It was a surprise inspection at more than a dozen Kentucky mines.
The federal government announced Wednesday it surprised 14 mines in Kentucky this past weekend. The mines were known to have problems with methane, coal dust and ventilation.
Investigators believe methane gas and coal dust caused this month's blast at a West Virginia mine that killed 29.
In all, 275 inspectors raided mines across the country.
The government has not said how many citations were issued.