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The material aboard a truck that blew up in Spanish Fork Canyon on Wednesday was made at plant in Spanish Fork that pumps out more than 4 million pounds of explosives a year.

Known as a pentolite explosive, the deadly substance is a mixture of TNT and PETN, a powerful explosive sometimes used in land mines and detonation cords.

"One of the benefits is that it's extremely impact-sensitive. But obviously, as with all explosives, it has a sensitivity to flame and extreme heat," said Peter Barnett, general manager of the Ensign-Bickford Co. plant, which has sat at the canyon's mouth since 1940.

On Wednesday, the truck was speeding uphill under a load of pentolite weighing almost 18 tons. The material had been formed into cast boosters - seismic charges used for oil and gas exploration. Cast boosters are inserted in bore holes drilled into promising geologic formations. Scientists use the resulting blast waves to create three-dimensional pictures of underground rock structures that may hold hydrocarbons.

To make cast boosters, Ensign-Bickford employees melt a mixture of TNT and PETN, one of the strongest known high explosives. PETN - pentaerythritol tetranitrate - is used in some land mines and as the explosive core of detonation cord.

The mixture is poured into orange plastic canisters that are loaded onto flatbed trucks and shipped to customers across North America. On Wednesday, the truck operated by R&R Trucking Inc. of Joplin, Mo., left the plant at about 1:10 p.m., bound for the Oklahoma oil fields. On board were hundreds of canisters in two sizes, one weighing 5.5 pounds, the other 2.5 pounds.

At around 1:35 p.m., a security guard heard a radio report that the truck had flipped over and the pentolite had exploded.

"We were pretty surprised. We were very shocked," Barnett said.

Barnett said R&R's chief executive officer, Daryl Deel, was coming to Utah on Wednesday to talk to the driver and his partner. Deal and other R&R executives did not return telephone calls seeking comment.

"I'm assuming they are going to handle this professionally. Obviously, this is something we will consider seriously. But it's premature for me to say one way or another" whether Ensign-Bickford will continue to ship explosives on R&R trucks.

The canisters were purchased by Buckley Powder Co., an Englewood, Colo.-based explosives distributor with operations in Oklahoma, Barnett said.

Buckley President Steve Buckley acknowledged his company buys explosives from the Ensign-Bickford plant. But he said he didn't know if the load aboard the truck belonged to Buckley.

"We don't take possession until they are dropped off," Buckley said. "I have not been told that it was going to us."

Ensign-Bickford's headquarters is in Simsbury, Conn. Its western sales and seismic exploration sales offices are on Highway 6 in Spanish Fork. The plant employs about 100 people. It was built to serve Utah's mining industry, but now ships to buyers as far away as Canada.

"We probably make at least 4 million pounds of explosives a year. Four to 5 million is a typical year," Bennett said.

He said the plant makes PETN, while the TNT is salvaged from decommissioned NATO explosives. Most of it is imported from Europe.

"It's bought from an intermediary. We get the material in a cardboard box," Bennett said.

R&R reportedly is the second-biggest munitions hauler in the trucking industry, with fleet operations across the United States and Canada.

About half of the company's revenues comes from handling arms, ammunition and explosives for the Department of Defense, according to Drivers magazine.

The rest is earned by transporting explosives for the construction and mining industries and low-level radioactive waste for other clients.