@MadScientist No, it's not and any announcement is not due by any means. The entrance to any lab, if restricted, should be specifically communicated. If that didn't happen in your case, it was a mismanagement from the employer and likely a safety breach. Of course, if the employer communicates the restrictions and an employee after the communications gets pregnant and doesn't say anything, it's on her; but the first communication is on the employer.

Following your logic, any employee should tell the employer any conditions they have, just because the workplace might be dangerous. If the workplace is dangerous for someone, it's of course the employer that must communicate it to someone who might possibly work there.

@nicola The employees generally know the dangers, or at least should know them. But that isn't enough, if your job involves handling dangerous chemicals you need to communicate to your employer if you can't perform those duties.

@MadScientist Do you really think that it's the employee who should verify whether the proper safety measures are taken? The employees might know the dangers but definitely don't have to. Who has to know potential dangers is the employer and must communicate them.

@nicola But once you know those are dangerous, you want to avoid those duties. You can't just say you won't perform them without explanation

and you really can't generalize that much, the work in a lab can vary enormously. You really need to get into the details sometimes

You go into the details by asking about the job, not by communicating your personal situation. You seem to imply that it's on the employee to check whether safety measures are taken and also should have the proper background to know what is dangerous in which circumstance.