Page 100 - Serious Incident Prevention How to Achieve and Sustain Accident-Free Operations in Your Plant or Company

CH07pp068-82 4/10/02 12:50 PM Page 78

78 Serious Incident Prevention

upper layers of the organization. Understanding an organization’s safety
risks requires an understanding of both “at-risk” actions that can directly
lead to incidents and the role of latent conditions that are like hidden land
mines waiting for the right circumstances to cause destruction.

Classifying and Prioritizing Risks

Organizations have finite resources and must continually make deci-
sions regarding the level of resources that will be applied to control risks. It
is important that the organization classify and prioritize its risks to provide
the right guidance in making these strategic decisions. Risk classification
methods include those that quantify risks by means such as probability of
occurrence, costs, number of expected fatalities, or other potential out-
comes. Other classification methods are commonly used that provide only
a qualitative description of potential consequences (e.g., catastrophic, crit-
ical, negligible) and the probability of occurrence (e.g., frequent, occa-
sional, improbable).
The Department of Defense’s Standard Practice for System Safety is
provided in MIL-STD-882D, and is an example of a classification method
that incorporates both qualitative and quantitative factors in the risk priori-
tization process. The standard utilizes four separate tables to describe and
classify risks as described below.

Mishap Severity
Mishap severity categories provide a qualitative measure of the most
reasonable credible mishap resulting from personnel error, environmental
conditions, design inadequacies, procedural deficiencies, or system, sub-
system, or component failure or malfunction. Suggested mishap severity
categories are shown in Table 7-1.
Note: These mishap severity categories provide guidance for a wide va-
riety of programs. However, adaptation to a particular program is generally
required to provide a mutual understanding between the program manager
and the developer as to the meaning of the terms used in the category defi-
nitions. Other risk assessment techniques may be used provided that the
user approves them. 6

Mishap Probability

Mishap probability is the probability that a mishap will occur during the
planned life expectancy of the system. It can be described in terms of po-
tential occurrences per unit of time, events, population, items, or activity.