Toxicology of hydrogen fluoride in relation to major accident hazards

A major industrial accident involving the release of hydrogen fluoride has the potential to cause serious injury and possibly death in the surrounding human population. Given the potential for such serious and large-scale effects, there is a need for scientifically based risk assessments for determining appropriate on-site risk control measures, as well as for informing off-site emergency plans and land-use development decisions. Within Great Britain, the Health and Safety Executive (HSE) has the statutory responsibility for providing land-use planning advice in the vicinity of major accident hazard sites. The advice is based on quantified assessment of the individual risk of exposure to a specified amount of the toxic substance. Among other things this requires a consistent, reliable, and transparent understanding of the major hazard toxicology of the substance concerned. An assessment of the toxicology of hydrogen fluoride in relation to major accident hazards, based on conventional inhalation toxicity studies, was published by HSE in 1993. Recently, studies have been reported in which rats inhaled hydrogen fluoride via a mouthpiece attached to an endotracheal cannula. HSE has explored the use of this "mouth-breathing" rat model as a possible basis for human health risk assessment for hydrogen fluoride in the context of major accident hazards. A number of uncertainties in the use of this animal model have been identified that warrant caution in the use of this model for regulatory purposes. Overall, the results from the "mouth-breathing" rat model did not lead to a change in the HSE assessment of hydrogen fluoride, which remains based on experimental data obtained following "mainstream" toxicological practices.