State regulators have fined Mammoth Mountain Ski Area almost $50,000 for several job safety violations relating to the deaths of three ski patrol members in April this year. The men were trying to fence off a toxic volcanic fumarole near a piste, when the snow collapsed and two of them fell in. ...The third patrol member died while trying to rescue his colleagues. All three died from lack of oxygen due to the presence of carbon dioxide gas. Seven more patrol members were seriously injured due to the carbon dioxide gas spewing from the vent.
The California Department of Industrial Relations’ Division of Occupational Safety and Health, the state's workplace safety enforcer, found that the catastrophic event might not have occurred if standard practices had been followed.
http://snowheads.com/ski-forum/viewtopic.php?p=306163&highlight=mammoth#306163