios, many organizations overlook physical security. In many smaller organizations, the placement of servers, switches, routers, and patch panels is determined based on space restrictions, and equipment often ends up in odd places, such as in the coat closet by the receptionist’s desk in the lobby, in the room with the copy machine, or in a storage room with a backdoor exit that is unlocked most of the time. Securing physical access and ensuring that access requires proper authentication are necessary to avoid accidental exposure of sensitive data to attackers performing physical profiling of a target organization.
Be familiar with physical security descriptions that indicate potential security flaws. Watch for descriptions that include physical details or organizational processes. Be particularly careful when exam questions address processes that use the same physical area for both common business traffic and data transport media or when data resources are placed in publicly accessible areas.
Physical access to a system creates many avenues for a breach in security. Unsecured equipment is also vulnerable to social engineering attacks. It is much easier for an attacker to walk into a reception area, say he or she is there to do some work on the server, and get access to the server in an unsecured area than it is for the attacker to get into a physically secured area with a guest sign-in/sign-out sheet. In a secure design, physical security controls parallel data controls. When it comes to physical security, the most obvious element to control is physical access to systems and resources. Your goal is to allow only trusted use of these resources via positive identification that the entity accessing the systems is someone or something that has permission to do so, based on the security model you have chosen. The following section briefly describes physical security components used to protect the perimeter.

Signs, Fencing, and Gates
Some organizations are bound by regulations to warn employees and visitors about workplace hazards. One of the most common ways to accomplish this warning is to use signs. Warning signs can be both informative and deterring. For example, if an organization deals in caustic chemicals, signs warning of the chemicals can inform visitors while also deterring intruders. Agencies such as the Occupational Safety and Health Administration (OSHA), American National Standards Institute (ANSI), and the National Electrical Manufacturers Association (NEMA) have established specifications for safety signs.
A common deterrent is a fence or similar device that surrounds an entire building. A fence keeps out unwanted vehicles and people. One factor to consider in fencing is the height. The higher the fence, the harder it is to get over. To deter intruders, fence height should be 6 to 7 feet. For areas that need to be more secure, or to provide protection against a determined intruder, the fence should be 8 feet tall, with barbed wire on top.
Another factor to consider is the fence material. Removing wooden slats or cutting a chain-link fence with bolt cutters is much easier than drilling through concrete or block. Keep in mind that if the fence is not maintained or the area around it is not well lit, a fence can easily be compromised.
Another form of fencing is data center cage fencing, a secure cage that provides an additional physical security layer.
Where fences are used, gates usually control access through the fencing. They can be staffed or unstaffed. One of the main advantages of using automatic gates is the capability to use keycard readers and touchpad systems to control entry and exit. Unstaffed gates allow entry only to people who have clearance to enter an area. An additional benefit of using an automatic gate with keycard readers is that the system maintains a log of all area entries and exits. Hybrid staffed and automatic systems use a feature that checks entry via intercom; the gate can be opened when verification is complete. This type of system is often used for visitors and outside vendors.

Lighting
From a safety perspective, too little light can provide opportunities for criminals, and too much light can create glare and blind spots, resulting in potential risks. Protective lighting improves visibility for checking badges and people at entrances, inspecting vehicles, and detecting intruders both outside and inside buildings and grounds. Protective lighting should be located where it will illuminate dark areas and be directed at probable routes of intrusion.
Proper placement and positioning of fixtures can dramatically reduce glare. In areas where crime is a concern, install lamps with a higher color rendering index. Bright lighting and cameras reduce the likelihood that an area will experience unauthorized access attempts. A good design provides uniform lighting, minimizes glare, is compatible with CCTV, and complies with local light pollution and light trespassing ordinances. Regular maintenance ensures that the safety and security of both people and property are not compromised. Twice annually, conduct an audit of all exterior lighting.

Barricades and Bollards
To enhance the security of critical or vulnerable facilities, physical access control structures or barricades can be used to protect against unauthorized people, vehicles, explosives, and other threats. Barricades provide a high level of protection and can withstand direct-impact forces. Vehicle barricades often are used in restricted areas to stop a vehicle from entering without proper authorization. A common barricade in many environments is a bollard, a short post that prevents vehicles from entering an area. Crash-rated barriers and bollards provide the best security but can be costly. Other examples of vehicle barricades include drop-arm gates, active bollard systems, planters, and crash barrier gates.

