A dynamic sieve-tray model is used to investigate the effect of suddenly placing a concentrated absorber on standby by replacing the feed gas with inert gas. Model predictions show large desorption rates during the transient, resulting in a dramatic increase in gas flow rates, which leads to extremely high entrainment. The model also predicts a large pulse of solute in the vent gas and a large rise in the downcomer liquid level. The results indicate a strong possibility of design failure during the transient. We discuss methods to reduce the severity of the transient behavior.