Practically speaking

Few in the security industry would dispute that CCTV is effective in reducing crime and in helping the police to secure convictions, even though a recent independent report for the Home Office seemed to do just that.

It is, however, true that CCTV systems need to be well implemented if they are to achieve their objectives. And it is the need for guidance in this area that has led to the publication of BS 8418:2003 – Installation and remote monitoring of detector-activated CCTV systems – Code of practice.

This standard has the backing of the Association of Chief Police Officers (ACPO) as a tool for providing better police response, and for reducing false alarms. It is well presented and practical, but it is, nevertheless, useful to examine its contents and their implications for security installers. (This article deals only with the design and installation of CCTV systems – not other areas covered by the standard, ie commissioning, operational procedures and owner responsibilities. It is an introduction, and reference should always be made to the standard itself when making decisions affecting installations.)

Detector installation and positioning

BS 8418 deals only with detector-activated CCTV systems, and its design and installation section starts with recommendations relating to detectors. Careful consideration needs to be given to matching the detector to the application. The detectors must be fit for purpose, and must be installed in accordance with the manufacturer's guidelines and appropriate standards.

The standard also emphasises that the field of view of the detector should match that of the camera or cameras, so that, in the event of a detector being activated, the operator at the remote monitoring centre can readily determine the cause (Fig 1). This may appear to be a common-sense requirement, but the inability of the remote monitoring station to view the event which caused an activation was a common shortcoming of early detector-activated CCTV.

Zone spill-over

Another problem with early systems was spurious detector activation caused by events outside the area which the CCTV system was intended to protect. This happened, for example, when detection zones spilled over into common areas or public rights of way. The solution, when it is necessary to cover gates and fence lines, is to ensure that the detectors are of the active beam or curtain type, and that they face inward (See Fig 2).

When siting detectors, environmental conditions must be considered. In particular, sunlight shining into a detector could potentially cause a false actuation. Where this is a possibility, the standard recommends using a pair of detectors with different orientations. An alarm should only be generated if both detectors are triggered simultaneously.

In some installations, multiple detectors are used with a single camera, usually of the PTZ (pan, tilt, zoom) type. In these cases, it is important that each detector generates a separate alarm at the remote monitoring centre, so that the operator can easily assess the pattern and progress of incidents (see Fig 3).

Experience suggests, however, that even when this condition is satisfied, using multiple detectors with a single PTZ camera is less successful than using individual static cameras, each with their own detector.

Camera positioning and configuration

Like detectors, cameras must be installed in accordance with appropriate standards and the manufacturer's guidelines. As previously mentioned, the cameras must also be capable of monitoring all of the areas covered by the detectors.

Attention also needs to be given to the size of the images which the cameras produce on the viewing screen. Depending on the purpose of the system, there are four main criteria:

• For event confirmation and general viewing, without identification, a target in the form of a person 1.6m tall should occupy 10 per cent of the height of the screen.
• For recognition of a person known to the operator, such as a member of staff, the same target should occupy 50 per cent of the screen height.
• For recognition of an unknown person, the target should occupy 120 per cent of the screen height.
• Where the system is used to monitor vehicles, they should represent a minimum of 50 per cent of the screen height. A bigger image is, however, much preferred.

The standard recommends that fixed cameras are used to monitor key areas such as entry and exit points, and that PTZ cameras are used only in conjunction with pre-set alarm positions. Where PTZ cameras are remotely controlled, they should be capable of tracking an intruder moving at an average of two metres per second.

Care must be taken to ensure that the cameras cannot look into public areas adjacent to the installation. Site plans should be used to identify cameras, and all cameras should be clearly labelled so that system users can quickly orientate themselves. Finally, the cameras should have protection appropriate to the environment in which they are installed.

Site illumination

A subject which often receives less attention than it deserves, effective site lighting is essential if the cameras are to provide good images during the hours of darkness. Street lighting is rarely satisfactory, since it usually produces very poor colour rendition, and is deficient in infrared.

