Select The Right Door Interlocking Solution
Controlling access to your facility has always been of utmost importance – but it’s probably one of the security concerns that has moved higher on users’ list of priorities over recent years. In addition to protecting people, property and assets, there are more and more mandated regulations coming into play that apply to various types of facilities and activities within them, and the consequences for non-compliance transcend simple fines to encompass new sources of liability. But even when compliance is not an issue, security still prevails as the primary motivator for improved access control.
The good news is that door control technology continues to improve with new highly cost-effective and versatile solutions like programmable door interlock systems (often called mantraps for use with people and sallyports when used for vehicles) that can be tailored to meet specific security requirements. By gaining a better understanding of how different door interlock systems work, you can implement the most appropriate configuration for your customers’ facilities.
Myriad applications exist for door interlock systems spanning numerous industries, which may open new sources of revenue for your business. The most prevalent installation classifications include: casinos, armored car facilities, prisons and police stations, medical and pharmaceutical facilities, secure government and military R&D sites, high risk wholesale and retail establishments, check cashing facilities, schools, laboratories, and Sensitive Compartmented Information Facilities (SCIF pronounced SKIF) in any type of facility where sensitive information and conversations take place. Unlike conventional access control systems, door interlock systems provide a higher level of protection.
In its simplest form, a door interlock system is composed of two doors electronically connected so one cannot open until the other has closed. Using some form of access control device, an individual is granted access through the first door to enter the hallway. Once the first door is closed, the second door can then be opened automatically or triggered by an operator.
Such simple applications are often used in applications like jewelry stores where an employee visually screens the person requesting access before allowing them entry into the sales area. This same basic door interlocking set-up has countless applications across many different industries. Office complexes and industrial vestibules increasingly employ door interlock systems, as they represent a reliable and secure means of managing both pedestrian and vehicle traffic.
Types of Door Interlock Systems
Air Lock Control Systems are frequently employed low-security systems used only for environmental control. Operation is simple: all doors are normally unlocked, and opening any door will lock the related doors so that only one door, in a designated area, can be accessed at a time. This provides easy ingress or egress to an area without destabilizing the environment of the adjoining areas, whether they be interior rooms or an exterior door. Air Lock Control Systems are the least secure type of door interlocking system since all of the doors are always open, and two or more doors can actually be opened simultaneously.
A Secure Entry/Free Egress system provides a more secure entrance solution and will allow a faster method of egress through a combination of locked and unlocked doors. Exterior doors are normally secured and interior doors normally unlocked. An electronic access system controls entry from the exterior and a card reader or an REX (request to exit) device is used on the interior of the outside door. A valid access card will unlock the exterior door only if the interior door is closed. Unlocking the exterior door will lock the interior door. Once the exterior door is re-secured, the interior door is unlocked to allow access into the facility. And opening the interior door prevents the exterior door from being unlocked. From a practical perspective, envision an entryway into an apartment building. An access card or code entered into a keypad unlocks the exterior door allowing entry into a vestibule. Once the exterior door is closed and automatically locks, the interior door can be opened using the same credentials, or by having the individual ‘buzzed in’ by the resident. If the interior door remains locked, the individual in the vestibule can exit the exterior door enabling “free egress”.
Highest security is provided with a Restricted Entry & Exit System, whereby a door is unlocked by a request for access only if no other related doors are unsecured. Opening any one door keeps all other related doors locked. Restricted Entry & Exit Systems will buffer simultaneous requests for access to prevent two or more doors from being unlocked.
Application Uses
Banks and other financial institutions require a higher level of security than most commercial sites given the value of their assets. Integrating door interlock systems with other monitoring devices can provide high levels of security. For example, a door interlock solution can automatically lock doors if a possible concealed firearm is detected. In this application, an interlock door system provides unrestricted access to an interior vestibule, where customers then pass through a metal detector before entering the inner lobby. Access is only allowed if no metal is detected. Should an individual be deemed suspicious, an alert sounds, the individual is denied entry to the lobby, and may only exit to the street.
Door interlock systems are also commonly used in cleanrooms, which need to comply to mandatory industry standards (Federal Standard 209E), known as ISO14644. However, many modular cleanrooms are not supplied with door interlock systems which need to be retrofitted in the field. The addition of door interlocks not only assures the cleanroom meets the necessary ISO classifications by enforcing clean air control but can also add a level of security within the controlled environment of the cleanrooms.
Determine the User’s Specific Needs
The first best practice is to evaluate the user’s facility and/or environmental control objectives to help determine the level of door interlock solution required. For example, data centers typically have restrictions on entering a facility with portable memory devices; cleanrooms may require numerous sensors to monitor air pressure or temperature before granting access; and an office building with a high amount of pedestrian traffic in the morning and late afternoon may want two doors operating during peak hours with the ability to switch to a single door during midday hours.
Some door interlocking systems also include intercom communications between the person(s) inside the “mantrap” and a security guard or operator. Advanced configurations are also deployed with biometric devices that read faces, eyes and/or fingerprints to provide highly accurate identity verification, adding a much higher level of sophistication and security.
With their high degree of programmable operations, door interlock systems are also often subject to meet specific building code requirements, such as BOCA codes. Some municipalities may not allow any doors in a public facility to be locked at any time. In some instances, this has been addressed with the use of red/green traffic lights mounted on either side of the doors to indicate when access is allowed. Adding a built-in sounder which annunciates a door violation can also minimize such actions.
In an emergency, the door interlock system must also enable people to evacuate the facility. For example, if the power fails, an emergency override would ensure that the door can be opened manually. Life safety codes may require that the door interlock systems be integrated with the facility’s fire alarm control panel to allow emergency egress. A local emergency pull station may be required to allow doors to be unlocked in non-fire alarm emergencies or to interface the system with NFPA 101 delayed egress controls.
Selecting the Proper Interlock Controller
Perhaps the most important consideration when specifying a door interlock system is choosing the proper interlock controller. The number of doors, types of doors and other monitored and/or controlled devices all play into the equation.
While totally independent interlocking doors can be controlled from a single PLC controller, the separation distance of the doors to be controlled can limit the number of doors per controller. Inputs to be monitored by the controller must also be assessed, and should include door status, latch monitor, maglock bond sensor, the request-for-access device, card access lock relay, local push button or other REX device. Other monitored devices could be emergency override stations, tailgate detectors and more. All inputs must be dedicated dry contacts, not shared with other systems, and if required, mirrored with PLC relay outputs.
Outputs (relays and powered outputs) can be used to operate the electric locking devices, indicator lights, alarm sounders and to signal other systems (card access, guard station consoles and more). At least one output relay is required for each controlled door to operate the electric lock. The lock relay contacts can also be used to signal door access status (example: Red = Locked / Green = Unlocked).
There are numerous commercial and industrial access applications for door interlock systems. Users with as few as two doors or those with several all need to be thought through as if their use were equated with the security efforts used for highly specialized vehicular applications like armored cars or prison carriers. In any case, door interlock systems provide a highly efficient and effective solution for myriad security and environmental control applications.