Cameras
Cameras and closed-circuit television (CCTV) are commonly used for perimeter surveillance. The video signal is processed and then transmitted for viewing at a central monitoring point. Traditionally, CCTV has been analog; however, recent technologies have taken advantage of the digital format, including IP video surveillance that uses TCP/IP for remote or wireless recording and monitoring. CCTV is a critical component of a comprehensive security program. It is important to appropriately plan and set clear and measurable objectives for a CCTV system. Failing to do so from the outset can be costly.
Many types of CCTV systems are available. Organizations should take into account technical, administrative, and legal considerations (including privacy) before and during the implementation of a CCTV system. Modern systems include a number of advanced features, including the ability to detect motion as well as identify and even alert upon specific recognition of objects. For example, camera systems have been combined with advanced intelligence to be able to detect weapons and other threats.

Security Guards
The presence of security guards can be reassuring to employees and can discourage intruders. Security guards are often armed, and they must be trained properly. The range of duties for guards can include staffing security gates, checking credentials, conducting active patrols, and monitoring CCTV feeds. Guards tend to be a greater visual deterrent than cameras alone and are often used in combination with other measures, such as deterrent signs.
The exam might include questions about the various physical barrier techniques. Be sure you are familiar with the methods previously listed.
Perimeter security deterrents do not necessarily have to be designed to stop unauthorized access. As the name implies, they need to help deter access. That is, a potential attacker might think twice about an attempt if he or she sees security deterrents; even an attacker considers the concept of risk/reward. Common examples include a sign indicating that the property is protected by a dog or an alarm system. Lighting, locks, dog, cleared zones around the perimeter, and even life-size cutouts of law enforcement officers can make a location appear less inviting to potential attackers.
In high-security environments, or when dealing with controls of grave importance, two-person integrity controls are sometimes used. This mechanism, known as the two-person rule, ensures that two people are required to authorize any access or operation. A relatively well-known example you may be familiar with involves the launching of weapons systems. In the United States, it’s common practice for two people to verify and go through specific procedures before missiles are launched. Such a procedure helps prevent a single rogue guard from having significant negative impact, and it also provides greater certainty that mistakes will not occur.
Recent advances in camera systems and robotic technology have been combined to create robot security guards. These systems are most often seen in malls and parking lots. In addition to serving as visual deterrents, these robots have the capability to capture massive amounts of data that can later be used for investigations.

Internal Security
Mandatory physical access controls are common in government facilities and military installations, where users are closely monitored and very restricted. Because they are being monitored by security personnel and devices, users cannot modify entry methods or let others in. Discretionary physical control to a building or room is delegated to parties responsible for that building or room.
In role-based access methods for physical control, groups of people who have common access needs are predetermined, and access to different locations is allowed with the same key or swipe card. In this model, users generally have some security training and are often allowed to grant access to others by serving as escorts or by issuing guest badges. The security department coordinates the secure setup of the facility and surrounding areas, identifies the groups allowed to enter various areas, and grants access based on group membership.

Internally, security guards, surveillance cameras, motion detectors, limited access zones, token-based and biometric access requirements for restricted areas, and many other considerations could be involved in physical security planning. In addition, users must be educated about each measure taken to prevent circumvention and improve ease of normal access. The following sections briefly describe physical security components used to protect an organization when a person gets past the perimeter of the property.

Alarms
Alarm systems detect intrusions and monitor or record intruders. Electronic alarm systems are designed to detect, determine, and deter criminal activity or other threatening situations. An alarm system can detect an event such as an invasion, a fire, a gas leak, or an environmental change; determine whether an event poses a threat; then send a notification about the event. Alarm systems can also be combined with CCTV surveillance systems to automatically record the activities of intruders. Alarm systems can also interface with access control systems to electrically lock doors, for example.

