Section 7. To protect the safety of employees in all hazardous occupations, in mining, smelting, manufacturing, railroad or street railway transportation, or any other industry the legislature shall enact an employer's liability law, by the terms of which any employer, whether individual, association, or corporation shall be liable for the death or injury, caused by any accident due to a condition or conditions of such occupation, of any employee in the service of such employer in such hazardous occupation, in all cases in which such death or injury of such employee shall not have been caused by the negligence of the employee killed or injured.