This is a west country/rural word of old. It means a burning smell or a smell so bad you think you can see it.
My mother, having been born on the Mendips in 1932 uses it alot.
My late mother who came from Cheltenham used 'smeech' to mean 'over-heating fat', i.e. a combination of 'smoke' and 'steam' so my brother and I still thought it was only used in our family as we'd never come across anyone who knew it. but now we know better.
When I arrived at a pancake party I exclaimed 'What a smeech and everyonesaid 'What?''