Ammonia Chiller Explosion

Dear Forum

I am a system Integrator , Recently i supplied ammonia rack chiller.
with Bitzer ammonia screw compressors x 3nos.
After Running Successfully for Two Months , Yesterday it had taken a huge Blast.
The blast taken in oil separator, The Oil Separator escaped like a rocket.
It has not happened due to High Pressure , it just happened in fraction of seconds, when it was in running mode.
Only the end cover of the oil separator was separated along with discharge lines also.
Upto my knowledge it may happen due to Air + Ammonia mixture, its my view only.
Can any one help me ,what may be the Reasons?

at that time only one compressor is running.
HP - 190 Psi
LP - 28 Psi
OP - 160 Psi
Cold Room Application - Temperature - 0 Deg.

Thanks