The monthly inspections, which began in April 2010 following the explosion at the Upper Big Branch Mine, involve mines that merit increased agency attention and enforcement due to their poor compliance history. These matters include: high numbers of violations or closure orders; frequent hazard complaints or hotline calls; plan compliance issues; inadequate workplace examinations; a high number of accidents, injuries or illnesses; fatalities; adverse conditions, such as increased methane liberation, faulty roof conditions, inadequate ventilation and respirable dust.