Recommended Hay Storage

South Wales Fire and Rescue Service would like to draw attention to the following Fire Safety issues that can be encountered at premises where hay is stored and how the risk of fire can be reduced.

Oddly enough, wet hay is more likely to lead to a spontaneous combustion fire than dry hay. If hay is put into a barn or stack when it has more than about 22 percent moisture, not only does the hay lose forage quality, but it has an increased risk of spontaneous combustion.

High moisture hay stacks can have chemical reactions that build heat. Hay insulates, so the larger the haystack, the less cooling there is to offset the heat.

When the internal temperature of hay rises above 130 degrees Fahrenheit (55 degrees C), a chemical reaction begins to produce flammable gas that can ignite if the temperature goes high enough.

Hay fires generally occur within six weeks of baling. Heating occurs in all hay above 15 percent moisture, but generally it peaks at 125 to130 degrees F, within three to seven days, with minimal risk of combustion or forage quality losses. Temperature within a stack then declines to safe levels in the next 15 to 60 days, depending on bale and stack density, ambient temperature and humidity, and rainfall absorbed by the hay.

To avoid hay fires, small, rectangular bales should not exceed 18 to 22 percent moisture, and large round or rectangular bales should not exceed 16 to 18 percent moisture for safe storage.

In addition, you should check your hay regularly. If you detect a slight caramel odour or a distinct musty smell, chances are your hay is heating. At this point, checking the moisture is too late, and you’ll need to keep monitoring the hay’s temperature.

What do you do if you suspect that your hay is heating?

A simple probe inserted into the haystack can accurately monitor temperature. You can make a probe from a 10-foot piece of pipe or electrical tubing. Sharpen the pipe or screw a pointed dowel to one end, then drill several 1/4-inch diameter holes in the tube just above the dowel. Drive the probe into the hay stack and lower a thermometer on a string into the probe. The thermometer should be left for 10 minutes in several areas of the stack to ensure an accurate reading.

Watch for the following temperatures:

  • 150 degrees F (65 degrees C) is the beginning of the danger zone. After this point, check temperature daily.
  • 160 degrees F (70 degrees C) is dangerous. Measure temperature every four hours and inspect the stack.
  • At 175 degrees F (80 degrees C), call the fire department. Meanwhile, wet hay down and remove it from the barn or dismantle the stack away from buildings and other dry hay.
  • At 185 degrees (85 degrees C) hot spots and pockets may be expected. Flames will likely develop when heating hay comes in contact with the air.
  • 212 degrees (100 degrees C) is critical. Temperature rises rapidly above this point and hay will almost certainly ignite.