They also spoke about fertiliser and compared its ammonium nitrate content with sports injury cold packs.
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The Safe Explosives Act only requires that ammonium nitrate manufacturers submit samples upon request.
Forensic reports suggested substances used in the explosion had included RDX, ammonium nitrate and petroleum hydrocarbon, he added.
Ammonium nitrate, a solid fertilizer composed of ammonia and nitrogen, is also a component of explosives widely used in mining.
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The blast ignited a fire on a second ship docked in Galveston Bay that was also loaded with ammonium nitrate.
Reports in the media say that ammonium nitrate was used in the small bombs which had been placed in confectionery boxes.
The state fire marshal's office had previously ruled out four potential causes: weather, natural causes, anhydrous ammonium and ammonium nitrate in a rail car.
The situation remains volatile because of an extremely dangerous substance, ammonium nitrate, found at the scene, said an official from the county sheriff's office.
It was Garcia who made the initial visit to Access in Hanwell to ascertain whether he could hire a unit to store the ammonium nitrate.
The area around the site of remains "very volatile" because of the presence of ammonium nitrate, according to Matt Cawthon, chief deputy sheriff of McLennan County.
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On Monday, the state fire marshal's office said it ruled out four potential causes: weather, natural causes, anhydrous ammonium, and ammonium nitrate in a rail car.
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On Monday, the state fire marshal's office said it had ruled out weather, other natural causes, anhydrous ammonium and ammonium nitrate in a rail car as possible causes.
"Anhydrous ammonia will burn but it is unusual for it to detonate, whereas ammonium nitrate has a track record of blowing up, " he told the BBC World Service.
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An expert on fertilisers at the University of London, Prof Andrea Sella, told the BBC it was possible that the highly explosive ammonium nitrate had also been stored on site.
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On 16 April, 1947, a fire on a ship loaded with ammonium nitrate set off a series of explosions in the port of Texas City, and fires that burned for days.
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"Anhydrous ammonia will burn but it is unusual for it to detonate, whereas ammonium nitrate has a track record of blowing up, " explained Prof Andrea Sella, a chemist at University College London.
Initial tests showed the device contained ammonium nitrate, the same volatile substance that sparked a massive explosion last month at a fertilizer distribution plant 110 miles north in West, Texas, said Austin fire Lt.
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The main reason people want to get hold of ammonium nitrate is for use in agriculture and to that end, says Mr Whitty, an "effective system" is in place for suppliers to inform the authorities of any irrregular and sudden inquiries about buying large amounts.
One of the worst disasters in U.S. history involving a form of ammonia occurred in April 1947 when a ship loaded with ammonium nitrate -- a solid fertlizer composed of ammonia and nitrogen -- caught fire while docked in Texas City, Texas, in April 1947.
General Barbero has worked hard with other federal agencies to curb the availability of ammonium-nitrate fertilizers made in Pakistan, since traces of the agricultural chemical have shown up repeatedly in the aftermath of Taliban bombings.
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