Safe Hay Storage


A separate hay storage building should be constructed if at all possible, but of course, that’s the ideal situation.  Property limitations may force you to have upper level hay storage in a new barn, or in an existing barn you may feel you are “stuck with it.” There are ways to help make these arrangements less of a hazard.

Upper-level hay storage with a solid floor, such as in a bank barn, is preferable to stall-level storage because heat, smoke, and flame move upward.  Should a fire begin on the upper level, upward movement of the fire and its products may allow a few more minutes for evacuation of horses from the lower level.

Barns with metal or tin sheet roofs, asphalt shingles over wood, or plastic skylight panels, will be breached by the fire allowing hot gases and flames to vent.  Roof vents or cupolas provide an immediate means of venting. That’s one reason why all barn roofs should have one or the other, spaced at regular intervals.

If  hay is stored at stall-level, the area must be completely separated from the stalls and enclosed in a room with two-hour fire-resistant roofing and wall materials.  This isn’t a practical solution to begin with unless you are purchasing and storing hay for only a few animals and you purchase hay frequently.  In reality, though, no one wants to be lugging hay bales a distance of 100 feet from one building to another on a daily basis, so many people keep a day or two’s supply of hay near the stalls or enclosures in their barn.  That’s not ideal, but it is kind of practical when you consider the labor involved in caring for animals on a day-to-day basis.

If you’re in the fortunate situation of building a separate hay barn, your first consideration must be the location of the hay barn in relation to other structures.  If you have the space, a 100-foot separation is ideal.  This provides protection for other buildings from wind conditions and heat radiation in the event of a fire.  With a 20 mph wind, sparks can be carried some distance, such as what happens in wildfires where the flames jump fire lines.  Heat radiation is another way fires spread, and 50-100 feet is not a great distance where radiation is involved.  The heat can be great enough to dry out adjacent structures and allow them to ignite.  So, if you can afford a separate hay barn, don’t build it too close to your other buildings because if it’s too close you risk losing your other buildings as well.

And speaking of saving buildings: it’s very unlikely that if your hay barn catches fire that it can be saved.  If there are no animals or humans in the building to be rescued, you may find the fire department handling fire suppression in one of several ways, depending on the situation and the necessity to save nearby buildings from catching fire.  Mike Weider, senior editor at IFSTA/Fire Protection Publications in Stillwater, Oklahoma explained that from a firefighting aspect in his excellent article “Hay Barn Fires” published in the April 1998 issue of FIREHOUSE, which follows this section.

Whatever your decision is regarding hay storage, the best fire prevention tool you have is your broom.  Keep loose hay and straw swept up, and if you have hay drops, don’t permit loose hay to hang over the edges; like cobwebs, flaming hay can drop through and start other fires.  The best prevention for this problem is providing a cover for each hay drop opening.  A plywood cover will do, and plywood covered on each side with one-hour rated gypsum board is even better.  Here’s a sketch of the hay drop covers I had in my barn:

Hay Drop

So, here comes the hay!  What can happen in that haystack after all our labor in building it?

Although we usually think of moisture as helping to prevent or extinguish a fire, when it comes to baled hay or straw, excessive moisture is the most common cause of fires.

Ideally, when hay is harvested and baled, its moisture content should be 20% or less.  If the moisture is greater than 20%, warm-temperature bacteria will grow and multiply, releasing more heat until the interior bale temperature reaches between 130-140°F.  At 130°F., most of the bacteria will die and the interior bale temperature will fall until it is at the ambient (air) temperature.  This is an expected part of the curing process which normally occurs within six weeks of baling.  However, if the interior bale temperature doesn’t cool after the warm temperature bacteria die, heat-loving bacteria can multiply and the heat released by their activity can raise the interior bale temperature to 170°F. before they die.  The hay becomes damaged and can then readily combine with oxygen, resulting in a fire.  This first six weeks after harvesting is the most common time for hay fires, but hay that has been stored for some time, even if it was baled at the proper moisture percentage, can become a fire hazard if it becomes wet.

In a stack of uncured hay two fire propagation requirements—fuel and heat—are at work.  The only thing  lacking in sufficient quantity is oxygen.  The hay may smolder unnoticed for quite some time before the edge of the stack is reached.  When that happens, and oxygen is suddenly available in abundance and there is a means for the generated heat to escape, you have a full-blown fire on your hands.  The same process may occur with damp grain, sawdust or wood shavings, too, and in these situations an explosion may result due to the greater amount of exposed surfaces in the material.

That means we must pay careful attention to how our hay is stacked and stored.  It’s important to protect the hay stack from water, either from rain entering through a barn or storage building roof or the side walls, since rain-dampened bales can allow the bacterial action to restart.


Air circulation is needed under and around the bales to allow the hay to dry and the heat to escape.  Wood floors with gaps between the boards, such as you would find on the upper level (or threshing floor) of a bank barn, usually provide adequate air circulation.  If you are stacking hay outdoors, on the ground, stack the bales on wood pallets or old tires so air can circulate and the hay will not be in contact with ground moisture.

Any hay stacked outdoors must also be completely covered, top and sides, with a tarp to keep it dry.

The presence of chemical and bacterial reactions leading to spontaneous heating and ignition may sometimes be detected by a “sooty” odor, and if your eyes become mildly irritated when you’re in the immediate area of the hay stack, that, too, may indicate spontaneous heating.

Monitor the heat in your haystacks to determine if spontaneous heating is taking place.  You can make a simple temperature probe using a 10’ piece of 3/4” diameter pipe.  Drill some holes in the pipe around three inches from one end and flatten the pipe to make a point for inserting between the bales.  You want to check the temperature in the middle of the stack, and one of the easiest ways to do that is from the top, but you must not walk directly on the stacked hay because there may be burned-out pockets beneath you.  Walk on boards or a ladder to spread your weight evenly so you don’t end up falling into a burned-out void.  You should also be wearing a lifeline just in case.

Push the probe into the stack and lower a thermometer to the end of the probe.  Leave it there for about 15 minutes before pulling the thermometer out and checking the temperature.  Here’s what the temperatures indicate:

  • Below 130°F. there is no problem.
  • Between 130-140°F. there is still no problem.  The temperature can go up or down.  Recheck the temperature in a few hours.
  • At 150°F the temperature will very likely continue to rise.  Move the hay to allow for better air circulation and recheck the temperature often.
  • At 175-190°F a fire is about to start or is already present not too far from the probe. CALL THE FIRE DEPARTMENT IMMEDIATELY.  They will stand by with charged hose lines while the suspect bales are moved from the barn or storage area.  You need firefighters on the scene because the bales may ignite while they’re being moved.

If you don’t have a thermometer, you can use the probe alone.  Push it into the stack and leave it for ten to fifteen minutes before pulling it out.  If you can hold the probe comfortably in your hand the temperature is below 130°F.  If the probe is too hot to hold in your hand it means the temperature is above 160°F and a fire is about to start or already has.  AGAIN, CALL THE FIRE DEPARTMENT IMMEDIATELY.

One last pointer regarding wood shavings: If you get your shavings fresh from a local mill and heap the shavings into a pile, it’s possible there might be hot pieces of wood or metal (such as from a nail embedded in the tree) mixed in with the shavings from having made it through the sawmill.  If your shavings are fresh and mounded into a pile, check for smoke when the shavings are unloaded–and also several times later, just to be on the safe side.

Content Added: Some excellent information on hay storage from Ed Scott

Also read: Hay Barn Fires by Mike Weider (PDF)

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