U.S. CSB illustration
Today’s release of the U.S. Chemical Safety Board report on the Freedom Industries chemical spill might seem a little anticlimactic, given how much we’ve learned about the spill and the ensuing water crisis from various other investigations. But — despite the lack of strong reform recommendations (see previous post about what I was looking for) in the draft report made public this morning — we have learned a few new interesting things, thanks to the CSB’s hardworking and expert investigators.
Here are six things the jumped out at me:
1 — How did the stuff get out of the tank — While the CSB had discussed several times before (see here and here) its theory for what happened, this draft report offers more details and makes a more compelling argument that the leak from Tank 396 was caused by what’s called “pitting corrosion” that created two holes (approximately 0.75 and 0.4 inches in diameter). The draft report explains:
Corrosion is an electrochemical reaction between a metal alloy and its environment, and can lead to degradation of structures. It can attack materials uniformly, degrading metals at an even rate across the surface, known as general corrosion. However, pitting corrosion is confined to a point or small area that takes the form of cavities, some of which can perforate through the thickness of the metal. Pitting corrosion can be difficult to detect because it is highly localized and the rate at which the depth of the pit increases is often greater than the width.
In this instance:
CSB retained a tank expert to conduct a corrosion rate analysis based on the observed pitting and the data available during the incident investigation. Although it was recognized that the corrosion rates were variable and unknown, the best reasonable assumption at the time of the study was that the corrosion rate was constant over the life of tank 396 at 12.3 mils per year (mpy, or thousandths of an inch per year, a common designation for corrosion rate) with the corrosion rate bounded between 10 and 15 mpy.
2 — How long did the spill last — While the CSB team says it’s impossible to know the exact mechanism for the leak from the tank or how long the leak was going on, their draft report does offer and estimate — 24 hours — in this section, which describes one of the ways that those two small holes in the tank might have ended up leaking:
A frost heaving effect, caused by extremely low temperatures, may have contributed to the sudden release of MCHM from the bottom of tank 396. The severe cold weather in early January 2014, referred to as a “polar vortex,” brought bitterly cold temperatures to the Midwest, South and much of the eastern and northeastern United States. The Charleston area set a new minimum temperature record of -3°F just 2 days before leak discovery.
Frost heaving occurs when the freezing of water-saturated soil causes the deformation and upward thrust of the ground surface. When water freezes, it expands. This expansion is often referred to as frost jacking or frost heaving. Freezing weather prevalent at that time of year caused the frost heaving of the soil underneath the tank, which possibly led to the flexure or movement of the tank bottom in the vicinity of the holes. The movement provided enough bending on the bottom plates to possibly dislodge the PVA material or other debris blocking flow through the bottom holes.
Once the material became dislodged, the pressure from the filled MCHM tank may have enabled the sudden gushing flow of liquid from the tank bottom, which continued at a maximum flow rate of about 11.5 gallons per minute (GPM). Approximately 10,000 gallons of MCHM had leaked from tank 396 prior to leak discovery. Based on a CSB commissioned calculation of the flow rate, a sudden tank leak would have resulted in a flow loss of 1 inch per 17 minutes. At this rate, the tank contents would have leaked through the tank holes and into the ground for approximately 24 hours (1 day) before the leak was detected.
CSB concluded that tank 396 failed due to corrosion, which ultimately resulted from poor tank maintenance and inspections not in accordance with acceptable industry standards and best practices. Despite the freezing weather condition, which may have played a role in initiating the tank leak, the lack of rigorous tank inspections by ERT and Freedom directly contributed to the MCHM leak.