A fatal explosion occurred in a rural oil production field in Raleigh, Mississippi on June 5, 2006. Three contractor workers died and a fourth was seriously injured. The explosion is caused by a flammable vapor inside two tanks. Welding activities on a nearby tank ignited the explosion. The incident occurred at about 8:30 a.m. on June 5, 2006, when Stringer's Oilfield Services contract workers were installing pipe from two production tanks to a third. Welding sparks ignited flammable vapor escaping from an open-ended pipe about four feet from the contractors' welding activity on tank 4. The three workers standing atop the tanks were thrown by the force of the explosion and fell to the ground and died. The welder was also thrown off the ladder, but he was wearing a safety harness that prevented him from falling to the ground and was seriously injured. On the day of the incident, the four workers were completing the piping connection between the tanks. To connect the piping from tank 3 to tank 4, the workers had to weld a pipe fitting onto the side of, and a few inches below the top of, tank 4. To prepare for the welding operation, they removed the access hatch at the base of tank 4 and entered the tank to remove the crude oil residue. Then they flushed the tank with fresh water and allowed hydrocarbon vapor to evaporate for several days. They did not clean out or purge tanks 2 and 3. On the day of the incident, the welder inserted a lit oxy-acetylene welding torch into the hatch and then into the open nozzle on the opposite side of tank 4 to verify that all flammable vapor was removed from the tank before welding began. The welder was not aware that this act, called "flashing" the tank, was an unsafe practice. Almost immediately after the welder started welding, flammable hydrocarbon vapor venting from the open- ended pipe that was attached to tank 3 ignited. The fire, which immediately flashed back into tank 3, spread through the overflow connecting pipe from tank 3 to tank 2, causing tank 2 to explode. More Details are available at: http://www.csb.gov/partridge-raleigh-oilfield-explosion-and-fire/. Investigate and analyze the above accident from Human factor perspective. How safety of the above activities could be enhanced. Demonstrate using quantitative human reliability approach-SLIM methodology. [Hint: Use SLIM methodology to calculate human error probability in causing above incident, subsequently suggest safety measure, and then recalculate overall human error probability with additional safety measure]