The real issue here is are you really an employee or independent contractor. According to the IRS guidelines many freelancers employed on set who are under the direct control of the client (ie told where to be, at an exact time, how long to work before being allowed to go home etc etc) are not independent contractors but indeed are employees.
In this case the client needs to be paying you either via payroll and in addition in some states by law must carry workers compensation insurance.
As an employee you cannot be held sued for certain actions as you are protected under various state labor laws which all vary depending on which state you are in.
I would discuss with the potential employeer your actual status and tell them you do not have to provide liability insurance because you are a temporary employee in the eyes of the IRS and the responsibility is on the employeer not you to provide the proper insurance.
Tony Salgado