What are the elements of a URS for process automation? 
The URS needs to reflect the needs of the customer's specific business. Thus, no two URS documents are exactly alike. However, the following points are commonly addressed in the document. 
process and facility description 
The URS should provide a description of what the industrial process does. This should include descriptions of the process unit operations, process outputs, and how raw materials, energy, and water are used by the process. This description usually includes a P&ID diagram. 
The document should cover facility aspects which could impact the automation system. Hot, damp, or dusty situations which could affect component robustness requirements should be called out in the document. 
worker and process safety management 
The automation URS document should indicate what hazards need to be considered in the design of the automation system. These hazards usually involve worker safety hazards, or hazards of damage to equipment, which are identified through a risk analysis. The hazards can include physical hazards such as high temperatures, high pressures, or rotating parts, or potential hazards such as dust explosions or flammable vapors. 
The role of the process automation system in regards to worker safety continues to grow in importance. It is not unusual to find that special automation requirements must be taken into consideration for an organization to meet its worker safety objectives. These include special limit and proximity sensors with tamper resistant capabilities, safety rated PLC devices, safety related relays, or high reliability components. 
The process automation system often governs the safe sequence of machine operation such as ensuring the proper position of control valves before initiating cleaning, sterilizing, or maintenance operations. Automation is normally a consideration in Lock Out Tag Out procedures. 
The URS should specifically call out protection classifications such as PILS, or the need for safety rated process control components, if required. It should also specify what equipment must be managed by emergency stops. 

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