Whether white light or infrared site illumination is used, the lighting should be sufficient for the CCTV system operator to establish the presence of an intruder, occupying 10 per cent of the monitor screen height, within two seconds.

Care needs to be taken in positioning luminaires so that they enhance rather than degrade the images produced by the cameras. They should be positioned below or to one side of the camera, and should illuminate an area equal to or greater than camera’s viewing angle. Luminaires should never be positioned so that they can shine into any camera.

Where lighting is to be controlled automatically, the BS 8418 permits the use of a timeswitch, provided that this can easily be adjusted for British Summer Time. Alternatively, photocells can be used, or the lighting can be remotely controlled by the operator at the CCTV monitoring centre.

Audio

Audio challenge systems have proved to be extremely useful, and the standard recommends their use except in circumstances where there is a risk of noise becoming a nuisance. If used, the audio challenge must be clearly audible, free from distortion and matched in range to the relevant camera and detector. Ideally, each camera should have its own loudspeaker which is switched on by the associated detector.

System integrity and video transmission

BS 8418 requires CCTV systems to transmit images continuously while the reason for an activation is being evaluated. It also requires transmission to begin within one second of an event being detected. An exception is applications, such as entry and exit points, where delayed activation is appropriate. In these cases, however, the operator should have access to stored images of the initial activation.

To minimise false activation, the remote monitoring centre should, with the agreement of the end user, be able to bypass detectors which appear to be faulty, or which operate repeatedly without good reason.

To ensure system integrity, camera signals should be monitored for video loss, and, if this occurs, it should be reported automatically to the monitoring station. In some applications, it may be necessary to detect whether cameras have been moved or masked, possibly by making comparisons with reference images stored at the response centre.

Detectors should have continuously monitored tamper protection, with local reporting when the system is unset, and reporting to the monitoring station when it is set. The CCTV control equipment should also be physically protected against unauthorised access, and it should report faults and system restarts to the remote centre.

As a further integrity measure, BS 8418 recommends that uninterruptible power supplies should be used to power CCTV installations, so that at least limited functionality can be maintained in the event of a failure of the mains supply. It also requires that supply failures are reported automatically to the monitoring centre.

Logging system events

As an aid to evaluating system operation and detecting tampering, BS 8418 requires that automatic data logging is provided. The on-site log should contain information about changes in system status; system events such as activations and tampers; successful and unsuccessful attempts to communicate with the remote monitoring centre; mains failures and system restarts.

Communication

With remote-monitored CCTV installations, communication is clearly a key feature and, as such, it is given careful attention in BS 8418. One requirement, for example, is that a secondary communication route must be available, so that the monitoring centre can be alerted to problems with the primary route.

The standard requires the system to make up to six attempts to connect to the remote monitoring centre, either three attempts each on two differently numbered telephone lines, or six attempts on a single telephone number.

Once the connection has been established, but before any data is transmitted, an authentication procedure is required. If this fails, up to nine further attempts at establishing communication and obtaining authorisation are to be made. Should this still not result in success, the system is to switch to an alternative communication route and restart the procedure.

In order to comply with the requirements of BS 8418, this whole process must be completed within 10 minutes.

Conclusion

After reading this article, installers may well feel that it contains few surprises. That is, however, exactly as it should be. BS 8418:2003 is intended to codify good practice, rather than to impose new ways of doing things. In other words, the best installers will already be doing all, or at least most, of what the standard says.

That does not, however, make BS 8418 any less useful. It provides a helpful reference and aid to memory for all those involved in the design and installation of CCTV security systems, and it is a point of reference for the users of those systems, enabling them to be sure that their installation is up to scratch.

• Colin McLuckie, Siemens Building Technologies Ltd, Fire & Security Products, Hawthorne Road, Staines, Middlesex, TW18 3AY. Tel: 01784 412 692 Email: colin.mcluckie@siemens.com, www.sbt.siemens.com/FSP