This oxygen concentrator was being used by a 74-year-old female with a diagnosis of copd on 5/11/94 on the 3-11 shift. Oximetry reading that day was 85% and as a result the physician had increased the oxygen to 5 liters per minute. The resident complained that the o2 level was too high and continued to lower it to 4 liters per minute. During the 3-11 shift, the resident's family stated the o2 alarm sounded; however this was not observed by nursing staff. The resident was then given oxygen via o2 tank for the remainder of the shift and throughout the night. The following morning (5/12), the resident was sent to the hosp for arterial blood gases and admitted with respiratory failure. She died there on 5/20/94. On 5/13, the distributor was notified of the reported malfunction/alarm sounding on 5/12/94 and sent a representative to check the equipment. It was removed and not used until rechecked on 5/16/94. No problems were found by the representative and no alarms sounded during the recheck. The concentrator had been checked prior to use on this resident on 5/11/94. Oximetry readings of 92% from the concentrator and readings of 92% with oxygen from a tank were obtained from use with another resident earlier in the day on 5/11/94. This concentrator was put back into use on 6/9/94. On that date this concentrator was being used by a 82 year old female with a diagnosis of copd. On 6/16/94, during the 11/7 shift, the alarm began sounding repeatedly. The nurse removed the concentrator, placed the resident on pure oxygen for the remainder of the shift and removed the concentrator from service until it was rechecked. This second resident showed symptoms of lethargy the next day, but required no treatment. When checked by the director of nursing services on the day shift, on 6/10/94, it was noted that the concentrator alarmed randomly at various flow rates. Device not labeled for single use. Patient medical status prior to event: invalid data. There was multiple patient involvement. Number of patients involved: 2. Invalid data - on device service/maintenance. No data - regarding date last serviced. Service provided by: unknown. Service records not available. Invalid data - regarding whether event presents imminent hazard. Device used as labeled/intended. Device was evaluated after the event. Method of evaluation: actual device involved in incident was evaluated, performance tests performed, visual examination. Results of evaluation: none or unknown, none or unknown, patient's condition - predisposed event, alarm failure. Conclusion: device evaluated and alleged failure could not be duplicated. Certainty of device as cause of or contributor to event: invalid data. Corrective actions: device permanently removed from service, device temporarily removed from service, inserviced by manufacturer/distributor representative. Invalid data - on device destroyed/disposed of status.