Massey Energy has defended its safety record saying that air samples did not show high levels of explosive gases before the West Virginia coal mine explosion that killed 29 people this month.

Massey Energy board director Stanley Suboleski acknowledged that the Mine Safety and Health Administration (MSHA) had issued eight citations to the mine this year for violating pre-shift examination rules but said federal inspectors found no major issues with the Upper Big Branch mine a few days before the 5 April explosion.

He also said they found no hazards on the day of the explosion, according to

Suboleski said the MSHA required changes to the mine’s ventilation system in September that would have significantly reduced the amount of fresh air reaching the portion of the mine where work was taking place.

MSHA spokeswoman Amy Louviere said the MSHA’s accident investigation team will thoroughly examine the mine’s ventilation plan and any changes required by the MSHA in order to determine the volume of air flow.

A Senate panel will examine legislative solutions in the wake of the Upper Big Branch mine explosion.