Switching the Torrance refinery from using highly toxic hydrofluoric acid to a different commercial process would cost about $103 million, concludes a new study, although the figure is disputed as too low by owner PBF Energy.

The 41-page study, commissioned by the South Coast Air Quality Management District, also noted that while such a conversion would be unprecedented in the U.S., it could be done in as little as 60 days or take six months or more.

The AQMD released the study Friday ahead of a public meeting Monday with members of two grass-roots groups that formed in the wake of a February 2015 blast at the refinery, then owned by ExxonMobil.

Officials from the U.S. Environmental Protection Agency, which is studying whether the current mandated risk-management plan understates the risk to the community, also will attend the meeting.

“EPA’s primary objective and role on Monday is to listen to the community and provide them with the opportunity to express their concerns,” spokeswoman Nahal Mogharabi said via email. “EPA is steadfast in our commitment for candid and meaningful involvement with the community and will take all concerns raised into account as we continue our comprehensive evaluation of the facility.”

Federal regulators have said a catastrophic release of HF that could have killed or injured thousands was averted only by sheer chance in wake of last year’s explosion.

That prompted local activists to demand a study on possible commercial alternatives to HF.

The AQMD banned the use of HF in Southern California in the 1990s, but that move was overturned after the industry challenged the decision in court.

Sally Hayati, president of the Torrance Refinery Action Alliance, which is pushing for another ban on the use of HF, did not respond Friday to a request for comment.

There are 48 refineries in the United States that use HF.

Four, including two in the South Bay — the other is the Valero Wilmington Refinery — use modified HF, which is supposedly safer than unmodified HF.

But experts have said that, in reality, the modified HF used in Torrance will differ little from the unmodified form in an accidental release and is likely just as dangerous.

Seven technologies used in refineries were studied, but only one uses sulfuric acid that is in widespread commercial use and is a practical alternative to HF.

Unlike HF, an accidental release of sulfuric acid “will greatly reduce the potential for an acid vapor cloud to be formed upon release to the atmosphere,” the study found.

HF is immediately dangerous to life and health in concentrations of just 30 parts per million and can travel downwind for extensive distances, the study noted.

“Experimental testing” has shown that safety systems in place such as water sprays can reduce an HF cloud by up to 80 percent, but the report found “no study” that analyzed whether that’s also true for modified HF.

By comparison, a leak of liquid sulfuric acid — which does not form a large vapor cloud — would mean almost 98 percent could be recovered.

That’s why, unlike HF, the EPA does not require a risk-management plan for plants that use the substance.

Unlike HF, “there has never been any incident outside the fence line” of a refinery involving leaking sulfuric acid, the study found.

However, as many as 1,300 truck trips a month are needed to keep a refinery supplied with sulfuric acid compared with just two to four for HF, increasing the risk of a spill during transit.

Jeffrey Dill, president of PBF’s western region, said “the report does have a number of assumptions on the cost estimate that probably do not hold up.”

He estimated that converting the plant from HF to sulfuric acid would likely cost more than $300 million.

The company said Friday it is still reviewing the report.