This one just doesn't meet the "acid test" of insurance contract interpretation, pun intended. Sulfuric acid and the commercial property policy's rust or wear and tear exclusion is the subject. It's funny how what seems clear and simple almost never is. That's why there are mechanics (in every field).

A business with chemicals stored in tanks had a tank valve crack, either because it became rusty or just plain worn. Sulfuric acid spewed onto the insured's property.

This is important because not only the cost of the acid is at stake. That could be the least of it. The CP policy has an Additional Coverage that covers expense to extract pollutants from land at the insured premises if the discharge of the pollutant is caused by a covered cause of loss. There is a $10,000 limit to pollutant clean-up coverage. For example, if lightning hit this tank — certainly a covered cause of loss — and caused it to rupture, the insured would be able to recover both the cost of the acid and up to $10,000 for the expense to clean up the mess. I'm using the Insurance Services Office (ISO) building and personal property coverage form (CP 00 10 04 02) and the causes of loss — special form (CP 10 30 04 02).