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Situation: The manager of a major facility is concerned about the possible impact of the failure of the
landline communications system that provides the sole communications capability at the site. The
decision is made to do a Failure Modes and Effects Analysis. An extract from the resulting FMEA is
shown below.
Component
Function
Failure
Mode
& Cause
Failure
Effect on
Higher Item
System
Probability
Corrective
Action
Landline
Wire
Comm Cut-natural cause,
falling tree, etc.
Comm system
down
Cease
Fire
Probable Clear natural obstacle
from around wires
FAA System Safety Handbook, Appendix F
December 30, 2000
F-39
Wire
Cut-unrelated
operational
activities
Comm system
down
Cease
Fire
Probable Warn all operations
placement of wire
Wire
Line failure
Comm system
down
Cease
Fire
Probable Placement of wires
Proper grounding
Wire
Cut – vandals &
thieves
Comm system
down
Cease
Fire
Unlikely Placement of wires
Area security
1.3.4 THE MULTI-LINEAR EVENTS SEQUENCING TOOL
FORMAL NAME: The Multi-linear Events Sequencing Tool
ALTERNATIVE NAMES: The timeline tool, the sequential time event plot (STEP)2
PURPOSE: The Multi-linear Events Sequencing Tool (MES) is a specialized hazard identification
procedure designed to detect hazards arising from the time relationship of various operational activities.
The MES detects situations in which either the absolute or relative timing of events may create risk. For
example, an operational planner may have crammed too many events into a single period of time, creating
a task overload problem for the personnel involved. Alternatively, the MES may reveal that two or more
events in an operational plan conflict because a person or piece of equipment is required for both but
obviously cannot be in two places at once. The MES can be used as a hazard identification tool or as an
incident investigation tool.
APPLICATION: The MES is usually considered a loss prevention method, but the MES worksheet
simplifies the process to the point that a motivated individual can effectively use it. The MES should be
used any time that risk levels are significant and when timing and/or time relationships may be a source of
risk. It is an essential tool when the time relationships are relatively complex.
METHOD: The MES uses a worksheet similar to the one illustrated at Figure 4.1. The sample
worksheet displays the timeline of the operation across the top and the “actors” (people or things) down
the left side. The flow of events is displayed on the worksheet, showing the relationship between the
actors on a time basis. Once the operation is displayed on the worksheet, the sources of risk will be
evident as the flow is examined.
2 K. Hendrisk, and L. Benner, Investigating Accidents with Step, Marcel Dekker, New York, 1988.
FAA System Safety Handbook, Appendix F
December 30, 2000
F-40
Figure 1.3.4A Multi-linear Events Sequencing Form
(Time units in seconds or minutes as needed)
Actors
Timeline
(People or things
involved in the
process)
RESOURCES: The best sources for more detailed information on the MES is the System Safety staff.
As with the other advanced tools, using the MES will normally involve consultation with a safety
professional familiar with its application.
COMMENTS: The MES is unique in its role of examining the time-risk implications of operations.
1.3.5 THE MANAGEMENT OVERSIGHT AND RISK TREE
FORMAL NAME: The Management Oversight and Risk Tree
ALTERNATIVE NAMES: The MORT
PURPOSE: The Management Oversight and Risk Tree (MORT) uses a series of charts developed and
perfected over several years by the Department of Energy in connection with their nuclear safety
programs. Each chart identifies a potential operating or management level hazard that might be present in
an operation. The attention to detail characteristic of MORT is illustrated by the fact that the full MORT
diagram or tree contains more than 10,000 blocks. Even the simplest MORT chart contains over 300
blocks. The full application of MORT is a time-consuming and costly venture. The basic MORT chart
with about 300 blocks can be routinely used as a check on the other hazard identification tools. By
reviewing the major headings of the MORT chart, an analyst will often be reminded of a type of hazard
that was overlooked in the initial analysis. The MORT diagram is also very effective in assuring attention
to the underlying management root causes of hazards.
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