Hay Fire Safety

Spontaneous ignition is the leading cause of haystack fire in Victoria, and just one damp bale is enough to ignite a haystack.


hayHaystack fires

Haystack fires are also caused by sparks from machinery and equipment, and embers from burn offs or bushfires. Before you're able to prevent haystack fires you'll need to know something about how they start.

Why does hay heat?

Haystack fires can happen in any type of bale stored in a haystack.

If hay is cut too 'green' or if some of the hay becomes damp before, during or after baling, a complex series of biological and chemical processes may cause the hay to heat up.

This is because the plant material is still alive after cutting and using energy through respiration. Microorganisms such as bacteria and fungi, are able to grow in the moist environment. Their biological processes generate heat which may result in the loss of dry matter, nutritional value and reduced palatability as fodder.

If heating remains undetected the temperature within the bales will keep rising. When the temperature reaches 70oC, it may then increase rapidly to the point of spontaneous ignition (at about 180oC).

Spontaneous ignition may occur within two weeks of baling and may continue to pose a threat for more than 3 months.

Green or damp hay encourages bacteria and fungi to grow and decompose. A series of complex biological and chemical reactions can then cause temperature to increase in the hay. The process can produce flammable gasses which then ignite in the high temperature environment within the hay.


Watch for signs of heating hay

Regularly monitor all haystacks for signs that the hay is heating up. You can do this by using a temperature probe or crowbar. Other signs of heating include:

  • steam rising from haystacks
  • condensation or corrosion under hayshed roofing
  • mould growth in or on bales
  • unusual odours like a burning, musty, or caramel smell. Sometimes you may detect a smell like pipe tobacco.
  • slumping in sections of the haystack.

Temperature Guide

Insert a temperature probe or crowbar into the middle of the haystack for two hours, then take a reading.

Temperature Action

Less than 50oC. Can handle crowbar without discomfort

Check the temperature daily

50oC to 60oC. Can only handle crowbar for a short time

Check temperature twice a day

60oC to 70oC. Can only touch crowbar briefly

Move bales apart to improve air flow. Check temperature every 2 to 4 hours

Over 70oC. Crowbar is too hot to hold

Potential for fire. Call Triple Zero (000) immediately. Pulling the haystack apart may introduce the oxygen needed to ignite the hay. Avoid walking on top of haystack.


How to reduce the risk of haystack fires

  • Make sure hay is fully cured (dead and dry) and at the recommended moisture content before baling. This will vary depending on the type of crop and bale being used. Use a moisture meter to check hay moisture levels throughout the baling process. Be sure to test plant nodes and heads inside leaf sheaths for hidden moisture.
  • Know the history and moisture content of hay you purchase.
  • Limit the size of your haystacks and store hay in a number of different locations. This will reduce the risk of losing all your hay if a fire does occur.
  • Don't stack hay all the way to the top of a hayshed. Leave some air space above for circulation.
  • Prevent hay from getting wet. Keep bales away from rain, leaking roofs and spouts, and from runoff. Cover outdoor haystacks with hay caps or tarps.
  • Create and maintain fuel breaks around haystacks to stop a haystack fire from spreading to the surrounding area or to help stop a fire from reaching your stored hay.
  • Store hay away from possible sources of ignition (such as roadsides, workshops and fuel or chemical storage areas) and away from vegetation.
  • Be careful when using vehicles, machinery and equipment near haystacks, especially on fire risk days.
  • Do not store vehicles, machinery or equipment in the same location as your hay. You may lose more than just your hay.
  • Store hay well away from powerlines. If hay ignites under or near powerlines, it could be very dangerous and may disrupt local power supply, including your own.

What to do if your hay is heating

If there are signs that the hay is starting to heat up, pull the stack apart to improve airflow and allow the bales to cool.

Be aware that very hot hay may suddenly catch alight if it is pulled apart. This is because you introduce oxygen into part of the haystack which has already reached ignition temperature. If any part of the stack is near or above 70oC or if you see or smell smoke, you should call Triple Zero (000) immediately and ask for FIRE.

Do not walk across hay that may be heating. Charred bales inside the stack may suddenly collapse. You could be trapped in they hay and the rush of air may result in a sudden flare-up.



The following video provides some useful tips on avoiding haystack fires.

See also:

Preventing Haystack Fires (PDF 799.6KB)





Page last updated:  Tuesday, 18 October 2022 7:06:38 PM