Always open; always closed
Aug 1, 1997 12:00 PM
Some advantages of security revolving doors.
Keypad and reader access control systems are widely used. So are revolving doors. Both are well known and are not considered new technologies. However, when you combine the two, you get benefits that are not widely known. This article is about security revolving doors, their security capabilities and their potential for return on investment.
Not all the features mentioned in this article are available in every manufacturer's product line, but all are available from one or more of the following companies: Revolving Door Control/ SAFESEC, Ontario, Calif.; Boon Edam, Salt Lake City; and Horton Automatics, Corpus Christi, Texas.
Always open, always closed
Revolving door manufacturers often refer to the dual nature of revolving doors as "always open, always closed."
A security revolving door consists of four door wings and forms a permanent barrier between the interior and exterior of a building. Although three-wing revolving doors exist, they are impractical for security use due to their large section areas. Revolving doors allow free or controlled movement of pedestrian traffic without exposing the building to outside elements.
Unlike conventional doors, security revolving doors isolate the secured area from the unsecured or outside area at all times. A revolving door entrance is "always closed" to direct airflow, dust, pollution, sound, animals and objects. The door's control system is activated by sensors and an access control system, providing an entrance that is "always open" for those who have security authorization.
Good security revolving doors allow all four door quadrants to be used at once, supporting traffic in both directions. A security revolving door allows unobstructed passage for authorized individuals while supporting high pedestrian traffic flow. A single door can handle up to 300 people in 15 minutes (150 people in each of two directions). Revolving doors can also enhance a facility architecturally.
A benefit of security revolving doors is that they assume the full burden for entrance security. With conventional doors, once the access control system unlocks the door, responsibility for security passes momentarily to the authorized person about to enter the door. If another person approaches the door from either side, the authorized person can be directly confronted by an individual who may request or force entry. What's more, social etiquette tells us to be polite in such situations and hold the door for an approaching person. This is one reason innocent security violations are common and why attitudes toward security can become lax. A conventional door remains unsecure until the moment it re-locks.
A security revolving door permits only one person at a time in a single door section. When the door sensors detect two persons in the same section, the door stops and slowly reverses to gently back the two individuals out of the door, a feature called anti-piggybacking.
A security revolving door also prevents the passage of an unauthorized person who attempts to obtain a "free ride" in the opposite or adjacent section to the authorized individual. When the door sensors detect an unauthorized entry attempt, the door stops and slowly reverses to gently back both individuals out of the door, a feature called anti-tailgating. The authorized user must attempt entry again to obtain passage. See the diagram on page 26 showing how a revolving door defeats tailgate attempts.
All three manufacturers referenced in this article can provide bullet-resistant glass and material in their doors, where such security is appropriate.
Verified passage and anti-passback
Another feature is verified passage. Entry/exit control is often used to prevent security card passback (passing a security card to the next person ready for entry or exit). Under entry/exit control, once a person has been granted access in one direction, the person will only be granted access next in the opposite direction. A second access attempt in the same direction will be denied. Under entry/exit control with a conventional door, passage is assumed to take place when the door is opened. If the person does not actually pass through the door (for example, if the person drops something and lets go of the door to pick it up), the second access attempt will be denied. Since a security revolving door detects actual passage and not assumed passage, entry/exit control can be implemented accurately.
The anti-piggyback feature of revolving doors, which uses ultrasonic sensors or weight sensors, can prevent large objects such as computers or file boxes from being carried through the door. High-security facilities can adjust the door sensors so that even a briefcase cannot be carried out and must be taken instead to a manned security door for examination. Security revolving doors protect against overnight andweekend theft of business equipment.
Interface to security monitoring systems
Unauthorized passage attempts trigger relay closures for the interfaced security system and notify on-site or remote security personnel of the attempted violation. The revolving door control system can also provide a relay closure to notify an interfaced camera system, so that an attempted removal of property can be recorded on video.
