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HF leaks not a coincidence

11 August 2009

The safety authorities in the US are being kept very busy at present investigating a series of refinery leaks involving hydrogen fluoride (HF). Three incidents are currently under investigation; all involve petrochemical units operated by leading US refiners.

Citgo refinery, Texas
Citgo refinery, Texas

HF is a particularly noxious chemical which is used in the refinery as a catalyst in the alkylation process. Because it has exceptional antiknock properties and is clean burning the high octane alkylate produced by the process is a premium blending stock in the production of automotive fuel. Alkylate is also a key component of aviation fuels. The reaction, which takes place in the presence of a strong acid catalyst is carried out at mild temperatures up to 30°C in a two-phase reaction.

When inhaled, HF is a severe pulmonary irritant and as a liquid – known as hydrofluoric acid – it is corrosive to the skin and eyes.

Inhalation can cause fluid accumulation in the lungs known medically as pulmonary edema. Exposure to high concentrations of the vapours of hydrofluoric acid characteristically results in inflammation of the upper respiratory system. It is estimated that the lowest lethal concentration for a five minute human exposure to hydrogen fluoride is in the range of 50 to 250 ppm. This is not a high concentration so it is not surprising that the US Chemical Safety Boards has mobilised its investigation teams to investigate the three refineries.

A four-member team has been deployed to the ExxonMobil refinery in Joliet, Illinois where a mixture of propane and HF was accidentally released on August 6th. The problem occurred just after noon in the vicinity of a pump in the refinery's alkylation unit, which uses HF as a catalyst. The leak did not ignite, but one operator was transported to the hospital suffering from what were described as serious, HF-related chemical burns; he was initially reported in critical condition. A second operator was examined at the hospital and released. The unit’s water deluge system, which is designed to contain airborne HF releases, was activated and the alkylation unit was shut down. Refinery personnel were instructed to shelter in place.

CSB teams have also attended incidents at alkylation units at Sunoco’s refinery in Philadelphia, Pennsylvania, in March and at the CITGO refinery in Corpus Christi, Texas in July.

In the CITGO refinery incident, one worker was airlifted to a burn centre in San Antonio as a result of the accident at the 163,000 barrel per day refinery. The alkylation unit was reported to be shut down.

As well as being widely used in the petrochemical industry, HF is a component of many super acids. It is the principal industrial source of fluorine, often in the aqueous form as hydrofluoric acid, and thus is the precursor to many important compounds including pharmaceuticals and polymers such as Teflon. All in all, HF is a widely used compound.

CSB Chairman John Bresland stated: "We are concerned about the three apparent releases of hydrogen fluoride from refinery alkylation units in Pennsylvania, Texas, and now Illinois that have been reported since March 2009. Because of its high toxicity, any loss of primary containment for hydrogen fluoride is a serious matter."

No wonder that CSB wants to get the bottom of these leaks of noxious gas, which surely cannot be just a coincidence.

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