Workers who helped demolish one of the most contaminated nuclear sites in the U.S. may have been given faulty respirators, according to a Seattle Times report.

The newspaper, citing documents obtained from a project contractor, reports that more than 500 workers at the Plutonium Finishing Plant in south-central Washington were issued respirators that may have leaked between 2012 and 2016.

CH2M Hill Plateau Remediation Co. informed workers of the safety issue, but the contractor did not contact employees who had already left the job, according to the report.

The plant, also known as the Hanford site, opened in the 1940s as part of America’s efforts to create nuclear weapons. It produced large amounts of plutonium for more than four decades, but workers have spent most of the past 20 years decontaminating the site, according to the Seattle Times.

The newspaper reports that lack of worker safety had always been a concern at the site, but the new revelation about possibly leaky respirators underscores worries that employees’ health was sacrificed to finish the job quickly.

More than 20,000 workers’ compensation claims from nearly 12,000 site workers have been approved by a federal compensation program over the past two decades, according to the Seattle Times.

More than $1.3 billion has been paid to workers, according to the Seattle Times, which cited Department of Labor statistics.

Demolition at the Hanford site ended in February, and final cleanup efforts are expected to last through spring.