THE company which has been decontaminating heavily polluted land in York has sought to reassure residents that their health has not been put at risk.

Encia Consulting Ltd has told people living near the former gasworks site at Heworth Green that there is a big difference between odour nuisance and health risk.

It also claimed that the dilution in the atmosphere of hazardous vapours meant that they became "insignificant" away from the site.

Mark Perrin, the company's regional director, was responding to a series of concerns raised at a recent public meeting over the decontamination of the site, prior to housing development.

Residents said they feared the work had exposed them to cancer-causing chemicals.

One resident, Alastair Robinson, has since said that he left his home with his family in the middle of the night to escape odours, ending up sleeping in their car in a lay-by.

Mr Perrin has written to more than 100 local residents to alleviate concerns, claiming that the "fundamental issue seems to be one of communication".

He accepted that on occasions, information about forthcoming site operations posted on a notice board near the entrance had been out of date. But he said the use of the notice board was being revived and it would be kept updated.

Now a lengthy document had been posted on it to answer many of the concerns.

He said in the document that there had been extensive boundary monitoring for potentially hazardous dust and vapours during the excavation of contaminated soils.

Answering queries about whether odours associated with recent drilling operations posed a risk to health, he said the volume of vapour arising from a borehole was far less than from large earthworks.

He conceded there had been no monitoring during a recent drilling operation.

But if it had been (based on previous experience on similar remediation schemes, and at other boreholes drilled on this site which were monitored) it would have confirmed that dilution in atmosphere is huge, and concentrations of vapour are insignificant within a few metres of the borehole opening."

Referring to the difference between odour nuisance and health risk, he said the human nose was a "very sensitive receptor, able to detect tiny concentrations of many vapours".

He said drilling staff had been kitted out in protective clothing because they were working directly above the borehole mouth, where concentrations of hazardous vapours were highest. "Only people within ten metres of the borehole require such protective equipment."

Mr Perrin added that it was important to keep perceptions of the risks posed in context. One of the chemicals involved was benzene - but this was present in petrol, and most people were therefore exposed to vapours containing it on a fairly regular basis.

Updated: 10:05 Thursday, November 25, 2004