An investigation from WFAA's sister station KGW in Portland found hundreds of Transportation Security Administration workers have failed drug and alcohol tests at airports around the country.

Nationwide, 858 TSA workers tested positive for drugs or alcohol between 2010 and 2016, according to federal records obtained through a Freedom of Information Act request.

The TSA conducts drug and alcohol tests randomly. Tests are also given if there is reasonable suspicion an employee is under the influence.

The highest failure rates occurred at some of the nation’s busiest airports. Fifty-one TSA workers tested positive for drugs or alcohol at Los Angeles International Airport. John F. Kennedy International Airport had 40 employees test positive. Boston Logan International Airport had 35 failed tests.

Dallas-Fort Worth International had 21 TSA workers test positive for drugs or alcohol from 2010-2016. Dallas Love Field had eight.

DFW International is ranked the fourth busiest airport in the nation, according to the latest data from the FAA.

TSA employees who fail a drug or alcohol test are fired, an agency spokesperson said.

“Illegal substances include, but are not limited to, cocaine, marijuana, opiates, amphetamines, and phencyclidine [PCP],” wrote TSA spokesman Nico Melendez in an email to KGW.

Last year the TSA conducted random drug tests on 17,649 workers. Of those tested, 97 employees or 0.55 percent tested positive, which is far below the positive testing rate for other federal employees.

According to Quest Diagnostics, the overall percentage of positive random drug tests for federal employees in “safety sensitive” jobs was 1.5 percent.

“To think that we are going to eliminate that entirely is an unreasonable expectation,” explained homeland security analyst Scott Winegar. “We can optimize what we expect from the screeners and we can optimize the people we select, but I don’t think we are ever going to be able to have absolutely zero mistakes.”

A July 2016 report from the U.S. House Homeland Security Committee found increased employee misconduct at the TSA.

“TSA employees have been criminally charged for using cocaine on the job, facilitating large-scale drug and human smuggling, and engaging in child pornography activities,” the report said.

Earlier this month, U.S. Rep. Scott Perry (R-PA) introduced legislation requiring senior TSA officials to oversee the review of discipline when a TSA agent misbehaves. Under current rules, disciplinary actions vary from case to case depending on the supervisor.

The TSA has roughly 60,000 employees working at about 450 airports.

“Our expectation is that they will keep us safe in the airways, so when you put that type of expectation on somebody, you would certainly want them fully alert and not inhibited by alcohol or drugs in any way,” explained Winegar.