Con Ed has suspended safety inspections of natural-gas lines while the 8,500 members of its biggest union are locked out, leaving residential areas in grave danger, the union says.

Every year, Con Ed surveys 4,300 miles of city gas lines with a fleet of “leak mobiles” that carry air-sniffing equipment.

The utility insists the 2012 survey is finished, but the union claims checks of residential areas aren’t done.