Motion and Infrared Detection
The main purpose of a motion detector is to provide security against intruders by alerting security personnel to an unexpected presence or suspicious activity on the company’s premises. A motion detector contains a sensor that is integrated with other technologies to trigger an alert when a moving object is in the sensor’s field of view. Motion detectors can be based on light, sound, infrared, or ultrasonic technology. In addition to motion sensors, other sensors are available—for detection of motion, noise, proximity, moisture, temperature, sound, fire, steam, vibration, tilt, and touch. Even inexpensive off-the-shelf computer technology such as the Raspberry Pi can easily integrate with different types of sensors.
Infrared detection is based on an electrical signal that uses infrared light beams connected to a detector. It can be either active or passive. In active infrared detection, an alarm goes off when a constant light beam is interrupted. In passive infrared detection, a heat source event must trigger the alarm. Because infrared detectors pick up movement, they are useful when a high level of security must be maintained, such as in banks and restricted military facilities. These devices must be properly configured because they are extremely sensitive and can issue false alarms if they are set too stringently.

Access Control Vestibules
An access control vestibule is a holding area between two entry points that gives security personnel time to view a person before allowing him or her into the internal building. One door of a access control vestibule cannot be unlocked and opened until the opposite door has been closed and locked. In the most basic implementation of a mantrap, one door connects to the non-secured area, and the other door connects the portal to the secure area. Access control vestibules are often used to prevent tailgating and used in areas such as data centers. Mantrap doors are operated mainly via radio-frequency identification (RFID) cards and can be sophisticated enough to record a person’s weight coming in and out—for example, to trigger an alarm if the person might be taking equipment from the data center.
An access control vestibule is a physical access control system consisting of a small area and two interlocking doors. One door must close before the other door can be opened, creating a temporary “trapped” space. Access control vestibules were formerly known as mantraps.

Locks and Lock Types
Locks must be easy to operate yet deter intruders. Beyond the normal key locks, several different types can be considered. A cipher lock has a punch-code entry system. A wireless lock is opened by a receiver mechanism that reads a card that is held close to the receiver. A swipe card lock, such as those in hotels, requires a card to be inserted into the lock. Factors to consider related to locks are strength, material, and cost.
Access can be controlled by physically securing a system within a locked room or cabinet; attaching the system to fixed, unmovable furniture using cable locks or restraints; or locking a case to prevent the removal of key components. Nonstandard case screws add another layer of security for publicly accessible terminals. Securing an area also involves ensuring that air ducts, dropped ceilings, and raised floors do not provide unauthorized avenues for physical access.
You can have the most secure lock on a door and use biometric devices for identification, but if the walls don’t go up all the way and ceiling tiles can be removed to access rooms with sensitive equipment in them, someone can easily walk off with equipment and sensitive data. Be sure to consider all areas of a room.

Equipment Security
The next layer of physical security is the security of equipment. Physical access to a system creates avenues for security breaches. Many tools can be used to extract password and account information that can then be used to access secured network resources. Given the capability to reboot a system and load software from a USB drive, attackers might be able to access data or implant Trojan horses and other applications intended to weaken or compromise network security.
A more serious threat is theft or loss. Laptops and handheld devices are easy targets for thieves. Theft of laptops and handheld devices in an office setting is nearly as high as theft in cars and other forms of transportation. To prevent theft or loss, you must safeguard the equipment in your organization.

Cable Locks
To protect organization resources and minimize liability costs, each employee should take responsibility for securing office equipment. Laptops should never be left in an area where anyone can easily access them. Laptops, Apple iMacs, and any other easily transportable office computers should be physically secured. Security cables with combination locks can provide such security and are easy to use. The cable is used to attach the computer to an immovable object. Computers have one and sometimes two security cable slots. The security cable slots allow you to attach a commercially available antitheft device to the computer.
Computer locks commonly use steel cables to secure the PC to a desk; they are often found in computer labs and Internet cafes. A laptop lock is meant to protect both privacy and the computer. These locks come in different types: cable locks, case locks, and twist locks. The most common type of antitheft devices for portable computers usually include a length of metal stranded cable with an attached locking device and associated key. The cable is looped around an immovable object, and the locking device is inserted into a security cable slot.
Antitheft devices differ in design, so be sure yours is compatible with the security cable slot on the computer. Never leave a laptop unsecured. If an area is not safe, do not leave a laptop even if it is secured by a cable-locking device. Thieves have driven off with whole ATMs, with a goal of finding a way to bypass the lock later.

