A city of Fort Collins mulch pile continues to smolder, sending up visible smoke five days after it ignited by spontaneous combustion from days of dry, windy weather.

On Tuesday, the city had two payloaders and an excavator digging into the 50,000-cubic-yard pile at its Crushing Operations facility, 1380 Hoffman Mill Road, trying to cool hot spots.

The fire was reported shortly before 5 p.m. Friday.

Poudre Fire Authority continued working on scene until Saturday morning, at which time the city took over monitoring the smoldering pile and using heavy equipment to spread it out. Workers were aided Monday and Tuesday when a storm system cooled temperatures and dropped about 0.4 inches of rain in the city, which is four times more than what fell during the entire month of April.

"Anytime you have high wind and dry conditions like we have had, you have a high risk of a spontaneous combustion igniting,'' said Annie Bierbower, PFA spokesperson. "The combustion opportunity happens when the wind moves part of the pile, allowing oxygen into the pile's hot pockets and sparking it.''

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The fire forced the city to postpone at least the first of its two free mulch days at the facility. The first day was scheduled for Saturday and the second for May 21.

Rafael McLeod, city Forestry Department crew chief, said he is unsure of the reschedule date for Saturday's free mulch day or if the May 21 event will take place. 

He said an undetermined amount of the pile was contaminated with ash, dirt and mud during the fire suppression. McLeod said the pile, which is taller than the heavy equipment used to spread it, has been accumulating over the last year or more.

He said some of the mulch came from trees damaged in the March 2021 snowstorm, including from the huge pile of tree limbs and branches temporarily stored at the former Hughes Stadium property. That storm dumped around 20 inches of heavy, wet snow on the city, costing $2.75 million in tree cleanup.

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PFA firefighters had responded to the mulch pile that morning and were onsite for three hours, according to Bierbower. City crews were working the pile when the wind picked up later that afternoon and reignited the fire.

Firefighters also responded to a manure pile fire and the mulch pile fire Friday and a slash pile fire Sunday. Bierbower said the manure and mulch fires were started by spontaneous combustion and the slash fire by a chainsaw spark.

No structures were damaged in any of the fires, and there were no related injuries,

The city mulch pile fire burned a small section of the Kingfisher Point Natural Area and came within about 100 yards of the city's Natural Areas Department Offices located at Nix Farm, 1745 Hoffman Mill Road. 

"These fires create a lot of energy,'' Bierbower said. "You use a tremendous amount of water and resources on fires like these, and at some point it's really not feasible or reasonable to put out the fire but just separate the pile and let it sort of work its way out.''

PFA has responded to 22 grassfires already this year, including in backyards, ditches and in open spaces.

Bierbower said homeowners should be aware of other opportunities for spontaneous combustion fires to start, such as piles of grass clippings or rags containing highly flammable stains, varnishes or polishes that can spark on dry, hot, windy days.

She said piles of grass clippings should be watered down and spread out. Rags should be separated, spread outdoors and allowed to thoroughly dry before disposing of them.

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Reporter Miles Blumhardt looks for stories that impact your life. Be it news, outdoors, sports — you name it, he wants to report it. Have a story idea? Contact him at milesblumhardt@coloradoan.com or on Twitter @MilesBlumhardt. Support his work and that of other Coloradoan journalists by purchasing a digital subscription today.