To get an idea how dangerous hydrogen fluoride is, consider just half an ounce — one tablespoon or ⅓ of a whiskey jigger — released into a large 10×10 meter conference room with a 3-meter ceiling (33′×33′×10′). A simple calculation, which a high-school chemistry student could easily verify, shows that the room would be raised above the Emergency Response Planning Guidelines’ ERPG-3 level of 50 parts per million, resulting in life-threatening health effects. Now consider that each of the two alkylation-unit settler tanks at the Torrance Refinery contains up to 50,000 lbs of hydrogen fluoride, or 1.6 million of the 1/2-oz samples. That’s nearly twice the population of the entire South Bay. It’s important to note that MHF is just as toxic as HF.
The TRAA Science Advisory Panel made an important discovery about toxicity of sulfuric acid that reveals a fatal flaw in the Consent Decree, which settled the lawsuit between the City of Torrance and Mobil. The Consent Decree was modified in the mid-1990s to allow MHF if Mobil’s Quantitative Risk Assessment (QRA) could show MHF was no more dangerous than sulfuric acid. However, QRAs are notoriously infamous for wildly varying over orders of magnitude in predictions depending on the numerous assumptions made. Mobil’s QRA is kept from public disclosure by claims of “proprietary and sensitive” information.
It’s a mystery to the public that defies common sense how Mobil’s QRA could predict very-low-volatility sulfuric acid, which doesn’t require an EPA Risk Management Plan, could be as dangerous as highly volatile hydrofluoric acid. And it is especially troubling that Quest Consultant’s excellent 1995 paper, Effectiveness of Mitigation Systems in Reducing Hazards of Hydrogen Fluoride Leaks by David W. Johnson and John B. Cornwell, which directly contradicts Mobil’s assertion that MHF is as safe as sulfuric acid, was not mentioned in reports to the Court by the Safety Advisor, who was handpicked by Mobil.
Johnson and Cornwell’s assessment was that for the major release they considered, the worst-case toxic distance (to ERPG-3) was 300 feet for sulfuric acid, compared to 14,000 feet (2.7 miles) for MHF with 50 wt% sulfolane additive (see Table 2 — Acid Dispersion Analysis for Alkylation Unit in the paper referenced above). Note that Quest’s 1995 assessment of sulfuric acid’s behavior was confirmed in the 84,000-pound sulfuric-acid release from an alkylation-unit settler tank at the Tesoro Refinery in Martinez, California on February 12, 2014. There was no offsite consequence to the community.
We do know a thing or two about Mobil’s QRA from the Consent Decree’s Safety Advisor in his 1995 Report, where he writes (page V-36),
“The quantitative risk comparison uses ERPG-3s, which can be regarded as thresholds for potentially fatal effects, as a basis for comparison of the two substances. The Safety Advisor considers that this is a reasonable choice because the ERPGs have been carefully developed and peer reviewed”.
We discovered that the ERPG-3 used in Mobil’s Quantitative Risk Assessment overstates the toxicity of sulfuric acid by a factor of four. The 1995 Safety Advisor Report shows that 30 mg/m3 for the EPRG-3 value for sulfuric acid was used in Mobil’s QRA (see Table V.4 on page v-36). Today’s accepted value is 120 mg/m3. An unbiased competent engineer would immediately recognize that such a large change in a primary parameter invalidates Mobil’s QRA. Thus, there is no legal basis for Mobil Refining Company to be using MHF.
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