Cages and Safes
Tower-style computers can be targets for thieves not only because they have a higher resale value than laptops but also because of the data they might hold. For example, financial businesses have been hit hard by theft of desktop computers that hold a lot of personal data. Secure computer towers and server cages that are bolted to the floor can improve physical security and prevent theft. In machines that are bolted to the floor, drive access can be either completely restricted or left available for ease of use. Server cages are most often found in data centers to protect server equipment and separate customer equipment. Colocation data centers can host the information of multiple customers, and a standard data center cage made of rigid metal is typically used. Cages can be modified based on customer specifications, such as stronger locks, restricted backside access, or military-grade requirements.
Some laptop security cases have special features to protect an organization’s computers and data out in the field. For example, vendors make a safe that is designed for people who take their laptop computers home from work. In addition, high-security laptop safes store laptops in a manner similar to bank vault storage. Individual storage accommodates laptops in locking compartments, and those compartments can then be additionally secured behind the high-security main safe door when required. The open compartment version offers open shelves (usually one laptop per shelf) for storage that can be secured by the safe’s main door. Other computer safe options include types made to securely store laptops and carry cases, plus other valuable equipment in reception areas, mobile car safes made to prevent smash-and-grab attacks, and home computer safes with electronic locks similar to the safes provided in hotel rooms.

Locking Cabinets and Enclosures
A locked cabinet may be used to hold equipment that is not in use or that does not have to be physically accessed on a regular daily basis. Enclosures are a common form of locking device more appropriate for data centers, where the systems are still active but can be locked away in an area that is adequately cooled. Vendors provide solutions such as a security cabinet enclosure that secures CPU towers and server blades. The housing is made of durable, heavy-duty steel for strength that lasts. The sides and door are ventilated to reduce the risk of overheating.
Another option is a wood laminate security computer cabinet that provides a computer workstation that can be locked away into a cabinet for space as well as security concerns. A computer cabinet includes a keyboard drawer and an adjustable top shelf. A slide-out bottom shelf accommodates a CPU and printer. It has built-in cable management grommets. Depending on what needs to be secured, some computer enclosures can hold everything from LCD/LED flat screens to entire systems. This type of security is often used for training rooms, where the computers can be secured without having to be removed after each training session.

Screen Filters
A computer privacy screen filter might be a requirement, depending on the type of business an organization conducts. For example, HIPAA has stringent standards for patient privacy protection and requires medical, insurance, and other healthcare businesses and practitioners to protect the privacy and security of medical information, including information that is visible on computer screens. A computer screen filter limits the reading radius of the screen so that someone looking at the screen from the side cannot read what is onscreen. Many organizations require screen filters to shield important documents. In addition, privacy screen filters are often used by employees while traveling to protect information while sitting in airports, using public transportation, or working from other public places.
Privacy screen filters can help prevent shoulder surfing.

Air Gaps
An air gap is a physical isolation gap between a system or network and the outside world. With an air gap, no system is connected to the Internet or connected to any other system that has Internet access. In a true air-gapped system, data is transferred to the system via removable media or a direct connection to another computer. Air gaps prevent unauthorized access and keep malware away from the systems. Air gaps are often used in industrial control systems (ICS), military classified networks, and credit and debit card payment networks. Air gaps are used for highly secure systems. However, they can be and have been compromised in the past, even though these systems are not connected to the Internet. Perhaps the most high-profile case involving the infection of an air-gapped system is Stuxnet.
Remember that an air gap is a physical isolation gap between a system or network and the outside world. It prevents unauthorized access and keeps malware away from the systems.

Environmental Controls
Not all incidents arise from attacks, illegal activities, or other forms of directed threats to an enterprise. Many threats emerge from physical and environmental factors that require additional consideration in planning for security controls. The location of everything from a building to wireless antennas affects security. When picking a location for a building, an organization should investigate the type of neighborhood, population, crime rate, and emergency response times. This information helps in planning the physical barriers needed, such as fencing, lighting, and security personnel. An organization must also analyze the potential dangers from natural disasters and plan to reduce their effects when possible.
When protecting computers, wiring closets, and other devices from physical damage from either natural or human-caused disasters, you must select locations carefully. Proper placement of the equipment might cost a company a little money upfront, but it will provide significant protection from possible loss of data due to electrical damage, flooding, or fire.

