Amateur winemakers suffocate from fumes of stomped grapes.

From the Daily Mail:

Two amateur French wine makers have died after they were suffocated by the fumes from the grapes they were treading with their bare feet.

The victims had volunteered to help a friend make wine at his vineyard in the northern Ardeche region and had climbed into the six-foot wide vat to begin the traditional process of extracting the juice from the grapes.

But police believe Daniel Moulin, 48, and 50-year-old Gerard Dachis were overcome by carbon dioxide fumes that are given off during fermentation and collapsed.