Dryness, nitrates possible explanations for Fraser Valley dairy farm fires

Farmers in Agassiz, Rosedale still unsure how fires started

It’s every farmer’s worst nightmare: the orange hue of a fire waking them up in the night, having to rush out to try to save their animals, property and livelihood.

This summer, a number of Fraser Valley farms caught fire, some with more devastating impacts than others.

But two fires were eerily similar and occurred less than a week apart.

Two dairy farms – one in Agassiz and one in Rosedale – experienced fires that started in bunker silos. And these were only two of five incidents of smouldering corn silage reported across the Fraser Valley, according to a notice sent out by the BC Dairy Association.

For non-farm folks, a bunker silo is essentially a storage compartment farmers use for bulk storage of fermented feed, like corn. They are made from varying materials, like concrete or wood, and don’t have a standard size or shape. Older models are typically made from wood, and have a cover so they can be entirely ‘anaerobic’ – oxygen-free.

But newer silos are more frequently made with poured concrete – a more convenient material that inadvertently makes the structure less vulnerable to fire.

The fires

On Sept. 19, a warm Wednesday night took a turn for the worst on a small 70-cow Agassiz dairy farm when a fire started in their silo bunker and ripped through buildings on the property, ultimately killing three cows and leaving piles of smoldering rubble in its wake.

The Agassiz Fire Department confirmed that the fire did indeed start in the silo, but couldn’t explain why. The family had been packing the silo bunker the same way for 40 years. What was different this time?

Read More: Most cows saved during massive fire on Agassiz farm thanks to fast work of farmers, neighbours

It was only days later that a Rosedale farm nearly met the same fate. A silo bunker on a larger dairy farm – 300 cows – caught fire. The difference was that the fire started during the day.

The Sache family, who own the Rosedale property, along with a number of neighbours who ran to help, hooked up an irrigation wheel and beat the fire down before it could spread. The family lost only the bunker and even most of the silage was saved.

But Sarah Sache, who lives on and operates the farm with her husband and inlaws, is still trying to figure out how the fire could have started.

She told the Observer they had finished chopping the corn the day before around 6:30 p.m. before they started packing it in the bunker. The next morning she said they saw signs of nitrates being released.

“We’ve been building the same bunker the same way for a long, long time…” she said. “This year seems to be a different year and the presence of the gas seems to be the difference.”

“To us that’s the best we can attribute it.”

And Sache noted that the temperature of the silage didn’t rise or seem to have any hot spots – something farmers were told to look out for.

As farmers harvest and pack their silos this fall, Sache said many in the community are worried.

“I think people are really, really nervous.”

Read More: Chilliwack firefighters battle Rosedale barn fire

A fire on an Agassiz farm in September burned almost all buildings on the property. The family has been rebuilding since. (Nina Grossman/The Observer)

A dry summer

University of the Fraser Valley (UFV) agriculture professor and farmer Paul Gumprich emphasized that he isn’t a scientist, but he speculates that the dry summer could be connected to the fires.

In theory, the silage itself can’t catch fire because there’s no oxygen inside the bunker – but outside heat and dryer materials could be the perfect recipe for igniting a wood silo, he said.

“My suspicion is that, because it might be dryer than a normal year, the plant itself, instead of maybe being 65 per cent moisture might be 55 per cent,” he said. “In which case it may give off more heat which could lead to the outside structure catching on fire.”

“The silage itself produces the heat [and] if it gets hot enough on the outside then there could be spontaneous combustion.”

In essence – spontaneous combustion means the fermentation process has created enough heat that no outside heat source is needed to start a fire.

Davis Hill, the former program director of the Managing Agricultural Emergencies Program for Penn State University, wrote a paper about the vulnerability of silos.

Heat, explained Hill, is generated by the silage material as it goes through the fermentation process, and once ignited alongside the presence of oxygen, the silage itself can act as fuel.

According to Dairy-Crop Solutions consultant Gerry DeGroot, one practice that puts structures at further risk is piling combustible material like hay bales on top of silage tarps.

“If you have a combustible material on top – yeasts or mold – you can have a hay fire that starts on top of your bunker,” De Groot explained.


But the Sache’s say their silage didn’t heat up – so what exactly started the fire?

One theory is nitrate absorption.

After a hot, dry, smokey summer, some farmers are speculating that their corn absorbed nitrogren differently than in other years. Combined with early, pre-harvest rains in September, De Groot said the plants could be holding onto more nitrates and releasing more gases through the fermentation process.

But nitrogen on its own isn’t flammable.

“I think the number one thing is – we’ve always dealt with nitrates in the silage,” said De Groot. “Some people have had hay and other combustibles on top of their silage and gotten away with it. There’s some sort of reaction coming in there and I don’t know what that is.”

Considering silos

Newer cement bunkers may not be vulnerable to fires the way wooden ones are, but many farmers in the Valley have buildings on their properties that have stood for generations, and according to Sache, bunker silos aren’t exactly top of mind when it comes to expensive upgrades.

“It’s just not a place on your farm that you’re really, super eager to invest in. If you have something that’s working and you could invest instead in animal care or other things…” she said. “I mean, as long as it’s working we haven’t had a need to fix it,”

But Sache said that might change if there are more bunker fires.

“Now I think there is definitely a lot of consideration going towards whether those are safe to still use.”

And De Groot agreed that wood bunkers could be a bit riskier, depending what’s packed on them.

“A wood bunker might allow a bit of air to get through. When you have a source like hay…that gets hot and starts to burn, now you’ve got something that will burn quicker than the newer concrete ones,” he said, adding that newer silos are usually built further away from other farm buildings.

Older silos are also more likely to have holes – allowing moisture or old material to get trapped inside and increase the risk of spontaneous combustion.

When a bunker silo went on fire, the Sache family was able to use irrigation wheels to battle the blaze while they waited for the Chilliwack fire department to show up. Fortunately the fire was put out before it could spread to other buildings. (File photo)

Stopping a fire before it starts

The simplest solution, experts say, is to monitor your silo bunkers. But for many farmers, especially those operating small family farms, 24-hour monitoring is impossible.

“Any farmer, whenever they put their crop in, they know to walk around the outside of their bunkers and keep an eye on their bunker and watch for any signs of overheating,” said Gumprich. “The trouble is, if it occurs at two or three in the morning and you didn’t catch it before you went to bed or during the day.”

Dr. Michael Pate of Penn State University told the Observer via email that farmers can take a few steps to try to protect their bunkers.

“Make sure the bunker is clear of any old material before placing any new silage in the bunker,” he wrote. “Harvest the crops at the proper moisture content and use proper equipment and techniques to pack the silage tight to limit air space. Keep storage structures well maintained and monitor the product for any spoilage or pests.”

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