Protected Cabling, Protected Distribution, and Faraday Cages
It is important to take shielding into consideration when choosing cable types and placement of cable. Coaxial cable was the first type of cable used in network computers. Coaxial cables are made of a thick copper core with an outer metallic shield to reduce interference. Coaxial cables have no physical transmission security and are simple to tap without anyone noticing and without interrupting regular transmissions. The electric signal, conducted by a single core wire, can easily be tapped by piercing the sheath. An attacker can then eavesdrop on the conversations of all hosts attached to the segment because coaxial cabling implements broadband transmission technology and assumes that many hosts are connected to the same wire. Another security concern with coaxial cable is reliability. No focal point, such as a switch or hub, is involved, and a single faulty cable can bring down the whole network. Missing terminators or improperly functioning transceivers can cause poor network performance and transmission errors.
Twisted-pair cable is used in most of today’s network topologies. Twisted-pair cabling is either unshielded (UTP) or shielded (STP). UTP is popular because it is inexpensive and easy to install. UTP consists of eight wires twisted into four pairs. The design cancels much of the overflow and interference from one wire to the next, but UTP is subject to interference from outside electromagnetic sources and is prone to radio-frequency interference (RFI) and electromagnetic interference (EMI), as well as crosstalk. Longer cable lengths transfer a more significant environmental measure of noise because wires can inadvertently act as antennas for broadcast emanations.
STP is different from UTP in that it has shielding surrounding the cable’s wires. Some STP has shielding around the individual wires, which helps prevent crosstalk. STP is more resistant to EMI and is considered a bit more secure because the shielding makes wiretapping more difficult.
Both UTP and STP are possible to tap, although it is physically a little trickier to do so than tapping coaxial cable because of the physical structure of STP and UTP cable.
With UTP and STP, adding devices to the network via open ports is easy on unsecured hubs and switches. As a result, hubs and switches should be secured from unauthorized access, and cables should be clearly marked so a visual inspection can quickly pinpoint whether something is awry. Software programs also can help detect unauthorized devices and the ports on which they will accept attempts at connection.
The plenum is the space between the ceiling and the floor of a building’s next level. It is commonly used to run network cables. The cables in this part of a building must be plenum grade to comply with fire codes. The outer casing of this type of cable is more fire resistant than in regular twisted-pair cable.
Fiber-optic cable was designed for transmissions at higher speeds over longer distances, such as in underwater intercontinental telecommunications applications. Fiber uses light pulses for signal transmission, making it immune to RFI, EMI, and eavesdropping without specialized equipment capable of detecting transient optical emission at a fiber join or bend. Fiber-optic wire has a plastic or glass center, surrounded by another layer of plastic or glass with a protective outer coating. On the downside, fiber is still quite expensive compared to more traditional cable, it is more difficult to install, and fixing breaks can be time-intensive and costly as there may be hundreds or thousands of individual fibers in a single bundle. As far as security is concerned, fiber cabling eliminates the signal tapping that is possible with coaxial cabling. Tapping fiber is impossible without interrupting the service and using specially constructed equipment. This makes it more difficult for an attacker to eavesdrop or steal service.
Secure Internet Protocol Router Network (SIPRNET) and Non-Classified but Sensitive Internet Protocol Router Network (NIPRNET) are private government-run networks used for exchanging sensitive information in a secure manner. SIPRNET carries classified information up to the secret level. These systems use a protected cable distribution system called a protected distribution system (PDS). A PDS consists of copper or optical cables that are protected from unauthorized physical or electronic access. The purpose of a PDS is to deter, detect, and make it difficult to physically access the communication lines carrying national security information.
A more efficient way to protect a large amount of equipment from electronic eavesdropping is to place the equipment in a well-grounded metal box of conductive material, called a Faraday cage. Named after its inventor, Dr. Michael Faraday, this type of box can be small enough for a cell phone or can encompass an entire building. The idea behind it is to protect the contents from electromagnetic fields. The cage surrounds an object with interconnected and well-grounded metal, typically a copper mesh that is attached to the walls and covered with plaster or drywall. The wire mesh acts as a net for stray electrical signals either inside or outside the box. New forms of wall treatment (wallpaper) can be used to embed a Faraday mesh atop existing structural materials, retrofitting older buildings with Faraday-style protections to create cell phone-free zones in restaurants and theaters.
Using a Faraday cage is an efficient way to protect a large amount of equipment from electronic eavesdropping.

