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Provide relevant information to your audience as soon as possible. In the heart of an emergency, it's ok to say that you don't have all your answers in line but that you're working as quickly as you can. Be empathetic to those getting your message and consider what they’re going through as you craft your message.
Also, be mindful of sending too much information or small bits of information too frequently. Most people are very understanding that you won’t have all the answers at first and will need to send updates as time goes on. But daily updates can become overwhelming and will likely result in changes to prior updates, simply because situations are changing so fast. This can cause unnecessary chaos in a situation that's' already chaotic.
How can you be most helpful to them?
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