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BACKGROUND
Chapte r 1
TNTRODUCT TON
1
Explosions in grain elevators and mills have been documented for over
100 years but probably have occurred ever since structures for handling
grain in large quantities were developed. Although long recognized as an
industrial hazard, elevator explosions received wide national attention
recently when during an eight day period in 1977 beginning on December 21
and ending on December 28, five explosions occurred resulting in 59 deaths
and 4 8 injuries (U. S. Department of Agriculture 1980) .
In the past, explosion prevention efforts in the grain processing
industry were concentrated on mills, mainly flair and starch. The federal
government first gave attention to the dangers of grain dust explosions
following the explosion of a feed mill in 1913, and the continuing emphasis
on mills may have been due to the very large number of fatalities that
occurred in early mill explosions (e.g., 43 fatalities and 30 injuries in a
starch mill explosion in Cedar Rapids, Iowa, in 19191. However, the danger
of explosions due to collections of grain dust in elevators had not been
totally ignored (U.S . Department of Agriculture 1918, U.S . Grain Corporation
19 20a and b} .
In Ju ly 1978, at the request of the Department of Agriculture, the
National Academy of Sciences conducted an international symposium on -train
elevator explosions (National Materials Advisory Board 19781.
Shortly after
the symposium the Occupational Safety and Bealth Administration (OSHA) of
the Department of Labor requested that the National Academy of Sciences form
a group to study the causes and make recommendations for the prevention of
grain e levator explos ions .
In November 1978, the Panel on Causes and
Prevention of Grain Elevator Explosions was for~d under the Academy's
National Materials Advisory Board. The panel is part of the Board's
Canunittee on Evaluation of Industrial Hazards. The Nonmember panel is
composed of experts in systems analysis, explosion dynamics, investigations
and prevention, instrumentation, grain handling and processing, agricultural
insurance practices, employee relations, dust control methods, and
aerodynamics. Its objectives were to:
1. Study the federal government's investigation of grain elevator
explosions and make recommendations for improvement,
2. Investigate grain elevator explosions selected by OSHA occurring
during the panel's tenure and determine their causes,
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3. Recommend actions to be taken to reduce the occurrence of.
explosions ingrain elevators and mills and to identify any needed research
and development, -
4.. Produce a handbook on dust collection methods and systems for
grain elevators and mills, and
5. Develop a methodology for investigating explosions in
grain-handling facilities based on the panel's experience.
RISK MANAGEMENT METHODOLOGY
.
. . .
Explosions in grain elevators and mills have been studied from many
viewpoints in the pant. However, none of these studies has considered all
aspects of explosions in relation to one another simultaneously.
· The panel undertook to overcome these deficiences by employing a
systematic approach to risk management that permits all aspects of a
situation to be considered simultaneously rather than separately or
sequentially (Maritime Transportation Research Board 19811. In applying the
systems approach, the panel attempted to identify every possible hazard that
contributes to grain dust explosions in elevators and mills. Preventive or
corrective actions for each identified hazard were then proposed, and the
costs of these actions were estimated.
It was then possible to evaluate each identified hazard in teems of
its severity, probability, and cost of hazard elimination or control so that
a ranking of significance to explosion potential could be established. This
ranking then formed the basis for the panel's recommendations.
Figure 1-shows the functions of risk management (Grose Or' item
guided the panel's efforts to be systematic in their study of grain dust
explosions. Activities related to all five functions were conducted by the
panel and illustrate how this method could be applied by the grain-handling
industry.
Administration of Risk-Related Tasks
. .
The first step in managing risk is to define the situation or location
where risks are to be controlled. The panel therefore had to identify
clearly and precisely all functions (tasks or activities) performed in a
grain elevator or mill. me most c ammo n means of displaying these functions
is a functional flow block diagram (baud) that depicts functions in separate
boxes or blocks connected by arrows to indicate their order of occurrence.
Using such a diagram helps to avoid a random or piecemeal attempt to
identify explosion hazards. The FFBD for a grain elevator is shown in
Figure 2. Note that it does not indicate who, why, where, or how; it simply
describes what is being done. me inputs to any task or activity are shown
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/
/ FINANCING \
f Uncontrolled Risk \/
1—
/ ADMINISTRATION ~:
\of Risk-Related Task,/ \
\ CONTROL
\of Significant Risk
FIGURE: 1 Functions of risk management.
/IDENTIFICATION
of Risk Exposure
-
EVALUATION
of Identified Risk /
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s
on the left and the outputs appear on the right. Thus, the FFBD shows
graphically the interdependence of all tasks or activities taking place in
the facility. Since it is one single and complete display of all essential
functions, the probability of overlooking any factor related to an explosion
is vastly reduced.
