Wednesday was a blast, but today the hard work begins.

And there will be a test.

DRC/Gary Payne

A camping trailer explodes into pieces as part of an explosives and post-blast investigator school put on by the Denton Fire Marshal’s Office in conjunction with the Bureau of Alcohol, Tobacco, Firearms and Explosives on Wednesday in Denton. Attendees of the class learn about different types of explosives and how to identify them after they have been detonated.

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Members of a class on explosives and post-blast investigation met at the city landfill to watch the effects of different explosives. They will return today to investigate what is left from each explosion and convince teachers that they learned from what they saw.

“It’s all still there,” explained Tom Crowley, information officer with the Bureau of Alcohol, Tobacco, Firearms and Explosives. “It’s just in tiny pieces.”

The ATF taught the course in cooperation with the Denton Fire Marshal’s Office. Fire Marshal Rick Jones said completion of the week-long course is one step in certification as a bomb technician.

DRC/Gary Payne

An explosive charge of PETN or Pentaerythritol tetranitrate cuts out the shape of Texas as it goes off during a post blast investigator school hosted by the Denton Fire Department in conjunction with the Alcohol Tobacco and Firearms Wednesday, March 8, 2009 in Denton. Attendees of the class learned the effects of different types of explosives.

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“Most certified bomb technicians have to take it, and anyone who investigates after explosions should take it,” Jones said.

Members of the class included Denton police officers, sheriff’s deputies and members of the Tarrant County Medical Examiner’s Office.

Johnnie Green is an explosives enforcement officer with the ATF. He told class members that they would learn several things from watching the explosions set off in a big patch of open ground at the landfill. He demonstrated explosive powder, a pipe bomb, a grenade and more dangerous explosives like C4, TNT and dynamite.

“There is no redeeming social value to a grenade except to fragment and injure or kill,” he said.

Sometimes, it is simply too dangerous for investigators to open a container believed to contain an explosive, he said. In that case, an investigator might use a “witness donor charge.”

That charge is first detonated alone and videotaped. Then an identical charge is detonated next to the unknown package, blowing it up as well. It is possible to demonstrate in court the difference in the explosions, he said, and that difference can prove that someone made a bomb.

DRC/Gary Payne

Johnnie Green, a Bureau of Alcohol, Tobacco, Firearms and Explosives agent, talks to students taking an explosives and post-blast investigator school hosted by the Denton Fire Marshal’s Office on Wednesday.

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And so the sunny afternoon was punctuated with explosions. Some simply popped. Some blew things apart. One sent a blazing tire spiraling into the sky, and another that had been specially wired for effect blew a Texas-shaped hole in a sheet of plywood.

Green told the students to watch, to listen and to feel the differences.

Green allowed several visitors, including a Denton County prosecutor, several women and a little boy, to press the button that detonated the explosives at a safe distance. That was the fun part, he said.

Today, he will see if the class was paying attention.

DONNA FIELDER can be reached at 940-566-6885. Her e-mail address is dfielder@dentonrc.com .