Howard Duhon

Introduction to Layer of Protection Analysis (LOPA)

Is it safe enough? This can be a difficult question. Level of Protection Analysis (LOPA) is a structured method that yields a defendable answer to that question.

LOPA uses conservative, order of magnitude values for initiating event frequency, consequence severity and likelihood of failure of protective layers to approximate a risk level for any given scenario. In rigor, it falls between a typical risk matrix approach (as commonly used in HAZOPs) and a quantitative method (QRA). A LOPA is frequently performed after a HAZOP to further investigate significant findings.

Control Systems Part 3: Rules For Tuning Loops Prior to Startup

In this GATEKEEPER series, we introduced the Ultimate Gain Plot (Figure 1) and the variables dead time (DT), time constant (TC), and controller gain (Kp). These four aspects along with a basic understanding of the control loop to be tuned, are all that is required to develop preliminary tuning parameters. The examples in this GATEKEEPER demonstrate simple tuning rules.