Is sulfuric acid still hazardous after it dries? One of our housemates decided to pour battery electrolyte (which is 30-40% sulfuric acid) into a motorcycle battery on our back porch next to our laundry washer and dryer.  He did so extremely sloppily, and we don't know exactly what he might have spilled the acid on.

Is the acid safe to touch after it dries, or is it still a safety hazard?

If it isn't safe when dry, what can we do to neutralize the acid?  I know baking soda can neutralize acid, but I'm not really sure how to easily coat an entire porch in baking soda.

My boyfriend suffers from severe, debilitating OCD with a chemical contamination obsession, so this is an absolute nightmare for him.  Thank you in advance for any help you may have!
Sulphuric acid won’t dry — meaning evaporate; what water does when one typically thinks of drying — at any noticeable rate. It will, however, given time penetrate deeper into the material if the material is porous or susceptible to degradation.

Depending on how much sulphuric acid was actually spilt, I suggest either mopping up the area with lots of water (if not much was spilt) or first semi-generously applying dry baking soda to the area. Once the baking soda has stopped generating bubbles immediately on application, you can use normal amounts of water for wiping up.

While I would love to suggest you get the sloppy housemate to do it, I think you might be disinclined because they again will do it sloppily.