There are at least two important points to make in such an argument.
First, you can argue that it is the employer that is putting the employee in a situation where safety equipment is needed. Since the employer requires workers to perform tasks where safety equipment is needed, the employer should provide that equipment.
Second, you can argue that the employer should provide the equipment so as to be completely sure that all employees are safe. If employees are left to buy their own safety equipment, they might opt for low-quality equipment because it is cheaper. Alternatively, they might not completely understand what types of equipment are needed. Either way, workers would be put in danger. It is in the financial and ethical interests of the firm to be sure that its employees do not suffer any unnecessary injuries.