HYDROGEN-SULFIDE AND SULFUR-DIOXIDE EVOLUTION FROM A VALVE-REGULATED LEAD ACID BATTERY/

Two incidents concerning the contamination of copper-conductor surface s associated with uninterruptible power systems (UPS) were recently ob served. Valve-regulated lead/acid (VRLA) batteries used in the UPSs fo r backup powering were diagnosed as a possible source of the contamina tion. One of the VRLA batteries from the UPS unit was subjected to ove rcharge in the laboratory, to simulate the incident. Overcharge curren ts greater than 10 A, coupled with battery temperatures over 60 degree s C, can cause a VRLA battery to release significant amounts of hydrog en sulfide and sulfur dioxide. Under extreme conditions, hazardous lev els of hydrogen sulfide could be generated. We conclude that the conta mination was due to copper sulfide, Cu2S, and copper oxide, Cu2O, form ed on copper surfaces as a consequence of hydrogen sulfide evolution a nd the high humidity inside the UPS enclosure resulting from battery v enting.