Recently there was news about Ex CEO of Union Carbide Warren Anderson. The news had me thinking about the safety issues that the plant in Bhopal faced and negligence which caused the disaster. Also there was this incident abroad in Piper Alpha offshore along the North Sea which is considered one of the worst in terms of casualties and loss of industrial value.
These incidents were of the high intensity and recovery seemed out of hand only because not only that the design of these plants were bad, but the design did not take into consideration of the industry behavior in the long run, when the plant is in full production.
So the question raise that in a plant which is operational and running continuously 24 X 7 for years around what is the guarantee that the safety systems and fire and gas systems will function when need arises?
So the Industries need was given a solution with safety standards which are even now followed and have proven beneficial to all the plants.
Some of the safety standards are found to be mentioned in wiki.
These incidents were of the high intensity and recovery seemed out of hand only because not only that the design of these plants were bad, but the design did not take into consideration of the industry behavior in the long run, when the plant is in full production.
So the question raise that in a plant which is operational and running continuously 24 X 7 for years around what is the guarantee that the safety systems and fire and gas systems will function when need arises?
So the Industries need was given a solution with safety standards which are even now followed and have proven beneficial to all the plants.
Some of the safety standards are found to be mentioned in wiki.
The accepted safety standards such as ISA-S84.01 and IEC 61508/61511 are used to measure the acceptable level of performace of the safety systems.
A Safety Instrumented Loop is essentially a measure of the system performance in terms of Probability of Failure on Demand (PFD).Also we need to understand that Risk is Probability or the number of times the hazard might occur multiplied by its consequence.
SIL is defined in 4 categories:
SIL-1 which has risk reduction factor of 100 to 1 and PFD of 10^-1 to 10^-2
and the highest SIL rating being SIL-4 which has risk reduction factor of 10000 to 100000 and PFD of 10^-4 to 10^-5. These details can be found here .
How a classification of SIL for the instrument is given is based on analysis and calculation which also required the in-depth of process knowledge. An example is found here.
To conclude, I have taken excerpts from a website for the basics of SIL as stated:
the basic concepts of SIL are:
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