"People's lives are devastated here. It's hard to imagine,'' Hall said.
Federal investigators and the state fire marshal's office planned to begin inspecting the blast site Friday to collect evidence that may point to a cause.
Franceska Perot, a spokeswoman for the Bureau of Alcohol, Tobacco, Firearms and Explosives, said investigators would begin at the perimeter of the explosion and work inward toward the destroyed fertilizer company.
As investigators move inward, residents will gradually be allowed to return to their homes, authorities said.
It was clear was that the town's landscape would never be the same. An apartment complex was badly shattered, a school set ablaze and a nursing home left in ruins.
Garage doors were ripped off homes. Fans hung askew from twisted porches. At West Intermediate School, which was close to the blast site, all of the building's windows were blown out, as well as the cafeteria.
The fertilizer facility stores and distributes anhydrous ammonia, a fertilizer that can be directly injected into soil. It also mixes other fertilizers.
Records reviewed by The Associated Press show the U.S. Pipeline and Hazardous Materials Safety Administration fined West Fertilizer $10,000 last summer for safety violations that included planning to transport anhydrous ammonia without a security plan. An inspector also found the plant's ammonia tanks weren't properly labeled.
The government accepted $5,250 after the company took what it described as corrective actions, the records show. It is not unusual for companies to negotiate lower fines with regulators.
In a risk-management plan filed with the Environmental Protection Agency about a year earlier, the company said it was not handling flammable materials and did not have sprinklers, water-deluge systems, blast walls, fire walls or other safety mechanisms in place at the plant.
State officials require all facilities that handle anhydrous ammonia to have sprinklers and other safety measures because it is a flammable substance, according to Mike Wilson, head of air permitting for the Texas Commission on Environmental Quality.
But inspectors would not necessarily check for such mechanisms, and it's not known whether they did when the West plant was last inspected in 2006, said Ramiro Garcia, head of enforcement and compliance.
That inspection followed a complaint about a strong ammonia smell, which the company resolved by obtaining a new permit, said the commission's executive director Zak Covar. He said no other complaints had been filed with the state since then, so there haven't been additional inspections.