Quantifying the effectiveness of impaction by using physical objects as a method for mitigating accidental releases of liquid ammonia and sulfur dioxide.

Previous studies on mitigating accidental releases of toxic liquefied gases have mainly focused on the use of water sprays with different shapes. There have been no experimental studies on impaction, in which the released material is impacted against an object and confined to maintain it in the liquid state. To assess the effectiveness of impaction, readily available objects such as metal plates, a fire jacket mounted on a ladder, and a pipe were placed in front of controlled releases (with flow rates of 0.1 and 0.7 kg/s) of sulfur dioxide (SO2) and ammonia (NH3) in an intermediate-scale field trial. Digital scales were used to measure the released and impacted amounts of chemicals, while gas concentrations downwind of the release point were measured with gas analyzers and compared to concentrations determined without impaction. Impaction using a solid object placed close to the release nozzle allowed up to 84% of the released mass to be recovered and attenuated downwind gas concentrations by as much as 85%. Increasing the distance between the object and the nozzle reduced the mass recovery, but it remained above 50%. There were no differences in recovery between releases of SO2 and NH3, indicating that the impaction method is applicable to various kinds of liquefied gases. This study highlights the potential usefulness of impaction as an initial measure to be used in an emergency that can be implemented more simply and with less preparation time than established mitigation methods such as those involving water curtains and foam covering.