Obarrio is an area of offices and corporate towers inside the city’s business district, with restaurants and hotels around it. From Monday to Friday its floors are occupied during the working day, and every floor depends on the same air conditioning system.
On office floors the ducts run above the ceiling, so nobody checks them unless there is a reason. In a climate as humid as Panama’s, the dust they hold can encourage mold and biofilm, and office systems almost never stop long enough to dry out. That is why a dirty duct can go unnoticed for a long time, until tenants start complaining about the air.
Data point: At the Tocumen station the mean relative humidity drops to 64.9% in March, the least humid month, and rises to 82.4% in October (ETESA, 1977 to 2010, in Spanish). The EPA recommends keeping indoor air below 60%.