This paper presents a simple rule-of-thumb for dealing with uncertainty in safety function failure probability calculations. Typical levels of variability in safety function performance suggest that a factor of x3 should be applied as a design margin.
There is a story going around that we can make up for limited proof test coverage of automated safety functions by reducing device mission time. It is a convincing story, but it is (almost) completely wrong.
IEC 61511 §11.9.4 requires us to take into account uncertainty in reliability data. What is the uncertainty in the reliability data that we use? How should we take the uncertainty into account?
SIL verification calculations are meaningless if systematic failures are not actively and effectively controlled.
This paper discusses the reasons for the wide variability and uncertainty in measured failure rates. It draws conclusions on how failure rates and failure probability can be controlled in practice.
Failure probability calculations are based on the assumption that failure rates are fixed and constant. That assumption is completely invalid, but the calculations are still useful.
Design and engineering is only effective when it serves its intended purpose and is constructible within desired budget, time, quality and safety objectives.
In a safety instrumented system how should we calculate risk reduction for a set of safety functions that shares a common final element?
The extent of the hazardous areas should be reduced as far as practicable by applying principles of safety-by-design.
What can we expect to see in the new revised edition of IEC 61511? The new edition is expected to be released by the end of 2015.
The main driver for functional safety is the need to demonstrate duty of care in managing risks.
How can we make better use of competency based assessment in functional safety?
Managing the risk of systematic failures is not difficult; the principles are essentially the same as in quality management and risk management.
Independent audits and assessments reveal the commonly recurring and widespread problems.
This paper is on the topic of avoiding errors and failures due to the design, implementation and operation of the systems.
Many users in the process sector have not been able to comply fully with the requirements for hardware fault tolerance – but there are practical ways of achieving compliance.
Even the ‘simplified’ equations for probability of failure can seem to be a bit mysterious. Here is an explanation in plain language.
Assessing the impact of RFIs in Electrical and Instrumentation
Engineering Contracts – Research Paper
The cost of managing RFIs in todays complex E&I projects is much higher then generally expected.
A typical MES or MOM System adheres or adopts the principles of a 3 – tier architecture.
Poor design and documentation has been identified as a major factor contributing to poor performance and productivity in the construction industry.