The correct answer is that as long as employees are absolutely compensated for assuming them and that they accomplish that freely and knowingly. However, if wages aren't proportional to the risks, or the chance is widely wide-spread unknowingly or out of desperation, then the contract between corporation and worker isn't truthful, and is consequently unethical. Employers should offer salaries that mirror the dangers of high-danger jobs and provide their employees with suitable health insurance packages.
