Inerting to make petroleum tanks safe for removal
Because of the harsh atmospheres – such as high LELs, or low oxygen and high carbon dioxide – in empty USTs, failure of tank atmosphere monitoring equipment is always a possibility. But with the right equipment, problem solving and precautions, challenges are avoidable.
However, more extreme hot or cold weather conditions present some obstacles that can’t be avoided. For example, vapors become denser in hotter temperatures, tend to accumulate in low places and don’t flow out of vents as quickly. To combat this, CGRS technicians may add a greater quantity of dry ice or, in some cases, small amounts of warm water or an environmentally friendly, non-toxic cleaning product. This technique, called encapsulation, “suppresses hydrocarbon molecules and renders flammable liquids and vapors nonflammable,” according to Recommended Practices for the Closure of Underground Storage Tank (PEI, 2020, p. 12). Other methods may include simply shading the UST from direct sunlight, when possible.
Similarly, during the winter, temperatures may be too cold for dry ice to go through the process of sublimation and it may remain a solid, making it near impossible to inert a tank. The best way to avoid this issue is to schedule tank removals when temperatures are well above freezing.