The relative cost and duration of Initiation and Scoping are so small that they are not visible at the scale of the bar graphs.
The relative ease of MOC creation has policy implications. In the interests of safety and encouraging employee participation, most sites permit almost anyone to initiate an MOC. But MOC initiation has huge leverage: for every dollar spent on initiation (i.e. the initiator’s salary for the time involved), the company will spend another ~$300 on pursuing the change (and this doesn’t even include material cost). Therefore, it appears reasonable that the manager who is responsible for the asset should be required to accept the MOC after it has been scoped. In the absence of this prioritization function, the MOC system at the site will become clogged with dozens of hundreds of in-process MOCs.
Scoping also has huge leverage, like Initiation. Typically, scoping represents about 1/500th the cost of the overall MOC. Yet, the “work” of the MOC is determined during the scoping activity. This suggests that adequate attention must be paid to effectively scope the change.
4.4 Implementation: (Typically) The Largest Cost
The Petri net model attempts to realistically model the implementation process. Key features include:
- unit or equipment shutdown may be required (see Table 2)
- development of detailed change specifications, in addition to the redlines created during Change Design
- purchase requisition generation, ordering, material receipt, work order generation and issuing
- activities of representative crafts
- procedure updates
- training material development and training activities.
With this scope of work, it is not surprising that the Implementation state has the greatest cost.
4.5 Impact Analysis: (Typically) The Second Largest Cost
The MOC Standard Model considers three kinds of impacts:
- process safety impacts, usually addressed using a process hazards analysis
- environmental impacts
- financial impacts
It is assumed that the risks associated with small changes require less detailed analysis. So, the process safety impacts are analyzed using a checklist for small changes. Similarly rapid analysis techniques are used for environmental and financial analyses. Large MOCs are assumed to have risks that require more detailed analysis. So, the process safety risks are analyzed using the HAZOP methodology. Similarly detailed techniques are used for the environmental and financial analyses.
The detailed analysis techniques have two common features:
- They require multiple people to assemble for a meeting to discuss the specific impacts of the MOC, thereby increasing the resource costs significantly.
- The meetings must be scheduled in advance, thereby significantly increasing the duration of the impact analyses.
Clearly, when a detailed impact analysis is needed for risk mitigation purposes, its expense and time are unavoidable. However, if there is no reason for a detailed impact analysis, then there are significant cost and time benefits to performing only the necessary analysis.
How and when would one determine what kind of impact analysis is necessary? This has been done using pre-established rules, applicable to the site and its inherent hazards. The best time to identify the impact analysis methodologies is during scoping, since this allows the necessary resources to be arranged ahead of time.
4.6 The Effects of Errors
The Standard model uses a zero-error assumption. Of course, that is not realistic—errors occur all the time, and error mitigation creates extra cost. The kinds of errors represented in the Standard Model are:
- Errors discovered during Impact Analysis: If the change proposal, as documented in the redlines, does not provide sufficient information, the team/person conducting the impact analysis may stop and await additional information.
- Approvers rejecting the change: Approvers may reject a change if it is improperly or inadequately described. The process stops awaiting additional information.
- Errors discovered during Implementation: Prior to implementation, the change could be considered somewhat abstract—during implementation, the change is most definitely concrete. During implementation four kinds of problems are commonly encountered:
- Design deficiencies: These are errors in the design of the proposed change. “Design” is to be interpreted as any error in documentation, which makes it difficult or impossible to continue work on the change.
- Physical discrepancies: This is a common problem whereby it’s discovered that the documentation does not correspond to what is actually installed in the plant already. When the documentation does not accurately reflect the current plant configuration, it brings into the question the adequacy of the change proposal as well as the adequacy of the various impact analyses.
- Execution deficiencies: These are mistakes made by the resources implementing the change.
- Material deficiencies: These are inadequate parts or materials, whose inadequacy may be due to the incorrect materials being installed or damaged during installation.
In all cases, the errors are further classified as follows:
- Minor errors: Minor errors are those that can be remedied quickly, and will not change any of the impact analyses in any way. The MOC remains in the same state, and the process continues after the error is remediated.
- Major errors: Major errors are those where documentation is significantly altered, and the changed information causes one or more of the impact analyses to be modified. When a major error is encountered, the MOC is usually demoted to the Change Design state. Once the documents are modified, the change must work its way through its lifecycle again, beginning at Change Design.
Reasonable values were selected for the probability of major or minor errors of types 1 thru 3(d), from the previous list. The minor errors have little effect on the already expensive MOC process. The charts in Figure 6 compare results with and without errors. The minority of MOCs that do have major errors (~10%), have their costs and durations almost double. But, when the doubling of costs and durations is averaged over all MOCs, the average results are still significant, but not that startling.