# Real Consequences

Modern industry relies more than ever on alarms, trips, safety devices and other protection to provide safe and trouble-free operation. How do we ensure that protective systems can actually deliver a level of risk that is acceptable to our business?

*Real Consequences* shows how modern risk management techniques can ensure that protective systems deliver the level of risk that their designers intended. It covers both practical issues and the mathematical background needed to analyse systems.

The first half of the book is now available as a single PDF with contents and references. See the download link at the bottom of this page

# Section 1: Basic Principles

### 1 Hidden failures, Real Consequences

This chapter draws out lessons for the maintenance and design of protective systems from high profile accidents and disasters in which they have been implicated.

### 2 Hidden Functions

After introducing basic hidden function concepts, this section looks at some of the subtleties of hidden and evident functions and tries to answer an apparently simple question: when is a function evident, and when is it hidden?

### 3 Managing Hidden Failures

Any management policy that focuses on the effects of a hidden failure is doomed, simply because there are no effects to manage. This chapter examines the factors that affect the selection of maintenance tasks for any failure, and emphasises those that are relevant for hidden failures.

### 4 Failure-Finding Basics

This chapter builds the foundations that you will need to apply failure-finding and other failure management policies to real equipment.

### 5 The Basis of Decision-Making

The frequency of a scheduled test can be driven by risk or by cost. This chapter shows how to apply these criteria to real systems, and demonstrates how simple availability targets can be misleading.

### 6 Tolerable Risk

Far from being fixed by design, the risk of a multiple failure can be managed by increasing the availability of the protective system, or by reducing the demand rate. Developing the concept of tolerable risk, the one-time friend ALARP (As Low As Reasonably Practicable) is put to the sword.

### 7 Writing Failure-Finding Tasks

What could go wrong with a periodic test? This chapter looks at the practical issues surrounding invasive maintenance checks, and at the unfortunate psychology of task reporting.

# Section 2: Failure-Finding Task Intervals for Simple Systems

### 8 Availability

The availability of a protective system is a single number that sums up its effectiveness. This chapter introduces simple availability calculations and explores the relationship between availability and failure rate.

### 9 Risk

This chapter derives test intervals for simple systems from the key criterion: the maximum tolerable risk of a multiple failure.

### 10 Economic

Some multiple failures have no safety or environmental consequences, but they have a direct monetary impact on the organisation. Find out here how to balance the risked cost of multiple failure against the cost of checking and to determine an optimum task interval.

### 11 Parallel Systems

Designers use redundant systems to deliver higher availability than could be achieved by a single protective device. This chapter expands the model and enables you to calculate the availability of more complex systems.

### 12 Imperfect Testing

So far, the models that we have used assume that failure-finding tasks are perfect: a protective device is never passed as working when in reality it has failed. Most tests disturb the equipment in some way, and this chapter expands the model to deal with imperfect tests and testers.

### 13 Practical Analysis Guidance

Moving from theory to practical application, this chapter discusses the problems and pitfalls encountered in trying to calculate failure-finding intervals for real systems.

### A Mathematical Annex

Contains full mathematical derivations of the main results used in sections 1 to 3.

### B Equation Summary and Reference

This chapter collects together all the main results from sections 1-3, with an explanation of the terms used in each equation.

### C References

### D Biography

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