First of all, before I talk about this I need to say that everyone involved is totally safe.
They are in the area of the wildfires out west, in fact they are completely surrounded by wildfires! But my friend and her family are all very safe, because they live above the timberline, so there is no forest to catch fire up there.
But even though they are safe from the flames, they are still trapped at home, and as the fires worsen so does the outdoor air quality, so to breathe easily they need to stay in the house. She sends pictures of how the entire sky is tinged orange and red, like the world is on fire, and even at that altitude they have needed the house HVAC system to keep safe. The smoke engulfs there entire property, at times for hours on end, so the air filters in the central HVAC system are always in use, even when the heating isn’t turned on the fans stay running. The air had to circulate constantly, and she has gotten pathological about checking the air filters two or three times a day to make sure they aren’t getting too dirty. Thankfully she has an extra package of 12 air filters in her garage, but she is still very worried so she keeps the old ones and tries to scrap them as clean as possible. Hopefully it will burn out quickly, but if they end up trapped on the mountaintop for a longer period of time, she may have to reuse and recycle those HEPA air filters.