Hair and other human fibers are accumulating in Washington D.C. Metro tunnels in such large quantities that the gunk poses a threat of electrical sparks and fire, a transit consultant tells News4.

So much hair and skin cells built up on insulators that support the electrified third rails that the mess looks like a thick layer of felt, said a safety specialist from Amalgamated Transit Union, the largest labor union representing transit employees in North America.

"I was flabbergasted -- flabbergasted -- at the amount of hair that's in the Metro," Brian Sherlock said.

It's not just hair and fibers -- dust and debris also are gathering, according to Sherlock.

He said the issue can become especially dangerous when debris gathers near the high-voltage third rail.

"The amount of debris is just beyond vulgar to think of," Sherlock said.

Metro General Manager Paul Wiedefeld acknowledged the issue.

"Hair literally comes off of people and off of clothing and gets sucked up," he said.

This hair issue is not one that Metro has independently studied, but Metro has made efforts to increase the regularity of trackbed cleaning since 2016, Metro spokesman Dan Stessel said.