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Watch For Heating Hay Stacks

Despite the severe drought conditions being experienced over most of Victoria, there have already been several stacks of hay go up in flame. Over 80%

By Department of Primary Industries - 6th December 2006 - Back to News

of the fires in haystacks, both inside and outside sheds, are large square bales of hay. Even in these extremely dry conditions, large rectangular bales baled at a seemingly "safe" moisture level have still resulted in several stacks undergoing spontaneous combustion, ie. caught fire.

It is thought that in pasture situations experiencing severe drought conditions that the plants actually contain higher than "normal" sugar levels in their cells. This then leads to higher than normal plant respiration and microbial activity once baled. The extremely dense nature of large squares, and the large volume to surface area of round bales, severely restricts the loss of heat produced by the plant and microbial activity. Heat begets more heat and may eventually cool down but can also result in stacks "going up".

The risk of fire has been increased this year by the baling of many frost and/or drought affected canola crops. Most crops were at the flowering or early podding stage when cut and their stalks, and to a lesser extent their branches, were becoming reasonably thick. These stems contained high levels of moisture and if mown without treatment to increase their curing rate, would have necessitated the curing period to be extended over several extra days to ensure that the stem and branches were "dry" enough to bale.

However, the stems and branches of the canola crops which were mower-conditioned or super conditioned, would have cured much more quickly, and evenly, allowing reduced curing time and "safer" baling. This greatly reduces the risk of severe heating.

In some situations the canola crop would probably have been baled late in the day, during the night or early in the morning with dew on the windrows to avoid losing too much leaf at baling. However, if baled before the moisture content of the whole windrow was suitable, or when the stems were still too moist, or if the plants were too wet from the dew, the risk of heating and potential for fire is substantially increased. This is especially so if baled by a large square baler and to a slightly lesser extent with a round baler.

If shedded or stacked tightly in the paddock, these large square and round bales, being baled so tightly or having the large volume to surface area characteristics, reduces heat loss substantially and will become hotter and hotter possibly leading to a fire.

Table 1 indicates the recommended moisture levels for safe baling of hay for each type of baling system.

Table 1. Recommended Moisture Contents (%) for Safe Storage of Hay

Several hay preservatives are now on the market and should be considered in future situations where the moisture levels are known or thought to be higher than desirable for safe baling. When material is baled with slightly more moisture than desirable, less leaf and colour is lost and quality is often slightly higher. This does not mean that baling can now occur at substantially higher moisture levels than the above recommended rates.

Watch for signs of heating

Keep an eye out for signs of your haystack heating. Steam condensation on the roof, mould growth, acrid fumes, and hot, humid air at the top of the stack are all good indicators. When you build stacks with suspect wet hay, always stack the bales loosely to allow air movement through them. Also spread the stack over a wide area, ie. over several bays, thereby reducing heat build-up.

Most heating will occur over the first one or two weeks but has been known to reach "flash point" up to approximately eight weeks after baling. Monitor the stack temperature regularly from when heating is first noticed. Do this using a crowbar inserted into as deep as possible into the stack. The crowbar, when pushed into the stack and left there for two hours, can be felt by hand to give you a rough guide of the internal stack temperatures.

The temperature is up to about 50°C if you can hold the bar without discomfort. It is up to 60°C if the bar can be held for a short time only and up to 70°C if the bar can be touched only briefly. If you can't hold the bar, temperature is above 70°C and fire is a real possibility. Treat the stack with caution.

In the past it has been suggested to push a small pipe into the stack and lower a small thermometer to the end of the pipe to measure the temperature. While this is fine for warming hay, it is not so for severely heating hay. This action could actually allow oxygen to gain access to the inner oxygen deprived section of the stack, and CAUSE a fire to start. Very dangerous!

What can be done if hay heats to danger levels?

If a stack starts to get ‘dangerously hot’ pull it apart as quickly as possible. Avoid walking on the stack if you can because the extremely high temperatures may have charred the centre of the stack. You won't see this from outside. Your extra weight on top of the stack might be enough to cause the top of the stack, and you, to collapse into the dangerously hot centre. Please believe me when I say that it will be a lot more serious than just having your hair singed! If you must walk on the top of the stack lay down a ladder or long wide plank to walk on.

Be aware that as the bales are pulled out, especially in a tightly built stack, oxygen will now be able to get to the hot spot and actually cause ignition, similarly to throwing petrol on a simmering fire. Have the local fire brigade on hand, or at least a fire cart and definitely other people for safety purposes.

Warning

If there is the slightest risk of a fire starting due to wet hay, NEVER keep machinery in the hayshed and do not allow the children to play in or near heating stacks.

Source: http://gippsland.com/

Published by: news@gippsland.com

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