Remote-Controlled Monitors for Fixed Firefighting Systems
06 January 2020 | Web Article Number: ME201917396
By Fritz Zimmermann
THE requirements for automated firefighting are continuously increasing. Remote-controlled monitors, especially in combination with automated fire detection, allow a targeted but flexible firefighting operation in limited areas. The technical development in the field of drive engineering, sensor technology and control technology offers some great future potential.
Automated firefighting systems are well known as sprinkler systems and also spray nozzles. But for several years automated firefighting systems with remote-controlled monitors have been used for fire protection of tank farms, petroleum loading terminals, aircraft hangars, production facilities, recycling plants and waste incineration plants.
The big range of monitors and the possibility to select from a variety of mountable nozzles provide flexibility and enhance performance to achieve effective fire protection for high risk areas. Remote-controlled monitors allow a targeted firefighting operation in confined spaces and can be used for extinguishing agents like water, low-expansion foam and, if required, even powder. The nozzles are fine-tuned to suit the type of extinguishing agent, allowing extended reach. Combined with a suitable fire detection and control, effective fire protection can be guaranteed while requiring just a minimum number of firefighting personnel.
To fully utilise the range of potential offered by remote-controlled monitors for firefighting, introducing a programmable (PLC) control system with state-of-the art communication facilities is mandatory. This allows the connection with automatic fire detection systems and fire alarm control panels also for very large and complex facilities. The response times are as fast as known from present automatic firefighting systems.
Using remote-controlled monitors in automated firefighting systems requires a consideration of some function-relevant parameters with regard to design and construction of the monitors. In order to achieve the requirements of repetition accuracy for pre-programmed extinguishing operations, zero-clearance bearings are necessary to effectively prevent any tilting of the pivot mounting. In addition a design aimed at reducing the repulsion of the water jet and decreasing the power needed to swivel the monitor, such as the optimised FireDos octagonal ‘Oval Flat Design’, is essential.
This also includes suitable, contact-free and thus wear-free absolute encoders in order to implement a high repetition accuracy and precise nozzle direction in the case of automated firefighting systems. It is vital to use such sensors which can monitor and save movements and positions even when electricity is shut off. In case of manual manipulation of the monitor by the use of the fitted hand wheels, i.e. during maintenance or commissioning, this ensures that no reference adjustment is necessary for recalibration of the programmed automated swivelling movements. In addition the drives which regulate the spray pattern must be able to be fitted with absolute encoders.
Beside the right / left and up /down movements, this provides a third parameter which allows influencing the shape and range of the spray target area. Furthermore, a larger spraying angle also reduces the impact forces of the extinguishing agent jet and thus prevents a fire of bulk materials from spreading.
To achieve the necessary degree of freedom, remote-controlled monitors should allow wide swivelling ranges. Preferably, the horizontal swivelling range is 360° and the vertical swivelling range reaches from +90º to -90°. Both swivelling axes should have self-locking worm gears to prevent the monitor from an unintended adjustment by an external force. Additionally self-locking gears help to stop remote-controlled monitors at the desired position without requiring additional brakes.
In order to achieve the corrosion resistance required for a long-term use of the monitor, components made of seawater-resistant cast aluminium along with additional special hard anodized coating are used and have proven themselves for many years. Using only cast parts to build monitors eliminates the risk of stress corrosion cracking, which occasionally appears in welded parts. Further the development process of monitors using cast parts increases the design flexibility and optimization process significantly. The components can be flow-optimised by the use of CFD (Computational Fluid Dynamics) simulation software. Low pressure loss figures can be achieved even with comparatively compact dimensions. This reduction in pressure loss indicates that the extinguishing water turbulence on the way through the monitor is reduced to a minimum. Flow-optimisation however does not end with the so-called pivot mounting, i.e. the body of the monitor, but also includes the nozzle.
A sufficiently long nozzle design reduces the turbulences from the pivot mounting effectively and creates the basis for the long reach of CFD flow-optimised nozzles. As it has already been practised with manual controlled monitors for a long time even nozzles for remote-controlled monitors can optionally be fitted with regulators for the extinguishing agent flow-rate. FireDos monitors offer this option to take place remote-controlled during operation. The flow can thus be adapted to the actual requirements of firefighting.
The range of electric control systems for remote-controlled monitors reaches from standalone control systems to control one single monitor to complex systems with multiple monitors where decentral individual controls are connected with a central control unit via a fibre optic network. Dependant on the requirement, compact PLC systems or systems consisting of several interconnected assemblies make up the control system. Where high functional safety is required, redundant CPUs can be installed or, alternatively, PLC control systems in accordance with the required safety level (SIL). A daily automatic self-test is one standard feature of today’s control systems. During this process, the functionality of all drives and sensors fitted on the remote-controlled monitors is tested.
If a fault is found at one of the components, a corresponding error message is sent to the supervising body. This ensures that possibly occurring failures are reported immediately and can be eliminated before a malfunction during operation happens. This significantly increases the reliability and availability of the automated firefighting system, compared with such systems which are tested for functionality in more or less long and possibly irregular intervals. For easier commissioning, the automated control systems are fitted with an HMI (Human-Machine Interface) option. During commissioning or a change in program, all threshold values which must not be exceeded by the remote-controlled monitors can be adjusted in the control cabinet without having to make any settings directly at the remote-controlled monitors. In the case of very large systems, this is an invaluable gain of time during commissioning, service and use.
But not only thresholds and rest positions can be programmed via a display. Also the best oscillation mode for the respective system can be individually selected and programmed for the single or multiple monitors. Currently, four different oscillating modes are generally used which allow adapting to the various requirements in different applications. This allows the hazardous areas within these applications to be separated into individual zones where one or even several monitors will apply their extinguishing agent in case of an alarm.
If control systems for remote-controlled monitors are interconnected with fire detection systems (i.e. on the basis of IR cameras), pre-selection of individual zones can be skipped. The monitor will then swivel to an area identified by the fire detection system and will start the extinguishing operation directly at the source of the fire. In case of locally confined initial fires, this results in maximum firefighting success while consuming just a minimum amount of extinguishing agent and affecting only a limited area.
The technical development in the field of drive engineering, sensor technology and control technology offer some great future potential to detect fires in their initial phase as well as to fight fires in a localised and resource-conserving manner by use of monitors.
The successful to application of experience and procedures from practical firefighting to automated firefighting systems means the seeming paradox of “less extinguishing agent leads to a higher level of fire protection” can become reality.
Fritz Zimmermann is Head of Engineering for FireDos GmbH