18.4 Sealing and air

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Ready-to-use sealing kit

The procedure for sealing a room against a chemical leak is in chapter 16. What this chapter adds is having it assembled and precut, because in an emergency there is no time to measure:

2–4 mil (0.05–0.1 mm) plastic cut to the size of each window, vent grille, and exhaust fan in the core, with 2–3 in (5–8 cm) extra per side, labeled with a marker ("BATHROOM – EXHAUST FAN").
Duct tape: 2 rolls or more. Test today that it sticks to your paint.
Old towels for the bottom of the door.
Scissors, marker, and a printed copy of the measurements.
Floor plan of the home or apartment showing the location of the thermostat and the air conditioning switch, so you can turn it off in seconds.

Chemical sealing lasts hours, not days: the air runs out (see chapter 16). Against fallout, an airtight seal is not needed; it is enough to close everything, turn off what draws in outside air, and avoid drafts that stir up dust (CDC).

DIY fan filter (Corsi-Rosenthal type)

A 20 in box fan with one or more 20 × 20 in MERV 13 furnace filters taped on is an inexpensive air purifier. In EPA laboratory tests with simulated wildfire smoke, these homemade filters reduced fine particles (PM2.5) about as much as a small commercial purifier; with two or more filters they clean more air.

Fan: box fan, 20 in, 2012 model or newer, UL or ETL certified (the EPA recommends fans with a fused plug and thermal cutoff).
Filters: MERV 13, 20 × 20 in (1 or 4 in thick). Follow the filter's airflow arrow: it must point toward the fan.
Simple version: one filter taped to the back of the fan (the side it draws air from).
Cube version: four filters forming the walls of a cube, cardboard on the bottom and the fan on top, blowing outward. It cleans more air.
Add a cardboard shroud at the corners of the front of the fan: the EPA found it improves performance by keeping air from flowing back around the tips of the blades.
Change the filters when they get dirty: a filter loaded with smoke or dust barely works.