Sammy Sadak: Grain Bin Fires

For combustion to happen in a grain bin, we need three critical requirements:

  • Fuel, which in this case could be the grain or the fines.
  • Oxydizer, which comes from the air.
  • Ignition source, which could be hot spots from grain respiration or other practical issues such as heat from friction.

The minimum ignition temperature of grain varies.

The minimum ignition temperature for wheat flour, corn starch, and grain dust is in the range of 750 to 930 degrees F (400 to 500 degrees C). When corn burns, the temperature could reach 1,472 degrees F.

We have two ways to monitor temperature inside of grain bins – manually monitoring the grain temperature or grain temperature monitoring cables.

If hot spots develop close to one of the cables, it automatically would be detected by the temperature sensors.

If it happens far away from the cables, it will not be detected easily.

So we need to turn on the aeration fan once every two weeks for maybe a couple of hours, especially when the ambient temperature is above freezing.

That will move the hot air through the grain, and then the cables potentially could easily detect the high temperatures.

In addition, we can measure the CO2 concentration in the airstream from the negative draft aeration duct.

You can use a handheld CO2 monitor or install a wall-mounted CO2 sensor to measure the CO2 concentration, which is a measure of hot spots in the grain bin.

Then we need to take the appropriate action, such as aeration.

Once the hot spots reach ignition temperature, however, we need to shut off the fans to avoid adding more oxygen that will increase the potential for fire.

One action we need to take is unloading the grain bin, starting from the top to the bottom.

We need to take it to ground and move all of the high-temperature or burning grain away from the bin.

We have to be careful not to unload the grain from just one side of the bin, not to solve one problem by creating another with the collapse of the bin due to the pressure differential.

Reprinted from Grain Journal July/August 2020 Issue