I think that what we're going to find out is that prior to this incident, there had been a great abundance of either false alarms, or low-level alarms miscategorized as high level alarms that did nothing but disrupt peoples' sleep. Crews got sick of getting awakened and alerted by useless alarms and in turn did what any sane individual would do - disabled the audible alarm.
I deal with alarms every day. Nuisance alarms are disruptive and take ones' mind off what they are doing. They should be weeded out so that if the system is giving a high level warning, then something that requires immediate attention is happening or has just occurred.
I doubt they needed an alarm....the movement of the explosion must have been enough to alert everyone. After that...it was finding the best exit..and a place to jump ship....