Humidity ranges?

We have sensors in our datacenters that report, among other things, humidity. One data center is exceeding the predefined humidity alerts of the devices, but given that cisco says the operating humidty of routers is 10% to 85%, I dont know if humidity of, say, 65% is anything to worry about. Anyone know if increased humidity correlates with decreased MTBF? And reasonable thresholds that I can tolerate, and when I should complain to the datacenter operators? (References I can point to would be nice.) Thanks