HVAC
When doing facilities planning, you need to take into consideration the cooling requirements of computer data centers and server rooms. The amount of heat generated by some of this equipment is extreme and highly variable. Depending on the size of the space and the age and type of equipment the room contains, energy consumption typically ranges from 20 to 100 watts per square foot. Despite being smaller and more powerful, newer servers might consume even more energy than older ones. Some high-end facilities with state-of-the-art technology can require up to 400 watts per square foot. These spaces consume many times more energy than office facilities of equivalent size and must be planned for accordingly. Smaller, more powerful IT equipment is considerably hotter than older systems, making heat management a major challenge.
When monitoring an HVAC (heating, ventilation, air conditioning) system, keep in mind that overcooling causes condensation on equipment, and too-dry environments lead to excessive static.
Monitor the area for hot spots and cold spots, ensuring that you don’t have one exchange that is frigid cold under a vent and hot elsewhere. When water or drainpipes are located above facilities, it is important to ensure that upper-floor drains do not clog. One solution is to use rubberized floors above the data center or server room. Above all else, timely air conditioning maintenance is required.

Fire Suppression
Fire is a danger common to all business environments and must be planned for well in advance of any possible occurrence. The first step in a fire safety program is fire prevention.
The best way to prevent fires is to train employees to recognize dangerous situations and report them immediately. Knowing where a fire extinguisher is and how to use it can stop a small fire from becoming a major catastrophe. Many of the newer motion and ultrasonic-detection systems also include heat and smoke detection for fire prevention. These systems alert the monitoring station of smoke or a rapid increase in temperature. If a fire does break out somewhere in the facility, a proper fire-suppression system can help the organization avoid major damage. Keep in mind that laws and ordinances apply to the deployment and monitoring of a fire-suppression system. An organization has the responsibility to ensure that these codes are properly met. In addition, the organization should have safe evacuation procedures and periodic fire drills to protect its most important investment: human life.
Fire requires three main components to exist: heat, oxygen, and fuel. If you eliminate any of these components, the fire goes out. A common way to fight fire is with water in an attempt to take away oxygen and heat. A wet-pipe fire-suppression system is the type of system most people think of when they think of indoor sprinkler systems. The term wet describes the state of the pipe during normal operations. The pipe in the wet-pipe system contains water under pressure at all times. The pipes are interconnected and have sprinkler heads attached at regularly spaced intervals. The sprinkler heads have a stopper held in place with a bonding agent designed to melt at an appropriate temperature. When the stopper melts, it opens the valve and allows water to flow from the sprinkler head to extinguish the fire. Keep in mind that electronic equipment and water don’t get along well. Fires that start outside electrical areas are well served by water-based sprinkler systems, but all these systems should have both manual activation and manual shutoff capabilities. You want to be able to turn off a sprinkler system to prevent potential water damage. Most sprinkler systems are designed to activate only one head at a time. This works effectively to put out fires in the early stages.
Dry-pipe systems work in exactly the same way as wet-pipe systems, except that the pipes are filled with pressurized air instead of water. The stoppers work on the same principle. When a stopper melts, the air pressure is released and a valve in the system opens. One reason for using a dry-pipe system is that, when the outside temperature drops below freezing, any water in the pipes can freeze, and the pipes might burst. Another reason for justifying a dry-pipe system is the delay associated between the system activation and the actual water deployment. Some laws require a sprinkler system even in areas of a building that house electrical equipment, and there should be some delay so that someone can manually deactivate the system before water starts to flow. In such a case, a company could deploy a dry-pipe system and a chemical system together. The delay in the dry-pipe system could be used to deploy the chemical system first and avoid serious damage to the running equipment that would occur with a water-based sprinkler system.

