Volcanic ashfall

Abrasive and irritating, not poisonous

Volcanic ash is not the soft, fluffy ash left by burning wood. It is pulverized rock and glass, ground fine enough to become airborne. USGS describes it as highly abrasive and mildly corrosive. The particles irritate the eyes, nose, and throat, and can worsen asthma and other respiratory conditions significantly.

Volcanic ash is not acutely toxic to breathe in the concentrations experienced by communities in the ashfall zone, rather than the immediate eruption zone. However, USGS identifies people with asthma, chronic obstructive pulmonary disease, emphysema, or other respiratory conditions as being at higher risk from even modest exposure. For those people, avoiding outdoor exposure is a health necessity, not a precaution.

Ash is also heavy. A single inch of wet ash weighs about 10 pounds per square foot. Accumulations beyond 4 inches can threaten roof collapse on older or less sturdy structures. This is one reason USGS guidance explicitly advises clearing ash from roofs when accumulations reach that threshold, but only by people who are physically able to do so safely and only if it can be done without extended outdoor exposure.

Close up, bring pets in, avoid driving

Ready.gov and USGS both direct households in the ashfall zone to take shelter in the building where they are, close windows and doors, and cover ventilation openings. USGS's keeping-ash-out guidance recommends placing damp towels at door thresholds and using tape to seal non-essential gaps. This is practical, not excessive: ash is fine enough to penetrate ordinary gaps around doors and windows.

Bring pets and livestock inside. Ash irritates animals' eyes and lungs the same way it does people's, and ash accumulation on fur or feathers can be difficult for animals to manage on their own.

Avoid driving in heavy ashfall. USGS identifies two specific problems. Ash dramatically reduces road visibility, and it creates a slippery surface similar to wet mud. Additionally, volcanic ash is abrasive enough to damage vehicle engines and filters. If you must drive, drive slowly and use low-beam headlights. Change the engine air filter after any significant ashfall exposure.

Do not use water to wash ash off sidewalks or driveways during active ashfall. The water turns ash into a dense, cement-like slurry that is heavier and harder to remove than dry ash. Wait for ashfall to stop, then use dry methods first.

N95, goggles, and long sleeves

USGS identifies the N95 mask (also designated P2, FFP2, or DS2 in different markets) as the most effective respiratory protection during ashfall. The certification is printed on the mask. Surgical or cloth masks provide some protection but are not rated for fine particle filtration at the level needed for heavy ashfall.

Protect your eyes with goggles, not glasses. Ash particles are sharp enough to scratch corneas, and they can become trapped behind contact lenses and cause serious damage. USGS advises removing contact lenses and wearing glasses or goggles instead during ashfall.

Cover exposed skin with long sleeves and long pants. Ash irritates skin on contact. Shake out or bag clothing before re-entering the building to avoid tracking ash inside, which increases indoor exposure and cleanup effort.