The spectacular fire and explosions that launched flaming gas cylinders high over Dallas on Wednesday have touched off a federal investigation and raised concerns about the safety of the city's industrial plants.

MICHAEL MULVEY/DMN

A Dallas police officer watched Wednesday morning as flames from a series of explosions shot high above the Houston Street viaduct near Reunion Arena.

Dallas officials said they had no record of safety violations at Southwest Industrial Gases, which supplies acetylene, used in welding, and other gases. They also said the city had not inspected the company in at least the last 5 ½ years – but that's not an unusual or troubling interval, Dallas officials and one independent safety expert said.

Although the explosions rocked an area along the Trinity River zoned for industrial manufacturing, they also pointed toward potential chemical dangers near where people work and live. Dallas' trend toward urban living, especially in neighborhoods transitioning from industrial to residential, could make such problems more likely.

"The city has probably thousands of heavy industry and chemical storage facilities all over the city," said Brigham McCown, a former federal hazardous materials official now practicing law in Dallas. "Should the city have these types of activities so close to two interstates and a major rail line?"

Several City Council members said they want the city to assess the risk posed by those industries. "The reality is that there is a safety concern with some of these businesses so close to residential areas and downtown," Mayor Pro Tem Elba Garcia said.

"I want to know what went wrong because we need to be very careful that this does not happen again."

Dallas Assistant Fire Chief and Fire Marshal Debra Carlin said she did not believe the lack of a recent formal inspection at Southwest Industrial Gases contributed to the explosion. Inspections check issues such as materials storage and the presence of open flames, she said – neither of which was believed to be a factor in Wednesday's incident.

"An inspection would not have caught this," Chief Carlin said.

Mr. McCown also discounted the inspection interval as a major issue. "I don't think that's a smoking gun, and I don't think that's atypical, and I think if you went to any city you'd probably find that," he said.

The U.S. Chemical Safety and Hazard Investigation Board sent a team of five federal investigators and board member William B. Wark to Dallas from Washington, D.C., for a preliminary look at the incident, which apparently began while workers loaded gases into canisters on a truck.

The chemical safety board, similar to the National Transportation Safety Board, investigates industrial accidents and makes recommendations but has no enforcement powers. Last year, it completed an investigation into a similar fire and explosion in St. Louis that sent burning gas canisters into a surrounding neighborhood, setting numerous fires.

If the board launches a full investigation, a formal report might take as long as a year. Its investigators would examine the plant and equipment, interview employees and witnesses, and comb through company records.

"That would include ignition sources, whether there were any defects to the cylinders, whether they were stored or maintained properly or whether there were any human factors involved," said Mr. McCown, who was chief operating officer for the U.S. Pipeline and Hazardous Materials Safety Agency, a Transportation Department branch, from 2005 until earlier this year.

The fire started on a loading dock on the back side of the company's complex, said Lt. Joel Lavender, a spokesman for Dallas Fire-Rescue. It spread into the building, where tanks of oxygen, helium and acetylene began blowing up.

Fire officials said two employees were filling canisters with acetylene using a series of connecting tubes in what is known as "pigtailing."

A connection malfunctioned, apparently creating enough pressure for one of the canisters to ignite. For safety, pressure in acetylene tanks must be kept below a certain point.

The canisters exploded in a chain reaction, burning two men on their upper bodies. For more than an hour after the incident began about 9:30 a.m., fireballs shot from the company's site at 538 Industrial Blvd., and a column of thick, black smoke rose on a slight northward wind, headed mostly across other business and industrial areas.

Repeated explosions shook downtown buildings and lofted burning debris like fireworks. Local streets and Interstates 30 and 35E were shut down for much of the day.

Eddy Parker, branch manager for AirGas, next to the plant, said at first he thought a car had smashed into his building. Running outside, he saw black smoke rising like a small mushroom cloud.

"I just advised my teams to get out. ... We ran and just kept hearing explosions," Mr. Parker said.

County health officials said they had no indications of immediate risks to the public from the smoke that rose thousands of feet high.

"The gases look like they've dissipated," said Dr. John Carlo, health authority for the Dallas County Department of Health and Human Services. Given the chemicals believed to have been on the site, the fire would have quickly consumed toxic substances, Dr. Carlo said.

Still, environmental agencies were monitoring air quality. Test results were expected by this afternoon.

According to the last U.S. census, only 11 people lived within a half-mile of the plant, but more than 12,700 people lived within a one-mile radius. Numerous downtown, Oak Cliff and Cedars neighborhood businesses occupy the area. Tens of thousands of people pass the site and other industrial plants every day via major highways.

Enforcing safety rules for the thousands of industries, gas stations, petroleum storage tanks, and other potential hazards in Dallas is mostly a city job. The EPA and the Texas Commission on Environmental Quality have broad authority over pollution-related issues, while workplace safety is under the federal Occupational Safety and Health Administration.

But guarding against fire and explosion risks generally falls to local officials. They do most inspections and are in charge of planning for emergencies.

Mr. McCown said the city should take this event as an opportunity to revisit its emergency procedures – for example, to determine whether local officials were slow to shut down surrounding roads.

"In this case, the cordoning off of the highways and the area is a top priority that could have been done faster," said Mr. McCown.

Council member Pauline Medrano, whose District 2 includes the explosion site, said she wants that review to start immediately.

"It's probably a good idea for the city of Dallas to look at businesses with flammable material, at least those so close to the freeway and downtown," she said. "And now is probably a good time to begin that."

Staff writers Holly Yan and Holly K. Hacker contributed to this report.