Should emergency venting be included in the emergency stop function of the SIS system?
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In the current process, the SIS system has conditions for activating emergency relief; for example, when the temperature reaches 50°C and the pressure reaches 0.03 MPA, the emergency relief valve opens automatically, allowing the material to flow under gravity into the emergency relief tank； Some experts have suggested that emergency relief should also be included in the emergency shutdown functions of the SIS. However, according to our process design, in the event that an emergency shutdown is required, the DCS system first ensures that operations remain within safe process limits. Should the DCS measures prove insufficient, the SIS then takes action. In such cases, if the temperature and pressure continue to rise until they meet the conditions for emergency relief, the emergency relief system will be activated automatically ； So we believe there is no need to add an emergency release within the emergency stop ； Once the emergency is resolved, production can resume ； According to experts, this workshop needs to be shut down immediately; therefore, the reactor must be depressurized urgently ； This will result in the complete scrapping of this batch of materials ； Dear friends, please let me know if there’s any standard requirement to include emergency relief in the emergency stop mechanism. Or feel free to share your opinions
How to write HAZOP and safety risk assessments?
I think emergency relief should be placed before the SIS system; after the process parameters exceed the set limits, an emergency relief process should take place. If this relief is not sufficient to ensure safety, then the emergency stop function should be activated. If, due to process reasons, emergency relief is a measure taken after an emergency stop is activated, then it should be incorporated into the SIS system. Since the SIS system has been activated, it means that the situation on site can no longer be controlled through process measures; considerations regarding material waste are no longer relevant, as safety becomes the top priority.
What types are included in your emergency stops? Is it a manually controllable emergency stop or uncontrollable?
Sis, safety first – don’t worry about wasting materials
In accordance with the protection layer analysis and regulatory requirements, SIS should be implemented to the minimum extent possible. Reference.
I’ve found it. To answer just one question: personally, I believe that when issues arise during chemical processing operations, the sequence of responses should be: manual control → DCS protection → SIS protection → activation of safety accessories. The safety accessories included are burst discs, safety valves, and emergency discharge systems; from this perspective, emergency discharge should not be incorporated into the SIS emergency shutdown system – it is acceptable to have it operated via interlock or manual control. But from a safety perspective, interlocked discharge is more appropriate. For example: the human control setting is 30 degrees, 35 degrees when the DCS interlock is disabled, 40 degrees when the SIS takes over, and 50 degrees during emergency discharge. Of course, this temperature and pressure should be chosen properly. If DCS interlocking is used, it must be effective in ensuring this.
Take a look at how PSM is written, as well as the definition of HAZOP at that time. Experts heheheh; currently, experts just heheheh and laugh