Home > NRC Library > Document Collections > General Communications > Information Notices > 1994 > IN 94-26
UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF NUCLEAR REACTOR REGULATION WASHINGTON, D.C. 20555 March 28, 1994 NRC INFORMATION NOTICE 94-26: PERSONNEL HAZARDS AND OTHER PROBLEMS FROM SMOLDERING FIRE-RETARDANT MATERIAL IN THE DRYWELL OF A BOILING-WATER REACTOR Addressees All holders of operating licenses or construction permits for nuclear power reactors. Purpose The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice to alert licensees to the potential for large amounts of thick, acrid smoke to be produced from smoldering fire-retardant plastic sheeting. It is expected that recipients will review the information for applicability to their facilities and consider actions, as appropriate, to avoid similar problems. However, suggestions contained in this information notice are not NRC requirements; therefore, no specific action or written response is required. Description of Circumstances On December 28, 1993, a fire occurred in the drywell of the Shoreham Nuclear Power Station (Shoreham). Shoreham, a boiling-water reactor with a Mark II containment, is currently undergoing decommissioning. The fire was caused by hot slag that fell from the 137-foot elevation of the drywell where workers were cutting a biological shield wall stabilizer support with an oxyacetylene torch. The hot slag dropped through an opening in the biological shield wall onto paper toweling and a coil of hemp rope at the 102-foot elevation, setting them on fire. The burning rope subsequently dropped to the 78-foot level and landed just below a temporary water collection system in the annulus space between the lower portion of the reactor pressure vessel support pedestal and the shield wall. The collection system was constructed of rope and fire-retardant plastic sheeting (Herculite and Griffolyn) and had been installed to collect the runoff of potentially radioactive water expected from cutting the shield wall. The burning rope made the plastic sheeting smolder, giving off a large quantity of thick, acrid smoke. Because of the smoke, it was difficult for personnel in the area to breathe and to see in which direction to go to leave the drywell. Workers in the area saw the smoke and alerted the control room to a suspected fire. The control room operators activated the plant fire brigade which entered the drywell wearing self-contained breathing apparatus. However, the fire brigade was unable to locate the source of the smoke because the dense 9403220237. IN 94-26 March 28, 1994 Page 2 of 3 smoke blocked their vision. To help locate the source, the fire brigade asked the control room to place the reactor building normal ventilation system on standby. This action was not effective and the fire brigade leader informed the control room that the fire brigade could not find the source of the smoke. The control room operators called the local off-site fire department to help find and suppress the fire. The plant fire brigade made sure that all personnel had been evacuated from the area and again searched for the source of the smoke. The local fire department entered the drywell to search for the fire and found some burnt paper toweling and charred rope. About this time, the smoke in the drywell began to clear, apparently because the combustible material feeding the fire had been consumed. No flames were observed during the event. The plant fire brigade checked the area for ignition sources and found none. The licensee suspended work inside the drywell and continued to investigate. The licensee determined that the smoke had come from an approximately 5.5-square-meter [60-square-foot] section of the plastic sheeting that made up the collection trough. The licensee determined that the fire had not harmed station equipment or affected nuclear safety. However, 11 personnel reported to the first aid station suffering from smoke inhalation. The licensee found the following weaknesses in industrial safety practices: Openings in the biological shield wall had not been covered to prevent hot slag from passing through. Fire protection measures were not adequately understood or were not adequately specified in the fire permit. The fire permit did not clearly assign responsibility to check the area for combustible materials before cutting the structural support. Workers were not required to look for day-to-day changes in the work area, such as the presence of combustibles in vulnerable locations. Discussion The plastic sheeting materials involved in this event are commonly used at many nuclear power stations. Although these materials are fire-retardant, they are capable of generating large amounts of smoke when involved in or exposed to a fire condition. The total amount of material that was burned or smoldered at Shoreham was small; however the smoke from the smoldering plastic created significant hazards for personnel in the drywell and made it impossible for the fire brigade to locate the source of the smoke. Because of the smoke, personnel in the drywell were unable to see in which direction to go to exit the drywell or to avoid the fire. Several of the plant personnel suffered smoke inhalation. . IN 94-26 March 28, 1994 Page 3 of 3 The Material Safety data Sheets for the Herculite and Griffolyn sheeting state that those materials produce hydrogen chloride gas when burned and that self-contained breathing apparatus should be worn when attempting to extinguish fires involving these materials. In addition to the hazard of smoke inhalation, there is a potential for toxic side-effects from these fires. Because these and similar plastic materials are routinely used at nuclear facilities for contamination control, welding flash shields, and other purposes, it is important to recognize that, if these materials are exposed to or are involved in a fire, they generate a large quantity of smoke that creates hazards for plant workers and may adversely affect plant operations or fire-fighting efforts. These problems are exacerbated in confined spaces or in areas with limited ventilation. This information notice requires no specific action or written response. If you have any questions about this matter, please contact one of the technical contacts listed below or the appropriate Office of Nuclear Reactor Regulation (NRR) project manager. original signed by Brian K. Grimes, Director Division of Operating Reactor Support Office of Nuclear Reactor Regulation Technical contacts: R. L. Nimitz, RI (215) 337-5267 F. L. Bower III, RI (215) 337-5328 P. M. Madden, NRR (301) 504-2854 Attachment: List of Recently Issued NRC Information Notices
Page Last Reviewed/Updated Wednesday, February 16, 2011