The project under construction was the Bruce R. Watkins Memorial Drive; more specifically, an area near the intersection of U.S. Highway 71 and 87th Street in Kansas City, Missouri. The highway project required the moving of substantial quantities of limestone that was routinely broken up by drilling holes into the rock, placing a blasting agent in the holes, and then detonating it. Kansas City has large quantities of limestone throughout the area, and there were in fact several limestone quarry operations going on.
Professionals who deal with blasting have indicated that high explosives such as dynamite are too expensive to use as the routine blasting material. There also is greater instability with high explosives as opposed to blasting agents.
One of the most common blasting agents used throughout the United States is a mixture of ammonium nitrate with fuel oil. The common name for the product is ANFO, although it can be marketed under other names by individual manufacturers. If a more powerful explosive is needed, aluminum dust or pellets can be blended in. This creates a "hotter" load. Reportedly, of the approximately 50,500 pounds of ammonium nitrate/fuel oil mixture involved in these explosions, 47,000 pounds contained the mixture of 5 percent aluminum.
Personnel at the construction site indicated they used between 10,000 and 16,000 pounds a day on the average. The material came in 30-pound socks that were placed into the drilled holes, then detonated with a device such as a blasting cap.
The material was divided between two trailers/magazines less than 100 feet apart. There were no built up berms or barriers between the trailers. Section 55.218, Table of Distances for Storage of Explosive Materials in the ATF Explosives Law and Regulation Handbook, states that with 25,000 to 30,000 pounds of explosives there must be a distance of 224 feet between trailers/magazines if unbarricaded.
The trailers/magazines were less than 600 feet from Highway 71 and less than 350 feet from 87th Street. There was a berm between the trailers/magazines and Highway 71. The minimal distance from Highway 71 should have been 933 feet.
There was not a berm between the trailers/magazines and 87th Street. Elevation of the land is such that the trailers/magazines were above most of the street. Traffic on this street is less than on Highway 71. If it was considered a class A to D highway, the minimal distance should have been 680 feet. NFPA 495, Table of Distances for Storage of Explosives, generally agrees with the ATF Handbook distances.
The Kansas City Office of the Bureau of Alcohol, Tobacco and Firearms (ATF) described ANFO as one of the safest blasting materials in use. Its volatility comes about when it is enclosed or is in a "compressed area." 2 If it then ignites, it has substantial explosive capabilities. This may explain the delayed ignition of the second trailer. The stability of the ANFO may have kept it from exploding from a shockwave and flying debris, but tires and wooden parts of the trailer/magazine may have ignited, eventually causing the ensuing explosion.
The Kansas City Office of the Bureau of Alcohol, Tobacco and Firearms (ATF) described ANFO as one of the safest blasting materials in use. Its volatility comes about when it is enclosed or is in a "compressed area." 2 If it then ignites, it has substantial explosive capabilities. This may explain the delayed ignition of the second trailer. The stability of the ANFO may have kept it from exploding from a shockwave and flying debris, but tires and wooden parts of the trailer/magazine may have ignited, eventually causing the ensuing explosion.
The permanently attached, foldable placards on the back of the trailer were in the "up" (covered) position. It is standard industry policy, according to the president of a blasting mixture company, to place placards down when the trailers leave the plant loaded, and to turn them up when they park on a site. Having placards covered or removed on site would not have been in violation of existing ATF regulations.
The separation distances were in violation of ATF regulations.
Also on the site were two yellow high-explosive magazines used to. store dynamite and blasting caps. It is possible that the crews on the scene saw these other magazines and thought they were the "explosives" referred to by the dispatcher. However, they did continue to question the contents of the trailer. One of the firefighter's bodies was found in the vicinity of one of these containers with a portable hand radio nearby. It is thought possible (but is again speculation) that he was scouting these magazines when the explosion occurred.
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