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Colorado’s smoke seasons
DFPC says wildfire 'seasons' were historically a four-month summer event, but the average core wildfire season is now 78 days longer than in the 1970s and Colorado sees large fires every month of the year. [1] DFPC's list of Colorado's largest fires by acreage (as of 12/31/25) ranks Cameron Peak (208,913 acres, 2020) first, East Troublesome (193,812, 2020) second, Pine Gulch (139,007, 2020) third, Hayman (137,760, 2002) fourth and the Lee Fire (137,758, 2025) fifth. [2] DFPC ranks Colorado's most destructive fires by homes lost as Marshall (1,084 homes, 2021), Black Forest (489, 2013), East Troublesome (366, 2020), Waldo Canyon (346, 2012) and High Park (259, 2012). [2]
Boulder County's January 6, 2022 damage assessment for the Marshall Fire counted 1,084 residential structures destroyed and 149 damaged (550 destroyed in Louisville, 378 in Superior, 156 in unincorporated county) plus 7 commercial structures destroyed and 30 damaged, with residential losses valued at about $513.2 million. [3] The National Weather Service says the Marshall Fire started shortly after 11 a.m. on December 30, 2021 as a grass fire near Marshall and was driven east into Superior and Louisville by mountain-wave winds gusting 80 to 100 mph, with a peak gust of 115 mph measured in Arvada. [4] Smoke does not respect the fire perimeter: in Colorado the houses that never saw a flame spend days inside the plume, and their air is the subject of this page.
Air quality in Colorado: reading the numbers
Colorado’s air-quality agency is the Colorado Department of Public Health and Environment — Air Pollution Control Division. CDPHE says Colorado's wildfire smoke season typically runs May through September, that fine particles (PM2.5) are the main health concern, that only an N95 respirator (not cloth or surgical masks) filters smoke outdoors, and that a MERV 13 or higher furnace filter or HEPA air cleaner is best for a home clean room. [5] The Air Pollution Control Division issues Action Day Alerts for fine particulates, ozone or multiple pollutants for the Denver and northern Front Range region when air quality is expected to reach the Unhealthy or Unhealthy-for-Sensitive-Groups AQI categories, and maintains a Colorado Smoke Blog tracking wildfire, prescribed burn and out-of-state smoke. [6] In its May 28, 2026 summer air quality guide CDPHE said wildfire smoke is the primary driver of particulate pollution in Colorado summers even from distant fires, and that subscribers to its 'ozone front range' list get daily emails May 31 through August 31 flagging any Ozone Action Day Alert for metro Denver and the northern Front Range. [7]
Nationally, the AQI [8] turns PM2.5 concentrations into six colour bands; from 101 (orange) sensitive groups are affected, from 151 (red) everyone is, and the AirNow wildfire map [9] shows the Colorado monitors and the smoke plume together. What the outdoor number does not tell you is the indoor number, and that is where the health question actually lives.
What the smoke does, and to whom, in Colorado
Wildfire smoke is mostly fine particulate — PM2.5 — with carbon monoxide, volatile organic compounds and, when structures burn, the metals and plastics of a Colorado neighbourhood. The particles are small enough to reach the deep lung and the bloodstream. CDPHE runs a Wildfire Smoke Preparedness Program, funded by EPA's Wildfire Smoke Preparedness in Community Buildings grant, that trains schools and community partners to monitor indoor air, use HEPA portable air cleaners and operate Clean Air Centers because smoke infiltrates buildings during Colorado smoke events. [10] CDPHE's indoor-air guidance for smoke-impacted homes says ash and soot deposit particulate matter and VOCs such as benzene that keep off-gassing for weeks, recommends HEPA plus activated-carbon air cleaners and an N95 or P100 respirator during cleanup, and warns never to run ozone generators in occupied homes. [11]
- Children in Colorado breathe more air per pound of body weight and their airways are still developing.
- Older adults and anyone with heart or lung disease, including asthma and COPD, feel Colorado’s smoke at lower concentrations.
- Pregnant people and their pregnancies; outdoor workers in Colorado; people who cannot afford to close the windows in the heat.
Symptoms run from stinging eyes and a scratchy throat through coughing and wheezing to chest tightness and shortness of breath. A Colorado household that notices the last two — or anyone with a heart condition who feels palpitations or unusual fatigue during a smoke episode — should call a clinician; our after-exposure guide covers the first days.
Keeping it out of a Colorado house
The EPA’s guidance on wildfires and indoor air quality [12] is the standard playbook: close windows and doors, set the HVAC to recirculate and fit the highest-MERV filter the system tolerates, run a HEPA air cleaner in one room and make that the clean room, do not add to indoor particles (no candles, no frying, no vacuuming without a HEPA vacuum), and open up to ventilate when the outdoor AQI drops. In Colorado’s heat that trade-off is real, which is why a clean room with a portable air cleaner is the practical unit of protection rather than the whole house.
When the outdoor air clears, the Colorado house may not have. Residue that settled on surfaces and in the ductwork keeps releasing what it absorbed, and the smell that returns on warm days is that residue. That is the point at which a health question becomes a measurement question — and then a claim question.
After the smoke: test, then claim
If your Colorado home smells of smoke, two kinds of professional are relevant and it helps to know which you are calling. Certified Industrial Hygienists (CIHs) and environmental consultants test: they measure what settled on the surfaces and what is still in the air, and they put a number on it. Fire damage restoration technicians — disaster restoration specialists — clean: soot comes off with chemical sponges and HEPA vacuums, odor is treated with air scrubbers and thermal fogging, and any firefighting water is dried out before it becomes a mold problem.
Testing before cleaning is the rule for Colorado homes that sat in a plume: United Policyholders [13] explains that smoke and ash damage to a standing home is covered and that independent CIH testing is what makes the claim specific to your house; the hygienist’s report is also what tells you whether the children’s bedroom is safe to sleep in tonight. The health-first sequence on this site walks through the first week; the Colorado claim guide on our sister site handles the paperwork.
Embers and heat, not smoke, damage roofs — but a Colorado house inside a wildfire perimeter may have had both, and the attic is where residue persists longest. Smoke odor in decking and attic insulation [14] explains why the attic is a separate inspection; the picker below finds a Colorado roofer for it.