The huge wildfires on the west coast of the United States and last year in Australia are reminders of how quickly areas known for good air quality can turn into smoke and ash filled atmospheric nightmares. White ash falls like snow in nearby areas and blue skies are replaced by a reddish hue that will last even after the flames are extinguished. It doesn’t take a 12.6-million-hectare fire like the one in Australia to make life miserable for people downwind. A brushfire in a neighbor’s field or even a large industrial fire can affect nearby communities. The news will be full of stories about people escaping fires as their homes are destroyed but houses untouched by the direct flames face another threat as the soot and ash covers their houses and infiltrates their HVAC systems. The results can be devastating and while insurance policies may pay for burned houses, they usually don’t pay for dirty ones. During a fire, the best advice is to stay indoors, keep plenty of fresh filters with a higher MERV rating on hand, and most importantly, close the fresh air intake vents. Be sure that windows and doors are closed and if they are leaky, use masking tape or duct tape to provide a temporary barrier. After the smoke clears open the windows and doors and set your HVAC system on the fan-only setting. Let it run for at least an hour to air out the system. Then, turn on the AC setting and check that it can blow cool air again. Next, call a qualified HVAC technician as soon as possible to clean the HVAC system of fire residue that can corrode cooling coils, ducts, and other metallic surfaces.