In a caring and calm voice, you might say something along these lines:
“Please speak in a calmer tone so I can listen better.” – Take the onus on yourself; you can’t listen well when there is screaming.
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“I need to stop you for a moment.” And once they stop, “This is much too important for me not to hear you clearly and understand exactly what happened. I’m already having a difficult time hearing you because of how you’re expressing yourself. So, can you please take it from the top and tell me exactly what happened?” People who are angry often feel that their concerns have not been made a priority. Statements such as these, said with calm confidence can help them begin to calm down. Also, reminding them that what they’re saying is important will hopefully cause them to pause and retell you what happened with less anger.
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“Time Out. Right now I feel like you are attacking me, while I’m sure you feel like I’m attacking you. When in fact, all we are doing is defending our own positions. Can we start fresh and take the tension out of the air?”