If Another Company May Be Responsible: What a Third-Party Claim Has to Show
If you are considering a claim against a company other than your employer, the main difference is that fault has to be proven. In general terms, a person bringing a third-party claim has to show four things: that the other party owed a duty of care, that it breached that duty, that the breach caused the injury, and that the injury led to damages, meaning losses the law recognizes. Where the claim is about a product, such as a machine, the question often turns on whether the product had a defect and whether that defect caused the harm. Whether any of these elements is met depends entirely on the facts. An injury, however serious, does not by itself prove that anyone was at fault, and an accident does not by itself prove a machine was defective.
Federal safety rules can bear on what duties companies at a shared worksite carry. One example is the lockout/tagout standard, which governs how dangerous machine energy is controlled during servicing. Under 29 C.F.R. § 1910.147(f)(2), "whenever outside servicing personnel are to be engaged in activities covered by the scope and application of this standard, the on-site employer and the outside employer shall inform each other of their respective lockout or tagout procedures," and the on-site employer "shall ensure that his/her employees understand and comply with the restrictions and prohibitions of the outside employer's energy control program."
A rule like this shows that federal safety law can place duties on more than one company at the same site. It does not, by itself, decide who is legally responsible for an injury in a civil claim. Congress said so directly. Under 29 U.S.C. § 653(b)(4):
"Nothing in this chapter shall be construed to supersede or in any manner affect any workmen's compensation law or to enlarge or diminish or affect in any other manner the common law or statutory rights, duties, or liabilities of employers and employees under any law with respect to injuries, diseases, or death of employees arising out of, or in the course of, employment."
In plain terms, the federal safety law leaves each state's workers' compensation law and injury law where it was. A safety standard may be part of the story a third-party claim tells, but state law decides the claim.
The stake here is a trade-off. A third-party claim may reach categories of damages that a state's workers' compensation system does not address, as that state's law allows, but it asks for proof of fault and causation that workers' compensation generally does not. For someone weighing this track, useful questions include which companies were involved with the equipment or the work, and what each one's role was at the moment of the injury. The OSHA worker rights page describes the separate safety rights workers have, including the right to "work on machines that are safe" and to "report an injury or illness, and get copies of your medical records."