Humidity ranges?

[Steve Francis <steve () expertcity com>]

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