We had a similar issue back at ExJob...in the building we worked in, we had "non-panic" inducing fire alarm where there would be an announcement, the lights would flash, a low-pitched alarm would go off, and the current floor, the floor above and the floor below would be evacuated.
This system always generated confusion. The day it was a real alarm, one person, who was profoundly deaf (they did have hearing aids but didn't have them in at the time), didn't hear the announcement or the alarm, so we had to go to their desk and let them know the alarms were going off, and we had to go outside. We moved to a new building soon after but not with the same system - the alarms were distinctive and loud enough that if they went off, you had to leave.
I think the employees should have a serious re-education on fire alarms first before OSHA gets involved. If you have a safety officer there, they should be telling the employees what the difference is between testing, a drill and a real alarm. If the employees are doing their due diligence, but managers are telling them to stay put, then it's an OSHA issue.
EDIT: BSMP made a great comment below re: the deaf person who we had to tell to leave as the fire alarms were going off...if I remember correctly, this incident wasn't reported to OSHA, but was roundly reported by several people to the safety officer, who then told all of us in a meeting that if the alarms did go off again to go to this employee's desk and tell them the alarm was going off. That person ended up retiring six months later, and when we moved to the new building across the way, the alarm system was designed to alert people immediately and actively - i.e. it was loud and unavoidable.