# Security and Independence of Process Safety and Control Systems in the Petroleum Industry
## 2 Aspects of Independence
### Functional Safety and ICT Security--Unintended and Intentional Risk Elements  
Historically, there has been a distinction in industry between administrative computer systems (office support systems) that process data and information (IT and ICT systems) and computer systems that monitor and control operations (OT systems) on production and drilling facilities.  
The OT system (industrial automation and control system) is a collection of personnel, hardware, software, procedures, processes, and policies involved in the operation of the industrial process and that can affect or influence its safe, secure, and reliable operation. The Purdue model [7] is a generalized network topology model for industrial facilities, and is often used as a reference architecture to organize systems and their interconnections. As shown in Figure 1, this model outlines the following principles:  
* The network topology is split into several levels, here named 0, 1, 2, 3, 3.5, and 4, mainly to organize sub-networks according to their main purposes.
* The four lowest levels (0-3) cover the OT systems, while the highest level (4) is the IT system. The networks at levels 0-3 are sometimes referred to as the technical networks.
* The separation between the OT and IT systems is ensured through a demilitarized zone (DMZ), referred to as level 3.5.
* At each level, there may be one or more security zones, i.e., logical or physical grouping of systems that share common security requirements.
* Conduits are used to define the secured link between each zone.  
The PSA's regulations refer to ICT systems as systems that address the need for the collection, processing, and dissemination of data and information (Cf. SF SS15). Industrial ICT systems are generally used for OT systems that can control changes in physical equipment and processes, such as control and monitoring systems and security systems. The PSA's area of authority in relation to ICT systems is mainly aimed at industrial ICT systems (OT systems) and, in particular, systems that have a barrier function (safety systems).  
Safety has traditionally been linked to the need to protect people and the environment from the uncontrolled flow of energy as a result of accidental events and malfunctions. Technical safety encompasses many different types of technical barriers, while functional safety is used specifically for barriers implemented with electrical/electronic and programmable systems.  
Safety is affected by ICT security in both IT and OT systems, and ICT events include both intentional actions and unintended incidents. Important attributes of the ICT system are confidentiality, integrity, and accessibility. Confidentiality, data protection, and information protection against intentional (malicious) actions are often emphasized in IT systems, while availability related to unintended events and error conditions is often emphasized in OT systems.  
As a result of new links and dependencies between different systems, the energy area and information area will increasingly intervene.  
It should be noted that the PSA's regulations and traditional barrier management have primarily been about controlling energy, and that the information area has been relevant to the extent that it can adversely affect the energy area and have the potential to cause physical damage.