Farmers need to be mindful that even well-made hay can still be prone to spontaneous combustion.
Agriculture Victoria Program Manager for Dairy – North, Brett Davidson said spontaneous combustion is usually caused by excess moisture at baling.
‘Fires can also start due to heavy rainfall events which has soaked into stacks.
‘Intense rainfall could compromise even well covered stacks, as water can pool at the base of a stack, seep into gaps or could be blown under covers.’
For those with moisture meters, ideally hay moisture levels should be in the ranges below.
Recommended moisture contents (%) for safe storage of hay
Type of bale | Recommended moisture content ranges for baling hay (%) |
|---|---|
Small square bales | 16 – 18 |
Large round bales | 14 – 16 |
Large square bales | 12 – 14 |
Export hay |
Even at 2 – 3% above the maximum moisture contents recommended in the table, hay will start to lose dry matter (DM) and nutritive value due to plant respiration or mould growth, resulting in heating of the bale/stack.
Higher moisture contents, well above the maximum (greater than 4%), could lead to more mould and heating, possibly resulting in spontaneous combustion.
Mr Davidson said it will be vitally important to regularly monitor the stack from one week after rainfall for signs of heating.
These are:
- dampness on the tops of bales
- steam rising from the stack
- moisture build-up on roofing iron or under tarps of outside stacks
- unusual odours (e.g. pipe tobacco, caramel, burning, musty)
- sometimes the stack may slump in places
- corrosion on underside of tin roof.
Mr Davidson said unfortunately, much of the heating will occur in the stack centre which is difficult to pick up. To try and get an idea on how hot a stack has become, using a crowbar pushed into the stack as far as possible is one strategy that can be used.
‘After a couple of hours, remove the crowbar and feel how hot it is.’
A rough guideline to check a haystacks temperature using a crowbar, is as follows:
- 50 – 60° you can handle the bar for a short time. Check temperature twice daily
- 60 – 70° you can touch bar only briefly. Check temperature every 2 hours. Move hay from top layers to improve air flow
- >70° the bar is too hot to hold. Potential for fire – avoid walking on top of stack.
Mr Davidson said an alternative monitoring method can be achieved by using thermal couplings, which can be placed into various areas of the stack at stacking and monitored simply and regularly.
