Producing Quality Oat Hay

Storing domestic hay
The criteria for storing export hay will also
maintain the best hay quality for the domestic
market. However, hay for the domestic market
may be baled at a higher moisture content
therefore, care must be taken to avoid conditions
that promote the potential for self combustion
during storage, (Figure 8.1).
For a hay stack to combust it must undergo a
process of self heating that even now is not fully
understood. However, it is known that several
sources of heat can contribute to the process.
Image 8.2 High moisture bales may need to be stored
outside until the moisture content and temperature
has dropped.
Primary heating
Respiration
Respiration of freshly cut plants and subsequent
bacterial action causes bale temperature to
increase to a maximum of between 48 to 70°C.
If the heating hay is located on the outside of the
stack, where the heat can dissipate, the process
may very well stop here.
However, if the heating is located at the
bottom or inside of the stack then the heat may
continue to build. This would appear to be the
time that the moisture content of the hay may
be most critical.
80 PRODUCING QUALITY OAT HAY
Biological
For vegetable material to continue heating it is
generally due to a biological process reliant on
oxygen and living microorganisms. If the hay
is well cured it will not allow this destructive
fermentation to occur. Conversely if too wet,
not enough oxygen can diffuse into the mass
and no fire will occur.
It would appear that partially cured hay (moisture
content between 12 to 21%) is the most prone to
fire due to biological heating. This will heat the
hay to the thermal death point of the organisms
involved; that is in the vicinity of 70°C.
Regardless of how well the heated hay is
insulated, temperatures of 70°C fall far short of
the ignition point of hay, which is in the vicinity
of 280°C (Figure 8.1).
Secondary heating
Exothermic
Once hay reaches the limit of the primary heating
(70°C), the exothermic process can be initiated to
raise the temperature much higher.
Many theories can explain this process including
the production of pyrophoric carbon, pyrophoric
iron, heat from enzyme action, and even the
auto-oxydation of the oils contained in seeds.
What is known is that this process is generally
accompanied by the production of much acid in
the early stages and is accompanied by a marked
browning of the hay.
If insulated, this process can progressively raise
the temperature inside the stack to 240 to 280°C
at which point the slightest introduction of
oxygen will result in the ignition of the stack.
Some research has shown that hay does not
need to reach such high temperatures to ignite
spontaneously. If hay is subjected to long
periods of heating at temperatures as low as 88°C
and remains in the presence of volatile gases
produced by oxidation, it may ignite when
introduced to air. In other words a relatively
low temperature for long periods may have the
same effect on hay as high temperatures for
short periods.
Combustion can therefore occur in two different
ways, in a hot pocket of carbonised hay or in a
larger volume surrounding the hot pocket.