Models of idealized systems can sometimes help investigators find BBs and analysts develop user actions after the episode scenario is known. The MANAGEMENT OVERSIGHT & RISK TREE (or MORT) model of a System Safety Management Program is an example of such a model. MORT is included in this Guide Set to show how such generalized guidance can be utilized in STEP-MES-based investigations to find input DBs.

The general procedure for using models is to:

1. access the model.
2. determine if the model is relevant to the STEP-MES Matrix array.
3. step through Matrix data BBs to find applicable ideas from model.
4. refer to model for BackSTEP hypothesis ideas.
5. develop the ideas into candidate dataBBs for Matrix array.
6. refer to model for user action option ideas.

INTRODUCTION

In the 1970s, work performed at the United States Department of Energy's System Safety Development Center (SSDC) at Idaho Falls ID USA (now closed) contributed numerous models of this type to the knowledge base available to help user action development. Similar tools are available in other fields.

The MORT User's Manual (SSDC 76-45-4, Revision 3 1992) provides numerous helpful tools for investigators to use as "thought starters" within the framework of the STEP-MES investigation. However, observe the Warning below. While some of the material has aged, the ideas behind the materials can still be helpful to new users. MORT materials are still available on the Internet. See below.

MORT and MORT-based investigation processes like Root Cause Analysis variants use the MORT Events and Causal Factors charting method to support MORT investigations. E&CF was based on early and now obsolete research that led to STEP-MES, and still incorporates conditions and other abstractions in the charts, among its other problems. Because of the high degree of subjectivity in typical usage, its use during the development of the episode descriptions is not recommended.

OBJECTIVE

To provide ideas about options during the certain stages of an investigation and the user action development effort. This Guide describes how to use the MORT model to assure that mishap investigations do not overlook any significant "programmer" actions that might be considered when filling gaps in STEP-MES Matrixes, and to influence future management of the occurrence. Programmers are individuals who "program" behavior of others people, objects and energy flows, e.g., - designers, trainers, managers, supervisors, family members, other employees, regulators, etc.

APPLICABILITY

The MORT model is applicable during BackSTEP tree and user action development tasks. During gap filling hypothesis development, the MORT chart might suggest possible scenarios or aspects of scenarios for a BackSTEP tree. After an episodic occurrence is understood, MORT can help with the problem discovery and definition tasks, and provide potential guidance to identify performance improvement options. It is most useful for suggesting potential BBs for useraction in specific cases.

DATA REQUIRED

The MORT model and companion Department of Energy MORT User's Manual[1] or MORT training are needed to use this method adequately. An understanding of the safety assurance system in the organization where the episode happened, and the description of the known behaviors during the episode are needed before the MORT model ideas can be expected to add to the hypothesis or user action options developed.

DATA SOURCES

The data sources when the MORT model is used are the STEP-MES Matrix array BBs, and the MORT model and MORT Users Manual.

THE MORT MODEL

First time users are urged to read the legend on the MORT chart, and to acquire and read the MORT User's Manual, The MORT model itself contains a listing of:

STEP-MES STEP-MES STEP-MES - almost 100 generic problems,

- around 240 "bubbles" representing more specific problems, and

- 1500 possible specific safety assurance system problems if followed in every detail.

The MORT model is laid out in a logic tree form. The main tree begins with the loss types described at the end of this Guide. The trees are supplemental branches from each of the main branches shown, further detailing areas on the main tree.

The MORT model uses several construction and layout techniques to permit all the information to be shown on a single (large) sheet of paper. When using the tree, knowledge of 4 ELEMENTS of its construction is useful:

A. Question codes. Each block on the tree has a label below the lower left corner. These labels are used to relate the questions in the MORT USER'S MANUAL to the tree, and to coordinate discussion by groups during their use.

B. Watch Nomenclature. The MORT model uses 5 ways to instruct the user to track the tree to other parts of the charts. These instructions are not conventional fault tree instructions. Differences include:

1. If a triangle comes off the sides or top of a block or gate, that means the tree branch should be repeated below the event identified by the label(s) in the triangle, and tracked from there down to the bubbles.

2. If a triangle is shown at the bottom of a box, that means a branch from the location specified in the triangle should be "copied" below the box, and tracked downward to complete the examination.

3. If a triangle is below a box, and it has no numbers in it, then look to the right or left of that triangle, at the same level in the tree, until you come to a branch below a box at the same level. That branch is to be repeated below the event just observed.

4. Large letters (A-G) called "drafting breaks" show where the detailed branch originates or is detailed. Look for these big letters. Note that A and E are located in places on the chart.

5. The ovals with R# below some diamonds in the tree show where the ovals under the ASSUMED RISK box in the second tier of the tree originate.

C. Watch the gates. The lines between blocks, with the logic gates in them, show how lower level problems can lead to losses up through the chart. Remember, if any event below an OR gate occurs, the event above the gate occurs. Watch for and/or gate relationships in STEP-MES matrix arrays was well as the MORT model.

D. Watch box contents. The contents of the boxes are cryptic reminders of the kinds of questions to be thinking about as when considering hypothesis or action options. These contents are detailed in the MORT Users Manual.

USING THE MORT MODEL

1. Select a data BB, pair or set on the STEP-MES Matrix.
   

2. Try to locate a similar kind of entry on the MORT model. This may require raising the level of abstraction of the event set to relate it to one or more MORT entries, of find parallels with the MORT entries.
   
   
3. Note any candidate problem statements or options for changes that MORT suggests.
   
   
4. Analyze and evaluate candidates suggested by MORT as prescribed in Guide 9.
   
   
5. Step through the remaining EBs, pairs and sets, looking for similarities with the MORT Model in the same way until all the EB pairs or sets have been examined.
   
   
6. Develop the candidates suggested by this process into problem statement and change options, and evaluate them.

COMMENTS ABOUT MORT USE