Journalists take no Hippocratic Oath. There is little question that tackling a difficult story is a hazardous process for both journalist and source. In times of international strife, stories chronicling suffering and loss, and exposing injustices, are the stock and trade of the profession. The issue is how to minimize the risk.
Remember: Everyone in your newsroom may be affected differently. Some may be affected immediately while others will take days, weeks, months or even years to see the effect. The journalists who either claim or seem to be the most unfazed by the event may, in fact, be affected the most. Others may have developed mechanisms to help them deal with tragedy, and they may have minimal effects.
Know your limits. If you've been given a troublesome assignment that you feel you cannot perform, politely express your concerns to your supervisor. Tell the supervisor that you may not be the best person for the assignment. Explain why.