On Tuesday, the Piedmont Tobacco Equipment Company issued a release to all gas companies, barn service companies, and tobacco farmers regarding the location of the capillary tube in Roanoke tobacco barns.
In their release, they state, "We have investigated reports in order to determine the cause of these fires and have come to the conclusion that the capillary line, connected to the thermostat, is not properly signaling the burner due to its improper location, causing the burner to burn well beyond the prescribed temperature, causing extreme excess heat, which may in some cases cause the barn to ignite. In order to avoid further volatility, we urge all farmers using Roanoke barns to immediately take action to relocate the capillary line to a more appropriate location. A proper location is below the floor."
They also provide instructions on how this should be done.
According to Grant Ellington, engineering specialist with the North Carolina Cooperative Extension Service, the capillary tube should be located in an area below the tobacco where there is free air movement around the device.
Representatives of the manufacturing company and Ellington agree that a good place for the location of the sensing device would be 6 inches below the floor and 6 inches from both the side wall and the inside wall separating the furnace from the curing chamber. Caution should be taken in changing the capillary tube, as a pinched tube can cause additional problems with the sensing device.
Johnston County farmers, regardless of the make and model of tobacco barns they are using, must be proactive in inspecting their barns for possible hazardous conditions. At least one barn fire in Johnston County did not involve a Roanoke barn.
Generally, wood will ignite when the temperature reaches between 400 and 450 degrees fahrenheit. In some cases, wood will ignite below this range, especially if it is dry. It is not uncommon for burners in tobacco barns to reach 1300 degrees Fahrenheit. This means that any part of the barn made of wood should be several inches away from the burner or the heat exchanger.
Last year, Cooperative Extension Agents in North Carolina used a combustion efficiency analyzer to determine the efficiency of tobacco barn retrofits. One measurement was the stack or exhaust temperature. In Johnston County, these stack temperatures ranged from 345 to 822 degrees.
Higher stack temperatures indicate a low efficiency rating. It is not just the fire chamber that becomes hot, it can be any part of the retrofit.
The length of time that a burner stays on has a direct effect on efficiency and the amount of heat it generates in the heat exchanger. Some burner manufacturers suggest that tobacco burners should not run more than 90 seconds at any one time. The burner may remain off for a longer period. Growers with burners that remain on for more than 90 seconds should contact their burner manufacturer or gas supplier technician.
While thermostats rarely cause problems, growers should also check the thermostats on the barns. There are barns in Johnston County with thermostats that are over 25 years old. While thermostats rarely give problems, it is important that they be checked against a simple tobacco curing thermometer.
These suggestions, if followed, should help reduce the likelihood of tobacco barn fires.
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