Taal Volcano has erupted, and ashfall has started to wreak havoc in surrounding areas, including Metro Manila. It seems to be getting worse as the hours go by. Among those affected are motorists operating their vehicles under such conditions.

In light of the situation, we have a number of readers asking whether it is safe to use their vehicle’s air-conditioning system with all that volcanic debris in the air. Here’s some useful information from the United States’ Centers for Disease Control and Prevention:

Keep your car or truck engine switched off. Avoid driving in heavy ashfall. Driving will stir up ash that can clog engines and stall vehicles. If you do have to drive, keep the car windows up and do not operate the air-conditioning system. Operating the air-conditioning system will bring in outside air and ash.

In addition, the United States Geological Survey also shares the following warning:

Air intakes on heating, ventilation and air-conditioning (HVAC) systems are vulnerable to volcanic ash ingestion. Ash ingress may cause ash accumulation in the radiator and air filters, reducing airflow and HVAC condenser system performance. Reduced airflow may cause stalling and overheating.

Your air recirculation doesn’t completely filter out all that volcanic debris and keep it from entering the vehicle’s cabin and your respiratory system

To simplify: Heavy ashfall can certainly affect your car’s air-conditioning system and/or even damage it. Furthermore, your air recirculation doesn’t (and cannot) completely filter out all that volcanic debris and keep it from entering the vehicle’s cabin and your respiratory system.

Speaking from experience, I’ve driven numerous cars through smoke from a bushfire or other sources. Despite having the AC and air recirculation on with all the windows completely shut, I could still smell the smoke from the external environment—proof that a car’s air-recirculation system doesn’t create a completely filtered bubble in your vehicle’s cabin.

If you’ve driven through heavy ashfall, clean your cabin air filter (or replace if necessary) and immediately hose down your air-conditioner’s condenser—usually found behind your vehicle’s front grille—to remove volcanic debris caught in its cavities.

Bottom line: Avoid driving under significant ashfall unless absolutely necessary. Just stay indoors and be safe.