The waste in Hanford tanks generates a mixture of flammable gases and releases it into the tank headspace. The potential hazard resulting from flammable gas generation requires that controls be established to prevent ignition and halt operations if gas concentrations reach levels of concern. In cases where only hydrogen is monitored, a control limit of 6,250 ppm hydrogen has been in use at Hanford for several years. The hydrogen-based control limit is intended to conservatively represent 25% of the lower flammability limit of a gas mixture, accounting for the presence of flammable gases other than hydrogen, with ammonia being the primary concern. This report reviews the technical basis of the current control limit based on observed and projected concentrations of hydrogen and ammonia representing a range of gas release scenarios. The conclusion supports the continued use of the current 6,250 ppm hydrogen control limit
Revised: April 1, 2003 |
Published: November 30, 2002