Fire suppression systems are rated according to class:
- Class A: For Class A fires (trash, wood, and paper), water decreases the fire’s temperature and extinguishes its flames.
- Class B: For Class B fires, foam extinguishes flames fueled by flammable liquids, gases, and greases. Liquid foam mixes with air while passing through the hose.
- Class C: Class C fires (energized electrical equipment, electrical fires, and burning wires) are put out using extinguishers based on carbon dioxide or halon. Halon was once used as a reliable, effective, and safe fire-protection tool, but in 1987, an international agreement known as the Montreal Protocol mandated the phase-out of environmentally damaging halons in developed countries due to emissions concerns. Therefore, carbon dioxide extinguishers have replaced halon extinguishers in all but a few locations. Carbon dioxide extinguishers do not leave a harmful residue, and exposure can be tolerated for a while without extreme protective measures, making them a good choice for an electrical fire in a data center or in other electronic devices.
- Class D: Class D fires are fires that involve combustible metals such as magnesium, titanium, and sodium. The two types of extinguishing agents for Class D fires are sodium chloride and a copper-based dry powder.

Know the classes of fire and what is used to extinguish each type:
- Class A: Combustible materials; extinguish with water
- Class B: Liquids and gases; extinguish with foam
- Class C: Energized electronics; extinguish with carbon dioxide
- Class D: Combustible metals; extinguish with sodium chloride or copper-based dry powder

Hot and Cold Aisles
Data centers and server farms can have server racks be arranged with alternating rows facing opposing directions. Fan intakes draw in cool air vented to racks facing the cold aisle, and the fan output, which is hot air, is vented to the alternating hot aisles for removal from the data center (see Figure 15.1). This data center organization provides efficiency in thermal management by allowing supply ducts to serve all cold aisles and exhaust ducts to collect and draw away heated air.


Simplified side view of hot aisles/cold aisles in a data center

Overcooling causes condensation on equipment, and too-dry environments lead to excessive static. In addition to monitoring temperature, organizations should monitor humidity. Humidity is a measure of moisture content in the air. A high level of humidity can cause components to rust and degrade electrical resistance or thermal conductivity. A low level of humidity can subject components to electrostatic discharge (ESD), causing damage; at extremely low levels, components might be affected by the air itself. The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) recommends optimal humidity levels in the range of 40% to 55%.
Environmental monitoring solutions can raise alerts or trigger automated responses, as needed. Alerting systems must be capable of sustaining operations during the event, and a water-sensing monitor should be able to function and raise an alert even when the environment is filled with water.
Monitoring systems must also be able to communicate in the event of service disruption so that alerts can be passed to responders even if the email server cluster has shut down due to thermal overload conditions. If a monitoring solution relies on networking for sensor measurement or raising alerts, environmental issues that degrade or prevent network communications might go unnoticed, or alerts might not reach responders in a timely manner.

Secure Data Destruction
Sensitive and privacy-related data (including log files, physical records, security evaluations, and other operational documentation) should be managed in an organization’s retention and disposal policies. These policies should include specifications for access authorization, term of retention, and requirements for disposal. Depending on the relative level of data sensitivity, retention and disposal requirements can become extensive and detailed.
Clear policies and procedures should be put into place for secure data destruction, which is the proper disposal of data and associated hardware. Such practices should dictate that equipment the organization uses should be disposed of only in accordance with approved procedures, including independent verification that the relevant security risks have been mitigated. Procedures should be in place when disposing of old computer hardware, whether for recycling, disposal, donation, or resale.
The most prominent example of a security risk is a hard drive inside a computer that has not been completely or properly wiped. Some concerns about data erasure sufficiency in newer solid-state drives (SSDs) might require organizations to destroy drives instead of simply erasing them for normal disposal channels.

With the secure disposal of equipment, a wide range of scenarios needs to be considered:
- Breaches of health and safety requirements
- Inadequate disposal planning that results in severe business loss
- Remnants of legacy data from old systems that might still be accessible
- Disposal of old equipment that is necessary to read archived data
- Theft of equipment in use during cleanup of unwanted equipment

Proper disposal of removable media is also important. An organization must properly handle removable media when the data should be overwritten or is no longer useful or pertinent to the organization. Generally, all electronic storage media should be sanitized or purged when it is no longer necessary for business use, as well as before its sale, donation, or transfer of ownership. Sanitization and purging is the process of removing the contents from the media as fully as possible, making restoration of the data extremely difficult (or close to impossible). The following methods are acceptable for some forms of media sanitation:
- Declassification: This is a formal process of assessing the risk involved in discarding information.
- Degaussing: This method involves using a tool to reduce or remove the magnetic field of the storage media.
- Wiping: This method, which applies to magnetic storage devices, writes over all data on the media (often multiple times) and destroys what was originally recorded.
- Encryption: This method requires a strong key, effectively making the data unrecoverable without the key. This process can be combined with crypto shredding by purposely purging the key used to encrypt the data.
- Destruction: This process physically destroys both the media and the information stored on it. For USB flash drives and other solid-state nonferric removable storage, this might be the only solution acceptable for certain controls and legal mandates. For paper records, destruction is the only viable option.
An organization’s information sensitivity policy defines the requirements for the classification and security of data and hardware resources, based on their relative level of sensitivity. Some resources, such as hard drives, might require extensive preparation before they can be discarded.

