Statistical control charts, safety performance

Miner s safety performance recognition, circa 1920s 20 The systems model of health and safety management 24 The size of mobile mine equipment continues to increase 27 Simple model of outcomes dependent on culture and systems 32 Statistical control chart with incident rate variation 33 Universal Copper and Metals Mine accident frequency rate control chart 55... 

Statistical process controls (cause-and-effect diagrams, control charts, etc.), as applied in quality management, can serve as performance measures for safety, if they are used prudently and with caution. 

A control chart is a statistical device used for the study and control of safety performance in the workplace. The basis of control chart analysis is the knowledge of chance variations in the data (Duncan 1974,375). If a series of safety measurements are plotted and the obtained measurements are truly random, the distribution would approximate the normal bell-shaped curve. Plotting the data on a control chart, one would obtain measurements over time that fall into the ranges depicted in Figure 4.1, with more measures occurring at or near the average more frequently and readings at the extreme ends of the possible measurements infrequently. 

Because of the underlying statistical processes used with control charts, the safety manager can identify safety performance problems when they become statistically significant. The safety manager can also use control charts to implement continual improvement programs related to safety activities. 

Valid statistical measures, such as control charts, are convincing. In some situations, such as initiating the cultural change necessary to call attention to serious injury prevention, the frequency of occurrence data on such incidents that would be placed on a control chart will not be available since the subject is low-probability/severe-consequence events that do not occur often. Cost data for such events can be influential. For an additional reference, see Measurement of Safety Performance in On The Practice Of Safety. 

Petersen (2005) included an 18-page appendix on Statistical Process Control in Measurement of Safety Performance. Janicak (2010) has a 30-page chapter on Run Charts and Control Charts in Safety Metrics Tools and Techniques for Measuring Safety Performance. Other authors in years past have suggested the use of control charts to track safety performance. Yet, the subject does not appear in the current safety-related literature. 

---