“A Fatal Flaw in the Consent Decree” by Jim Eninger, Ph.D.

Jim EningerTo 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.

Dramatic Large-Scale Demonstration that Sulfuric Acid Is Vastly Safer than HF for Alkylation


In 2014, there was a very large release of sulfuric acid at a refinery in Martinez, California that demonstrated its safety in the community compared to what would have happened if the refinery had used hydrogen fluoride. Before going into details of the Martinez release, first some background on the two chemicals. It is widely acknowledged in the industry that sulfuric acid alkylation is vastly safer than hydrogen fluoride (HF) with respect to offsite consequences. An additive refineries uses in a failed attempt to make HF safer is at such a low level it hardly makes a difference.

Sulfuric acid is vastly safer because its molecules are strongly bound in the liquid state. Even at elevated  temperature, there is no tendency for them to go airborne as an aerosol or vapor. One measure of sulfuric acid’s extremely low volatility is its high boiling point of 639F. Sulfuric acid in a beaker placed in a kitchen oven at 500F will remain as a liquid and not boil. Compare this to HF, whose molecules are only weakly bound in the liquid state. Considered a “fuming liquid,” HF boils at 67F. An open beaker at room temperature on the kitchen counter will spontaneously spew a white vaporous cloud. Another measure of volatility is vapor pressure. At room temperature, HF’s vapor pressure is a million times higher than sulfuric acid’s.

Quest Consultants’ Summary chart for 36 releases of sulfuric acid in the 1991 field-scale test series. Virtually all of the sulfuric acid released was collected on the floor of the test cell.

Definitive field-scale experiments on the release of sulfuric acid from an alkylation unit were conducted in 1991 by Quest Consultants in Oklahoma and documented in Sulfuric Acid Release Report. Thirty-six releases of sulfuric acid — alone and mixed with hydrocarbons — were conducted. In every case, virtually all of the released sulfuric acid was collected on the floor of the test cell downstream of the release.

Quest Consultants repeated the experiments in 1993 with hydrogen fluoride. In their paper Effectiveness of Mitigation Systems in Reducing Hazards of Hydrogen Fluoride Leaks, Quest’s assessment is that when mixed with hydrocarbons, 100% of the hydrogen fluoride will go airborne, even with 50% sulfolane added to the HF to suppress its volatility.

The United States Environmental Protection Agency (EPA) requires facilities that use extremely hazardous substances to develop a Risk Management Plan (RMP). Hydrogen fluoride is on the list of extremely hazardous substances that require one. Sulfuric acid, so long as it’s not mixed with sulfur trioxide, which makes it fume, is not on the list. Thus the EPA explicitly acknowledges the stark difference in the threat to the community between sulfuric acid and HF.

The 2014 Sulfuric Acid Release at the Tesoro Refinery in Martinez CA

Loss of containment, from a tubing separation (yellow oval) after the valve (red square) was opened, released 84,000 pounds of sulfuric acid at the Tesoro Refinery in Martinez, California. There were no offsite consequences.

The U.S. Chemical Safety Board (CSB) reported on an accidental release of 84,000 pounds of sulfuric acid over two-and-a-half hours from an alkylation-unit settler tank at the Tesoro Refinery in Martinez, California, on February 12, 2014. The release was onto the refinery grounds and into a process sewer system. There was no vapor cloud or offsite consequences to the community. The spill burned two workers, who were transported to the nearest hospital burn unit by helicopter. They survived and returned to work after five months.

A Modified Hydrofluoric Acid (MHF) release of this magnitude would have had cataclysmic consequences not only for refinery workers, but also for the surrounding community. A ground-hugging toxic cloud would be lethal for more than eight miles downwind. (For comparison, there are 50,000 pounds of MHF in one Torrance refinery settler tank.) This full-scale incident is further dramatic evidence that sulfuric acid alkylation is vastly safer than MHF alkylation, contrary to the claims of Exxon-Mobil and the Torrance Refining Company.

In addition to sulfuric acid, there are two other alkylation processes commercially available: Solid-Acid and Ionic-Liquid Alkylation.


“Developments in the debate over hydrofluoric acid” – Daily Breeze


Nearly 300 residents march in protest to the PBF Energy refinery in Torrance on Saturday, Feb 17, 2018. It has been three years since the refinery explosion rocked the neighborhood and now residents are calling for a ban on the use of hydrofluoric acid at the refinery. (Photo by Scott Varley, Contributor)

“When the Torrance refinery exploded in February 2015, showering residential neighborhoods with industrial ash, the event ignited a three-year public debate over hydrofluoric acid that continues to this day.

“Here are the major developments we’ve seen since then:

Meet the TRAA Science Advisory Panel

TRAAThe TRAA Science Advisory Panel is an ad hoc volunteer group of eight local scientists and engineers with extensive relevant experience with highly toxic chemicals including hydrogen fluoride:

Charles Clendening, Ph.D.
CharlieClendeningDr. Charles Clendening completed his undergraduate work at the Case Institute of Technology in 1968, and earned his doctorate in physics from Cornell University in 1974. He has worked in high energy laser development for over thirty years, first for the United States Air Force and then for TRW, which later became Northrop Grumman. He is a past recipient of two TRW Chairman Awards for Innovation, and a TRW Distinguished Patent award. Dr. Clendening served as Chief Scientist at Northrop Grumman for the Air Force’s Airborne Laser Program and won the 2009 AIAA Plasmadynamics and Lasers Award. Charles resides in Torrance.

James Eninger, Ph.D., Editor of the TRAA Science Advisory Panel Blog
Jim EningerDr. James Eninger retired in 2005 after a 33-year career at TRW in Redondo Beach. At TRW, he was a Senior Staff Engineer and Project Manager of programs that included safely dealing with hydrogen fluoride in the exhaust of high-energy chemical lasers. He holds a B.S.M.E. and an M.S. & Ph.D. in Aeronautics and Astronautics from Stanford University, specializing in Fluid Mechanics and Physical Gasdynamics. He resides in Torrance and is a past member of the Torrance Refining Company Community Advisory Panel.

Continue reading “Meet the TRAA Science Advisory Panel”