Since the page is refreshed often, the participants list is read every time. Without reading the entire list, though, it was impossible to know if anyone had entered or left the chat.
New messages appear at the bottom of the screen, but again, without reading it's not possible to tell how many new messages there are.
Why it matters
It's important to make every effort to include blind and vision-impaired users in this real-time communication. With some changes this feature could be very usable.
1. Include a short use note at the top of the page, telling users that they must manually refresh the page to see new messages.
2. On every page load, include a short description of what is new, e.g., "There is 1 new user and 7 new messages."
3. Change the order to "Messages," "Send message," and "Participants."
4. Break messages into two groups: new messages since last page load, and old messages.