Eruption may hurt people with breathing problems: WHO

GENEVA (Reuters) - The eruption of an Icelandic volcanic that has paralyzed air traffic in much of Europe could also harm people with breathing problems, the World Health Organization said on Friday.

The U.N. health agency said the fine particles in the ash cloud were not harmful so long as they remained in the upper atmosphere, but could be more problematic if they fell to earth.

About a quarter of the ash particles were believed to be less than 10 microns in size, the most dangerous because they could penetrate deeper in the lungs, the WHO said in a statement.

"People with chronic respiratory conditions like asthma, emphysema or bronchitis may be more susceptible to irritation if ash is in the lower atmosphere in high concentrations," it said.

"If people are outside and notice irritation in their throat and lungs, a runny nose or itchy eyes, they should return indoors and limit their outdoor activities."

A British expert on respiratory disease said ash falling on Britain was unlikely to cause much harm.

"There is a massive diluting effect in the atmosphere as it gets dispersed by wind which means the amount reaching land is very small," Ken Donaldson, professor of respiratory toxicology at the University of Edinburgh, told Reuters.

The WHO said people with asthma or respiratory problems should take "normal precautions" such as those on days with high air pollution, for instance avoiding strenuous exercise.

Donaldson agreed that people with lung disease should stay indoors if there was a measurable change in particle levels. The eruption which began on Wednesday has caused chaos in European air travel not seen since the September 11 attacks in the United States nine years ago.

(WHO paper on air pollution is at r.reuters.com/suz97j )

(Additional reporting by Nina Chestney in London; editing by Andrew Dobbie)