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Silo explosion rocks first responders

Firefighters arriving on scene discovered smoke coming out of one of what appeared to be the loading doors at the top of a 20 x 80 Harvestore silo.

At 19:17 hrs on Aug. 16, the Bathurst Burgess Drummond & Elmsley Fire Rescue (BBD&E) in eastern Ontario was dispatched to a reported silo on fire at 381 Prestonvale Rd., which is about 13 kilometres from the fire hall, near the village of Balderson. Firefighters arriving on scene discovered smoke coming out of one of what appeared to be the loading doors at the top of a 20 x 80 Harvestore silo.

Initially, firefighters thought they should attack the fire by climbing the silo and putting water into it but a captain on scene, who is also a local farmer, advised the crew to hold off until the local Harvestore service rep could be contacted. The captain made a landline call to a service rep, who recommended that water not be put into the silo and advised firefighters to close the unloading door at the base of the silo and to try to determine whether the loading doors at the top were open or closed.

The service rep also recommended to the captain that firefighters not climb the ladder attached to the silo.

The unloading door at the base was open only about half an inch on one side. Two  firefighters were assigned to close this door.

To verify the status of the loading doors on the top of the silo, a decision was made to call for mutual aid for an aerial ladder from the Town of Perth Fire Department.

The aerial ladder from the Perth department arrived at about 20:00 hrs. At 20:17 the aerial was raised so firefighters could view the loading doors. Two firefighters (a captain and a firefighter) from BBD&E were assigned to the aerial to check out the doors. The aerial was raised to the top of the silo but it was too far away for the firefighters to see the doors clearly.

The aerial was retracted and relocated closer to the base of the silo. A dry run to see if this was a more feasible location was conducted. This appeared to be a good location. As the two firefighters were being raised to the top of the silo – they were at about the 65- to 70-foot mark – the silo began to rumble and at about 20:50 hrs the roof lifted off the silo and there was a large explosion.

This caused some chaos, as there were pieces of the silo flying through the air and a couple of firefighters on the ground were tossed around like sacks of potatoes. Sparks and burning haylage flew through the air. The two firefighters on the aerial were lowered to the ground and appeared to be OK. There was an emergency response vehicle on scene and the paramedic checked these individuals. They appeared shaken but not injured.

The accountability officer and incident commander immediately conducted a personal accountability report but this was difficult because firefighters were scrambling in all directions to ensure there were no major injuries and that all other structures were OK. At 20:59, it was reported to dispatch that all personnel where accounted for.

Immediately police and hydro were dispatched to the scene.

The Harvestore service rep was called again and was astounded to hear of the explosion, saying he had never heard of a similar incident in his 30-plus years of experience, although there have been some reported similar cases in the U.S. The service rep was asked to look at the structure to ensure it was structurally sound. He arrived on scene and said he felt that it was OK to leave the structure. He observed the debris in a field south of the silo, where just four of the 21 sections of the silo’s roof ended up. The other 17 sections were unaccounted for.

On Friday, Aug. 17, the remaining section of roof and other debris were located in a 360-degree debris field. A sketch of the debris was made and it was noted that four sections of the roof fell at 113 metres from the silo.
  
We are hoping that experience, which we as a department are very lucky to have walked away from with no injuries, opens the eyes of all fellow firefighters to be aware of the dangers when responding to this type of reported fire.

As they say in EMS training, everyone goes home. At this call, we were lucky and everyone went home.

ON SCENE
Bathurst Burgess Drummond & Elmsley Fire Rescue
Aug. 16, 2006, 7:17 p.m.
Response: Bathurst Burgess Drummond & Elmsley Fire Rescue, two pumpers, two tankers, equipment van, bush/water source truck, tactical command unit, Lanark County rescue unit, 24 personnel. Mutual-aid unit from Perth Fir Department. 100-foot aerial ladder, tactical command unit, seven personnel.
Details: Call for silo fire that results in explosion. Debris lands up to 100 metres away.

Corn bin rescue
The Inter-Township Fire Department in Ontario, with assistance from the nearby Owen Sound Fire Department, responded to a 9-1-1 call on Sept. 8. Workers had been cleaning out a corn bin using a piped blower. One inside of the bin was helping to remove residue from waste corn. Realizing the man inside had become trapped in loose material, his co-workers tried to free him. Unable to do so, they called for help. The emergency call went for a man "trapped up to his waist in a corn bin."
"When we arrived the material was up to his nose," said Inter-Township Chief Carl Linthorne. Firefighters went up the bin's exterior ladder and down the interior ladder. With a rapid intervention team in place at the top of the bin, two firefighters descended to the trapped worker. The confined space was very warm. At the time of entry, an air system line was placed and the air was being monitored. To free the worker from the shifting loose material, firefighters built a timber box around him. Using a five-point hitch rapelling harness, the worker was lifted to the door at the top of the bin. The rescued worker was checked over at the hospital and returned to work. Asked if this rescue was unusual, Chief Linthorne said, "It's the sort of thing we train for." – Ted Shaw

Preventing  haylage fires

According to the website for the Ontario Ministry of Agriculture, Food and Rural Affairs (www.omafra.gov.on.ca), silo fires are common but preventable. The ministry says that every year in North America there are fires and feed damage caused by spontaneous combustion and heating and that millions of dollars are lost in structures, feed and cattle from hay and silo fires.

Spontaneous combustion for hay usually occurs within the first two months of storage. In silos, forage can dry down if air enters the silo through leaks in walls or doors.

Spontaneous heating and combustion occurs when sufficient moisture (above 25 per cent and below 45 per cent moisture content for forages), oxygen and organic matter are present together to support the growth of bacteria and moulds. This growth results in an initial temperature peak of 54 C to 65 C (130 to 150 F). When the forage reaches this temperature range, a chemical process called the Maillard Reaction can occur, causing additional heat generation. This reaction can be self-sustaining and does not require oxygen to continue. The gases produced will ignite if they have reached a high enough temperature and are exposed to oxygen.

The ministry says there are several causes of these types of fires:

• Hay that is too wet (above 25 per cent moisture content) will heat and then enter the spontaneous combustion cycle.

• Silage and haylage that is too dry (below 40 per cent moisture content) will heat and then enter the spontaneous combustion cycle.

• A large mass of forage that allows the heat to build up.

• A slow trickle of air moving into the material.

• Old silage (two years) in silo drying down to critical level.

The key to fireproofing silos is the elimination of the combination of dry silage and fresh air by keeping silo doors closed and ensuring walls are in good repair.

The ministry says firefighters called to a silage or haylage fire will require full turnout gear including self-contained breathing apparatus due to dangerous silo gases. In conventional open-top silos, firefighters should locate the hot spots with a probe and put out fires by injecting small streams of water through the probe directly to the seat of the fire. Gases may be produced when injecting water into a hot silage fire. However, there is no containment of gases since the silo is open and not sealed, which practically precludes the occurrence of an explosion.

In oxygen-limiting silos a fire is potentially very dangerous, since there is containment of explosive gases. The method of control is to inject liquid nitrogen or carbon dioxide into the silo to cool the fire.

Every oxygen-limiting silo should have valves specifically designed to inject gases for fire control.