World Grain -- December 2013 - 84

gRAinoperationS

Stored grain
compaction factor
Accurate factors are necessary
because volume measurements will
not give an exact measure of grain
by Rumela Bhadra

It is well known that grain undergoes compression when
subjected to cumulative weight exerted from the overlying
material in a storage unit. The extent of compression depends
on several factors associated with the stored materials (crop
type, test weight, moisture content) and bin characteristics
(type of bin wall material, size and geometry of the grain bin).
Compression of grain leads to packing and thus adjusts the
bulk density of the material. Therefore, accurate compaction
factors are necessary, because volume measurements of the
stored grain alone will not allow us to determine the exact
amount of grain in the bin.
compAction histoRy
One of the earliest compaction factor data collections in the
U.S. was performed by the U.S. Department of Agriculture
(USDA)-United States Warehouse Examiner's group. The
current U.S. Warehouse Licensing and Examination Division
deals with issuing licenses to elevators and records bin inventory and storage data.
The USDA-FSA warehouse examiners use a handbook,
known as "Warehouse Examiner's Handbook Grain Pack Data
WS-3, Exhibit 9" for determining grain compaction factors.
This book presents a detailed method for determining compaction factors for grain bins based on bin shape (round or
interstice concrete bins) and average test weight of the grain
bin. The exact publication date of this book is not known, but
it appears that it was published in the 1950s.
According to the original documentation and communication letters that led to the development of the handbook, approximately 95 bins were analyzed to measure compaction
factors. These bins were primarily located in Kansas, Texas
and Oklahoma. Most of the bins (95%) were constructed out
of concrete although a few of them were wooden warehouses.
Clearly the latter storage structures were very outdated as per
modern industry design.
84

Some of this field data dates back to 1939. The bins had an
average diameter of 18 feet. USDA-FSA warehouse examiners closely followed the procedure outlined in the handbook
to collect this initial field data. In order to meet the needs
of the modern grain industry (increased bin size, varying
shapes and grain capacity), the Federal Warehouse group
has made slight adjustments over the years, but its primary
compaction factor data remains unchanged. However, many
of these updates are not widely known among researchers
and grain industry stakeholders.
Grain producing states in the U.S. all have their own state
agricultural warehouse control officials that license elevators similar to the USDA-FSA warehouse examiners and
use compaction factor tables from Warehouse Examiner's
Handbook. And, it is believed that their procedure is very
similar to that of the USDA-FSA warehouse examiners for
most of the crops.
The USDA-Risk Management Agency (RMA) is associated with operating and managing crop insurance programs
through the Federal Crop Insurance Corporation (FCIC).
RMA through FCIC develops and approves insurance preGrain compaction
Depth is reduced as
grain compacts from
overbearing pressure.
the bulk density of
grain below increases

December 2013 / World Grain / www.World-Grain.com

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World Grain -- December 2013

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