Storing hay safely

Storing wet hay can pose a fire risk. This advice gives information on how to store hay safely, and what to do if you are worried about the temperature of your hay. 

It’s important for farmers to store hay safely because it can be extremely costly losing stocks. Wet hay poses a higher fire risk than dry hay. If hay is put into a barn or stack when it has more than about 22 percent moisture, not only does the hay lose forage quality, but it is also at a higher risk of spontaneous combustion.

Reduce your risk of barn fires

  • Remove hay from fields as soon as possible after harvesting, and ensure it is dry before storing, to prevent spontaneous combustion.
  • Fires can very easily spread. Store hay and straw away from other buildings - especially those containing fuels or chemicals, and separate from livestock.
  • Store hay and straw in stacks at least 10 metres apart and ensure there is sufficient space between the top of the stack and electrical roof lighting.

Causes of hay fires

Wet hay is a fire risk. Hay bales or stacks with high moisture levels (more than 22 percent) can have chemical reactions that build heat. Hay has insulating properties – so the larger the haystack, the less cooling there is to offset the heat that is building.

If the temperature of a haystack rises above 55 degrees Celsius, a chemical reaction begins to produce flammable gas that can ignite if the temperature gets high enough.

Timing of hay fires

Hay fires are most likely within six weeks of baling. All hay above 15 percent moisture will heat up within three to seven days, but this generally does not get to dangerous levels and causes minimal loss of forage quality. After this first week of heating, temperatures within a stack should then decline to safe levels in the next few weeks.

To avoid hay fires, small, rectangular bales should not exceed 18 to 22 percent moisture, and large round or rectangular bales should not exceed 16 to 18 percent moisture for safe storage.

Monitoring hay temperatures

It’s important to check your hay regularly - ideally with a thermometer probe. You can insert a thermometer probe into the haystack to monitor the temperature.

You can also use your nose. If it starts to smell of caramel, or there is a distinct musty smell, it is likely that your hay is heating. At this point, you’ll need to keep monitoring the hay’s temperature.

Watch for the following temperatures

65 degrees Celcius

This is the beginning of the danger zone. After this point, check temperature daily.

70 degrees Celcius

The temperature is getting more dangerous. Measure temperature every four hours and inspect the stack.

80 degrees Celcius

Hay temperature is becoming critical. Start to make the hay wet and remove it from the barn, or dismantle the stack away from buildings and other dry hay.

85 degrees Celcius

You are likely to find hot spots. Flames will likely develop when heating hay comes in contact with the air.

100 degrees Celcius

Critical temperature - hay is very likely to ignite. Call 999 immediately.