I would setup a trap receiver, and look out for the below trap.
Name extremeFanfailed
OID .1.3.6.1.4.1.1916.0.7
MIB EXTREME-TRAP-MIB
Objects sysUpTime, sysDescr, extremeFanNumber
Description: A fan failed trap indicates one or more of the cooling fans inside the device has failed. A fanOK trap will be sent once the fan has attained normal operation.