Our expert says:
If I understand you correctly, you mean that he smokes outside the classroom (inside the classroom is of course illegal). Toxins from cigarette smoke do cling to a smoker's hair and clothes ("3rd-hand smoke", as you've correctly called it). We don't know how much of a health risk they are yet, but there is no safe level of these toxins: it's better not to be around them, but it's likely the risk is low. In any case, it is perfectly legal for your teacher to be a smoker, as long as he doesn't smoke in the classroom.
As for hitting you with the duster (!): No, he is definitely not allowed to do that. Corporal punishment (i.e. physical punishment) is illegal in our schools. You and your parents/guardians have the right to complain about this to your teacher's employer.
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