Letting dust reach one's throat
1612. On the basis of obligatory precaution, allowing thick dust to reach one's throat makes one's fast void, whether the dust is of something which is halal to eat, like flour, or of something which is haraam to consume like dust or earth.
1613. Allowing thin dust to reach one's throat will not invalidate the fast.
1614. If thick dust is whipped up by the wind and if a person does not take care in spite of taking notice of it, allowing the dust to reach his throat, his fast becomes void on the basis of obligatory precaution.
1615. As an obligatory precaution, a person who is observing fasts, should not allow the smoke of cigarettes, tobacco, and other similar things to reach his throat.
1616. If a person does not take care to prevent dust, smoke, etc. from entering his throat, and if he was quiet sure that these things would not reach his throat, his fast is in order; but if he only felt that they might not reach his throat, it is better that he should observe that fast again as qadha.
1617. If a person forgets that he is fasting and does not exercise care, or if dust or any other similar thing enters his throat involuntarily, his fast does not become void.