Kenneth P. Katen, a federal mine safety official during the Reagan administration, said the groups would work together in the Sago investigation but release separate reports.
Sago's history of federal health and safety violations, which nearly tripled from 2004 to 2005, would immediately draw scrutiny, said J. Davitt McAteer, who was assistant Labor secretary for mine safety during the Clinton administration.
"The number of violations was increasing, not decreasing" at Sago, McAteer said. "The severity and importance of the violations were increasing. We're talking about issues such as roof control, ventilation, accumulation of combustible material."
Two areas that particularly troubled federal inspectors last year were the mine's ventilation plans and its placement of methane monitors. Katen and other mine safety experts say reports that the mine explosion originated in an unused section of shaft raise concerns that explosive methane gas might have built up.
The risk of methane-fueled explosions has been cited before as a serious concern in abandoned mineshaft sections, Katen noted.
Mining companies typically send inspectors to take methane readings from cinderblock seals that block off unused mine chambers.
But such measurements, while useful for checking methane near the seals, do not reliably give a complete picture of what's happening behind the seals, Katen said. Methane levels can build farther inside the chambers. When barometric pressures rise, the gas can become volatile.
"All you would need is an igniter," Katen said. "We've had situations where a simple falling stone causes a methane explosion."