MILWAUKEE -- Milwaukee's police chief said investigators continue to look Thursday for the flash point that caused propane vapors to explode at the Falk Corporation, killing three employees and injuring dozens of others.

SLIDESHOW: Falk Corp. Explosion | VIDEO: Watch The Report

At a news conference Thursday afternoon, Chief Nan Hegerty said it was liquid propane, not natural gas, that pooled in an area, vaporized and ignited.

Hegerty said that employees of the Falk Corp. were investigating the propane leak as others evacuated the building on Wednesday morning when the explosion occurred. Three workers died in the explosion and nearly four dozen others were injured.

The chief said employees were about 10 to 14 minutes into an evacuation of the Falk complex when the annex building exploded.

Hegerty said that the death toll could have been much higher had the evacuation not started.

Besides the three deaths, 46 people were hurt in the blast. One of those injured is currently listed in critical condition, WISC-TV reported. Barrett said that all of the Falk Corp. workers have now been accounted for.

Reports from the Milwaukee County medical examiner's office on the employees' deaths said workers at Falk had been testing the backup propane system prior to the explosion.

Mayor Tom Barrett and Gov. Jim Doyle pledged government resources to help the families and company recover from Wednesday's explosion and fire.

"I really do want to say to the police and fire, public works and other emergency responders (that) they really did a good job here," Doyle said. "And we're going to work from this point on as a city and state to try to help people get their lives back going, to get the business back going and to have people be able to have life go on."

The explosion and fire occurred shortly after 8 a.m. in the industrial Menomonee Valley, which is near Interstate 94, about a half-mile from Miller Park and a half-mile from the Potawatomi casino. The blast created a debris field about 2½ blocks wide, WISC-TV reported.

The chief said that the explosion seems to be accidental, but authorities have opened a criminal investigation, which is normal procedure.

The Milwaukee County District Attorney's Office, the state fire marshal, the federal Bureau of Alcohol, Tobacco, Firearms and Explosives and the Occupational Safety and Health Administration are investigating.

Barrett said the company has a clean safety record with the city. He said that the last inspection was in September and any violations were corrected on the spot.

Victim's Family: 'It's A Big Tragedy'

The huge explosion and fire was a personal tragedy for families of three workers who died.

Police identified the victims as Curtis Lane, 38, of Oconomowoc, Thomas Letendre, 49, of Milwaukee, and Daniel Kuster, 35, of Mayville.

Kuster's father, Melvin, said that his son was a third-generation Falk worker and had been there more than 10 years.

Lane's father-in-law, William Borgiasz, of Oconomowoc, said that Lane was the father of two children, ages 2 and 4, and his wife, Tina, operates a day care.

He said that the explosion is hard to deal with and the only thing the family can tell the children is that their father isn't coming home.

The Letendre family declined comment.

On Wednesday night, workers got together at the nearby Milwaukee County Fairgrounds to lend support to one another.

Police said that the investigation into what caused that blast is expected to take at least a week, WISC-TV reported.

The Falk Corp. is headquartered in Milwaukee and manufactures power transmission equipment. It has been I the city for 150 years, WISC-TV reported.

Stay tuned to WISC-TV and Channel 3000 for continuing coverage.