Fire & Gas Systems Integration
Integration of Fire & Gas Networks with IT Systems
Preface:
This article presents an overview of how Fire & Gas Systems can be integrated into mainstream IT systems. An actual application currently in use in the Middle East is used as a case study to show the capabilities and benefits of integrating these systems together. Analysis of the solution shows several benefits for the user.
Introduction:
Traditionally Fire & Gas Systems used stand-alone techniques to monitor information from field devices such as Fire & Gas Detectors and pass to other devices such as horns, beacons and mimic panels. For example a gas detector could be used to monitor for the presence of chlorine in air, if the gas reaches a set-point value, the Fire & Gas System senses this as an alarm and creates an alarm via the horns, beacons and visually represents this on a plant mimic panel. With the advent of computers and network technologies there is a standard requirement now for passing this information to other systems for control and monitoring.
For many years control systems were based around PLC's (Programmable Logic Controllers) that had their own proprietary networks and interfaces. Standard networks became available such as ModBus, Fieldbus and Profibus. These networks were used to connect the various field devices and control networks together. This approach came with its own difficulties, costly to program and interface into other systems. The software used was typically customised, drivers and interfaces were proprietary, therefore any subsequent changes or enhancements to the Fire & Gas System required costly specialised support from the system suppliers.
Fire & Gas Systems specifications are mainly driven by approvals, in the main these relate to IEC61508. This approval requires that Fire & Gas Systems as well as DCS (Distributed Control Systems) and ESD (Emergency Shutdown Systems) systems meet a certain SIL level (Safety Integrity Level). Typically Fire & Gas Systems are requested to meet 4 SIL levels, from SIL0 to SIL3 where SIL3 is the most rigorous approval to meet (SIL0 simply means that no SIL level is required). In order to meet SIL3 this requires that fault detection and diagnosis is implemented in the control system and network architecture. In Fire & Gas Systems this typically requires dual or triple redundancy throughout the control hardware and network components.
This article presents a current Fire & Gas System that is being used in the Middle East to monitor for the presence of Chlorine and Hydrogen Chloride. The system uses ModBus as a communications medium between the field devices and a simple PLC. The information from this PLC is then passed to two neighbouring chemical processing plants via their standard IT Ethernet network to monitor the status of the gas detectors. From the SIL levels previously described the system only has to meet SIL0.
Solution:
Reference to 'Diagram 1 - System Architecture', shows the main components of the system architecture. The requirement from the customer was to provide a simple and efficient system for monitoring the presence of Chlorine and Hydrogen Chloride gas from a process plant. The gas from the process plant had caused complaints from a neighbouring plant that leaks were being detected. The request was therefore to monitor the fence bordering the two plants for gas leaks and to raise alarms to both neighbouring plants. The customer did not wish to lay new network cables due to costs, but required to integrate the Fire & Gas System into the existing plant IT systems. A further requirement was the provision of standard software solutions so that subsequent changes and additions could be performed by the customer.
Available solutions to this request would typically have been to use a discreet control network such as ModBus. This would require a separate cable network to the locations of the system components. If the system was part of an overall safety system, i.e. required executive actions to shutdown a process or plant then the proposal would have been around individual connections from the field devices to the PLC.
For this solution the decision to use the existing plant IT networks gave advantages to the customer, these being:
- Networks existed, no new cable network required
- Standard solution requiring no custom software or drivers
- No specialised maintenance required
- Customer can move PC's to new locations with no impact on the network
- Additional viewer PC's can be added easily and by the customer
With the integration of the Fire & Gas System to the plant Ethernet networks this gives access to the many features that are available. These include firewalls, web portals and future developments of IT networks further enhancing the overall system capability for the customer.
The only disadvantage that was highlighted related to the security of the system, normally a fire & gas network is safety related and interference from other systems is not allowed. However for this application the system was for monitoring only, no critical information or actions are required. Note that in another system application the system was safety related, the network therefore was a separate dual redundant Ethernet configuration and approved by TUV. The network was solely used for the fire & gas application, no other systems were allowed access.
The decision to use the plant IT network could have been further enhanced at installation by the use of OPC (OLE for Process Control). This is a software driver first developed by Microsoft and has been widely accepted by the control systems industry. Many independent companies are now offering OPC as a solution to the problem of communication between components and networks. OPC provides a standard that allows devices to pass information around and many software companies are now driving the use of OPC and providing further enhancements. For this application the customer required OPC at a later date together with additions to the system such as gas and fire detectors.
Case Study:
The system architecture shows the 12 gas detectors being connected serially on two Modbus RTU networks. The length of each network is approximately 1km and 500m. These networks are then interfaced into a standard PLC with Ethernet communications. The system then comprises of a server PC running standard available visualisation software, and two viewer PC's running the same visualisation software. The visualisation software is configured to show the layout of the plant, location of each detector and real time activation of alarms and graphic symbols. The alarm and status information is stored on the server and can be viewed/recalled from the viewer PC's over the plant networks.
The main server PC is located in the company that has the process producing the chemicals and a viewer PC is located in the control room. The neighbouring company has a viewer PC and this is connected on the Ethernet link via fibre-optic cables. The server PC is only allowed to accept alarms, the viewer PC's give status indication only, however it is possible to trend alarms from the alarm and history logs located on the server PC.
The benefits for the customer in integrating the Fire & Gas System with the plant IT infrastructure are reduced cost, flexibility of the system and easier maintenance by local engineers. Also as enhancements and upgrades are made to the plant IT system then this is integrated with the Fire & Gas System.
Summary:
This article has given an overview of the requirements for Fire & Gas Systems and has shown that although these systems are driven by strict approvals there is a movement into integrating such systems with mainstream IT systems. From the case study example discussed it can be seen that there are many advantages in using IT systems for the end user. It is clear that the integration of control systems and IT systems is a prospect for the future and provides many advantages.
Diagram 1 - System Architecture
Author:
Robert Kyle
Technical Director
MSA EUROPE Fire & Gas Systems Group