Paper records that contain sensitive information need to be destroyed. In addition to organizational requirements, regulations often include specific rules and recommendations. For example, in addition to requiring electronic PHI to be destroyed, HIPAA requires that PHI in paper records be properly disposed. Many large organizations now depend on third-party vendors to collect and properly dispose of records on their behalf. Methods of media and paper destruction that organizations or third-party organizations may engage in include the following:
- Burning: Government organizations commonly use this method. Sensitive data is temporarily contained in burn bags and then incinerated.
- Shredding: This commonly used method involves destruction using blades, with varying degrees of effectiveness. Simple, low-cost solutions present problems because shredded documents sometimes can be reassembled.
- Pulping: This process involves dissolving paper, reducing it to its cellulose fibers. Organizations that provide shredding services often later pulp the shredded material before recycling it.
- Pulverizing: Special systems that contain rotating hammers crush materials at high speed before passing them through a sizing screen to turn them into tiny particles (or even dust).

Quiz:
1. The aerospace company you work for is developing a highly secret new component. The computers to develop the component need to be isolated to prevent connections to the outside world. Which of the following should you put in place to provide the most secure setup? A. Firewall B. Air gap C. Hot and cold aisles D. Pulverized network
2. Your training director has an unsupervised room that he wants to use as a training lab for the next few months. The lab will hold 20 laptops and confidential training manuals. Which the following controls are most appropriate in this situation? (Select two.) A. Cable locks B. Locking cabinets C. Mantrap D. Biometric reader
3. Employees in your data center have notified you that they are receiving minor electrical shocks when they touch the metal enclosures and are worried about handling equipment such as servers and hard drives. Which of the following should you consider doing? A. Decrease the humidity B. Increase the humidity C. Increase the temperature D. Decrease the temperature
4. Which of the following is a type of barricade used to prevent unauthorized vehicles from entering an area? A. Screened subnet B. Faraday cage C. SIPRNET D. Bollard

Answer 1: B. An air-gapped network provides the most secure setup. The computers inside the air gap may be interconnected but have no external access. Answer A is incorrect because a firewall may be required to be connected to the outside; although it could possibly secure the network, this setup would not provide the security of a completely closed network. Answer C is incorrect because hot and cold aisles are for data center HVAC. Answer D is incorrect because pulverizing is related to the secure destruction of materials.
Answer 2: A and B. The unsupervised training lab will benefit from cable locks and locking cabinets. The laptops can be secured to prevent theft. The locking cabinets can potentially be used to store the laptops and can also be used to protect the confidential documents. Answer C is incorrect. A mantrap is a holding area between two doors. Answer D is incorrect. Because this is an unsupervised lab where many people may have open access, the focus should be on protecting equipment and material from being taken. Biometric readers do not prevent this.
Answer 3: B. Humidity is a measure of moisture content in the air. A low level of humidity can subject components to electrostatic discharge (ESD), which can cause damage; at extremely low humidity levels, components might be affected by the air itself. Answer A is incorrect given the circumstance, although a high level of humidity can cause components to rust and degrade electrical resistance or thermal conductivity. Adjusting the temperature is incorrect, so both C and D are incorrect.
Answer 4: D. A barricade used in many environments is a bollard, a short post that prevents vehicles from entering an area. Answer A is incorrect because a screened subnet is an isolated network that sits between the public Internet and a private internal network. Answer B is incorrect because a Faraday cage is a well-grounded metal box of conductive material used to protect electronic equipment from eavesdropping. Answer C is incorrect because Secure Internet Protocol Router Network (SIPRNET) is a private government-run network used for exchanging sensitive information in a secure manner.