For large outdoor events that host vendors, has anyone ever run into the problem or been posed with issues regarding carbon monoxide with vendors using generators?

Does anyone have any specifications on vendors for placement - "x" amount of vendor in "x" amount of space - to prohibit this problem?

Does anyone not allow vendors to utilize generators at events, and requires them to either be 1) self-sufficient or 2) provide power for them?

Any help or other contacts you have that could have some feedback in this area would be great!

Thanks!