Identification of Risk Exposure
The primary mechanism used by the panel to identify the caused of
grain dust explosions was the hazard scenario. Every accident is comprised
of many elements--not just some singular, isolated event, and the hazard
scenario is a brief description of the combined causative factors that could
lead to an explosion. Hazard scenarios are not an end in themselves in that
they identify only facets of exposure to risk {Grose 1982~. However, one of
the major values of hazard scenarios is that they can describe explosions
that have not yet occurred but that are possible. Thus, they serve to
emphasize the need for preventive or corrective actions.
Appendix A presents a representative sample of the more than 150
scenarios that were prepared by the panel. Some of them describe actual
occurrences investigated by panel members while others are hypothetical
possibilities proposed by employees of the grain-handling industry
experienced in elevator operations.
Early in their attempt to identify causal factors for grain elevator
explosions, the panel concluded that existing data were insufficient to
permit the identification of needed preventive actions. Therefore, a team
of panel members was formed to investigate significant explosions that
occurred during the panel's tenure. The primary function of the
investigation team was to obtain data that identified the hazards leading to
a grain elevator explosion. A secondary function was to establish and
refine investigative techniques for identifying and analyzing causal factors
at the scene of an explosion.* The team was staffed with panel members and
liaison representatives who had diversified professional specialties.
Evaluation of Identified Risk
Identifying the many and varied explosions risks in a grain elevator,
whether by means of hazard scenarios or on-site investigations of
expicsions, is a difficult process. It is especially important that hazard
identification not be inhibited by any initial concern for the significance
of an individual identified hazard; if it is, many subtle hazards probably
will be overlooked.
* A report entitled, The Investigation of Grain Elevator Explosions,.
NMAB 367-1, 1980, National Academy of Sciences, Washington, D.C., was
issued.
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Ultimately, however, all identified hazards must be evaluated for
their significance because there are never enough resources available to
prevent or correct every hazard that can be identified. The panel ranked
all identified hazards into a hierarchy of importance using three
measures--the severity of the hazard, its frequency or probability of
occurrence, and the amount of' resources required to control it. Each
scenario was assigned three letters--one for severity, one for probability,
and one for control resources as described in Appendix A. Since historical
data for many of the scenarios did not exist, the panel's judgment was
important in this ranking. '
Once the three letters-were assigned to each scenario, all the
scenarios could be evaluated by the panel to determine their relative hazard
significance.
This r'anking procedure can be used in the future by grain elevator
owners and operators. Using this decision-making tool, they can judge the
significance of all identified hazards on the same basis and efficiently
allocate resources for the reduction or control of explosions e
Control of Significant Risk
Once the evaluation of all identified risks revealed those that were
most significant, the panel sought expert counsel on how such hazards might
be best controlled. This counsel was of several types. Knowledgeable
experts in grain dust control, elevator design,'environmental protection,
grain economics, and grain handling were invited to address the panel on
dust explosion prevention. Other groups and spokesmen met with the panel to
offer control measures. (See Preface for a list of those contributing to
this effort.) Individual panel members also visited selected grain-handling
sites to review specific preventive actions for explosion scenarios.
Financing of Uncontrolled Risk
- There are three classes of uncontrolled hazards: (a) those for which
there is no effective preventive action, {b) those considered insignificant
but which turn out to be consequential, and (c) those that were unforeseen.
While the panel has made no recommendations regarding the various options
for financial coverage of bosses due to these three classes of risk, the
economic impact due to dust explosions was ' of constant concern. Among the
options discussed were loss write-off, assumption of debt, self-insurance,
and other means of transferring the risk of loss.
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REFERENCES
Grose, V.L., Converting health hazard control from moralism to management,
Professional Safety 25~3) March (1980, :31-40.
Grose, V.L., Managing medical malpractice risk via system science,
Journal of Medical System 6~) (1982) :89-103.
. . .
Maritime Transportation Research Board, Research needs to reduce maritime
collisions, ratings, and groundings, National Academy Press,
Washington, D .C., May 19 81 .
Nationa1 Materials Advisory Board, International Symposium on Grain
Elevator Explosions, Proceedings, Volume 2, Report AHAB 353-2,
Washington, D.C., July 11-12, 1978.
U.S. Department of Agriculture, Prevent grain dust explosions and fires,
USDA Circular, 1918.
U.S. Department of Agriculture, Prevention of Dust Explosions in Grain
Elevators An Achievable ~1, USDA, Washington, D.C., 1980.
U.S. Grain Corporation, Grain dust explosion prevention, (in cooperation
with the Bureau of Chemistry, U.S. Department of Agriculture), New
York, 1920a.
U.S. Grain Corporation, Proceedings of Conference of Men Engaged in Grain
Dust Explosion and Fire Prevention campaign, (in cooperation with the
Bureau of Chemistry, U.S. Department of Agriculture), July 1920b.
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Representative terms from entire chapter:
grain dust
