The wellbeing of employees should be the primary concern of an employer. Period. If an employee approaches you about a perceived danger at work take it seriously, look into it and do your due diligence. This is one of the most important steps in preventing illness or injury in the workplace.
Depending on your jurisdiction there are steps that the employee and the employer must take to act reasonably and safely. Please click on the country below that relates to your location or look up your local legislation.
Excerpt: Any employee subject to Part II of the Code has the right to refuse dangerous work as long as they have reasonable cause to believe that it presents a danger. Specifically the Code states that an employee may refuse in the following circumstances: to use or operate a machine that constitutes a danger to the employee or to another employee, to work in a place, to perform an activity that constitutes a danger to the employee or to another employee. The Code contains certain exceptions regarding the right to refuse dangerous work. These exceptions include: if the refusal puts the life, health or safety of another person directly in danger; or, the danger in question is a normal condition of employment.
Excerpt: Your right to refuse to do a task is protected if all of the following conditions are met: where possible, you have asked the employer to eliminate the danger, and the employer failed to do so; and you refused to work in "good faith." This means that you must genuinely believe that an imminent danger exists; and a reasonable person would agree that there is a real danger of death or serious injury; and there isn't enough time, due to the urgency of the hazard, to get it corrected through regular enforcement channels, such as requesting an OSHA inspection.
Excerpt: An employee has the right not to be subjected to any detriment by any act, or any deliberate failure to act, by his employer done on the ground that in circumstances of danger which the employee reasonably believed to be serious and imminent and which he could not reasonably have been expected to avert, he left (or proposed to leave) or (while the danger persisted) refused to return to his place of work or any dangerous part of his place of work.