Additionally, a security revolving door can maintain full access control in one direction while allowing free passage in the other direction. This type of control is not possible for a conventional door, since once it is unlocked and opened, one or more persons can pass in either direction.
Boon Edam has worked with Infographic Systems Corp., Los Alamitos, Calif., to provide enhanced access control software capabilities for revolving door control weight-scale management. Revolving Door Control/SAFESEC has developed password-protected Windows 95/NT software, which provides a graphical representation of door operations, notification of specific door events, historical report graphs of door traffic profiles, and a way to manually control up to eight doors. The software also includes an OLE automation server to provide an interface to Windows-based security system software.
Compatibility with access control technologies
Security revolving doors are activated by the access control system's door lock relay. No special interface is required from the access control system. Thus security revolving doors are compatible with the spectrum of access control systems, from keypad and reader to biometric systems. Accurate anti-passback can be implemented, using the confirmed passage relay of the revolving door control system and an access control system that provides a verified entry/exit anti-passback feature.
If a rotating wing meets a stationary or slow-moving object, the door automatically slows down and, if necessary, stops. As soon as the obstruction is removed the door will continue to rotate. Revolving doors have soft safety wing edges that prevent a hand or foot from being pinched against the door enclosure. Emergency stops can trigger relay closures for the interfaced security system and notify on-site or remote security personnel.
Security revolving doors can also feature buttons for handicapped personnel that cause the door to shift into a slower speed appropriate for disabled person passage.
Appropriate recorded announcements are activated when unauthorized passage is attempted and when obstacles block the door rotation. Users are informed of the reason for the stopping or reversal of the door rotation and are told how to proceed.
Fire and emergency egress
Some revolving doors hold the wings in place using a high-strength electromagnetic mechanism. In the event of a fire alarm or power failure, the electromagnetic mechanisms release the door wings so that they can be pushed open to allow unrestricted evacuation of the facility.
How sensors make it work
Sensors determine how many persons are attempting to move through the revolving door. Only one person is allowed to enter each door section. When an unauthorized person attempts entry, the door stops and reverses; an authorized person will be denied entry if someone attempts to piggyback or tailgate.
The sensor technology used for security revolving doors varies from manufacturer to manufacturer, mainly due to specific technology research and patent awards. There are two main sensor types: ultrasonic sensors, which take a sound picture of the inside of a door section from above; and weight sensors, which take weight readings using floor mats and scales installed beneath them. Each has its advantages and disadvantages. Both technologies construct complex sensor profiles as the door turns. Accordingly, the sensitivity and range of the sensors must be adjusted during installation to provide the level of restriction and detection that fits a facility's security needs.
A good way to understand security revolving doors is to review the promotional materials from manufacturers (most offer a free video or CD-ROM), make a list of the facility's security requirements and objectives, and present it to one or more of the manufacturers. There are many factors involved in the design and implementation of a system. Each company will be able to demonstrate how their particular technology applies to any requirements and budget. Demonstrations are available at security trade shows and at manufacturer facilities.
The tradeoffs with security revolving doors are: *convenience vs. safety and security; *level of security vs. cost; and *architectural appearance vs. cost.
A facility's security goals and objectives guide determination of factors requiring priority over others. For example, some less expensive doors rest in the Plus (+) Position rather than the X (X) Position, which means that only one door wing separates the secure area from the outside. The safety flaps on such a door allow articles (such as a security card or even a handgun) to be passed around the door wing.
Security revolving doors can reduce HVAC costs, especially in multiple tenant office buildings. As calculated by ASHRAE, air infiltration in a motor-driven revolving door is approximately 32 cubic feet per passage compared to 900 cubic feet per passage in a conventional single swing door. Planning
As with any security system, planning is an important part of the picture. Facility pedestrian traffic patterns should be examined, along with possible changes to improve security or convenience. Fire and safety regulations must be reviewed. Plan for training and orientation for technical and security personnel, and also for orientation of other personnel. Allow sufficient time for implementing the access control system. Before activating the security doors, provide test stations so that personnel can verify their security IDs are in fact registered and working in the system.