If there are practical difficulties or unnecessary hardships in carrying out a rule of the Commissioner of Labor, the Commissioner, after public hearing, may make a variation from such requirements if the spirit of the rule and law is observed. Any person affected by such rule, or his agent, may petition the Commissioner for such variation, stating the grounds therefor. The Commissioner shall fix a day for the hearing on such petition and shall give reasonable notice thereof to the petitioner. A properly kept index of all variations shall be kept in the office of the Department of Labor and shall be open to public inspection.