BOSTON (CBS) – It is the state’s responsibility to conduct safety inspections on all passenger elevators. But, an I-Team investigation found thousands of elevators in operation with expired inspection certificates. It’s a backlog Greg Sullivan, of the Pioneer Institute, calls a disaster waiting to happen.

Broken elevators can be a serious danger to passengers. There are dozens of videos online showing out-of-control elevators causing injury to those inside. According to the CDC, thousands of people are hurt each year in the United States. Faulty elevators have also trapped people inside for hours.

Elevators are required to be inspected annually for safety, but the I-Team found the state has a backlog of 4,500 operating without a valid inspection certificate. Sullivan told the I-Team, “This is a serious problem.”

In May of 2014, Elisabeth Scotland was at a Red Sox game when she fell more than 20 feet down an elevator shaft. The 22-year-old suffered brain and spinal injuries and filed a lawsuit. At the time, the state said the elevator had a valid inspection certificate.

Greg Sullivan questioned the thoroughness of the inspections that the state is performing.

This isn’t the first time elevator safety has been called into question. In 2014, a state audit found more than 30 percent of passenger elevators had expired inspection certificates.

“The state auditor blew the whistle on this in 2014. She laid it out in spades,” Sullivan said, adding that there was a huge backlog back then and little has changed.

Recently, we found expired elevator inspection certificates at Boston City Hall, Logan International Airport and even in the state building where the Office of Public Safety and Elevator Inspections is located. That certificate expired more than a year ago.

In a statement, the state told WBZ: “The Office of Public Safety and Inspections and the Division of Professional Licensure take seriously the safety of Massachusetts residents and work diligently to ensure that business owners and members of the public, many of whom rely upon the use of an elevator, have access to safe and reliable elevators. The OPSI continues to work with elevator owners to ensure inspections are performed on time each year.”

According to state officials, there are 40,568 elevators and fewer than 70 inspectors. Sullivan says the state will never catch up.

“This is a life and safety issue for the general public,” he said. “This is something the legislature and the governor should take care of; it’s not complicated.”

The Office of Public Safety said that inspected elevators that are found to be unsafe are taken out of service. Those elevators are required to be repaired and re-inspected within three months, before being put back into operation.