A word of caution. You are undoubtedly aware of the concept of "personal space." Moving in too close to someone may make him or her uncomfortable. The generally quoted range of 4 feet is a North American average. But don't be misled by this generalization. Personal space is influenced by race, nationality, sex, age and even your mood. In fact, it's been found that people imprisoned for violent offenses have, on average, a larger "personal space" than non-violent individuals.
Contrary to conventional wisdom, letting someone "vent" may be the worst thing you can do. Caution should be exercised if you believe the situation could develop into a physical confrontation. Studies have found that letting people vent during these situations can actually increase the probability of incident escalation.
If someone is very upset and won't calm down, try distracting him or her. By changing a person's focus, you increase the opportunity to break down his or her resistance. Some things you might try include having the person write something, or dropping an item and having him or her retrieve it for you. This simple act can help you regain control of a discussion.
A very useful, persuasive technique incorporates the notion of reciprocity (giving something to get something in return). So what can you give? How about a cup of coffee, a cigarette, a good word on a report, or meeting someone at a time or place convenient to him or her? Almost anything.
Once you give something, the other person becomes indebted to you. The advantage of reciprocity lies in its power and flexibility. You can give something small (i.e. coffee) and ask for something significant in return (i.e. a statement). Also reciprocity isn't affected by personal likes, dislikes or biases. I can give something to someone who doesn't like me and still ask for something in return. As a negotiator, I might open a conversation with a suspect by saying something to the effect (true or not), "I've got some good news; I was able to convince the commander not to shut off the power." Before he's spoken a single word to me, he already owes me. Something I'll try to collect on later.