Agronomy Advice
August 02, 2023

Reduce the fire risk around hay

In hot, dry conditions farmers face increased fire risk, especially across the first six weeks after hay baling.

Farmer feeding hay to cows in a farm
Farmer feeding hay to cows in a farm

It feels counterintuitive when water is normally used to put out fire, but the risk of fire increases with a heightened moisture level within bales. This is more often an issue with hay due to the increased plant cell respiration. Straw is normally completely dry, but if the wheat used to make straw has been at various growth stages and the resultant straw seems to have more green stems than normal, plant cell respiration will still be active which in turn will increase moisture levels.

Here’s some advice to mitigate the risk of fire:

Bale Carefully 

  • Mow hay in the morning and let it dry out in the field for at least 24 hours before baling. Ideally, you want the moisture content of hay bales to be 20% or less. 
  • The fire risk is linked to the growth of a particular bacteria which grows in hay when moisture levels are high. You can use liquid propionic acid during baling to reduce the growth of this bacteria, thereby reducing the risk of fire.

Appropriate Storage 

  • When storing hay, make sure the barn is weathertight and has good drainage to prevent moisture build-up and lift bales off the ground. Don’t store hay in sheds with fuels or chemicals and keep hay in a separate shed to livestock 
  • If you’re storing bales outside, cover them with a waterproof material or arrange them so that air can circulate between them to promote quick drying. 
  • When stacking hay, ensure there is enough space between the top of the stack and any electrical lighting.

Monitor Haystacks Regularly 

  • Regularly check stored hay, if you detect a caramel or musty smell, it’s likely that the hay is heating. If you’re concerned, monitor the temperature of hay bales twice daily over the first six weeks after baling. 
  • If hay bales exceed a temperature of 78°C, be aware that exposure to oxygen can cause a fire to break out so ventilation should be shut off. 
  • If haystack temperatures rise to above 55°C it can spontaneously combust. The best thing to do if you think hay is getting too hot is to dismantle the haystack.

Call the Fire Service for assistance if your hay bales are measuring temperatures approaching 78°C or higher as you’re likely to start seeing hot spots and fire pockets. At 88°C you will need the fire service to help you move the hot hay to prevent a fire or at least stop it from spreading. At 93°C your hay is either already on fire or it is likely to burst into flames at any moment.