Texas Department of Public Safety Sgt. Jason Reyes said he could not confirm the number of first responders killed. Efforts to search the devastated buildings were continuing, he added.
The explosion Wednesday evening was strong enough to register as a small earthquake and could be heard for many miles across the Texas prairie. It demolished nearly everything for several blocks around the plant. More than 200 people were hurt.
Even before investigators disclosed the fatalities, the names of the dead were becoming known throughout the community of 2,800. Townspeople gathered late Thursday for a service at St. Mary of the Assumption Catholic Church.
"We don't know what to think," the Rev. Ed Karasek told those gathered at the service. "Our town of West will never be the same, but we will persevere."
Christina Rodarte, who has lived in West for 27 years, said, "Everyone knows the first-responders because anytime there's anything going on, the fire department is right there, all volunteer."
The only fatality who has been publicly identified was Kenny Harris, a 52-year-old captain in the Dallas Fire Department who lived south of West. He was off-duty at the time but went to help, according to a statement from the city of Dallas.
Brenda Covey once lived in the now-leveled apartment complex across the street from the plant. On Thursday, she learned that two men she knew were dead, both of them volunteer firefighters. One had been the best man at her nephew's wedding.
"Word gets around quick in a small town," said Covey, who has lived her entire life in and around West.
Firefighter Darryl Hall, from Thorndale, about 50 miles away from West, was one of the rescue workers helping with the house-to-house search.
"People's lives are devastated here," Hall said. "It's hard to imagine."
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 toward the destroyed facility.
As investigators progress, residents will gradually be allowed to return to their homes, authorities said.
But the landscape of the town has been severely transformed. An apartment complex was badly damaged, 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, close to the blast site, all the windows were blown out and the cafeteria was destroyed.
The fertilizer plant stores and distributes anhydrous ammonia, which can be directly injected into soil. It also mixes other fertilizers.
Records reviewed by The Associated Press show that the 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.
Because anhydrous ammonia is flammable, the state requires all facilities handling the substance to have sprinklers and other safety measures, 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 West Fertilizer resolved by obtaining a new permit, said commission Executive Director Zak Covar. He said that because no complaints had been filed with the state since then, there have been no additional inspections.