It has been a mystery for 20 or 25 years: what is that smell that sometimes floods one corner of Ironton High School, where does it come from? Ironton City School officials will try again to find an answer.

The smell, described as a strong sewer-type odor, will be very noticeable for 15 or 20 minutes at a time before fading away. No one can predict when it will appear. It has an irregular frequency.

"It's an ongoing problem; but it's not there constantly," Superintendent Stephen Kingery said. "It was first noticed in the 1980s. It seems to to be more prevalent in the corner of the building on Heplar and Seventh streets. It seems to be affected by weather. If it's rainy, it has an adverse effect (on the situation) or if the wind is blowing in a certain direction."

A Portsmouth firm that specializes in heating system malfunctions has been called in to assess the situation. This is the latest of several attempts over the years that have been made to find out where the smell is coming from. The EPA was called in at one point. The Ironton City Health Department has assisted the school system, and a Huntington, W.Va., firm was called in a couple of years ago to investigate the smell. No one has been able to provide a positive answer.

Kingery said the irregular pattern of the odor's appearance has made it all the more difficult to determine what is causing the problem.

"We've tried to isolate the source, but its very complex and very difficult," Kingery said. "If it were a constant problem, it would be easier to identify its source. Because it comes and goes it's harder to isolate. Chances are, there are multiple sources for the smell."

Kingery said all the tests conducted over the years have shown that, while the odor is annoying, it is not toxic.