- 1-1 Engineering Ethics
- 1-2 Myths about Process Safety
- 1-3 Safety Culture
- 1-4 Individual Risk, Societal Risk, and Risk Populations
- 1-5 Voluntary and Involuntary Risk
- 1-6 Safety Metrics
- 1-7 Accident and Loss Statistics
- 1-8 Risk Perception
- 1-9 Risk Tolerance/Acceptance and Risk Matrix
- 1-10 Codes, Standards, and Regulations
- 1-11 Safeguards
- 1-12 The CCPS 20 Elements of Risk-Based Process Safety
- 1-13 Inherently Safer Design
- 1-14 The Worst Chemical Plant Tragedy: Bhopal, India, 1984<sup><a id="ch01fn13_r" href="ch01.xhtml#ch01fn13">13</a></sup>
- 1-15 Overview of Chemical Process Safety
- Suggested Reading
- Problems
This chapter is from the book
This chapter is from the book
This chapter is from the book
1-6 Safety Metrics
A very important part of any safety program is measuring the safety program effectiveness. This is done using safety metrics. Each company must identify metrics that are effective for its operations. These metrics are not universal, will change between companies and even plant sites, and will change with time.
Metrics are usually measured over a period of time and at multiple plant sites to identify any important changes or trends. Adverse changes in the metrics will trigger a management review, with resulting recommended changes for improvement.
Figure 1-3 shows the accident pyramid demonstrating the relationship between various levels of accidents based on severity. The severity level increases toward the top of the pyramid. Accidents of lower severity occur more frequently. Indeed, for every fatality, there are orders of magnitude more accidents of lesser magnitude and even more near misses. A near miss is an accident with no consequences that might have resulted in a catastrophe if conditions had been slightly different. Accidents of smaller magnitude and higher frequency, in particular near misses, provide many opportunities to recognize problems and make improvements—and, one hopes, to prevent more consequential accidents.
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Figure 1.3 The accident pyramid showing the relationships between various levels of accidents. Metrics near the top are more leading; metrics toward the bottom are more lagging.
The problem with the accident pyramid is that the items listed are all lagging indicators. That is, the accident pyramid is based on incident outcome metrics derived after an accident or near miss has already occurred. It would be preferable to have leading indicators—that is, metrics that measure activities prior to the occurrence of an accident. Lagging metrics have historically been used more often than leading metrics because they are easier to identify and interpret, and typically must be reported to various regulators. By comparison, leading metrics are more difficult to identify and interpret.
Table 1-5 lists examples of leading and lagging metrics suitable for a chemical plant. The metrics at the top of Table 1-5 are leading indicators, while the ones at the bottom are lagging indicators. Notice that process safety culture—a leading metric—is at the very top of the table, while serious injuries and fatalities—lagging metrics—are at the bottom.
Table 1-5 Example Leading and Lagging Metrics for a Chemical Plant
Leading metrics - towards top of table |
Process safety culture: Number of monthly process safety suggestions Response time for process safety suggestions to be addressed Number of open recommendations Process safety budget reduction Number of meetings addressing process safety Time to complete an incident investigation and issue a report Attendance at required safety meetings Signs of worker fatigue |
Training: Percentage of workers who require remedial training Percentage of near-miss incidents with training root causes Change in training budget Number of workers with overdue training Training sessions canceled or postponed |
Operating procedures: No system to gauge whether procedures have been followed Number of operating procedures updated per year Number of incident investigations that recommend changes to procedures Percentage of procedures that are annotated in the field Tolerance of failure to follow operating procedures Fraction of operators who believe that procedures are current and accurate Number of procedures that are past due for review Operators appear unfamiliar with procedures or how to use them |
Maintenance procedures: Number of overdue maintenance tasks Number of unplanned repair work orders each month Work order backlog Change in maintenance budget Number of work orders that apply to equipment that no longer exists at the site Number of maintenance employees who hold required certification Number of management of change (MOC) requests Follow-up time on recommended actions |
Inspection frequency |
Safety system demands |
Inspections with results outside limits |
Excursions on safe operating limits |
Near misses |
Number of incidents |
Property damage |
Community response actions |
Loss of primary containment (LOPC) incidents |
First aid incidents |
Minor injuries |
Serious injuries |
Fatalities |
Lagging metrics - towards bottom of table |