PHILADELPHIA - Philadelphia Mayor Michael Nutter on Friday recommended random drug tests for heavy equipment operators and other safeguards as part of a sweeping set of reforms in the wake of this week's fatal building collapse.

Nutter issued the recommendations as local media reported that blood tests on a crane operator at the site where six people died and 14 were injured showed he had been using marijuana and was taking prescription pain killers.

At a press conference at his office, Nutter said he had no independent knowledge of the drug tests.

"If that is all true, that would be significant," he said. "Now you are talking about the possibility of criminal activity."

Local media reported that police were searching for the crane operator after not finding him at his home.

"No one has been charged with anything," said Tasha Jamerson, a spokeswoman for the district attorney's office.

On Wednesday, a building under demolition in downtown Philadelphia collapsed onto a neighboring building that housed a Salvation Army Thrift Store. At the time, the store was filled with shoppers and staff.

Six people were killed and 14 were injured, including a 61-year-old woman listed as being in critical condition. Authorities said the building that was being demolished had housed an X-rated book and video store.

The mayor announced several changes to improve safety during building demolitions, including a requirement for random drug testing of equipment operators.

The city will now also require demolition contractors to provide a site safety plan to protect pedestrians and adjacent property.

"We know something went horribly wrong," Nutter said. "Government must try to find out what happened, why and how did it happen, what human errors or judgments played a role, determine responsibility, and fix what needs to be fixed."

Lawsuits planned

Attorneys representing survivors have said they intend to sue the building owners, Richard Basciano, and the STB Investments Corp, and the demolition company, Griffin T. Campbell.

Basciano, STB Investments Corp and Griffin T. Campbell could not be reached for comment. ?

One victim who plans to sue is Nadine White, 54, a mother of three and a clerk working at the thrift store when chunks of concrete came raining down on her, burying her in the rubble, her lawyer Robert Mongeluzzi said in preliminary court papers.

"Mrs. White was trapped in a nightmare when the collapse occurred," Mongeluzzi said in a statement.

Another mother of three, Linda Bell, 50, was shopping in the store when the collapse occurred and also plans to sue, her lawyer, Joseph Marrone, said. She was buried under the rubble for about an hour before being rescued.