You might have recently read about the big hay shed fires in Victoria. Two separate fires in different towns on the same day, and in both cases the sheds were completely destroyed. Over 1,000 bales of hay disappeared in a cloud of smoke that day too.


Even though there were six fire engines and over two dozen firefighters at each site, it turns out arriving within 20 minutes isn’t good enough. These baled hay fires could have killed people and caused devastating damage to everything in their path, so it’s worth looking at how we can stop them.

How Hay Catches Fire In The First Place


Let’s get the obvious out of the way first. There are some simple ways hay could catch fire. We’ll discuss the big reason soon, but here are the ones I’m sure you’re already thinking about:

  • Deliberately Set Alight
  • Sparks From Equipment
  • Lighting Strikes

The biggest reason baled catches fire boils down to spontaneous combustion. It sounds weird that hay would suddenly burst into flames out of thin air, but it’s actually a completely natural mixture of biology and chemistry taking place. If the conditions aren’t right the bales of hay will turn into an uncontrollable fire you don’t want to be anywhere near.

Spontaneous Combustion Is Caused By Moisture

We’ll get into the science in a minute, but before we do it’s important you know where the moisture comes from in the first place. This will help when we talk about how to prevent hay fires from ever starting. There are two different ways a bale of hay can have a dangerous moisture content level, so let’s look more closely at them:

  • General Moisture – When you are going to bale hay the moisture content should ideally be less than 20 percent, but it could be higher inside the bale due to things like the weather and time of day. Also, there could be moisture sitting on the exterior of the hay bale too.
  • Sap Moisture – The sap moisture is a little more complicated, but it’s what you end up with when the plants are too green. You end up with high levels of internal cell moisture inside the plants when they’re not cured enough before baling, which means they’ve been touched too soon.

Moisture Is A Breeding Ground For Bacteria


When the moisture content inside a bale of hay is higher than 20 percent it turns into the perfect breeding ground for mesophilic bacteria. The bacteria will then heat the interior of the bale up to around 60 degrees Celsius, but unlike straw the heat doesn’t drop back down when the bacteria dies.

Now you end up with the perfect breeding ground for thermophilic bacteria, which is a kind that thrives on heat. In fact, when it multiplies inside a bale of hay the internal temperature can reach over 75 degrees Celsius. It’s at this temperature a bale of hay can spontaneous combust, and if it’s inside a packed shed everything is going to go up in flames.

How Big Hay Shed Fires Can Be Avoided

hay stored in a steel shed

Unfortunately you’ll always end up with accidents, but fires can be avoided in the first place when certain things are done. You’ve likely already picked out the two obvious examples based on everything we’ve talked about so far. Under no circumstances must the moisture content of the hay be higher than 20 percent when it’s baled, plus it shouldn’t be too green.

There are still plenty other basic things that need to be taken into consideration. It would be wise to keep the hay away from areas where it could accidentally catch on fire. Using things like specialised equipment and hay preservatives also helps. Bales with a lower density are always better, and you can take things to the next level by making sure they have enough ventilation and air flow.

Keep Checking Them And You Should Be Okay


Hay should be baled in the evening when there is lower moisture content, but even then it still helps to scan the hay for moisture and use a tool to gauge how high the levels are. Once the bales are in the shed they should also be checked on a regular basis, especially if they’re hot, stinking, or steaming. Don’t forget you need to do everything within your power to stop them from getting wet too.

News source: Shepparton News
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