Two utility contractors faulted for contributing to an explosion that leveled part of downtown Sun Prairie and killed a volunteer firefighter in July have been fined for “serious” violations by the federal Occupational Safety and Health Administration. In citation letters dated Jan. 4, OSHA said its inspectors found that Kansas-based Bear Communications and Michigan-based VC Tech failed to call a diggers hotline or utility owners to locate underground lines before starting work. The companies were each fined $12,934 for the “serious” violation, the maximum penalty allowed, said Scott Allen, an OSHA spokesman. Bear Communications representatives didn’t return a message seeking comment. An attorney for VC Tech also didn’t respond to requests for comment.