An inspection shows less than 2 percent of 250,710 light-fixture clips in the Big Dig tunnels were failing due to corrosion.

“We have begun washing all lighting fixtures and performing field reviews of the extent and severity of the protective coating and corrosion throughout the tunnel system,” MassDOT Secretary Jeff Mullan said yesterday, adding that selection and engineering of a backup support system for the fixtures should be complete in 30 to 45 days.

Mullan learned about a 110-pound light fixture falling from the I-93 tunnel a month after it happened on Feb. 8 and didn’t tell the governor about it until a week later, on March 15.