Issue link: https://www.e-digitaleditions.com/i/1263839
32 / July 2020 powderbulk.com located inside and is elevated with poor access, not to mention there has been no existing performance moni- toring or explosion protection. Zones and nodes. The first step in this DHA is to establish the zones and nodes. The zones represent var- ious portions of the system or systems, and the nodes represent each individual portion of the system that should be evaluated. The dust collection system is zone 3 and includes nodes P (dust collector), Q (rotary valve), R (fan package), and S (ducting and hoods). Checklist and what-ifs. The following are questions that were brought up for this DHA. Coal handling and milling system example DHA The coal handling and milling system schematic, shown in Figure 3, represents an actual system. Only the dust collection portion, shown in magenta, will be considered since it's universally applicable. Base information. The coal's explosivity test results showed a K St of 155, P max of 8.1 bar, MEC of 70 g/m 3 , and MIE of 500 millijoules. However, this material is also pyrophoric under certain conditions. Additional points to note are that the system is 27 years old and has had two small events over the years. The system is FIGURE 2 Typical risk assessment matrix example Probability of occurrence Severity Extremely improbable Extremely remote Remote Reasonably probable Frequent Catastrophic Review Unacceptable Unacceptable Unacceptable Unacceptable Hazardous Review Review Unacceptable Unacceptable Unacceptable Major Acceptable Review Review Review Review Minor Acceptable Acceptable Acceptable Acceptable Review FIGURE 3 Coal handling and milling system schematic Fan package Bucket elevator Positive-displacement blower Pulse-jet dust collector Rotary valve Coal storage bin Screener vent R P Q S