Texas VFD confronts uncertain silo situation

Making a proper on-scene assessment of a silo fire that forced an evacuation around a Texas grain mill in September 2017 proved awkward, said Easterly Fire Chief Jim Redden. An auger opening at the base of a 120-foot-tall, 24-foot-diameter storage silo was the only access to the intense flames roaring inside.

“Everybody thought the fire was in the very bottom,” Redden said. “But I could see smoke venting from the top of the silo. If the fire was buried under 35 feet of corn you shouldn’t be seeing that smoke.”

All that corn encased within eight-inch concrete walls made it difficult for thermal imaging to detect where the bulk of the fire lay, he said. Despite feeding a continuous stream of water into the silo, Redden became increasingly worried about the potential for a grain dust explosion.

Grain dust is a highly explosive substance that must be handled carefully. In 1977, two grain elevator explosions only five days apart in Louisiana and Texas killed 56 people. More recently, a 1997 grain dust explosion in Blaye, France, killed 11.

With no previous training in dealing with this type of emergency, Redden said he was open to any expert advice being offered.
 
ROASTED CORN
Easterly is an unincorporated community in Robertson County, located about 35 miles north of the Brayton Fire Training Field in College Station. The Easterly Volunteer Fire Department consists of seven trucks, 15 personnel and two fire stations.

At about 1:30 p.m. on Sept. 13, firefighters were alerted to a fire emergency at a feed mill for a large poultry operation. Confusion ensued for some time as to the exact nature of the emergency.
“I don’t think anyone fully understood what happened,” Redden said. 

Volunteer departments typically have the hardest time mustering a response during weekday working hours. Fortunately, Easterly has volunteer firefighters among local personnel who work a 24-shift as EMS providers, Redden said.

Management at the grain mill took the immediate precaution of evacuating the workers on site. Arriving firefighters found evidence of an explosion in a hammer mill, a small concrete building adjacent to the grain silo. 

“The windows had been blown out and the doors were all blown open,” Redden said.

From the hammer mill, flames had shot into the silo through the connecting auger used to move grain. Firefighters removed the auger cover at the base of the silo and began shooting water through the opening to reduce the flames inside.

 The water brought the internal temperature down from nearly 900 degrees Fahrenheit to about 160 degrees but no lower.

Redden, who manages security at a power plant, was unable to join the firefighters until 3:30 p.m., he said. His immediate concern was the possibility of a dust explosion inside the silo. 

Several factors must come together for a dust explosion. The critical parameter for grain particle size is 0.1 mm or smaller. As the size of the particle decreases, the risk of a deflagration or explosion increases.
Dust concentration contributes to flammability. The concentration must be between 40 grams per cubic meter and 4,000 grams per cubic meter, depending on particle size and composition. Also, the dust must be in suspension in order for an explosion to take place.

“The owners wanted to turn on the auger and try to remove the burning corn using that,” Redden said. “They didn’t want us putting any more water in there.”

Strangely enough, thermal imaging failed to detect a significant heat signature above the auger, a cone shaped device that funnels grain into the center of the silo, Redden said.
 
EVACUATION
Acting upon the owner’s decision, Redden ordered the hoses be disconnected and that apparatus and personnel under his authority be withdrawn to safer positions. A hazardous materials expert with Union Pacific railroad on scene agreed with the action taken, Redden said.

The attempt to move the burning corn failed when the auger jammed. Within 30 minutes the temperature inside the base of the silo rose to 969 degrees Fahrenheit, Redden said.

The lack of a distinct heat signature on the thermal imaging camera led to the conclusion that a column of fire was burning up through the center of the silo. 

“You could hear the fire roaring inside,” Redden said.

Hazmat experts wanted to pump inert nitrogen into the silo to replace the oxygen necessary to fuel combustion. However, the equipment needed was not on hand and not easily available. Redden said.
At the height of the emergency, Easterly VFD had five firefighters on hand, plus responders from Seale-Round Prairie, Marquez, Wheelock and Bremond. Four tanker trucks containing nearly 20,000 gallons of water were available on scene.

After the auger failed, the decision was made to evacuate emergency personnel and civilians within a one-mile radius of the silo. Redden was one of only six emergency personnel allowed to remain within 300 feet of the silo.

“Somebody thought it would be a good idea to send firefighters to the top of the silo to spray water inside,” Redden said. He rejected that idea.

Eventually, three employees of the grain mill closed and sealed the auger cover at the base of the silo. Contract firefighters with Williams Fire and Hazard Control began arriving at about 11 p.m., Redden said. Unfortunately, another arrival during the early morning hours that followed was smoke from a second grain silo nearby.
 
MISSION ACCOMPLISHED
At about 4 a.m., WFHC personnel took a 5-inch hose line up an elevator in the complex and worked their way downstairs to the top of the silo. Using a cellar nozzle designed to distribute a high flow of water over a wide 360 degree area, firefighters dropped the hose in through the top of the silo, firing it in 10-second bursts.

By 10:30 a.m. the fire was out, Redden said, with traffic restored on nearby U.S. 79 soon after. No injuries were reported during the emergency.

Redden said it is wise for departments like his to stop and study the bigger picture after an emergency such as this.

“We definitely need more training on this situation,” Redden said. “I think all fire chiefs should make their members understand the possibility that the worst case scenario can happen. That is definitely something we will discuss.”                                       C
 

 
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