1. In any potentially life-threatening situation, a kohen should not hesitate to become tamei in order to possibly save a person’s life, even if the threat to life is small.
2. A kohen should not go into a hospital unnecessarily, even if the majority of the patients are not Jewish. This is because almost all hospitals contain limbs, abortions, and other sources of tumas-mes. Furthermore, even a non-kohen should try to avoid opening doors in hospitals where the majority of patients are Jewish lest he cause tuma to spread to a room where there is a kohen.
3. If there are no definite sources of tuma in the hospital (that is, there is no likelihood of tuma spreading from a morgue, student labs, pathology labs, operating rooms, or abortion clinics), there are opinions that allow a kohen to enter the hospital in order to perform a mitzva.
4. Medical treatments, accompanying a sick person who requires assistance, and visiting the sick are all considered a mitzva. A kohen should not enter a hospital for a financial reason without first consulting a halachic authority. According to some opinions, a kohen must spend all his money rather than violate the prohibition of tuma. Therefore, a kohen needing medical treatment that can be performed in a private, but very expensive, clinic where there is no tuma, should ask a halachic authority whether he may go to a public hospital instead. Therefore, a kohen should generally not go into a hospital without consulting a competent halachic authority, even if the majority of its patients are non-Jews. Before asking the rav, he should find out as much as possible about the hospital and the specific needs of the patient. Many hospitals have specific days and hours when non-emergency surgery, amputations, and abortions are performed, and this possibility too must be investigated. Even when a kohen is permitted to enter a hospital for medical treatment, if the same procedure could be performed in a private clinic with no tuma but at a much higher cost, the kohen should ask a competent rav whether he may go to a regular hospital instead. As a rule, a kohen must spend all his money to avoid violating the prohibition of tumas-mes.
5. A kohen may not fly over a Jewish grave, nor may he travel in a train or other vehicle over a Jewish grave. A kohen should preferably avoid traveling over a non-Jewish grave as well.
6. Likewise, it is forbidden to travel in an airplane carrying human remains. If the deceased was not Jewish, a halachic authority should be consulted.
7. Many flights to Israel transport bodies there for interment. A kohen flying to Israel must make sure, shortly before boarding, that there is no dead person on his flight.
8. Many places (especially in Israel) are forbidden to a kohen, but are not marked as such. Every kohen must familiarize himself with such places before he travels.
9. Kohanim must avoid museums that have human remains, fetuses, or bones.
Miscarriages and Abortions
10. A fetus that died forty days or more after conception conveys tumas-mes like every other corpse. The forty days are counted from when the woman went to the mikve.
11. The fetus does not convey tuma in utero until labor begins.
12. A kohen whose wife miscarried should leave the house or go to an unroofed area (if there is no danger to the mother) and then call others to help.
13. A placenta is not considered a limb and does not cause tuma. Pieces of the fetus cause tuma only if they accumulate to an olive-sized piece or if there is a whole limb.
14. A kohen may not enter a clinic where abortions are performed, nor may he enter any part of the building where they are located, unless he is sure there is no tuma.