Analysing the grain size of volcanic ash particles might provide a quick and easy way to calculate their potential threat to human health, according to a British scientist. Volcanic ash can be a major health hazard after a volcanic eruption but assessing the potential toxic hazard of volcanic ash is a difficult and time consuming process.

Although the primary hazards of a volcanic eruption, such as pyroclastic flows, are of major concern after a volcanic eruption, secondary hazards, such as the short term and long term effects of the dust and ash ejected, are also a major problem. Volcanic ash may cause acute respiratory diseases and has the potential to cause chronic diseases, such as lung cancer. But assessing this risk can be difficult, as conventional medical studies may take months, years or even decades to conclude whether a dust is toxic or not.

What is certain, however, is that the ash cannot be harmful if the particles are too large to enter the lung. Therefore, Claire Horwell at the Institute of Hazard and Risk Research at Durham University has developed a method that allowed her to estimate the amount of fine particles in volcanic ash without needing state-of-the-art instruments.

By characterising the grain size distribution of volcanic ash after eruptions, Horwell has developed an equation for estimating the quantity of health-pertinent fractions when state-of-the-art techniques are unavailable. By focussing on techniques that allow cheap and quick assessment of the health hazards posed by volcanic emissions, Horwell hopes to provide hazard managers with a new tool to rapidly assess how bad an eruption is for the health.

'At the onset of future eruptions, local scientists can simply sieve the ash and immediately calculate the percentage of ash that is fine enough to enter the lung. This means that a preliminary assessment of the potential health hazard can be carried out in a matter of minutes rather than waiting for laboratory results. Hazard managers can then rapidly decide whether to distribute dust masks to a population or even to evacuate an area until ash fall has ceased,' explained Horwell.

Further research is needed to establish what actual health risk volcanic ash might pose. The biggest challenge, however, is bringing together scientists from across several disciplines (such as medics, mineralogists or toxicologists) to definitively determine the health risks of volcanic ash. In the meantime, Horwell's technique may help hazard managers make more informed decisions.

Edward Morgan