The August 10, 2007 incident at the Gibson operation in Evansville, Indiana involved two Frontier-Kemper Constructors contract workers and one retired employee: Christopher Todd Richardson, 38, Jarred Ashmore, 23, and Daniel McFadden, 66.

The three were touring the site when a basket carrying them tipped and they fell 550 feet to the bottom of the airshaft.

Five others were working at the bottom of the shaft at the time of the incident but were not injured.

“A nylon sling and shackle attached to the bottom of the sinking bucket lodged into a shaft collar door, thereby tipping the sinking bucket," MSHA noted of the accident in its investigation released this week.

“At the time of the accident, the shaft had not yet been connected to the underground mine workings."

The agency identified a trio of root causes that played a role in the triple fatality, each of which cited an insufficient or missing procedure, policy or management system in place that complied with federal regulations for safe mining.

First, MSHA found that a nylon sling and shackle utilised for lowering supplies were attached to the bucket while it transported the three.

“The lack of an effective administrative control to assure that extraneous objects were not attached to the bucket when transporting persons contributed to the loss of control of the hoist," MSHA said, adding that it has requested the contractors revise their shaft sinking plan to reflect such.

Additionally, the agency found that the mine's toplander was not present at the duty station to observe the mantrip as it travelled through the collar doors, again a shortfall in the operation's policies and procedures. An amendment to the shaft sinking plan was also made regarding this to bring policies into compliance.

“The independent contractor had no policy in place requiring the use of fall protection when personnel are transported in the sinking bucket," MSHA said of the third root cause.

“The independent contractor’s approved shaft sinking plan has been revised to include the use of fall protection when persons are transported in the sinking bucket."

According to statistics, the non-fatal days lost (NFDL) injury incidence rate for the Gibson Mine was 2.05 in 2006, versus a national average of 4.90, and Frontier-Kemper's NFDL for the same year was 10.90 compared to a national rate of 2.43.

Gibson County Coal is a subsidiary of Alliance Coal.