How standards can help you effectively design safety systems that can prevent tank overfills?
When it comes to working with hazardous materials, the possibility of a storage tank overspill is a daily battle for the chemical industry. While overspills do not occur on a regular basis, the number of incidents per year per operation is quite high and do not seem to be slowing down anytime soon. Since the effects of an overspill can impact your employees and the environment for years to come, ensuring compliance and identifying what safety protocols your process has in place are the most important factors of your operational set-up.
In another blog, we will focus on the reasons why overspills can occur as well as what technologies can act as safe guards and what alternative solutions to implement within your process (so that you’re not just relying on automated technology). In this blog, I’m going to focus on the safety aspect.
There are several regulations and standards in place; however, many of these standards are performance-based rather than set-in-stone. This gives the safety system design more leeway as it doesn’t have to necessarily be one way or the highway. There are recommendations and a preferred method; however, the standards are used more as a guideline rather than a law as each system set-up is different.
These standards also do not dictate which technology logic system to use (relay, solid state, or software based), which logic and field device configuration to use (single, dual or triplicated), or how often to test a system (monthly, quarterly or yearly). The standards do not give clear, simple, precise answers. They do not mandate technology, level or redundancy or test intervals. They merely list the performance requirements for the overall system. In other words, the greater the level of risk of the process, the greater the performance needed of the safety instrumented system.
Challenges with Adding New Innovations
There has long been a fundamental change in the way industry standards are being written. They are moving away from being prescriptive towards performance-based requirements. After all, it’s relatively easy to be strict about something we have a great deal of experience with. The same cannot be said of relatively new and unproven processes though, which means that each plant will have to decide for themselves what is ‘safe’, and how they will determine and document that their systems are, in fact, ‘safe’. Unfortunately, these are difficult decisions that few want to make, and fewer still want to put in writing.
Safety Design Life Cycle
Designing a single component may be viewed as a relatively simple matter – one that a single person can handle. Designing any large system, whether it’s a car, a computer, an airplane or a safety instrumented system, is typically beyond the ability of any single individual. Large systems require a multi-discipline team. The control system engineer should not feel that the entire burden of designing a safe plant rests on his shoulders alone, because it does not.
Experience has shown that a detailed, systematic, methodical, well-documented design process is called for in the design of safety instrumented systems. This starts with a safety review of the process, implementation of other safety layers, and systematic analysis as well as detailed documentation and procedures. The steps are described in most documents as a safety design life cycle. The intent is to leave a documented, auditable trail and make sure that nothing is neglected by falling between the inevitable cracks within every organization.
The figure above shows one example of such a design life cycle. Please note that here are variations of the life cycle presented in other industry documents and companies may wish to develop their own variations of the life cycle based on their unique requirements.
If you’d like to learn more about Siemens and their award winning safety lifecycle tool (Simatic Safety Matrix), please click here.
To read precursor to this blog, “Stop risking it all and learn how you can prevent your tank from overfilling,” please click here.
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