It's a good question, But the employees would have no right to sue McDonald's for any damages in civil court (negligence for example), and they would be limited to workers compensation claims/benefits.

Employees do not have no rights to sue for workplace injuries; intentional or reckless acts, and perhaps gross negligence, may be actionable even on situations where mere simple negligence would be subsumed into workers comp coverage.

I didn't say employees had no rights, I said these specific employees would have no rights to sue McDonalds, that is a major distinction.

The legal arguments are simple, presumably if there are employees who burned themselves, they would have: a.) likely set the coffee temp themselves (above the recommended temp); b.) at least been aware of the temp and risk; and c.) presumably have some responsibility for spilling the coffee on themselves. These facts would remove intentional/reckless/gross negligence on the part of McDonalds.

And I already know the counter arguments; However, if I'm actually wrong feel free to show me an a single case of a McDonalds employee suing McDonald's in civil court outside of workers compensation laws as the result of scalding coffee.