You cannot sign away someone else's right to sue, but waivers of various sorts are common in which, in return for a consideration such as continued employment, an individual signs away a right to sue for a variety of causes.  You can't sign away a right to such things as Worker's Compensation coverage, but getting a company to agree to a variation on policy such as use of lab coats in return for your not suing the company if your not wearing a lab coat damages your $700 suit is quite another matter.

Such a waiver will not protect the company if there is an injury as a result of not using proper protective equipment, but it at least puts the employee on notice that they are accepting some form of personal responsibility by that refusal.