How can I check the temperature of large hay bales?

To check the temperature of large hay bales, insert a thermometer into the hay to take a temperature reading. Monitoring the temperature of large hay bales can be dangerous, so it is important to take appropriate safety precautions when performing this task: 

  • Always work with a partner when monitoring the temperature of hay bales.
  • Before checking the temperature of stacked bales, place wooden planks or plywood across tops of the bales. The person checking the bales’ temperature should stand on these planks to help distribute his or her body weight and reduce the risk of falling into a burned-out cavity.
  • The person testing the hay should wear a harness and lifeline attached to a secure object. If an emergency occurs, the observing partner can pull the other person out of the hay.
  • Due to the potential dangers of this task, never assign youth workers to monitor the temperature of hay bales.

There are commercial thermometers available to test the temperature of stored hay. If your commercial thermometer is not long enough to insert into a bale, you can fabricate a probe from a 10 ft. length of 3/4 in. diameter iron pipe. Drill eight 3/16 in. diameter holes about 3 in. from one end of the pipe. Hammer that end of the pipe into a sharp edge to create a probe. After inserting the probe into a hay bale, use a piece of thin wire to lower a thermometer down to the end of the pipe. Keep the thermometer in this position for approximately 10 to 15 minutes to obtain a temperature reading. (The steps you should take next depend on the temperature of the hay.) 

If you do not have a commercial thermometer, you can use a 3/8 in. pipe that is 8 to 10 ft. long to check the temperature of baled hay. The person testing the hay should drive the pipe into a bale and leave the pipe in place for 20 minutes. When it is withdrawn from the hay, if the pipe is too hot to touch with a bare hand, the hot hay should be removed.

Click here to view the article “Preventing Fires in Baled Hay and Straw” to learn more about monitoring hay temperature and preventing fires in round bales.